Atheist Son Writes… Evidence for Evolution 1: Fossils

Dear mum,

This will be the first of several emails I intend to send where I will attempt to show you just a small cairn on the mountain of evidence that supports the fact of evolution by means of natural selection. This email will focus on historical cases of speciation, that is, fossils that clearly demonstrate a transformation over time from one type of species into another type of species.

Every species on the planet, including humans, are evolving gradually with every generation. Because large species tend to have longer generations large scale changes are only apparent when observed over long periods of time. This is why fossils are so useful since they are like snapshots of many species spanning hundreds of millions of years.

Before I begin I’d like to draw your attention to three predictions drawn directly from your creation hypothesis and the theory of evolution. Please read them carefully so that you understand why they are predictions:

Creation:
If all species popped into existence the same time as written in Genesis:

  1. Fossils of all modern plants and animals would suddenly appear fully formed at the same time in history where beforehand nothing existed.
  2. Ancient and recent fossils of plants and animals would look identical.
  3. You would expect most, if not all, species that appear in the fossil record to still be alive today.

Evolution:
If all species evolved from a common ancestor:

  1. There would be a gradual increase in species number and complexity from the most ancient fossils to the most recent.
  2. Natural selection would result in a large number of extinct species in the fossil record.
  3. There would be numerous fossil examples of transitional species (displaying a mosaic of features of organisms that came before and after it).

If you study these predictions carefully you will notice that the two lists are mutually incompatible. We also find that not a single one of the three predictions of creationism is observed in the fossil record. Meanwhile all three of the predictions of evolution are observed no matter where you look in the world. This empirical observation alone is sufficient to bury the creationist hypothesis forever. However, in case any doubts remain in your mind I will focus the remainder of this email on just some examples of the third prediction made by the theory of evolution – the presence of transitional fossils. I have placed the names of some species in bold type so that should you wish to see the fossils and recreations of the transitional species you need only look up their names in Google images!

It’s hard to convey the sheer numbers (in their thousands) of transitional fossils in existence for every type of animal both alive and extinct; plants, fish, amphibians, reptiles, mammals, birds, humans etc. In my job I’m occasionally lucky enough to see and hold some of them including beautifully preserved transitional species of pterosaurs (‘flying dinosaurs’) showing the move from small tree-climbing reptiles into flying creatures the size of jet planes over 160 million years of evolution. I’ve also observed the many different species of Archaeopteryx and other feathered-dinosaurs now found that trace the evolution of modern-day birds. In every case we find the later fossils sharing traits with earlier fossils, such as skeletal features, the laying of eggs and the possession of scales, but in also new adaptations like feathers, hollow bones, loss of teeth, etc, that allow them to better survive in their changing environment. It is a remarkable but unavoidable fact that your last chicken dinner was a descendant of the dinosaurs!

Now, before you shout “that’s crazy”, or “my gut tells me that can’t be true”, remember what I said in my last email – the human brain did not evolve to do science which is why so-called common sense is often wrong. However, fossil evidence is as real as the nose on your face and only when you ignore all your subjective biases and emotions does the objective truth emerge!

Another of my favourite examples of transitional fossils, which I think you might enjoy, are whales. As I’m sure you’re are aware whales are mammals not fish and so started out as a land creature that over several generations returned to the oceans (where all life started). Our understanding of this process has exploded in recent years with the finding of several transitional fossils that provide a remarkably complete record of one of life’s greatest evolutionary speciation events:

(1) Our first fossil is of a land mammal from 60 million years ago (mya) called Sinonyx, a wolf-sized primitive ungulate with several key characters that link it to whales including a long muzzle, enlarged jugular foramen and short basicranium (Zhou and others 1995). It also had other features including teeth that were adapted for eating fish, indicating that Sinonyx was already developing the adaptations that later became the basis of the whales’ specialized way of life.

(2) The next fossil in the sequence, Pakicetus, from about 52 mya, is clearly similar to Sinonyx although its teeth, skull had adapted even more to eating a fish diet and short dives underwater (Gingerich and others 1983). However, it lacked the means to hear well underwater or cope with high pressures so it still would have spent most of its time on land.

