Transitions: The Evolution of Life

DarkSyd at Unscrewing The Inscrutable has sent me another post. This time it is on the evolution of birds.

***************************************************************

OH! I have slipped the surly bonds of earth, and danced the skies on laughter’s silvered wings
Sunward I’ve climbed and joined the tumbling mirth of sun-split clouds
And done a hundred things you have not dreamed of- wheeled and soared and swung high on the sunset silence …

Who among us has not dreamt of flight? To coast effortlessly along on lazy thermals on a sunny day, the distant tapestry far below painted in pastel blues, browns, and greens? To dive at the ground at over 150 MPH and then pull out and blaze over a blurred landscape at breathtaking speed? From Daedalus to Da Vinci to Apollo and beyond, it is a vision that has driven mankind. The idea of flying informs our dreams, infiltrates our legends, and invades our nightmares. And now that we can fly by way of machines, it turns out to be every bit exciting as we imagined. But why are the birds heir to this ability? Why and how were they chosen to be among the lucky few who would take to the air and go on to dominate the land, sea, and sky?

Huge Grahics Below!

The most famous fossil ever found was unearthed with no ceremony in an old Bavarian stone quarry, a site known for high quality flat limestone rock called Plattenkalk since the days of Rome. It was at first a curiosity, later a sensation, and now reigns supreme among them all. It is so detailed it quickly earned the name Lithographica; lithos as in Latin for stone, and graphos as in Greek for writing. The new find was a volume literally written in stone.

The specimen would have been a star on its own. But because of the year it was discovered, 1861 when Darwin’s Dangerous idea is in full bloom having taken the scientific community by storm only two years earlier, it was propelled to fossil superstardom. The slab would become the most famous specimen preserved in the ancient medium of rock ever unearthed. But it harbored a secret kept hidden for a hundred years or more after it was dug out of the ground: The dinosaurs may not have gone extinct at all.

It looked like a lizard, down to the teeth and the tail, yet had some of the bones of a bird. And just case there was any doubt, fully functional flight feathers extending off of what look like short wings are preserved in the limestone matrix. It was called Archaeopteryx , meaning primitive wing. And it remains the oldest bird ever found.

                               

Archaeopteryx lithographica from the Late Jurassic Solnhofen limestones of Germany. The photo above is of the real deal; the original fossil itself. Most photographs you’ll see are of poor-quality casts. It ain’t easy for scientists to even get near this slab. It’s more valuable than diamonds

A word of caution: I have several friends who eat, breathe, and live dinosaur/bird evo AKA paleo-ornithology. They speaketh a strange language I do not understand full of morphological, anatomical, cladistics terms. But, every one of those folks is solidly behind the dinos-to-birds scenario and judges the opposing hypothesis as so bad it’s in their own words “Creationist Bad”. I’m not an expert. This piece may have some errors in it and I appreciate any pointers. But for the purposes of this article I’ve given those aforementioned dino aficionados the benefit of the doubt.

The parallels between birds and dinosaurs were not lost on early paleobiologigists. Even so eminent an evolutionary pioneer as Thomas Huxley made the case that birds might be direct descendants of dinos. But over the next few decades the Great Dinosaur Bone Wars heated up among rival fossil hunters and the emphasis shifted to bigger and meaner looking ancient beasts. Long-necked sauropods and toothy Carnosaurs soon filled the scientific literature and museum halls, and the impression of dinosaurs as big, brainless, slow moving, very unbird-like reptiles, took hold for generations.

That would not change until 1960 when Dr. J.H. Ostrom’s published an exhaustive study of Deinonychus antirrhopus illuminating similarities to Archaeopteryx. That work provided the impetus for a paradigm shift in ideas on the origin of birds and the evolution of flight.

By the time Jurassic Park rolled into cinematic history, the birds were accepted as likely descendants of a dinosaur group called Maniraptors, or ’seizing hands’, which includes the dromaeosaurids such as velicoraptors. The resemblance is clear:

               

                      Enlarge

I’m not qualified to delve more deeply into the anatomical congruencies between birds and dinosaurs and it’s a detailed subject beyond the scope of this modest effort. For those of you so inclined, this article by Chris Nedin in the Talk Origins archive called All About Archaeopteryx is a must read.

Exactly why feathers first evolved will likely never be known. They’re useful for insulation and protection, they provide a platform for coloration, and they can be used as both displays to ward off predators or attract mates. But the process of how it transpired may be coming to light, again courtesy of those wonderful fossils form China, and the relatively new field of evolutionary development.

                     

The chart above outlines a plausible evolutionary scenario. From simple stringy feathers, to more complex stringy feathers, to flight feathers. This idea is based on the two bodies of data we do have: The variety of feathers found dinos in the fossil record and how they develop in a bird embryo.

However feathers developed, it’s still a fascinating question as to how the precursors of birds learned to fly. The two possibilities are the ground up theory and the trees down theory. In the trees down theory early birds first become gliders and then refine that ability until they’re capable of powered flight. In the ground up theory the small dinosaurs flapped their feathered arms while running to provide extra power and maneuvering ability. No one knows for sure which one of these broad possibilities was the path by which birds first took to the air. But once they did, feathers offered them an advantage unavailable to their aerial competitors of the day such as pterosaurs and other flying reptiles: Feathered wings are better suited to flying in and around thorny trees and bushes. If a wing of stretched skin tears on close encounter with a plant, that animals is grounded until it heals or the critter dies. Feathers aren’t subject to this design flaw.    

For years creationists worked very hard to discredit Archy. Most were fond of saying “It has true perching feet” as if this somehow was a problem for the same process of evolution which turned forelimbs into wings. Another objection to Archy and transitionals in general was somehting like “Every animals appears ‘fully formed’ in the fossil record”. I’m unsure what a half-formed bird would be excatly … a flying squirrel or a sugar glider perhaps? A deformed bird with ‘half-formed’ body parts would not last long. Natural selection would make quick, grisly work of such an unfortunate animal. Finding lots of adult birds that were deformed in the fossil record would be evidence against evolution.

When it began to soak into the laypublic that raptorial dinosaurs were thought to be the direct ancestor of modern birds, and when this idea excited young movie goers, the creationists of course went full tilt, adopting the existing scientific dissent over the Bird-Dino origin theory.

Most creationist nonsense on bird transitionals now comes from Answers in Genesis; the crew of the Discovery Institute doesn’t talk much about birds preferring to focus on PR issue centered on philosophy or areas of mystery such as the Cambrian Explosion. But to get a taste of AiG’s duplicity and see an example of how evo-devo can utterly smite them, I heartily encourage any well informed laymen to read PZ Myers’ Digit Numbering and Limb development. It’s short, well illustrated, written for the educated layman and that article by PZ is the best intro into evo-devo and dinosaur homology I have ever read in my life.

The competing idea to the dino origin of assigns birds as descendants of Thecodantia; an ancient clade of reptiles which predate dinosaurs and gave rise to what are called basal archosaurs which gave rise to crocodiles and turtles. The Thecodont Theory/Hypothesis basically says that birds aren’t derivative dinosaurs. The primary proponents are Alan Feduccia and Larry Martin.

Then in 1995 dino hunters got lucky in an obscure quarry in the Liaoning Province of China: In series of amazing finds, one after the other, a whole new window was opened up on dinosaur evolution.

The first was this fossil of a Sinosauropteryx showing what appeared to be an exterior of stringy feathers. In rapid succession, more feathered dinosaurs were found, each one more exquisite and stunning:

Sinosauropteryx fossil in situ and artistic impression

                                               

Generic raptor fossil in situ and artistic impression

 

        Caudipteryx fossil in situ and artistic impression

 

     Microraptor Gui in situ and Artist’s Impression

Some of the Chinese dinos are enigmatic, such as the four winged microraptor above; or any member of the Therizanosaurids. Theriz’s are wierd!  Most of them have these giant claws the utility of which is wide open to speculation. Scooping fish out of streams or insects out of termite mounds? We have no idea: Therizanosaurs are an excellent field of study for any of you budding paleontologists because so little is understood about these creatures. Currently Therizanosaurs are thought to be descendants of early raptors and were in the process of evolving into generalists and herbivores. If so, they plausibly had feathers, as shown below in an artists rendition.

