New Study: "Frequency of variants associated with ADHD has steadily decreased since Paleolithic times"

New from Scientific Reports

Abstract

Attention-defcit/hyperactivity disorder (ADHD) is an impairing neurodevelopmental condition highly prevalent in current populations. Several hypotheses have been proposed to explain this paradox, mainly in the context of the Paleolithic versus Neolithic cultural shift but especially within the framework of the mismatch theory. This theory elaborates on how a particular trait once favoured in an ancient environment might become maladaptive upon environmental changes. However, given the lack of genomic data available for ADHD, these theories have not been empirically tested.

We took advantage of the largest GWAS meta-analysis available for this disorder consisting of over 20,000 individuals diagnosed with ADHD and 35,000 controls, to assess the evolution of ADHD-associated alleles in European populations using archaic, ancient and modern human samples. We also included Approximate Bayesian computation coupled with deep learning analyses and singleton density scores to detect human adaptation.

Our analyses indicate that ADHD-associated alleles are enriched in loss of function intolerant genes, supporting the role of selective pressures in this early-onset phenotype. Furthermore, we observed that the frequency of variants associated with ADHD has steadily decreased since Paleolithic times, particularly in Paleolithic European populations compared to samples from the Neolithic Fertile Crescent.

We demonstrate this trend cannot be explained by African admixture nor Neanderthal introgression, since introgressed Neanderthal alleles are enriched in ADHD risk variants. All analyses performed support the presence of long-standing selective pressures acting against ADHD associated alleles until recent times. Overall, our results are compatible with the mismatch theory for ADHD but suggest a much older time frame for the evolution of ADHD-associated alleles compared to previous hypotheses.

Which religious group is most likely to reject evolution?

The Left dislikes evangelicals as much as they dislike anybody, and one of the reasons they don't like them is because they tend to reject the theory of evolution--which is ironic since the Left rejects the implications of evolution for human nature. But what about Muslims? Don't they reject evolution as well? The Left is usually silent about Muslim fundamentalism.

How many American Muslims don't believe that humans descended from earlier species of animals? General Social Survey (GSS) respondents were asked this question. Here are the percent who answered no listed by religion (sample size = 6,353):

Percent who don't believe humans descended from animals

Muslims  65.6
Christians  65.5
Protestants  63.6
Catholics  36.2
Orthodox Christians  32.1
Jewish   20.1
No religion  19.8
Buddhists   4.5
Hindus   3.2

Muslims are at the top of the list. Compare them to Buddhists and Hindus. An enormous difference.

If fundamentalism is an impediment to a pro-science culture, why isn't it a problem when it's found among Muslims? For the Christian fundamentalists always you have with you, but inviting the growing Muslim world to move to the US is a choice.

UPDATE: My 12-year-old son informs me that Hindus naturally accept evolution because they believe in a God that is an elephant.

Richard Wrangham works hard to explain the violence gap we don't care about

Urban Americans worry quite a bit about violence in their cities.  Many of these places will rack up hundreds of homicides per year.  Urban black men face a pretty decent chance of being murdered.  So it was weird to read Richard Wrangham's new book The Goodness Paradox with its central claim that humans are very peaceful.

How could he have this view?  Well, he has studied chimps for decades.  Contrary to stories told by liberal primatologists in the 1960s, it turns out that chimps are mean bastards.  If you stuffed 200 of them into Boeing 737, by the end of the flight many would be murdered.  The human homicide rate is a tiny fraction of that seen among chimpanzees.

Wrangham then sets out to develop a theory to explain why we are so slow to lose our cool and attack others.  He claims that when our ancestors developed the ability for fairly sophisticated language about 300-500k years ago, men in a group began to handle their antisocial members by plotting to murder them.  Chimps will sometimes gang up on a cantankerous alpha and take him out, but it is spontaneous.  No planning is involved.

Men gained great power over individuals by using premeditated, coalitionary aggression against not only bullies but eventually against all non-conformists.  Over evolutionary time, this selected for humans who were motivated to get along with others and who were particularly interested in pleasing tribal elders--the men who had the power to kill them if they become sufficiently annoyed.

In developing his theory, Wrangham did exactly what I expected from a PC biologist: He avoids discussions of why human groups currently vary so much in their levels of homicide.  Some educated person reading his book wants to know why his neighborhood is so much safer than the black neighborhood on the other side of town. The homicide rate in Colombia, for example, is scores of times higher than in Japan.  Why?  Wrangham is silent on this type of issue.  He makes it sound like humanity has experienced the exact same selection pressures for hundreds of thousands of years, and that we all arrive at 2019 exactly the same in terms of genetic propensity for violence.  He admits that the speed of selection probably increased in more recent millennia, but is silent about what that means.

Wrangham also fails to discuss the scholarship of Greg Cochran, Henry Harpending, and Peter Frost which suggests that pacification of some human groups has happened over the past few thousand years. I guess I would be silent on such topics, too, if I valued my lofty perch at the Department of Human Evolutionary Biology at Harvard University.

Is there such a thing as a "superior race"?

In the last post, I analyzed answers to a General Social Survey question about whether one approves of someone who believes in the genetic inferiority of blacks being able to give a public speech about it.

That got me wondering, "Do I believe there are inferior and superior races?"

Some people might think of the question in terms of human accomplishment and might consult Charles Murray's book. I would call this an example of the social construction of superiority.  One group might value cultural achievement, some other group might value something else (e.g., the most pious group is the best).

With this kind of evaluative question, I typically take one of two approaches: either as a Christian or as an evolutionist. Since my religious values are not very interesting, I'll set those aside.

