Gene Duplications Give Clues to Humanness:
All told, the researchers found more than 4000 genes that showed lineage-specific changes in copy number, with the numbers steadily increasing over evolutionary time. Humans, for example, only had 84 genes with increased copy numbers over those of our closet relatives. In contrast, lemurs, which have evolved for 60 million years, have 1180 genes with extra copies. "This is further evidence that genomic differences between humans and other primates is far, far more complex than we originally imagined they might be," says Ajit Varki, who studies human/chimpanzee differences at the University of California, San Diego. "However, many of the differences may or may not be relevant for explaining 'humanness.'"
We've talked about copy number variation before. Obviously dosage of gene products can be directly impacted by this. We've come a long way from non-synonymous base pair changes baby! Though please note that loss of function (fewer copies) might be just as important as gain of function (more copies).
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Come to think of it, do we have any way of estimating of how rapidly adaptive loss of function tends to happen compared to gain of function once the fitness peak shifts? Intuitively it seems like the former would tend to happen faster than the latter all else equal, but it'd be nice to have some more rigorous reasoning (or better yet, data) to back that up. Time for another hunting expedition on google scholar...
Some empirical paydirt in human genetics: Wang, Grus & Zhang (2006) found 80 human-specific instances of loss-of-function by pseudogenization. And we already knew that humans have undergone some loss of function in both olfactory and taste receptors. Lost oestrus too.
i think we lost some muscle too.