Based on this new material, we can construct what an evolutionary progression from dinos to birds might have looked like. Again, this is not intended to represent a straight line order of ascendancy, but it does gives us a rough idea of how the transition may have occurred:

Given the new finds of feathered dinos in China, one might think the Thecodont idea would be history. But there remains one intriguing possibility: The feathered dinos of China lived more recent than archaeopteryx. That means either feathers first evolved in dinosaurs which later diversified into avian and non avian critters. Or birds did evolve from non-saurian ancestors and then later various clades of flightless birds evolved into what we think of as raptorial dinosaurs!

This Neoflightless Hypothesis is best summarized and criticized as the idea that raptors were a ‘Mesozoic Kiwi’ or ostrich. This idea is a long shot, I wouldn’t bet even odds on it. But it is possible, it is consistent with the fossil record. We know that very large predatory flightless birds have evolved from their winged ancestors on several independent occasions. (It’s also interesting that creationist use the neoflightless hypothesis to discredit evolution by way of birds and dinosaurs. Apparently a sparrow evolving into a one ton raptor is not ‘macro-evolution’ but going the other way is …)

The most recent such radiation includes the now extinct Moa of Australia along with the so-called terror birds which ruled the grasslands and forests of North and South America between 65 million years ago and just a couple of million years ago. These killer birds were three meters tall in some cases, with a skull the size of a watermelon sporting a broad beak shaped like an ax blade, and at least one of them even developed rudimentary hands! So yes, it is within the realm of possibility that birds evolved into raptorial dinosaurs.

But regardless if dinos evolved into birds or birds evolved into dinosaurs, it would be correct to say that birds are a type of dinosaur. So let’s take a look at a few of the dinosaurs among us.

           

Snowy owl                               Red Jungle Fowl, ancestor of the domestic chicken

A European Imperial Eagle guards its nest and chicks

A young Peregrine Falcon finishing off a tasty morsel. These are the fastest known animals and can reach speeds of almost 200 MPH when diving

Meet the Penguins courtesy of NATURE

An American Bald Eagle takes flight              A Kingfisher peering into a stream prepares to strike

Birds are among the most successful of all the ‘tetrapod’ vertebrates with roughly 10,000 species known or suspected. Not surprising: They can pull up stakes and fly away to remote islands and oasis no other large animal can reach, or travel across the entire globe in search of warmer climes; they’re equipped with the eyes of a surveillance satellite, the best in the entire animal kingdom; they have big brains and excellent memories; and if we humans don’t make it, given time I wouldn’t be surprised if a descendent of birds rose to sentience. Intelligent Dinosaurs: what an interesting race of beings that would be!

Perhaps one day in the not too distant future on a planet or moon of lower gravity, we too will be able to fly with the birds under our own power; to ply the alien winds as masters of the sky. Until then we can only dream of such a day and get a taste of what it might be like to soar and wheel and dance the skies on laugher’s silvered wings in our clunky aircraft; and that’s not a bad appetizer.

High in the sunlit silence. Hov’ring there, I'’ve chased the shouting wind along, and flung my eager craft through footless halls of air.
Up, up the long delirious, burning blue I'’ve topped the windswept heights with easy grace, where never lark, or even eagle flew.
And, while with silent, lifting mind I’ve trod The high untrespassed sanctity of space, Put out my hand, and touched the face of God

Caimans,

Gavials,

Alligators,

and Crocodiles

have a long and complex evolutionary history. The Crocodylia have undergone at least three separate episodes of adaptive radiation during their history. They are all members of the order Crocodylia - which in turn is a member of the superorder Archosauria. Fellow members of the Archosauria include the Saurischia (dinosaurs such as Diplodocus), Ornithischia (bird hipped dinosaurs such as Stegosaurus), the flying Pterosauria and the Thecodontia. The origins of the Crocodylia lie over 200 million years ago in the Triassic period. The earliest know genus of Crocdylia are known as Sphenosuchia. One of them, Gracilisuchus of the upper Triassic, is pictured below.

Such as the above fossil (found in Argentina). There are several features of the skeleton that distinguish Crocodylia from other reptiles. In humans, for example, three bones come together in the pelvis to form a structure called the acetabulum. The acetabulum is a cup shaped area where the femur (or thigh bone) joins the trunk. As you can see in the picture of a human pelvis below.

In the Crocodylia, however, this is not the case. The pubis is almost completely, or is completely excluded from forming part of the acetabulum. A second feature of the skeleton that distinguishes Crocodylia from other reptiles occurs in the ankle (yes, Alligators and Crocodiles have ankles). In humans, the talus sits ontop of the calcaneus.

In the Crocodylia, however, they sit side by side (note the talus is also called the astragalus).

This arrangement allows the foot to be twisted forward and allows the leg to be more underneath the body (compared to lizards). The Gracilosuchus pictured above shares these features with the Crocodylia.
One of the interesting things about the Sphenosuchia is that they were relatively long limbed and land dwelling. The Terrestrisuchus below is a good example.

The next group of Crocodylia are the Protosuchia which appeared in the lower Jurassic. Like the Sphenosuchia, the Protosuchia have long limbs and were largely land dwelling. Although we begin to see some of the adaptations to water that characterize later Crocodylia - for example the nostil cavity is becoming separated from the mouth.

The Protosuchia were distributed throughout the world.
The Mesosuchia evolved in the lower and upper Jurassic and are excellent transitional fossils between the Protosuchians and the Eusuchians (modern crocodiles, alligators, caimans and gavials). The Mesosuchians were a highly diverse group containing over 70 genera. The Mesosuchia are divided into aquatic, semi-aquatic and terrestrial species. The Teleosauridae are good examples.

In the Teleosauridae the limbs have become shorter and the snouts have become larger. Another group is the Metriorhynchidae which have become highly adapted to water living. For example their forelimbs have become transformed into paddles.

land dwelling species include Baurusuchus.

.
Semiaquatic forms were represented by the Goniopholidae and the Atoposauridae. It is from the Atoposauridae, and a species called Theriosuchus, that the modern Eusuchians are believed to have evolved.
Alligators first show up in the upper Cretaceous, Gavials in the Miocene (about 25 million years ago), Crocodiles in the Paleocene (about 60 million years ago) and Caimans in the Oligocene (about 30 million years ago).

Studying the evolution of insects can be difficult because they don’t fossilize well. But there are ways to study insect evolution. All life affects it’s environment in one form or another. In some cases the affect can be large, in others small. Occassionally, these affects remain behind long after the organism that caused them has died. Animal footprints, such as those of two dinosaurs below (from Glen Rose trackway), are good examples.

But organism leave other types of traces besides footprints. Below is a picture of a leaf. If you look closely you can see a black line zig-zagging around the leaf. This represents a track of an insect burrowing through the leaf and eating as it goes. The black bits are - well, I’ll leave that to your imagination.

The next picture shows what happens when an insect feeds on a leaf. The blackened edges, in this case, are caused by the plant trying to heal itself. The white parts (center middle) are plant cells that have become swollen and discolored due to the damage.

The above two picture are of fossil leaves found in Colorado and date to about 35 million years ago. Scientists interested in the study of insect evolution realized that different insects leave different kinds of damage and that the type of leaf damage could be used to identify the type of insect that caused the damage. You can go here for a quick overview on how this is done.
With this information you can learn a lot about how insects lived in the past. As one scientist puts it:

“Insect damage on leaves, the remains of insect meals, is uniquely valuable data,” … “While actual insect fossils can give us taxonomic information, leaf damage provides unique ecological data about which and how many kinds of insects were eating and interacting with ancient plant species in the deep past. Also, insect damage on fossil plants, which can be very abundant, can give us a great deal of information about insects at times and places with very few insect fossils.”

Recently, fossils in Patagonia were analyzed using the above ideas. Almost 3,600 plant fossils were collected and compared to fossils collected in North America. The fossils were examined for insect damage:

The researchers classified damage by feeding group and damage type. The four feeding groups are those insects that feed on the external leaf, chewing holes, edges and other leaf parts; those insects that mine tissues inside the leaf; those that produce bulbous galls and those that pierce and suck the leaves. Because different insects chew, mine, gall and pierce in different ways, the researchers recognized 52 discrete damage types from the four feeding groups. They applied these categories to both bulk samples from single quarries and to individual leaf species.

