Why Human Evolution Happened Only Once: The Question No One Has to Answer - Evolution News & Views

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Why Human Evolution Happened Only Once: The Question No One Has to Answer


Last time out, I asked, why, if information about chimpanzee behavior is supposed to provide insight into human behavior, nothing similar to human evolution ever happened to chimpanzees. This fact deserves more attention than it gets: It is a giant explanatory gap. Not only did chimpanzees not put a man on the moon, they would never have imagined it as a goal. The second gap is much bigger than the first.

Science-Fictions-square.gifSo when we look at explanations for human cultural evolution, we find unfortunately the same problems as we did with physical evolution, like bipedalism and throwing projectiles accurately. It never happened to any other life form.

And we get only trivial explanations. For example: Human evolution is said to be driven by art, cooking, sexual selection, and/or baby slings. Cooking, in particular, made digestion easier and freed up the extra energy our ancestors needed to grow bigger brains," maybe spurring evolution by cooking meat. Others say that eating fish and reptiles made the difference. Fluctuating environment gets a mention.

We are told that but for fresh pastures, "we would never have loosened up enough to learn to speak" (like cows do?). Also that baby apes' arm-waving or monkey lip-smacking provide insight into how humans acquired language. Fatherhood, others tell us, made us human because "A father who recognized his son in a neighboring group would be less likely to strike out against him, which would open the way for larger tribal networks." But, according to other sources, early man ate children (which might somewhat reduce the sense of child loyalty?), depending on who you ask, or else he ate Grandma -- or would have except that she looked after the children (provided he didn't eat them first, presumably).

Somehow, none of this (assuming it happened) ever had the same effect for any other species. If a coyote ate his grandma would it matter?

It is the question no one answers because it has been set up as the question no one has to answer, even though it is the key question. Start by insisting that absolutely everything is a big accident, and we never have to ask why it only happened to us.

Researchers were "very shocked" by recent new genes that form a distinctly human brain," appearing five to seven million years ago. Actually, it hardly matters. Much that we learn in passing about the human brain doesn't fit the materialist view very well because the brain is plastic. Remember the psych lab experiments on people whose corpus callosum, joining the right and left hemispheres, had been split (as a treatment for severe epilepsy), whose right hand apparently didn't know what the left hand was doing? When that defect occurs naturally, as opposed to surgically, the subjects apparently do know such things because their nervous systems simply form other connections. So, motivation matters, unless it is short-circuited.

Yet still a signal floats above the noise. Consider those primitive peoples who have not yet developed words for numbers. When tested, they did about as well as Europeans in geometry, which researchers say suggests that "our intuitions about geometry are innate." So the human mind does not, strictly speaking, evolve. It is rather cultivated in one direction or another. But these stories, and many others like them, fall down the memory hole reserved for inconvenient discoveries. The noise around human evolution resumes as before.

One recent walk on the wild side is worth noting just for what it shows about how little we really know -- and how much we are willing to believe. Much publicity was given in 2013 to the idea that the differences between humans and chimpanzees arise from humans' hybridization with pigs.

You think this is a joke? Well, yes, but in the current science press it isn't. That is, "humans are probably the result of multiple generations of backcrossing to chimpanzees, which in nucleotide sequence data comparisons would effectively mask any contribution from pig." This hypothesis, offered by geneticist and hybridization specialist Eugene McCarthy, incidentally reveals facts about human anatomy not usually offered as evidence by the proponents of the 98-percent-chimpanzee thesis, who don't seem to be interested in defending themselves against the following thesis:

The list of anatomical specializations we may have gained from porcine philandering is too long to detail here. Suffice it to say, similarities in the face, skin and organ microstructure alone is hard to explain away. A short list of differential features, for example, would include, multipyramidal kidney structure, presence of dermal melanocytes, melanoma, absence of a primate baculum (penis bone), surface lipid and carbohydrate composition of cell membranes, vocal cord structure, laryngeal sacs, diverticuli of the fetal stomach, intestinal "valves of Kerkring," heart chamber symmetry, skin and cranial vasculature and method of cooling, and tooth structure. Other features occasionally seen in humans, like bicornuate uteruses and supernumerary nipples, would also be difficult to incorporate into a purely primate tree.

In the face of inevitable controversy over such an idea (pigs?), science news site Phys.org doubled down on it, offering further support:

Under the alternative hypothesis (humans are not pig-chimp hybrids), the assumption is that humans and chimpanzees are equally distant from pigs. You would therefore expect chimp traits not seen in humans to be present in pigs at about the same rate as are human traits not found in chimps. However, when he searched the literature for traits that distinguish humans and chimps, and compiled a lengthy list of such traits, he found that it was always humans who were similar to pigs with respect to these traits. This finding is inconsistent with the possibility that humans are not pig-chimp hybrids, that is, it rejects that hypothesis.

Curiously, in 2009, when a similar idea was suggested for caterpillars in the National Academy of Science's publication PNAS, Scientific American promptly dubbed PNAS the "National Enquirer" of the sciences.

Clearly, the standard of evidence for hypotheses about human evolution favors less parsimony than for butterfly evolution.

And it goes downhill from here.

Editor's note: Here are links to the whole "Science Fictions: Human Evolution" series to date.

Photo credit: Elvire.R./Flickr.