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.
Brain Size 
If true then shortly after the black death when there was plenty of food and a high demand for labor IQ should also have decline.
Perhaps, though likely to a much smaller degree, because although there was dysgenic fertility, it wasn’t compounded by the severe reduction in infant mortality, that is allowing mutations to accumulate at a rapid rate, nor did people create more mutations by delaying parenthood to middle age.
Also, it is believed that the black death itself boosted IQ in Europe by removing the poorest 50% or so of the gene-pool, thus giving rise to the great Elizabethan renaissance, although dysgenic trends in the generations since negated those gains.
Certainly the 20th century has not been the only dysgenic era. Indeed a scholar named Rushton argued that the more intelligent K genotypes (nerds as I call them) create civilizations that become so wealthy that natural selection is eliminated, allowing the r genotypes (who flourish through sexual selection) to take over because of their high birthrates. But when the number of r genotypes reaches critical mass, society collapses because there are not enough smart nerds to run things, and we once again get a natural section for high IQ nerds.
The cycle just keeps repeating itself, explaining the rise and fall of civilizations.
I haven’t done enough research to say, but that sounds counter-intuitive to me. Jensen claimed that IQ was a major Darwinian fitness trait as evidenced by its large reduction in cousin marriages.
And thanks for re-tweeting me. This blog has never had so many visitors and views in its entire existence! I had no idea you had so much power. LOL!
@p- The paper referenced here could provide a way into the literature on accumulated mutation damage in other species. There seem to be a number of variables to consider – how many new mutations per generation, what proportion of offspring survive, how fast the populatino is growing and probably others.
Although this literature says 88% mortality or 12% surviving, but this could only be approximate – and there would have been considerable variation at different points in history. It also seems a bity high for human reproductive capability – since hunter gatherer women seem ssledom to have more than six children – which would not be enough.
So I guess the real number would be more like an average 1/4 or 1/3 of human offspring surviving for most of the time and in most places.
*
You are probably correct about delayed reproduction, although this also reduces the number of generations and the possibility of mutation accumulation from that cause – so that modern people only have two generations – i.e. two new lots of mutations – where in historical times there would have been three.
So slowing reproduction (by increasing the average age of reproduction) may perhaps reduce mutation accumulation temporarility, given that the effect of aging may be less than the effect of an extra generation.
*
@JM When the Black Death halved the population of England, the deaths were disproportionately among the poorest (i.e. apparently ‘eugenic’); then the population took about 300 years (until around 1600) to recover (from 2-4 million) all the time under strong ‘eugenic’ selection (probably, nearly all of the surviving children came from the elite skilled craftsmen type working class and the ‘intellectual’ middle classes).
That is a 300 year doubling time. Then it took another 200 years for the population of England to double to 8 million (around 1800); then about 50 years to double again; and about 50 years to double again to 32 million after 1900; and then about 100 years for the most recent doubling.
So, 4 million was probably the usual maximum population for agrarian England, and there have been five doublings of population in about 600 years since the Black Death (2, 4, 8, 16, 32, 64 million) falling before 1400 reduced it to 2 million – but the rate of increase was slow and child mortality was very high until about 1800 or later – so three of the doublings have happened in the ‘dysgenic’ 200 years since child mortality began to reduce, and fertility began to reduce.
I forgot to provide the link to the paper mentioned in the first paragraph
Yann Lesecque, Peter D. Keightley, Adam Eyre-Walker. A Resolution of the Mutation Load Paradox in Humans. Genetics 2012; 191: 1321-1330.
http://www.genetics.org/content/191/4/1321.full
The infant mortality statistics you mention are very interesting and my next post will explore the implications in more detail.
You make a good point about delayed parenthood expanding the length of each generation..the two effects may negate each other in terms of the amount of genetic change over a period of time.
Correction – in the above 300 should read 200 – i.e. the years between 1400 and 1600
Well, Newton was quite mentally ill, and had at least one nervous breakdown, but his genius helped create the modern world.
Geniuses often have mental health issues. Bruce Charlton writes about it here:
http://iqpersonalitygenius.blogspot.ca/2012/08/why-is-genius-so-rare_6.html
Another interesting source is:
http://www.news.harvard.edu/gazette/2003/10.23/01-creativity.html
However just because mental illness is linked to genius doesn’t mean it’s linked to high fitness. Charlton argues it’s bad for individual fitness, but useful for group fitness:
http://iqpersonalitygenius.blogspot.ca/2014/06/the-lop-sided-genius-mutations.html
@Pp
” Charlton argues it’s bad for individual fitness, but useful for group fitness:”
This is empirically true – it is what actually happens; but the big questino is whether this is true group selection. in other words, is the high incidence of genius a genetic strategy – or is it simply something that sometimes ;’just happens’ in some population by chance.
*
Off topic – Are you yourself a member of the Prometheus Society, and one of the ultra-high IQ people I have sometimes written about?
If so, I wonder if you might like to email me at hklaxness@yahoo.com – because there are some questions I would like to ask.
Newton left no descendants, so he lacked evolutionary fitness. The societal benefits of his works were an accidental, quasi-programmatic feature of his genius.
No, I am not a member of Prometheus Society, nor would I ever even compare myself to people at that level. I’ve just read a lot about them on the internet and they are a fascinating community.
Newton left no descendants, so he lacked evolutionary fitness. The societal benefits of his works were an accidental, quasi-programmatic feature of his genius
I don’t know that much about Newton in particular, but Bruce might be right about Genius being potentially an evolutionary strategy.