By comparing the Patagonian fossils with the North American fossils, researchers were able to learn about past environments and how past environments affected the number of different types of plants and insects in each area.

The current evidence from South America suggests that there were a large number of different insect lineages feeding on a large number of plant species.

Above is a 52 million year old fossil of a laurel leaf. The white circles with black centers represent the feedin activities of the fairy moth (pictured below)

“There was tremendous diversity and abundance of insects and plants in the Eocene,” … “Insects depend on plants to survive. If you have diverse plants, you get diverse animals. We know that plant and insect diversity are linked today and our study shows that plant and insect diversity were linked in the past as in today’s South America.”

.

Dave Winter over at Science and Sensibility has sent me the following post on Sea Squirts. Thanks David!

Take a close look at the picture above this text. If you haven’t
been introduced to a sea squirt before you may be surprised to learn
the blue blob depicted above is an animal. If that surprised you then
you’ll be flabbergasted to learn you are more closely related to that
animal than 97% of all the species so far described on earth and very
much more than 99% of the individual organisms here.

The animal
in question is a sea squirt (or Urochordate or Tunicate) and it fits
into the Phylum Chordata - the same one as you, me and all the
vertebrates. On the face of it that seems a puzzling designation, the
animal in the picture doesn’t look much like respectable chordates
like mammals or birds or fish, or even like visually similar
invertebrates like the lancelet. That is, until you realise that what
you’re looking at is one half of a lifecycle split into two such
disparate parts that it would do a butterfly proud. See, sea squirts
start out life as larvae that look more or less like tadpoles:

Now that’s a bit more like it. Sea squirt larvae contain notochords, nicely defined muscle segments and a
post-anal tail . Just like you. When you where an embryo. The tiny
tadpoles swim in the plankton before they metamorphose into their
adult form. When the time comes they plant themselves head first onto
some hard surface (rocks, reefs and piers being among their
favourites) and proceed in dispensing with all the stuff they needed
as a free swimming tadpole - including their tail and the head
ganglion which served the role of a brain From here the sedentary,
adult form develops. Essentially the adult sea squirt is a sack fill
of sea water with two syphons - one “sucking” water in and the other
“spitting” it out. These syphons ensure water flows over the
pharyngeal basket which filters out food.

The sea squirts are
also of interest to evolutionary biologists for a number of reasons.
Firstly they may be able to tell us something about the evolution of
the vertebrates. All the vertebrates share a common ancestor with the
sea squirts, there are two main schools of thought as to how each
lineage (vertebrates and sea squirts) got to where they are
today:

1. The common ancestor shared by sea squirts and
   other chordates was something like a sea squirt larva. After
   that point the sea squirts took up a sedentary “adult stage” while the
   vertebrates went on to form bones and limbs and all those great
   things.
2. The common ancestor shared by sea squirts and other chordates was
   something like a modern sea squirt. At some stage a sea squirt larva
   became sexually mature before it took on a filter feeding “adult”
   stage. In this scheme the individual larva that reached sexual
   maturity as a ‘tadpole’ would be the progenitor of all vertebrates.
   The development of sexual maturity in an otherwise ‘juvenile’ stage is
   called neoteny and is epitomized by the Axolotl which is a sexually
   mature salamander larva.

Richard Dawkins reports
in The Ancestor’s Tale that molecular data tends to support the
first of those schemes. Coincidentally, that scheme was proposed by
that most prescient of biologists, Charles Darwin.

The other
reason sea squirts interest evolutionary biologists is that, seen
through our vertebrate minds, they seem to be bristling with potential
for great things. Recent studies have shown that the sea squirts have
genes containing all the motifs needed to get a blood clotting system
going. Additionally they have some proteins that look a lot like
Toll receptors - proteins associated with identifying pathogens in our
system. In fact a glance through the genome of a sea
squirt revels the seeds of nervous systems, eyesight, the immune
system, and even the cardiovascular system.

Of course we
shouldn’t get carried away on thinking that the sea squirts are some
sort of museum piece displaying the seeds from which we sprung. The
sea squirts have kept what genes they have for a reason - living
organism can be primitive but they can’e be ancestral. It’s likely
that genes we share with sea squirts have been co-opted into
completely different roles and many that where in our common ancestor
500 million years ago have probably been lost. Still, not too bad for
a blue blob huh?

… if variations useful to any organic being do occur, assuredly individuals thus characterised will have the best chance of being preserved in the struggle for life; and from the strong principle of inheritance they will tend to produce offspring similarly characterised. This principle of preservation, I have called, for the sake of brevity, Natural Selection.
Charles Darwin, On the origin of Species, 1859¹

Another way to express what Darwin meant is that individuals with characteristics that are useful to them in their struggle to survive are more likely to produce offspring with the same characteristics. One straightforward consequence of Darwin’s idea is that animals that are sick or injured will be less successful to defend themselves against predators or to escape from them. Therefore, such individuals are more likely to be killed by predators before they have a chance to reproduce. This is so obvious that it should hardly need to be proven. Nevertheless, it has been demonstrated to take place in the wild many times. One example involving African wild dogs (Lycaon pictus) and their prey impala (Aepycerus melampus) in Zimbabwe was published recently².

African wild dogs
African wild dogs (also called African hunting dogs) hunt in packs and share their kill. One large animal that wild dogs prefer to hunt is impala. Once a pack finds an impala, or any other prey, they begin to chase it until the prey gets tired and they catch up with it. Such chases can apparently last for several kilometers at high speeds. Obviously, this hunting method is energetically very costly. Imagine yourself having to run, say, 2 kilometers (about 1.3 miles) as fast as you can before your every meal. Just to obtain enough energy to be able to run 3x2 fast kilometers a day, you would probably have to eat an extra meal every day, but that would make it necessary to run 2 additional kilometers!

This being the case, which impalas would a pack of wild dogs rather go after to minimize their energy expenditure during a hunt? Undoubtedly, the weak and the sick ones, because they will be slower than the healthier animals, and by chasing the slower impalas the wild dogs will spend less energy.

Impalas in Africa

To determine if this was indeed what was happening in the wild, British scientists² collected bone marrow from one group of impalas that had been killed by wild dogs and another group that had been killed non-selectively by humans. They knew from previous studies that impalas in poor condition had very little fat in their bone marrows. Therefore, as a measure of the physical condition of each impala they calculated the amount of fat it had in its bone marrow at the time of its death. The graph below shows their results.

The impalas that had been killed by wild dogs (bottom curve) had significantly less marrow fat than the impalas that had been killed by humans (top curve). Therefore, the authors of the study concluded that wild dogs selectively prey on impalas that are in poorer condition.

A more general result that we can derive is that the weaker impalas are less likely to live long enough to reproduce, while the stronger ones are more likely to escape from wild dogs (and other predators) and live long enough to reproduce. What does this mean in terms of evolution? It means that the healthier and stronger impalas are more likely to pass the genes that contribute to their good health and physical strength onto their offspring. In turn, their offspring will be more likely to be healthy and so on. This is basically how natural selection works.

Dinner is being served

For more information follow these links.

Natural selection 1
Natural selection 2
African wild dog 1
African wild dog 2
Impala 1
Impala 2

1. Charles Darwin, On the Origin of Species, 1859. full text
2. Alistair Pole, Iain J. Gordon and Martyn L. Gorman. African wild dogs test the ’survival of the fittest’ paradigm. Proc. R. Soc. Lond. B (Suppl.) Biology Letters 270, S57 (2003).

Wild dog and impala pictures were downloaded from the University of Michigan Museum of Zoology Animal Diversity Web

Cross-posted at Snail’s Tales

This is the second post DarkSyd has been kind enogh to allow me to post here. Please pay his site a visit and thank him. While you are there you should check out his series on human evolution - they are masterpieces!

**************************************

They serve as Icons for sports teams and multinational corporations, they live in lands of snow and ice, on mountain tops, and deep in lush, steamy, jungles. They can see in the dark, their ears are sensitive to a range of frequency fully three times broader than ours and sounds ten times as faint. They can run at 70 miles per hour across uneven ground and turn on a dime. They possess the strength, balance, and raw power any human athlete/gymnast would kill for. And, if they happen to lock in on you while you’re unarmed, helplessly alone in the twilight wilderness, their preternatural eyes gleaming, their toothy maws yawning in ghoulish anticipation of easy prey, you might as well cut your throat; before they do it for you.
More recently one version has ensconced themselves firmly into our domiciles, ensuring their evolutionary success for the next eon or two, whilst retaining more than any other domestic creature their feral, independent nature, enlisting humans not as owners, but as staff.

