20 Comments

From the “yes, they really think that” files, we have this assertion from a @Dunnam0127 who has decided that humans have not evolved.

monkey-evolution

This appeared to be the entire argument for why humans and chimps have not evolved from a common ancestor.  As an argument goes, well, that’s a pretty generous description. It depends entirely on two popular Creationist fallacies.

The first is the whole monkey-thing. Nowhere in human evolution is it claimed we descended from monkeys. It turns out, creationists really don’t get that there’s a difference between monkeys and apes. Of course, they don’t get much of anything in biology.

The second is a fallacious understanding of what a species is either. That’s kind of what prevents viable, fit offspring being produced by the mating pair.  Fortunately, no crocoducks were brought up in this discussion.

Actually, the poor guy doesn’t understand that both modern chimps and humans have adaptations to bipedalism. The foot/hand distinction isn’t that easy to establish. Especially when we sometimes transplant toes onto hands in the place of lost fingers or thumbs.

There are of course, all sorts of actual, real scientific facts that we use to establish that humans have a common ancestor with chimps.

The anatomical similarities- especially once you get to the skeletal level- are quite profound and striking. This is the sort of thing that Darwin noticed over a century ago [1]

There is the evidence from our own fetal development. In humans a layer of hair (lanugo hair) is formed during fetal development, a relic of our earlier, more hirsute ancestors.

The real smoking-guns though of our primate evolution has been the molecular. Chimps have a very similar genomes to people. But within that, its not just the similarities in the coding parts of the genome that show the trail. It’s the similarities in the non-coding parts.

One of the most compelling pieces of evidence is the vitamin C pseudogene [2] Chimps and humans have one extraordinary thing in common. Neither of these two species can synthesise vitamin C. That’s why we (& chimps) need to eat fruit and vegetables to get vitamin C in our diet. Otherwise we get scurvy and die. The curious fact is that this is caused by both chimps and humans having the same broken gene. This mutation occurred about 6mya. We are in effect, the only species to have this exact, same, broken gene. (Guinea pigs also can’t synthesis vitamin C but that’s caused by a different mutation).

The other ‘smoking gun’ are our endogenous retroviruses [2]. These are ancient viruses that have become inserted into our genome, but no longer generate disease.  For humans, these ERVs make up about 10% of the non-coding parts of our genome.  And yes, both chimps and humans share many of these same defunct ERVs.

The mutation rate in the human genome also means we can clock back into time when these events occurred. This converges on a common ancestor with chimps at about 6mya.

References

[1] Darwin, C. The Descent of Man, and Selection in Relation to Sex. D Appleton and Company, New York, 1871.

[2] The Chimpanzee Sequencing and Analysis Consortium, Initial sequence of the chimpanzee genome and comparison with the human genome, Nature 437, 69-87 (1 September 2005)