I don’t know if group selection is the mechanism, but let’s say you’re a Genius who got very rich off your talents like J.K. Rowling (who Bruce argues is a Genius) or Shakespeare (who was also extremely rich for his era). Even if you have no children, you could still use this money to benefit your gene pool by say giving money to charities that support your ethnic/religious identity or hiring people that look like you and think like you, and thus probably share genes similar to your own. In historical times when the poor would die young, sharing resources was the difference between life and death.
Or a Genius might cure a disease that he himself is afflicted with (thus saving the lives of millions of people who share his diseased gene) or invent a technology that only people with his genes can use efficiently or a Genius might write propaganda that promotes ethnocentric genetically self-serving ideologies or wars.
I don’t know if all this is group selection exactly because it benefits the individual‘s genes to help those who share copies of her genes, and the people you’re helping may be disparate groups, all sharing very different parts of your genetic structure.
J. Phillipe Rushton called the tendency of people to befriend and help genetically similar others “Genetic Similarity Theory” and he noted that best friends were most similar on the most heritable traits.
@PC and PP – What PP is describing is not group selection but inclusive fitness/ kin selection – which is just a type of individual selection but (properly) focused on the genes rather than the organisms.
The group selection idea is that most geniuses are more or less ‘failures’ in terms of their own inclusive fitness – and instead promote the fitness of the whole population (group) from which they were drawn – and therefore NOT specifically their own relatives.
The idea is that genius is actually (on average) a genetic dead-end – but that the large group has evolved some kind of mechanism whereby geniuses are thrown off from time to time – and these geniuses in a sense sacrifice themselves (i.e. devote their lives – but probably not consciously) to the group as a whole (instead of pursuing their own genetic fitness).
For example, the population of Europe threw off a tremendous number of geniuses between about 1500 and 1900. One result was that the population of European descended people expanded to be a quarter of the world’s population over that time (nowadays it is less than half that – especially if age adjusted).
However, the reproductive success, and even the wealth, of geniuses and great inventors was probably a long way below average – indeed many great inventors are unknown and only their work remains.
The above are the facts, but whether it all happened by chance or groups selection, I am somewhat unsure – Michael A Woodley is confident it was group selection, and on the whole I would go with him on this. If a clearer mechanism of group selection is discovered, then it may carry the day.
Rather than the mathematically difficult group selection, it seems much more likely that intelligence confers greater fitness in general, and that the very rare overshoot with disturbed genius doesn’t change that. Also, some geniuses like Bach, have a lot of kids, 20, of whom 10 survived to adulthood.
The group selection idea is that most geniuses are more or less ‘failures’ in terms of their own inclusive fitness – and instead promote the fitness of the whole population (group) from which they were drawn – and therefore NOT specifically their own relatives.
Yes, that’s an important conceptual distinction to make, but couldn’t one stretch the term “relatives” to include the entire population from which they were drawn, and thus argue that these Geniuses were actually wildly successful in terms of their own inclusive fitness, even if they didn’t help any “close” relatives?
I believe Rushton argued that compared to the world’s entire genetic diversity, two unrelated co-ethnics are equivalent to cousins, and that’s why unfortunately there’s so much racism. People give favorable treatment to members of their own race to enhance their inclusive fitness.
Also, some geniuses like Bach, have a lot of kids, 20, of whom 10 survived to adulthood.
Oh cool! I’ve argued that musical performers tend to be r genotypes, but I never imagined that even Bach might have been one:
Pingback: The average IQ of people who live long enough to be tested | Brain Size
Pingback: Forget IQ scores: A SHOCKING new scale for measuring intelligence | Brain Size
Pingback: Small gain in SAT scores suggests huge drop in genetic IQ | Brain Size
Pingback: Are HBD bloggers stupid? | Brain Size
Pingback: What motivates the dysgenics community? | Brain Size
Pingback: Radical theory for explaining the Flynn effect | Brain Size
Pingback: New thoughts on dysgenics & the Flynn effect | Brain Size
I will note that domesticated cats are thought to have lost a third of the neurons possessed by their wild ancestors, judging from examination of fetal pruning. And while dogs now interpret human gestures, and breeds bred for intelligence are quite bright, dogs overall are probably not nearly as bright as their wild cousins.
Domestication leads to stupidity. We’ve been domesticating ourselves for quite some time.
Indeed; dogs have smaller brains than wolves
If one looks at the very substantial decline in SAT scores in the last 50 years, at least 5 IQ points, the thesis doesn’t look so far fetched.
SAT scores have actually gone up if you include all 17 year olds (not just the ones who take the test) but they’ve gone up by such a small amount despite major advances in socioeconomic status, that I actually did argue this is evidence of dysgenics:
Oh nonsense, the college bound seniors scores that we are talking about are perfectly representative. The SAT scores were renormed in 1974 and especially 1995, adding more than 100 points to the average score, to remedy the drop which College Board accurately reported. That may have deceived you; an 1100 score today would have been less than 1000 40 years ago. And the tests were made easier to boot. Another dumbing down of the test is happening this year. In reality, it looks like much more than a 5 IQ point drop.
I was citing data showing there was a small net gain in combined SAT scores from 1955 to 1983. This is based on special norm studies where a nationally representative sample was tested not college bound seniors only. This data was reported in the book The Bell Curve,
But perhaps scores have declined since