How did this diverse group of profoundly graceful predators arise and what makes them so successful?

Warning: Large Graphics Below

Felus Catus is your taxonomic nomenclature.
An endothermic quadruped, carnivorous by nature.
Your visual, olfactory, and auditory senses
Contribute to your hunting skills and natural defenses.

I find myself intrigued by your sub vocal oscillations.
A singular development of cat communications.
That obviates your basic hedonistic predilection
For a rhythmic stroking of your fur to demonstrate affection.

A tail is quite essential for your acrobatic talents.
You would not be so agile if you lacked its counterbalance.
And when not being utilized to aid in locomotion,
It often serves to illustrate the state of your emotions.

Oh Spot, the complex levels of behavior you display
Connote a fairly well developed cognitive array.
And though you are not sentient, Spot, and do not comprehend,
I none the less consider you a true and valued friend.

Ode to Spot by Lt. Commander Data

Cats are mammals of course and members of the family Felidea. Cat species make up one of nine groups in the order Carnivora, which includes canids (Dogs, wolves, foxes), raccoons, and bears, as well as weasels, otters, skunks, and pinnepeds (Walruses, sea lions, seals). Carnivora arose from the hardy stock of critters such as basal Cynodonts, reptile-like mammals which predate the first dinosaur and have been around for a whopping 250 million years.

 

           Cynodont

Genetic analysis of cat DNA indicates the order carnivora split from the precursors of primates like ourselves about 80-100 million years ago in the middle Cretaceous Period, and both primates and carnivora split from insectivores; something like Cimolestes although the details are murky, perhaps as early as 150 MYA in the late Jurrassic Period. Long before the dinosaurs were exterminated, the ancestors of cats and people lived side by side in a strange evolutionary parallel of today. Both types of early mammals probably shared many a meal and competed for prey with one another in the nocturnal undergrowth of the ancient rain forests and woodlands dominated by ferns and pines, furtively scanning for raptorial predators of both the avian and terrestrial kind.

But like all mammals, the Day of the Cat would not begin to dawn until after the saurian overlords of a now bygone world had left the evolutionary scene in the hands of their more adaptive mammalian underlings.

In the late Paleocene, about 55 million years ago, the first recognizable candidate for a cat (And dog) ancestor appears: The Miacids. These sleek carnivores, most about the size of a bobcat, radiated into an array of predatory eco-niches left by the vanquished giants in a few million years. Miacids likely hunted smaller prey in the rain forest canopies and dim floors of the Eocene jungles roughly 50 MYA.

       Artist’s rendition of an early Miacid

Over the next twenty million years, the miacids diverged into the forerunners of modern cats and dogs, and by twenty million years ago the first true cats appear in the fossil record such as this Proailurus.

.  

Without a doubt the most famous prehistoric cat is the Saber toothed “Tiger”; which is not a tiger at all in the formal sense and describes a huge array of cats and protocats rather than a single species. The most commonly portrayed genus, known as Smilodon, boasts a South American species, S. populator, that is among the largest and undoubtedly one of the most dangerous felines to ever silently pad across the earth.

                         
Enlarge Saber tooth next to a quarter                                 The Saber Toothed Smilodon

Cats appear capable of evolving quickly. Most extant Great Cats are relatively new, reflecting the pace of feline plasticity. Tigers and Lions emerged so recently form a common ancestor that they’re still able to mate and occasionally even produce fertile offspring called Tigons or Ligers. Cheetahs apparently went through a genetic bottle neck at the end of the last ice age so severe only a few families survived. The animals are now all so closely related that tissue grafts from one to another take as though they’re identical twins.

The reason cats are so successful today and thus so widespread, is the same reason they’re so much fun to watch: They’re amazingly agile creatures, endowed with a big, socially adept, brain, and well-armed with an array of weaponry, which possess an astonishing repertoire of evolutionary plasticity allowing them to occupy and dominate virtually every predatory niche on land. They come in large and small sizes, live everywhere from jungle floors and canopies to alpine mountain tops, and they can get along in large packs, small harems and family groups, and as lone ambush hunters.

Cats have spines in which the vertebrae articulate in such a manner as to provide an enormous range of motion compared to most vertebrates and these back bones are sandwiched between fat, intervetebral disks able to withstand substantial violent force. Each padded foot is a springy ‘fourpod’ of toes, the end point of a complex, triple jointed shock absorbing system which can take falls and g-forces that leave a human broken and mangled. The feet, legs, and trunk may be riddled with what are essentially tiny three-dimensional accelerometers which act like a host of fully independent inner ears, sending dozens if not hundreds of separate signals to a brain which processes the data like a super computer and solves horridly complex, partial differential equations, routing that solution to all parts of the body and spine. The result is the cat can execute a flawless double-twisting, double-flip, contorting and even corkscrewing its spine almost forty-five degrees in any plane and controlling the angular momenta with its tail, feet, and head, all in less than a second, and land on its feet … to bat its tail in anger and race away unhurt, even it was thrown head-over-heels into the air for ten feet or more.

They can pad silently over dead leaves, freeze motionless for long periods of time, stare unblinkingly, barely breathing, and then flash out in a burst of blinding speed to strike without, so far as we can tell, being out of breath.

The fore claws are naturally retracted when not in use and are extended by a stout tendon actuated by a powerful muscle which runs the length of the ulna and anchors securely just below the elbow/knee. The claws themselves are made of bony protein, superhardened with mineral matrices almost to the point of a synthetic glass, which flakes off in natural conical layers leaving the claws with a permanent, needle sharp point and microscopic serrated cutting edge. With these weapons the cat first strikes and pierces the flesh, and then cuts a long laceration upon withdrawal. And larger cats such as a tiger or lion can do it with the force of a swinging sledgehammer, all focused on those tiny, sharp, edges, in the blink of an eye.

Guessing ebcuase I can’t quite make out the caption next to the exhibit … I think starting at the top right and going clockwise, it’s something like … the claw of a Siberian Tiger, African Lion, Cougar, Jaguar, Cheetah, another Cheetah, Leopard, Lynx, another Lynx(?) .. and a Bobcat?

 

The felid jaw is short and robust, giving all cats that characteristic cropped muzzle look. This architecture provides leverage and thus lends the animal a powerful bite akin to that of an english bulldog. If the cat wants to hang on, it can support several times its own weight with its entire dental arcade sunk firmly into flailing victims, crushing muscle and in some larger species even heavy bone, the long, upper and lower canines are usually quite slender and close in finely honed opposition like a pair of garden shears. They reach deep into the prey, reaching vulnerable blood vessels and arteries.  It can even reposition it’s bite with lightning speed, in mid-flail, searching for new vessels and organs with each attempt to deliver the knock out injury. They usually make straight for the neck or spine, all the while ripping into the hapless prey with all four clawed feet to gain a solid purchase and drive those killer teeth in deeper.

Between the teeth, jaw power, claws, brain, speed, eyes, ears, nose, stalking/ambushing skills, and agility, cats are probably the most precision made killing machines walking the earth today. Not since the days of velociraptor has such elegance, power, and coordination, all teamed up in one large animal. It’s no wonder warriors from Babylonian swordsmen to disciples of Shaolin kung-fu, have studied cats hoping to mimic just a portion of their gracefully lethal skills.

And, they have become our friends; among the best of our companions. The traditional story is that small Libyan Wild cats were first tamed in north Africa, enlisted as trusted domestic allies keeping down rodents and other pests in ancient horticultural civilizations on the banks of the Nile. But the reality today may be much less complimentary to our allegedly superior human management and negotiating skills: Sleeping where and when they wish, playing or hunting at their convenience, disappearing for days on end only to turn up demanding food, water, and love, we slave away in factories and offices while they loll around in abject leisure. It’s arguable cats have domesticated us more than vice-versa!

