Common descent, uncommon descent, and, hey, a ladder into ...
A while back, I wrote to a correspondent about the infant grasping reflex.
He had written to say that some Darwinist somewhere was fronting the ability of human infants to hang on a couple of minutes as evidence of common descent with chimpanzees, and wondered how I could possibly deal with this evidence. (Well, I guess it would buy the human infant a couple of minutes of life, right? Not an attractive prospect, in my view. Better look elsewhere for human survival.)
Look, I do not have a problem with common descent, until its advocates get up on their hind legs and start arguing for it. One gets some of the worst arguments in the world, fronted by vast academic paraphernalia - and, very often, implied threats if one doesn't agree thrown in.
Now, the story in question raised the question of what counts as evidence of common descent.
As a teenager, (I married when I was 20), I paid my way through school, net of scholarships, by looking after babies, toddlers, and other small children.
I am no expert, but I know a bit about such creatures. As I explained to my correspondent, the human infant does not use the grasp reflex primarily for hanging on to Mom, but primarily for stuffing any grasped object into its mouth.
This makes sense from the human infant's perspective, of course. While the child can recognize mom's voice before birth, her voice is mainly a source of reassurance, not information.
Eyesight is a very great benefit for a child - once he can distinguish the boundaries of one item from another. The first thing most kids learn to distinguish is smiles, which they begin to copy, typically around 6 to 8 weeks of age. Experts differ as to whether the child really reciprocates affection or is merely copying a routine.
I have no learning to justify entering this controversy, so let me note only note that, whatever may be the case with the child, millennia of humans have seen the results and said., "See! He knows I am his dad and I am so very proud of him!" or "She's my little princess! Just see how she smiles at me!" So the human race goes on.
It is curious that - if some expert opinion is true - the child is programmed to act like he knows what is happening before he does, because adults notice and react favourably.
Anyway , I told my correspondent,
Claims about common ancestry should be founded strictly on genome mapping, NOT on behaviour.I don't know. I just follow the story, unlike the pundits who KNOW.
Behaviour is simply NOT a reliable guide. Closely related life forms can have different behaviour - and life forms too distantly related to shed any light on each other can have similar behaviour because the behaviour is a necessary adaptation for the life they must pursue.
For example, opossums and koalas have offspring that cling to their mothers, but because they are marsupials, no one suggests that it demonstrates anything about close common ancestry with humans or other placental mammals.
Accounts of similar behaviour may feel good to the already convinced, but, as an enterprise in the serious study of evolution, this sort of thing is doomed to failure.
If the human and chimpanzee genomes overlap about 70-76% (a reasonable figure – forget the 98-99% chimpanzee hype), that suggests common ancestry as a reasonable probability, given other similarities. Also, there are apparent “errors” (e.g. Vitamin C pseudogene) that appear in both genomes, which adds strength to the argument. For example, ID advocate Mike Behe talks about the Vitamin C pseudogene in Edge of Evolution, as evidence for common ancestry.
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Labels: infant grasping reflex