Friday, June 29, 2012

The Implausibility of Unguided Human Evolution

Evolution News and Views takes a look at a new book by biologists Ann Gauger, Douglas Axe and lawyer Casey Luskin titled Science and Human Origins. One of the ideas the authors want us to understand is the very great difficulty, assuming that only blind mechanistic processes were at work, of constructing a plausible pathway from an ape-like ancestor to Homo sapiens. In her chapter Gauger writes this:
Let's begin by considering what distinguishes us from great apes. What are our distinctive characteristics? There are significant anatomical differences, of course: Our upright walking, longer legs, and shorter arms, changes in muscle strength, our significantly larger brains and skulls (three times bigger than great apes), and our refined musculature in hands, lips and tongues.

There are also our relative hairlessness and changes to our eyes. More importantly, there are whole realms of intellect and experience that make us unique as humans. Abstract thought, art, music and language: These things separate us from lower animals fundamentally, not just in degree but in kind....

Chimps are suited for life in the trees. Humans are suited for life on the ground, walking and running. The anatomical changes needed to move from tree-dwelling to complete terrestrial life are many. To walk and run effectively requires a new spine, a different shape and tilt to the pelvis, and legs that angle in from the hips, so we can keep our feet underneath us and avoid swaying from side to side as we move.

We need knees, feet and toes designed for upright walking, and a skull that sits on top of the spine in a balanced position. (The dome of our skull is shifted rearward in order to accommodate our larger brain and yet remain balanced.) Our jaws and muscle attachments must be shifted, our face flattened, and the sinuses behind the face and the eye sockets located in different places, to permit a forward gaze and still be able to see where to put our feet.
How many mutations would these changes require and how much time was available in which they could occur? ENV gives us some idea:
Varki and Altheide (2005) document hundreds of phenotypic traits that differ between humans and great apes.

Gauger goes on to consider whether there has been enough time (roughly one and a half million years) to render plausible the number of instances of anatomical novelty that are required to change an Australopithecus afarensis into a Homo erectus. Citing Durrett and Schmidt (2007, 2008), Gauger draws on their conclusions that "for a single mutation to occur in a nucleotide-binding site and be fixed in a primate lineage would require a waiting time of six million years" and that "it would take 216 million years for the binding site to acquire two mutations, if the first mutation was neutral in its effect."

Since the transition from our last common ancestor with chimps to modern humans is only about six million years, argues Gauger, the time allowed is nowhere near enough to accomplish such a feat of genetic and anatomical re-engineering, especially since "many of the anatomical changes seen in Homo erectus had to occur together to be of benefit."
That humans evolved from apes certainly seems possible, maybe even probable. That they accomplished this by the unguided forces posited by Darwinian evolution, however, seems improbable in the extreme. Indeed, it would be almost miraculous. The more one reads about evolution the more one sees it as a strong argument for the necessity of a superintending mind directing the process. It simply takes too much faith to think that it could have happened without one.