Watch the cat, even the fluff-ball of a kitten. Compared to a dog or a horse, he or she has given up almost nothing in terms of independence and feral abilities. Lurking just beneath the surface of that playful pussy is a serial killer. Their ancestral predatory intensity is easily seen with a ball of yarn standing in for a mouse, or the poor lizard who gets cornered and tormented to jazz up an otherwise boring day between naps; all in a day’s work for the common feline. When some asshole takes a kitten and throws him out of a car on the side of a rural road, odds are decent the poor thing will survive for months, maybe years, using its wits and prowess. Most dogs would be dead in a matter of days or weeks without the benefit of human resources (Hell my sheltie puppy is afraid of june bugs and cowers in fear from them on the other side of a window).

They are truly fascinating animals and I’m glad we have made an arrangement with at least some of them. And I’m hopeful we’ll preserve those magnificent great cats in the wild which are still left. Sadly for us and for them, many are barely managing to maintain viable population numbers as humans continue to encroach on their range, and they are dangerous to have roaming around your backyard. Let’s meet a few of those …

 

Felis ocreata or Libyan Wild Cat. Likely ancestor of the hundreds of modern breeds of housecat, first domesticated in ancient Egypt

Black leopard with cub. Contrary to popular belief, there is no single species of great cat called a Black Panther. Pictures of such are almost always unusually dark leopards or unusually dark Jaguars

Florida Panther; beautiful, powerful, and on the brink of extinction.

           
   Siberian Tiger Cubs                                     Lions, leopards, and tigers, oh my!

       

    A Cheetah blazing along at 50 MPH executes an abrupt, forty-five degree turn on rough, open savanna, without missing a beat. Extraordinary evolutionary adaptations such as a spine which virtually dislocates with each five meter stride and a small streamlined head allows Cheetahs to hold the land speed record at 70 plus MPH.

     

    A gorgeous Snow Leopard, now hunted for their skins, they now number only few thousand.

And what kind of Friday Cat Blogging would be replete without a goofy picture of our own cat? … But alas our cat Nikki, Absolute Lord and Life-time Ruler of DarkSyde Manor does not denigrate herself with goofiness. She regally declined an online interview or an invitation to be immortalized in film. However, in the interests of maintaining domestic non-human harmony in the Manor, and given this post has been almost exclusively about cats, I did allow our aforementioned, cowardly but lovable puppy-dog, “Darwin”, to ham it up for the digital camera instead, and have his say, below, which consisted of “Bacon?”.

Darwin adds, “Have a wonderful weekend!”

Now that you have read DarkSyd’s excellent post on the evolution of whales here is a website you can visit to explore whale evolution:

Whale Evolution Kiosk and have fun comparing whales, fish and cats.

DarkSyd has graciously allowed me to post this, in it’s entirety. Thanks!

They are the grandest beasts we know of to ever roam our planet. They come in a wondrous variety of shapes and sizes, some larger than a double decker bus, others smaller than humans. Endowed with two forms of vision, one a sonar enhanced acoustical over lay of optical images giving them the ability to take an ulrasound image or deliver a stunning taser like blow of focused sound, and the largest brains in the animal kingdom, they communicate across hundreds of kilometers of ocean with eerie, soulful music. And for many years these magnificent creatures served as the unwilling prey of both hunters wielding harpoons, and Creationists wielding confabulations.

They are the Whales, the cetaceans, our fellow mammals. And they are magnificent manifestations of megafauna and evolutionary biology alike. If you’d like a short break from the intensity of politics, let us talk of the Whale’s Evolutionary Tale and Creationist lies …

Warning: Lot of Largish Graphics Below

From playful Porpoises to the majestic great Blue, they all arose from humble beginnings in a brilliant burst of Punctuated Equilibrium over a few scant million years from an animal the size of a Great Dane. Since that time these giants have served as one of the most sobering, astonishing, examples of megafauna sown from the fertile fields of evolutionary biology, growing to a state of resplendent majesty unparalleled on our ocean world. They have no formal language, as far as we can ascertain, although they may have the intelligence to rival a chimpanzee, but we can speak for them, and we must.

For years Creationists have attacked evolution. It continues to this day, sometimes with breathtaking ignorance and outright dishonesty as in Creationism for Dummies. And one of their many lines of assault has been the incessantly repeated claim that “There are no transitional fossils!” For years in the 1970s and 1980s Young Earth Creationists used whales as an angle with which to pursue their agenda. ‘Where are the transitional whales’ they would ask in mock surprise, and then go on to conclude that because there were none, yet, we never would have any, and therefore, somehow, Young Earth Creationism “wins”. They don’t say that any longer …

A word on what a transitional fossil specimen really is: A transitional is not necessarily directly ancestral to the later organism. It might be, but we really can’t know for certain if a given transitional is the direct forebear of a later species or not. Consider the paleontologist who finds the partial skeleton of a Dachshund, a red fox, and a wolf. Is one ancestral to the other? Which way does the lineage flow; from big to little or vice-versa? What if you have only a few leg bones and some pelvis for the red fox, a partial skull of the Dachshund, and the lower jaw and a scrap of spine for the wolf? And what if you’d never seen a living canid of any kind! That’s the dilemma paleontologists are in when they try to assign ancestry. It’s pretty amazing, a testament to the dedication and expertise of paleobiologists, that they’ve been as successful as they have. This uncertinaty becomes increasingly resolved when the fossil record is more complete. In the case of some arthoropods or mollusks for exmaple, in some places for certian periods of time, the fossil record is like the pages of a book. It was for this reason Eldridge and Gould chose snails in a specific location as a data source for Punctuated Equilibrium: The transitions of direct anceastors to descendants were unamibigeous and detailed.

A transitional fossil only means that the intermediate exemplar possesses morphological characteristics (Physical features) which are also present in both modified and/or unmodified versions in a later, likely descendent, species. In an egregiously very broad sense, every fish is a transitional tetrapod, because every fish has a spinal column and fins which are present in later modified (Fins to limbs) and relatively unmodified (Spinal column) versions in all in land vertebrates such as amphibians or mammals. This means that a transitional population can over lap descendent populations in time: wolves are transitional to Dachshunds and directly ancestral to them, but wolf populations didn’t magically disappear when Dachshunds came to be!
Likewise, in another broad sense, every reptile is a transitional bird, because birds have modified arms they use as wings and relatively unmodified spines both of which are present in reptiles. That doesn’t mean every fish is directly ancestral to every species of reptiles or rodent or that every reptile is ancestral to every species of bird; all fish and all reptiles are obviously not directly ancestral to those respective clades!

Whales are closely related to Mesonychids but not directly derived from them. Mesonychids are a diverse group of proto-hoofed predators which first arose in the late Paleocene Epoch, beginning about 65 million years ago, in the ashes of a world still reeling from the K-T Impact which may have escorted the dinosaurs off the evolutionary stage. They diversified into a number of species. Some of them, especially early on, were the size of a collie, others rank as the largest mammalian land predator to ever tip the scales, such as Andrewsarchus above.
Because of this semi-hoofed ancestry, DNA comparisons, and recent fossil evidence, Whales are now technically classified in the order of Artiodactyls, meaning ‘even toed’. This order includes hippos, giraffes, and pigs.

Illustration courtesy UTI commentator, contributor, and wildlife artist, O’George

The first notable transition in our tale of the whale is a kind of cute looking critter called Pakicetus, from over fifty-million years ago early in the Eocene Epoch. This fellow looks kind of like a big, bad, long snouted wolf in size, but probably occupied the eco-niche of a sort of beach combing Hyena. Eeking out a living on crabs, mussels, and sundry carcasses washed up from the ocean.

                Ambulocetus

The next stop in our whale’s tale is what looks for all the world like the mammalian version of a crocodile: Ambulocetus meaning “walking whale”, at about 49 million years ago. This is a bad boy, a mean looking customer, long, powerful, low slung, partially aquatic, and the jaws are outfitted to clamp down, hold on to, and crush prey. It probably made it’s living a lot like crocs do; snapping up fish from the water and unwary mammals from the beckoning shores of lakes and bays.

Speaking of intermediates, how does Rodhocetus above look for a transitional whale candidate in both skeleton and artist’s rendition? This fellow was roaming the south Asian seas at 45-50 million years ago.

