Sunday, August 7, 2011

WEIT: The Naked Ape

This is why the "no transitional fossils"
canard just makes me laugh.
Coyne begins WEIT's penultimate chapter by expressing the cultural and religious importance of human evolution. Even many religious people and institutions that otherwise except evolution (the Catholic church, for example) still reject the notion that humans could have evolved from other primates. Incredibly, John Scopes was convicted of the crime of teaching such facts less than a century ago, in 1925. Because of the potential public outcry, Darwin barely mentioned the issue in the Origin, and another scientist reburied the bones of a Homo erectus specimen for 30 years.

Thankfully, though, we have a decent understanding of our lineage today. Our evidence includes things like homology and genetic data, but fossils are the focus of Coyne's chapter. Here's what we should expect if humans evolved:
"Around five to seven million years ago [based on molecular evidence], we expect to find fossil ancestors having traits shared by chimpanzees, orangutans, and gorillas, but with some human features too. As the fossils become more and more recent, we should see brains getting relatively larger, canine teeth becoming smaller, the tooth row becoming less rectangular and more curved, and the posture becoming more erect. And this is exactly what we see."
To summarize (and ignore over a dozen other important finds): First comes the 6 to 7 million year old Sahelanthropus tchadensis, possibly our last common ancestor with chimps, which has a long skull and small brain like apes, but a flat face, small teeth and brow ridges like later species in our lineage. Then there's Australopithecus afarensis, of which Lucy is one. We know they were bipedal because their femurs angle inward from the hips, making upright walking far more efficient. They may even be responsible for the 3.6 million year old Laetoli footprints.

At this point, brain sizes begin growing steadily. Homo habilis, from about 2.5 mya, still have some apelike characteristics, but also have larger (though not human-sized) brains and have been found with carved stone tools that would be used for things like butchering. Homo erectus "still had a flattened, chinless face," but used even more complex tools, along with fire for cooking. Finally, just a couple of hundred thousand years ago, we have Homo neanderthalensis, distinct from but extremely similar to modern Homo sapiens. We most likely wiped out the Neanderthals either by outcompeting them or killing them.

While these fossils finds are more likely to come from close evolutionary cousins than our direct ancestors, they still tell us an enormous amount about our history. Anyone who looks honestly at the fossil evidence (let alone things like DNA and vestigial organs) would conclude, as modern science has, that we have a common ancestor with the other great apes. Coyne drives this home with one particularly amusing yet compelling point. Creationists who look at the evidence must classify all fossils as either apes or humans. If we really are a distinct creation of God, this ought to be a simple matter, but here's what happens when they try:

Via TalkOrigins
They can't even agree amongst themselves.

As a questioning creationist investigating the evidence for evolution, the image above blew my mind. Self-proclaimed creationist experts like the infamous Duane Gish confidently asserted that there are no human transitional fossils. Yet ironically, their classifications of various fossils follow a gradient from "apelike" to "humanlike" that beautifully confirms the evolutionary paradigm. Some individuals can't even decide whether a given fossil is ape or human, while others have changed their minds. Their willful blindness to the obvious conclusion is, frankly, fascinating.

Coyne goes on to address a few other interesting topics, including a thorough debunking of evolutionary racism: we diverged only about 80,000 years ago—not enough time for any major disparities to develop—and most differences between races are physical, the result of differing climates and sexual selection. Most of the rest isn't relevant to this blog, though, so instead I'll sign off with an informative chart of growth in hominid cranial capacity over time:

How anyone can group these into "ape" and "human"
with a straight face is beyond me.

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