(3) In the same area that Pakicetus was found but in more recent rock layers we find Ambulocetus, “the walking whale that swims” from about 50 mya (Thewissen and colleagues 1994). Ambulocetus is best described as an amphibious, sea-lion-sized fish-eater that was not yet totally disconnected from the terrestrial life of its ancestors. It had short rear legs and bigger fore limbs that, while allowing walking on land, were better for propelling through water. Although its skull lacked a blowhole many other parts of its skull were intermediate to a whale.

(4) Around 46 mya Rodhocetus took all these changes even further yet still kept some primitive terrestrial features. It had developed a powerful tail for swimming, larger dorsal spines for muscle attachment seen in whales, 1/3 smaller legs and hips which would have made walking less easy but up-down tail swimming easer. Its skull was far larger and it’s teeth shaped more like a whales, and its nostrils had begun to migrate higher along its snout, showing blowhole evolution (Gingerich and others 1994).

(5) The next fossil we find is Basilosaurus (Gingerich 1994) from around 35-45 mya. This long, serpentine animal had almost completely lost its rear limbs and were useless for walking or swimming. Its pelvis had shrunk so that it could no longer bear it’s own weight and would have lived permanently in water. Many other skeletal and skull adaptations were also intermediate to a whale including a blowhole that had migrated near the top of its snout.

(6) Dorudon (about 40 mya) probably represents the group most likely to be ancestral to modern whales (Gingerich 1994). Like Basilosaurus it was a fully aquatic whale although it had very small limbs that projected slightly outside its body and ears adapted for underwater hearing and high pressure. Even if you look at the skeleton of modern whales you will see the vestiges of its ancestry, such as tiny rear foot bones now entirely hidden inside its body.

In summarizing the paleontological evidence, I have noted the consistent changes that indicate a series of adaptations from more terrestrial to more aquatic environments as we move from the most ancestral to the most recent species. These changes affect the shape of the skull, the shape of the teeth, the position of the nostrils, the size and structure of both the forelimbs and the hindlimbs, the size and shape of the tail, and the structure of the middle ear as it relates to directional hearing underwater and diving. The paleontological evidence records a history of increasing adaptation to life in the water – not just to any way of life in the water, but to life as lived by contemporary whales.

However, my summary of the fossil evidence that whales descended from terrestrial mammals is not exhaustive. The current view of whale evolution is supported by scientific research in several distinct disciplines including, morphological, molecular biological, vestigial, embryological, geochemical, paleoenvironmental, paleobiogeographical, and chronological.

Clearly, even if we look only at transitional fossils, your claim of “There is still no evidence!” is wrong. In fact, in the case of whales, we have several, beautifully arranged transitional fossils in morphological and chronological order.

I was planning to finish off with a similar length breakdown of the fossil evidence for human evolution from primates, which is not only better understood but has more transitional fossils, however I think this email has already gone on too long! Perhaps I will save that for another email in the future.

In my next email I will explain the genetic (molecular) evidence for evolution and speciation. Before then I will just say this: the real story of life on Earth is far grander and far more inspiring than any creation myth that religion can ever come up with, and has the additional benefit that it is true! Stories of naked couples, fig leaves, spare ribs, and talking snakes seem extremely parochial by comparison – like something a bronze age tribe might come up with perhaps?

If you want to read more about the fossil evidence for evolution there is an excellent and very easy-to-read introduction with helpful illustrations you can find online at http://www.agiweb.org/news/evolution.pdf.

Love and understanding,

Sam

References:

Gingerich P, Raza SM, Arif M, Anwar M, Zhou X. New whale from the Eocene of Pakistan and the origin of cetacean swimming. Nature 1994; 368: 844-7.

Gingerich P, Wells NA, Russell DE, Shah SMI. Origin of whales in epicontinental remnant seas: new evidence from the early Eocene of Pakistan, Science 1983; 220: 403-6.

Thewissen JGM, Hussain ST, Arif M. Fossil evidence for the origin of aquatic locomotion in Archaeocete whales. Science 1994; 263: 210-2.

Zhou X, Zhai R, Gingerich P, Chen L. Skull of a new Mesonychid (Mammalia, Mesonychia) from the late Paleocene of China. Journal of Vertebrate Paleontology 1995; 15 (2): 387-400.

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