Like so many people, I was extremely skeptical, of the claim that genetic intelligence has declined by nearly 1 standard deviation (15 points) since the Victorian era. In fact I was so skeptical that I ignorantly didn’t even look at the actual study until very recently, though I did peruse the excellent coverage and spirited debate on HBD Chick’s blog. And it’s understandable that so many of us didn’t believe it.
It took about 190,000 years for genetic IQ to increase by 23 points, and in only some populations. Then, after agriculture, there was probably at least an additional 13-20 point genetic increase in some populations. So the notion of a 15 point drop in just over a century made no sense.
But then again, the reason evolution is thought to be so incredibly slow, is that life stays largely the same for most life forms, for thousands, sometimes millions, of years. That doesn’t mean evolution can’t happen quickly when there’s a major change, like say, the ice age, or agriculture. Could the industrial revolution be an example of such a big change? Could it, and the events it unleashed, have been the biggest change of all?
Professor Bruce Charlton writes:
Through most of evolutionary history, most babies and children (probably a large majority of them) especially those with the worst genetic damage – have died before reproducing. Thus mutation load is filtered by differential child mortality rates with each generation…But since 1800, starting in England then incrementally spreading across the whole world with no exceptions, child mortality rates have got lower, and lower; the mutation filtering effect has got less and less complete – and the mutation load has got greater with each generation.
And on top of this is the fact that even before the babies mutate, they are most likely to be conceived by the least intelligent people, who prior to the modern social safety net, could not have afforded to feed children, if they could have even afforded to feed themselves.
And a third factor that Charlton doesn’t even mention (though he or Woodley have perhaps mentioned it elsewhere) is that people are having babies at older and older ages! So we have three major effects all contributing independently to the genetic decline:1) The least intelligent are having the most children, 2) parents of all IQ’s are having kids late in life, thus increasing mutation risk, and 3) the carriers of mutations are surviving at unprecedented rates to repeat the cycle.
In another fascinating post, Charlton cites an analogy by Michael A. Woodley explaining why dysgenic evolution occurs so much more rapidly than progressive evolution. In the latter, it’s like swimming upstream against the current because you’re constantly being pushed back by the flow of harmful mutations, so it takes a painfully long time for IQ to increase. But in the former, all the mutations propel your momentum, so it’s like rapidly skiing effortlessly down a hill. This makes perfect sense!
But here’s the question. Are there other examples of this? For example, animals who are kept in captivity must see even bigger declines in the mortality of their offspring. Are there examples of these animals changing by a full standard deviation in any trait in just four or five generations? And I’m not talking about deliberate selective breeding. I’m talking massive rapid genetic changes caused only by the elimination of natural selection. You would think, if this were true, that it would be a well understood phenomenon by now.