Our current civilization is selecting for lower intelligence and less physical fitness. Clever ideas spread around the world almost instantly, conferring no specific advantage to the inventor, and there is a negative correlation between education and number of children. nor are disabilities reproductively disadvantageous anymore (I type as I peer through my bifocals).
I wonder if any paper exists that proves at least parts of this. It's not so much that I doubt it, but a claim of this magnitude and relevance is something I'd want to verify so I would *know*... you know?
The key to meaningful data on the topic is large samples, women old enough to have had most or all of their kids, and examing the relationship within country and within gender and within racial group, since that makes IQ and fertility practices more an apples to apple comparison, reducing the number of confounding variables.
The two studies I could readily find that meet these criteria show highly similar results where within both groups of white and black women, those with IQs below 100 had about .5 kids more than women above 100 IQ.
The first is a study in 1982 study with 10,000 people aged 25-34.
The fertility rates of women with below 100 IQ versus those above 100 IQ were 1.7 verus 1.3 among white women, and 2.1 versus 1.5 among black women.
IOW, the difference in fertility rates was greater depending on IQ than the fertility difference between races.
A similar result was found in this 2010 study measuring fertility rates at ages 39-47.
The fertility rates of women with below 100 IQ versus those above 100 IQ were 2.2 verus 1.8 among white women, and 2.3 versus 1.5 among black women.
The higher fertility rate among white women in this study than the prior one makes sense, since all of these women were past common reproductive age. Black women tend to have kids while younger, so their rate wasn't much higher in this study than the prior study.
Here is the main conclusion of the latter study.
from article said:
Using what is arguably the best data set currently available, the results confirm previous reports (Lynn and van Court, 2004, Retherford and Sewell, 1988, Udry, 1978, van Court and Bean, 1985, Vining, 1982, Vining, 1986 and Vining, 1995) about a negative relationship between IQ and number of children in the United States during the last third of the 20th century. Thus the existence of IQ dysgenics can be considered firmly established for this time and place.
They also do a bunch of complex path model analysis to test various mediating mechanisms for the relationship, finding that attending college is the greatest mediating mechanism, namely women with higher IQ attend college and get careers which delays having kids resulting in fewer kids overall.
His other claim is just rather obvious on its face, so much so that no one would have bothered to empirically verify it. The products of intelligence and their utility is readily available to everyone who can access the internet. The person advantage to those with the minds that created this knowledge is largely non-existent. Also, the modern workplace contributes to this further, where people with wealth acquired via heavily on luck and unethical acts (not intellect) pay to reap most of the fitness benefits of other people's intellect. This is one example of the more general fact that civilized society, especially democracy and collectively shared resources and safety nets greatly reduces any relative advantage over others gained by one's own genetically impacted traits. Our collective aggregate traits more collectively impact us all. Of course this isn't 100%, but far moreso than throughout most of the centuries of past human evolution where people only benefited from the intellect (and other adaptive traits) of those in their own small kinship clan, creating a far tighter tethering of one's genes to one's survival and reproduction success.
skepticalbib said:
But if the line isn't extinguished by catastrophe then our descendants five million years from now will likely be as different from us as we are from our ancestors of five million years ago.
This is incorrect, due to the reasons above.
The rate of human evolution is a product of differential survival and reproduction rates of people, due to their genetic and thus phenotypic differences. By decoupling genetic variance between people from their survival and reproductive probabilities, civilization has greatly slowed down evolutionary change. Also, humans just are not migrating like they used to, where people entered into a completely novel climate, ecosystem, and geography for the first time without any stores of cultural knowledge, just playing roulette of trial and error to see who survives and what works.
Catastrophies can of course produce major leaps in change, and one that destroyed civilization and social contract would rev the evolutionary engine back into full speed. But the reality is that such catastrophe's are no more likely in the future than the past and actually we are better able to reduce their impact now than the past. Thus, odds are high that we will evolve far less over the next 1 million years than the previous million.