As an evolutionist, I'd say the simple, current answer in the context of the United States is that the superior races are: 1) Mexican Americans, 2) American Indians, and 3) blacks.

Why?  Because nature's definition of "superior" refers to how well one is adapted to his environment, and that is measured in terms of reproductive success -- who is having the most children. And we know from GSS data that three groups average the most kids (women ages 40-55, years 2010-2016, sample size = 1,156):

Mean number of offspring

Mexican  2.87
American Indian  2.57
Black  2.47

White  2.02

Whites are a much less successful group with an average around two.  And among whites, the biggest losers are people of Polish descent who have a mean of 1.56 children (looking at groups with at least 20 respondents).

Now, you can get more sophisticated about it and argue that evolution is about survival, and in the long-term, groups who are the most scientific are in the best position to survive, and that would be whites with northeast Asians also showing a lot of ability.  I would argue that the current fertility situation is much more certain than the future, and (non-Asian) minorities are thriving. 

UPDATE:  I should also say that I do possess a strain of modernism in me which is utilitarian: if our criterion of superiority is contributing the most to the welfare of the greatest number of people, whites win.

UPDATE II: The fertility gap between Mex-Ams and whites is fairly big: six-tenths of a standard deviation.

Do men with a history of many sex partners avoid marriage?

According to evolutionary theory, there is a tradeoff between mating effort and parental effort. If you put more time and energy into pursuing sexual partners, this is less time and energy to devote to raising children. High mating effort or high parental effort are seen as alternative "strategies."

So, are men with lots of sex partners less likely to be married -- a measure of parental effort? Or is it generally the case that men with many partners follow a combined strategy of marriage plus lots of women? And on the low side, does a man with undesirable traits have few partners and fail to convince a woman to marry him?

The General Social Survey asked men how many sex partners they have had since 18, and they asked about current marital status. Let's focus on men in their 30s. Here are the mean number of partners (I exclude men who say more than 100 because these outliers throw off the mean) by marital status:

Mean number of sex partners since 18 (N = 2,827)

Never Married  14.2
Married  9.0
Widowed  6.6
Separated  14.8
Divorced  17.1

Widowed and married men have had the fewest partners, while never-marrieds and separated/divorced have had the most. Put very roughly, the anti-marriage group has had double the partners compared to the pro-marriage group.

I suppose you could argue that marital status is driving the number of sex partners rather than reverse -- the idea being that marriage reduces promiscuity -- but the average never-married has been with as many women as the typical separated guy. It looks to me like men who are good at getting partners avoid marriage or are weakly attached to it. Many of them do get married, but it's less likely to last. There does seem to be some tradeoff going on here.
 

How to be right about people

If you want to be right about people, taking biology and evolution seriously is a big help.

A few years ago, researchers started telling us how the hormones oxytocin and vasopressin make us more loving and caring toward others; that biologically, we have this kumbaya side to our nature.

I was skeptical because I know that human genes, like those of all animals, have been selected over deep history to produce people who care about themselves and their families at the expense of others. We're not put together to sacrifice for all humanity like we would for a daughter.

So I was not surprised to learn from more recent research that, yes, oxytocin and vasopressin make us more nurturing, but only towards the ingroup; you know, friends and family. Towards outsiders, the hormones cause us to feel more, shall we say, ill-disposed.

It's almost as if you have two kinds of people: 1) those who are selfish and don't care about groups, and 2) those who love and sacrifice for the ingroup, and dislike the outgroup. And the true humanitarian--the man who would lay his life down for a stranger as quickly as he would his mother--is a rare specimen, indeed.

Less variation in family size

Using General Social Survey (GSS) data, I calculated the mean number of offspring for women ages 45 to 64 for each decade since the 1970s. I display these numbers below, along with standard deviations--a measure of variation--and estimates of kurtosis--the degree to which a distribution is flatter or more peaked than a normal distribution:

1970s
Mean 2.77
SD 2.04
Kurtosis .19

1980s
Mean 3.07
SD 2.05
Kurtosis -.09

1990s
Mean 2.54
SD 1.75
Kurtosis .86

2000s
Mean 2.14
SD 1.54
Kurtosis 1.38

2010
Mean 2.05
SD 1.60
Kurtosis 2.35

We all know that family size has shrunk over the past few decades: according to GSS data, from 2.77 children in the 1970s to 2.05 last year. The standard deviations indicate a reduced amount of variation in completed number of offsapring. In the 1970s, SD was 2.04, meaning that if we grabbed two random  women who had completed their families, our best guess is that one mom would have two more kids than the other. Moving forward to the 2000s, SD has dropped to roughly 1.5 which tells us that the two hypothetical moms differ by one and a half kids. In other words, families have become more similar in size. They are more and more converging on the number two.

If the kurtosis number is one or greater, that means that the distribution is more peaked than a normal curve. While there is no problem through the 1990s, one appears in the last decade. What this means in plain English is that a lot of women are having two children, and that puts a skyscraper right in the middle of the bell-shaped curve. In the 1970s, 24 percent of women had two children. By 2010, it was 34 percent.

Why am I interested in this? Well for one thing, reduced variation in family size means that people are contributing a more equal amount of genes to the next generation than in the past. A few decades ago, some people would have zero kids, some would have ten. Of course, we still have diversity, but there is greater convergence on having two offspring. If that convergence became complete (it won't) every woman would have two children and would contribute the same number of genes to the next generation. Since almost all children (not including fetuses) nowadays make it to adulthood (thank God), there is even less differential mortality than differential fertility. It looks like the evolutionary process ain't what it used to be.     

But what about the male contribution, you ask. That's next.