Then we get into Dalanistes at circa 45 MYA. Followed by Protcetidae some of which were the first fully aquatic whale ancestors, and then on into full blown early whales such as archaic Odontocetids (Early toothed whales), like Dorudons and Basilisaurids by about 40 million years ago-the latter incidentally still trailing tiny, but fully formed, rear legs

Basilosaurid skeleton. Note the vestigial rear leg bones. It possible Baslisaurus may have used these small limbs to lock together during mating

How do we know that these fossils, in some case just partial skulls, are really whales ancestors or early whales? Well, it happens that the Whale Ear, from the Pakicetus to modern whales, is highly distinctive and easily recognized if you know what to look for. The ear slowly turned into the receiver for cetacean sonar, preserving and modifying those distinguishable features during that transition. Since the ear cavity and inner structure is part of the skull and the crania in general is one of the most likely portions of the skeleton to be preserved as a fossil, the morphology of that ear cavity is a fantastically useful diagnostic trait for determining if you’re dealing with a whale and for discerning the particular stage of evolution of that specimen. Evolutionary biologist PZ Myers provides an outline:

Start with the top left diagram. This is the ear of a typical modern land mammal. The horn shaped structure angling down towards 8 o’clock is the external auditory meatus (EAM), your ear hole, which leads to the dark gray oval, the tympanic membrane (TyMe), better known as the ear drum. Sound in air travels down the EAM to the TyMe, which vibrates. The vibrations are amplified the the chain of inner ear bones, the malleus (Mal), incus (Inc), and stapes (Sta), or hammer, anvil, and stirrup (I know–the terminology gets a little dense). Finally, the amplified vibrations are transmitted to the cochlea, where they are transduced into localized deflections of hair cells that trigger pitch-specific nerve impulses.
That’s the path that works well in the air, but it doesn’t work so well in water. Try immersing your head in the bathtub or swimming pool, though, and sounds are immediately dampened; the EAM fills with water that puts pressure on the eardrum, reducing the amplitude. Instead, the vibrations are transmitted through the bones and tissues of the head, vibrating the tympanic bone (TyBo) and by that path the inner ear bones.

The next three diagrams show the progression of changes in the whale lineage. The top right picture (b) is a pakicetid from about 50 million years ago. It’s not much different from the generic land mammal, with an EAM, eardrum, etc., but note the one special feature: the tympanic bone isn’t connected to the periotic bone (Per), and it’s actually thickened into a structure called the involucrum. Basically, the bony structure of the ear is less tightly attached to the skull, and is more free to vibrate in response to sound transmitted through the tissue of the head.

The next step is seen in a group of whales called the remingtonocetid/protocetids, from 43-46 million years ago (c). The ear capsule is even less strongly attached to the skull, and the involucrum is more robust and even more remote from the skull–the whole thing is better at moving freely. The ear drum is reduced and conical in shape, and the malleus is fused to the bone, so although the pieces are all there, it’s not going to be particularly effective at capturing sound waves in air. Another feature is a deep groove in the mandible that indicates that these animals had a fat pad (FaPa) in the jaw that would better transmit vibrations from the jaw bone to the ear capsule.

Last (d) is the ear structure of a modern whale. All of the trends of the previous organisms are accentuated: the ear capsule is specialized to receive sounds transmitted through the fat pad, and has completely given up on sounds transmitted through air–the external auditory meatus is closed off and gone, and while the eardrum is present, it’s not connected to the external world.

In addition to the unique morphology of the ear canal and bones, whales also have a distinctive spine which was modified over time to provide motive force underwater. Most folks understand that whales move by swinging their large tail flukes up and down, rather than side to side as most fish. The modifications in the spine, especially around the pelvic girdle, is a dead giveaway if you have the requisite vertebrae.

Now that we’ve met a few of the actors in our Whale’s Tale, and armed with new found fossil specimens, ear analysis, and DNA comparisons, we can construct a rough, provisional evolutionary progression, showing a plausible series of whale transitionals, starting with a fully terrestrial animal and ending with modern cetaceans. Thanks again to O’George’s artistic skills here it is:

It’s not meant to be a perfect line of ascending cetaceans and the sporadic nature of the fossil record ensures it never will be. We don’t know for a fact who or what is directly ancestral to later specimens or any intermediate, or which ones are ancestral to which whales, or even if any of early lineage’s shown survived. Modern whales may be the descendants of a small offshoot of one of the earlier protocetids and never preserved, which we will therefore never know about in detail. But sequentially as a gross series, that’s all pretty damn reasonable. Each intermediate is definitely a whale or an indirect/direct precursor to a whale. Each is found in the correct chronological order in the geological record and exhibits the clear signs of a transitional form progressing from a four legged terrestrial mammal to a full blown, aquatic one.

Creationists claim we have No transitional fossils? Bullshit: Utterly fallacious! Here’s hundreds of vertebrate intermediates alone, whales are just the tip of the iceberg. For the most part Creationist claims that we have no intermediate candidates for whales have fallen silent. Now when they address the topic of whale evolution, they focus on disinformation regarding the rich series of transitionals whales we do have.

Of course the everyday Creationist victim you’re likely to encounter at work, church, or school, will sometimes pipe up with “Why aren’t dogs evolving into whales now, right now, before my very eyes?” Well obviously the question is loaded: Dogs did not evolve into whales in the first place and any future evolution is not going to produce a creature exactly like whales. Nor would the scope of human life permit such an observation. But we certainly have all kinds of examples of clearly terrestrial creatures which appear to be caught in mid evolution in various states of marine adaptivity, changing forms from land dwellers to water dwellers. Seals, walruses, sea otters, beavers, and Penguins, just to name a few, come to mind. Brown bears and Polar bears are still technically the same species as they can interbreeed and produce viable, fertile offspring. But a couple of hundred thousand years ago they went their separate evolutionary ways, and now the Polar Bear is so often found in water and so at home there, it’s taxonimic nomenclature is Ursus Maritimus or Sea Bear. Given the opportunity and time, any one of those groups could go on to become fully aquatic and get as big as a diesel rig, just like the descendants of ambulocetus did.

Top left: Blue Whale   Top Right: Sperm Whale   Bottom Left: A small pod of Narwhales (Note single tusk in males. It’s actually an elongated tooth)   Bottom Right: Bowhead Whale with Beluga Whale escort

A few whales and other creatures by size

Enlarge (Hi-res image warning)

Most nations are curbing whaling as an industry. Even the Blue-whale is making something of a comeback. But pollution and over fishing are just as much of a threat to the delicate balance of the marine ecosystem whales depend on as a Japanese Trawler with an explosive tipped harpoon gun.

Whales and their four-limbed ancestors were here long before humans or hominids or even the great apes and monkeys. They rose from the tableau of a shattered world, the smoldering remains of the long lost planet of the dinosaurs. In a little over ten million years they grew from the size of antelope to the most massive animals known, and now dominate the ocean in both intelligence and size. They have survived ice ages, continental drift, super-volcanic eruptions, and greenhouse gases. Now they face their biggest threat yet: The fleets of whalers both past and present, and pollution led by the United States headed by a cabal of neo-cons and their swindled right-wing Christian followers who enable them in the belief that God put whales and everything else on this planet to be plundered until the approaching glorious rapture (Any day now). Regardless of where they came from and how they evolved, looking forward, our world without whales would be a tragedy; a world poorer, a loss of riches, their extinction at our hands unacceptable.

But we must bear in mind these are wild creatures, born free in an alien three-dimensional realm of deep ocean; they are neither the Demons which tomented Captain Ahab or the tame, gentle giants of Seaworld. They can and have attacked humans, at times for no apparent reason, albeit rarely. And they have saved drowning people, again we have no idea why. They do not exist for crass amusement, but they surely provide us with wonder if observed with respect.

They are mysterious, mostly just curious, and generally, but not always, harmless. But after their recent experiences with the walking ape, I’d guess what they would really like, if they could speak for themselves, is simply to be left alone.

The ocean is vast, surely big enough for both whales, and ourselves, to co-exist. Maybe that’s what this guy is trying to tell us … If only we could decipher his song.

John Wilkins at Evolving Thoughts has a great post called Misunderstanding Evolution. Through the Creative Commons Licence and the kindness of John Wilkins I am able to post it here in it’s entirety. Please visit John’s site and thank him.

* * * * * * * *

Misunderstanding evolution
While I’m on the subject, this is a talk I gave a couple of years ago to secondary school students.

“Evolution is so simple, almost anyone can misunderstand it” – David Hull

“Nothing in biology makes sense except in the light of evolution” – Theodosius Dobzhansky

This talk is going to assume that evolution is a fact, that it is a fact of human biology as well as of every other organism, and that the explanations of modern biology are pretty well right.

Some of you may think this is not so, and I am more than happy to discuss this with you after the talk, should you wish, or you can email me at the address shown there and I’ll give you some URLs and book recommendations. For now, please just take this as a statement of what modern biology implies to my mind, and leave it to another time whether you think biology is wholly mistaken about evolution, for whatever reason.

Don’t take notes – just listen. The whole talk will be available online in PDF from the website above, and it will include references too.

Why are there still monkeys?

But since we are talking about creationists and other anti-evolutionists, let’s look at one of the more common “knock-down arguments” they use against evolution:
If humans evolved from monkeys, why are there still monkeys?

Laugh if you want, but it is evidence of a deep confusion about evolutionary theory. Why indeed are there still monkeys? Why would someone think that there would not be monkeys if humans evolved from them? Now not all creationists think this is a good argument, but even so, why does it have some immediate effect on people?

The answer is simple – people think that evolution is a progressive process. Similar errors are involved in the claims that humans are the end of evolution, or that if humans went extinct, some other species would evolve to take our place as intelligent and civilised creatures. Let’s look at the errors involved. There are four:

1. That evolution moves from simple and primitive to complex and sophisticated,

2. That intelligence is somehow the goal, the most sophisticated thing, a living organism can evolve towards,

3. That when evolution occurs, the entire species changes, and

4. That if evolution were true, we would see every intermediate form that ever lived.

Each of these is not only wrong, it is in fact opposed to the scientific, Darwinian, view of evolution. The first is known by historians of ideas as the Great Chain of Being. It is an idea that goes back to the ancient Greeks, and which was especially active in the Middle Ages. John Waller, who is talking after me, will talk more about this, but it’s enough to say now that according to this pre-Darwin view, change only goes one way, while for Darwin and all who have studied biology since him, it is sometimes more useful to an organism to get simpler than to get more complex.

The second encompasses a whole range of mistakes that are usually called “teleology”, which is a fancy Greek term for “goal-centeredness”. The idea here is that there is a goal towards which things evolved, and which made them evolve. This idea is something you will find often in science fiction, particularly in the Star Trek franchise. But evolution has no goal. It does not “look ahead” and “choose” what will happen – what happens happens first, and if it works better than before, or if it is no worse than before, it might get kept. Even more important is that if it changes or stays the same, it might still become extinct.

The third is a very basic mistake, and it’s one that even famous evolutionary biologists have made, although not for a long time now. It is the idea that whole species evolve together. This means that if evolution happens, the critics think, then the older forms should disappear, but we see them (those monkeys, remember?) so therefore evolution didn’t happen. In fact, modern evolutionary biology believes (and has observed) that evolution into new species happens only in populations. In short, the ancestor of a new species isn’t an old species, but a population, or part only, of the old species. There are several mechanisms and processes for this I won’t bore you with, but if anyone is interested, I can recommend a wonderful recent book called Frogs, flies and dandelions.

So, why are there still monkeys? Because the last shared ancestor of ourselves and monkeys did not go extinct when they split off from us, because the whole species turned our way or because theirs was somehow a lesser pathway to take. Monkeys and apes do just fine in survival and reproduction terms, and that is what counts in evolution. Evolution was not heading in our direction, it got there almost by accident. And if we stopped existing, there is no reason to think there’d be a Planet of the Apes afterwards. That is, other than the planet of the apes that now exists, for we are apes, biologically speaking. But if some animal did evolve to intelligence of a human kind, I like to think it would be those meerkats – social, almost bipedal, and living in the strong selective environment of Africa, where we evolved. On the other hand, if they had any brains, and any control over their own evolution, they’d probably do better to stay pretty much the way they are…

Survival of the strongest

“Natural Selection is not Evolution ” – Ronald A Fisher

Evolution is divided into two kinds, and they get badly confused with each other. One of these is what we just talked about – speciation. The other is the process of adaptation by natural selection. The technical terms for this are cladogenesis (Greek for “the origin of branches”, of the evolutionary “tree”, that is) and anagenesis (from the Greek for “regeneration” or “change through time”).

Natural selection is a pretty simple idea – if organisms vary in ways that are hereditable, then the better performing ones will come to dominate any population in environments that have limited resources. Seems fairly simple, right? Wrong. Not only is it not simple in the ways it works out – and it took over a century before it was mathematically understood – but many people, even quite smart people, insist on misinterpreting natural selection to mean that only the strongest survive or that competition in nature is “red in tooth and claw” as a poet in Darwin’s time had said it. An Australian philosopher well-respected for his work on the famous philosopher Hume (who influenced Darwin) wrote a book entitled Darwinian fairytales. In it, he says that if Darwin’s ideas were true, we should expect to see people and dogs fighting all the time in the street. A more complete misunderstanding of natural selection is hard to conceive.

One of the things about natural selection is that it does not involve conscious, deliberate, or active competition. Darwin himself said this, but the message got lost under the influence of another philosopher, Herbert Spencer, who insisted that a better term for Natural Selection was survival of the fittest. This naturally led people to think that “fit” here meant “stronger” or “faster”, or even just plain “meaner”. But it doesn’t. “Fit” in biology means something that seems a little odd at first. It means little more than “has the most grandchildren”. An organism is fitter than another if it ends up having more progeny over long periods of time, on average. This means that although I only have two kids of my own, I am fitter than someone who has 12 kids if my kids live to adulthood, raise kids of their own, and so on, and theirs only end up raising a few successful grandchildren.

Evolution isn’t nice, but it is an exact bookkeeper.

Now fitness is misunderstood in another way, too. We sometimes talk about two organisms differing in fitness as if they are in every circumstance always fitter or less fit that way. This is not true. There’s a gene in countries that suffer from malaria that causes sickle cell anemia. This is a disease in which the red blood cells are misshapen, and if you have one copy of that gene from one parent, then it doesn’t make a lot of difference to you, but the malaria parasite can’t as easily infect and affect you, because it uses the red blood cells to breed in, and the sickled red blood cells are less hospitable to them. So natural selection keeps this gene at a constant frequency in those populations.

Why doesn’t it take over the populations entirely? Because if you have two copies, one from each parent, you die before you reach five. Africans and Mediterraneans whose ancestors migrated to non-malarial countries are less fit than those who don’t have these genes, and the gene is slowly being eliminated from those populations in America and elsewhere. But in malarial countries, heterozygotes, as those who have one copy of a gene are called, are fitter than those who do not carry it.

All differences in genes are like this, and so also are all differences in the form and function of the organisms those genes cause. In one place a gene can be fitter than others, while in another it can be less fit. Fitness is relative to the environment of the organism. If you doubt that, consider which bear will live more effectively if transported to the tropics – a polar bear or a black bear. And which one is fitter in the Arctic?

By the way, this is a good reason not to take claims that we can “improve” the human race through breeding or genetic engineering. Unless we can foresee what environments these people will be in, and that includes what germs, pollutants, food sources, and so on, they will encounter, we just do not know if they will be fitter than their unmodified cousins.
Every day, in every way

So, what can natural selection achieve? How good can it make things? Back before Darwin there was a movement called “natural theology”, which was based on the belief that organisms were perfectly adapted to their environment. Many people think still that organisms are perfect in that way. Natural selection, rather than God’s design, is what makes them perfectly adapted, but they remain the same – ideal for what they are and do.

Only they don’t. One thing that Darwin’s view of evolution did was to draw attention to imperfection as a feature of organisms. There are lots of things that are just “bad design” – we ourselves are full of such less-than-perfection. Take the human spine, for example. We suffer from all kinds of back troubles in large part because we are trying to use in a vertical position a structure that was “designed” by evolution to bear a load when horizontal. Our remote ancestors walked on all fours – they, like we still are, were tetrapod, which means fourlegged, and at some point our ancestors shifted their mode of locomotion. And our spines haven’t yet caught up with that. Why?

Natural selection is not survival and reproduction of the best possible variation. It is only survival and reproduction of the relatively better variations in any population. If selection was a thinking agent, it would not care whether or not what beat out the competition was the best design that could be made, just whether each succeeding variation is better than the alternatives that are actually around. So if a variant happens to walk better, but suffers from back pain when it gets to my advanced age, selection is satisfied. In fact, that is what we should call it – selection is not an optimising process, it is a satisfising process (a term from Herbert Simon’s book, The Sciences of the Artificial). We really should call it survival of the more adequate. Mediocrity is OK if it’s a little bit less mediocre than whatever else is trying to make a living in the same population.

This is a general fact about similar processes in, for example, economics. Those with an abiding faith in the free market think that this will result in the best possible and most optimal outcome. But biologists know that natural selection can result in some very suboptimal situations, because selection really doesn’t look forward or care about perfection. In fact, selection can drive a population to extinction. Consider the following example:

There are two different varieties in a population of some organisms – greedy graspers and frugal misers, let us call them. The graspers get more food, more resources and will always out-compete the misers, because when there are resources, the misers get less for their children. But resources are limited and replenish at a fixed rate, say. So the graspers reduce the resources available for them to compete for. Graspers will always increase as a fraction of the population, but at the same time the population size has to reduce due to over-use of resources. Eventually, the fitter variant will drive the population extinct. In the mathematical theory of games that underpins both economic theory and evolutionary theory, this is referred to as the Tragedy of the Commons – where a common resource is used, those who use more have an edge, but overall the group loses out. And this is due to selection, both in economic markets and in ecosystems.

Another mistake therefore, is to think that natural selection works “for the benefit of the species”, as it is often put. What selection does is sort out varieties on the basis of their local efficiency at being relatively better at reproduction. If selection is for the benefit of anything, it is for the benefit of hereditable varieties; some people say that the “unit of selection” is the gene, because only genes persist over evolutionary time. This is in my view just another way of saying that traits that last for many generations do better than traits that don’t.

So we must not expect that evolution is a process that will correct our mistakes. A crucial part of evolution is what we are witnessing happen now more than any time in the history of the earth – extinction. Natural selection cannot overcome the massive challenges we are throwing at living systems if the rate at which the variants occur from which we get the “accidentally fit” mutations is less than the rate of elimination by selection in the novel environments we are creating. It is likely that evolutionary diversity will recover after we have driven most species to extinction (including ourselves in the process), but the timescale is daunting in a human perspective. It will take tens of millions of years to recover. Consider, when you think that number over – we humans are at most only 2.5 million years old, and our own species is around half a million years old. None of your descendents will see that diversity return (Wilson 1992).

Another reason why natural selection can’t achieve perfection is what we might call the You Can’t Get There From Here principle. The best example of this is a somewhat delicate subject – the vessel that transports semen in humans. In our four legged ancestors, this followed a short path from internal testicles to the penis. As the testicles evolved to be external in our lineage, and as we moved upright, the vessel, known as the vas deferens (the bit that gets the snip in a vasectomy) had to loop over the urethra, the vessel that transports urine from the kidneys. It would make a lot of sense to have the vas deferens move under the urethra, but the way it develops is based on how it developed in our ancestors, and that program can only be twisted, not recoded from the start, as it were.

So selection is neither all-powerful nor the universal acid for all problems. It is, however a sufficient explanation for the adaptation that we do see in living organisms, for those cases where there is a good fit between organisms and their environments.

Bon chance

To finish, I would like to address a mistake that predates evolution by 2000 years. It is the idea that evolution is due to chance, to randomness. Criticisms of “materialism” being based on chance and accident go back to reactions to Epicurus in Aristotle’s day. Since evolution was proposed, critics have repeatedly asserted that it is an explanation founded on chance, and so it is unscientific, against religion and the cause of all moral decay. Seriously, that is what they say.
So I want to talk a bit about chance in evolution. Darwin himself was pretty clear – for him “chance” merely meant something that we presently do not know the causes of. When genetics was developed, these “accidents” were called “mutations”, and as we have seen, mutations form the foundation of the variation on which selection acts. But chance in evolution is much more interesting than that.

Let’s get mutations out of the way first. A mutation is just a change in the genetic sequence. We know very well how they happen (and sometimes we know enough to predict where they will happen and under what circumstances); there is no sense in which we can say that chance alone acts to cause mutations. Each mutation is due to ordinary physics and chemistry acting on the molecules of genes.

More interesting is the role of chance in gene pools, in populations. Which organism mates with which is a statistical matter in populations – a population can be relatively similar all over, so that mates have a pretty well equal probability of mating with any other individual (of the opposite sex, of course!), or the population can be bunched up into subsections where mating is more likely within than between. Think of villages in a country. These probabilities affect how selection operates, because you can’t compete with someone for mating opportunities if you never meet your potential mate.

But more than this, if the population is small, then the “random mating” effect is increased. Suppose you have a dozen individuals in a very small population, one of which has a very rare gene in the larger population from which they came. That rare gene can disappear in the larger population and yet, just through random mating, end up dominating the resulting population that springs from these dozen. This is called genetic drift. It is worth remembering that selection is not always the explanation – often things get spread around just because a population is small, or because there is just no real selective difference in the fitness of the mutations.

But there is a sense in which new mutations are random, and this is perhaps the most interesting sense. It is the fact that since “evolution” can’t look ahead to see what is going to be needed, variations are random relative to those future needs. In fact, variation in natural evolution is random relative to the needs of organisms now. The varieties arise (through ordinary lawful physical processes) with no regard for what might be useful. What is useful is retained and spreads through the population if selection is operating, but the novelty is not caused by the need.

A critic of Darwin’s called this the contrast between “luck” and “cunning”, and many have felt intuitively that there has to be some cunning involved in evolution. So far as the biology is concerned, there isn’t – there’s no mechanism by which cunning could be employed. Although we talk about evolution as if it were an agent with intentions and the ability to calculate outcomes, in fact this is just a metaphor, a figure of speech. It’s really hard for humans not to use this figure of speech. Always bear in mind – evolution is not an agent. There really is no hidden hand behind it.

I hope that this has helped you understand evolution a bit better. There are many other misunderstandings of evolution that come up again and again, and, to be honest, most of them can be cured with a bit of exposure to the history of evolutionary thinking (Bowler 1984 – there’s a new edition in 2003). But these are the worst and most persistent.

Reading

Asterisked books are a good introduction to evolution. The double asterisked books are highly recommended.

Talk.origins Archive

*Bowler, Peter J. Evolution: The History of an Idea. Berkeley: University of California Press, 1984.

*———. Evolution: The History of an Idea. 3rd, completely rev. and expanded ed. Berkeley: University of California Press, 2003.

*Dennett, Daniel C. Darwin’s Dangerous Idea: Evolution and the Meanings of Life. New York: Simon and Schuster, 1995.

*Dawkins, Richard. The Blind Watchmaker. Harlow: Longman Scientific and Technical, 1986.

**———. Climbing Mount Improbable. New York: Norton, 1996.

*———. The Selfish Gene. New ed. Oxford UK; New York: Oxford University Press, 1989.

*Eldredge, N. Reinventing Darwin: The Great Evolutionary Debate. London UK: Weidenfeld and Nicholson, 1995.

*Gould, Stephen Jay. Life’s Grandeur: The Spread of Excellence from Plato to Darwin. London: Jonathon Cape, 1996.

*Jones, Steve. Almost Like a Whale. London: Anchor (Transworld Publishers), 2000.

**Maynard Smith, John. The Theory of Evolution. Canto ed. Cambridge; New York: Cambridge University Press, 1993.

**Patterson, Colin. Evolution. 2nd ed. Ithaca, N.Y.: Comstock Pub. Associates, 1999.

Simon, Herbert A. The Sciences of the Artificial. 3rd ed. Cambridge, Mass.: MIT Press, 1996.

**Schilthuizen, Menno. 2001. Frogs, flies, and dandelions: the making of species. Oxford: Oxford University Press.

Stove, D. C. 1995. Darwinian fairytales. Aldershot, Hants, England; Brookfield, Vt.: Avebury.

*Wilson, Edward O. 1992. The diversity of life. London: Penguin.

posted by John Wilkins @ 2:50 PM

Darksyd at Unscrewing the Inscrutable has an excellent post on the evolution of the felidae. Check it out.