Robert Plomin‘s Blueprint is a must read. That would be true even if it were “merely” an account of recent stunning breakthroughs that have greatly expanded our understanding of the links between our DNA and behavior. However, beyond that it reveals an aspect of history that has been little appreciated to date; the guerilla warfare carried on by behavioral geneticists against the Blank Slate orthodoxy from a very early date. You might say the book is an account of the victorious end of that warfare. From now on those who deny the existence of heritable genetic effects on human behavior will self-identify as belonging to the same category as the more seedy televangelists, or even professors in university “studies” departments.
Let’s begin with the science. We have long known by virtue of thousands of twin and adoption studies that many complex human traits, including psychological traits, are more or less heritable due to differences in DNA. These methods also enable us to come up with a ballpark estimate of the degree to which these traits are influenced by genetics. However, we have not been able until very recently to detect exactly what inherited differences in DNA sequences are actually responsible for the variations we see in these traits. That’s were the “revolution” in genetics described by Plomin comes in. It turns out that detecting these differences was to be a far more challenging task than optimistic scientists expected at first. As he put it,
When the hunt began twenty-five years ago everyone assumed we were after big game – a few genes of large effect that were mostly responsible for heritability. For example, for heritabilities of about 50 per cent, ten genes each accounting for 5 per cent of the variance would do the job. If the effects were this large, it would require a sample size of only 200 to have sufficient power to detect them.
This fond hope turned out to be wishful thinking. As noted in the book, some promising genes were studied, and some claims were occasionally made in the literature that a few such “magic” genes had been found. The result, according to Plomin, was a fiasco. The studies could not be replicated. It was clear by the turn of the century that a much broader approach would be necessary. This, however, would require the genotyping of tens of thousands of single-nucleotide polymorphisms, or SNPs (snips). A SNP is a change in a single one of the billions of rungs of the DNA ladder each of us carries. SNPs are one of the main reasons for differences in the DNA sequence among different human beings. To make matters worse, it was expected that sample sizes of a thousand or more individuals would have to be checked in this way to accumulate enough data to be statistically useful. At the time, such genome-wide association (GWA) studies would have been prohibitively expensive. Plomin notes that he attempted such an approach to find the DNA differences associated with intelligence, with the aid of a few shortcuts. He devoted two years to the study, only to be disappointed again. It was a second false start. Not a single DNA association with intelligence could be replicated.
Then, however, a major breakthrough began to make its appearance in the form of SNP chips. According to Plomin, “These could “genotype many SNPs for an individual quickly and inexpensively. SNP chips triggered the explosion of genome-wide association studies.” He saw their promise immediately, and went back to work attempting to find SNP associations with intelligence. The result? A third false start. The chips available at the time were still too expensive, and could identify too few SNPs. Many other similar GWA studies failed miserably as well. Eventually, one did succeed, but there was a cloud within the silver lining. The effect size of the SNP associations found were all extremely small. Then things began to snowball. Chips were developed that could identify hundreds of thousands instead of just tens of thousands of SNPs, and sample sizes in the tens of thousands became feasible. Today, sample sizes can be in the hundreds of thousands. As a result of all this, revolutionary advances have been made in just the past few years. Numerous genome-wide significant hits have been found for a host of psychological traits. And now we know the reason why the initial studies were so disappointing. In Plomin’s words,
For complex traits, no genes have been found that account for 5 per cent of the variance, not even 0.5 per cent of the variance. The average effect sizes are in the order of 0.01 per cent of the variance, which means that thousands of SNP associations will be needed to account for heritabilities of 50 per cent… Thinking about so many SNPs with such small effects was a big jump from where we started twenty-five years ago. We now know for certain that heritability is caused by thousands of associations of incredibly small effect. Nonetheless, aggregating these associations in polygenic scores that combine the effects of tens of thousands of SNPs makes it possible to predict psychological traits such as depression, schizophrenia and school achievement.
In short, we now have a tool that, as I write this, is rapidly increasing in power, and that enables falsifiable predictions regarding many psychological traits based on DNA alone. As Plomin puts it,
The DNA revolution matters much more than merely replicating results from twin and adoption studies. It is a game-changer for science and society. For the first time, inherited DNA differences across our entire genome of billions of DNA sequences can be used to predict psychological strengths and weaknesses for individuals, called personal genomics.
As an appreciable side benefit, thanks to this revolution we can now officially declare the Blank Slate stone cold dead. It’s noteworthy that this revolutionary advance in our knowledge of the heritable aspects of our behavior did not happen in the field of evolutionary psychology, as one might expect. Diehard Blank Slaters have been directing their ire in that direction for some time. They could have saved themselves the trouble. While the evolutionary psychologists have been amusing themselves inventing inconsequential just so stories about the more abstruse aspects of our sexual behavior, a fifth column that germinated long ago in the field of behavioral genetics was about to drive the decisive nail in their coffin. Obviously, it would have been an inappropriate distraction for Plomin to expand on the fascinating history behind this development in Blueprint. Read between the lines, though, and its quite clear that he knows what’s been going on.
It turns out that the behavioral geneticists were already astute at dodging the baleful attention of the high priests of the Blank Slate, flying just beneath their radar, at a very early date. A useful source document recounting some of that history entitled, Origins of Behavior Genetics: The Role of The Jackson Laboratory, was published in 2009 by Donald Dewsbury, emeritus professor of psychology at the University of Florida. He notes that,
A new field can be established and coalesce around a book that takes loosely evolving material and organizes it into a single volume. Examples include Watson’s (1914) Behavior: An Introduction to Comparative Psychology and Wilson’s (1975) Sociobiology. It is generally agreed that Fuller and Thompson’s 1960 Behavior Genetics served a similar function in establishing behavior genetics as a separate field.
However, research on the effects of genes on behavior had already begun much earlier. In the 1930’s, when the Blank Slate already had a firm grip on the behavioral sciences, According to the paper, Harvard alumnus Alan Gregg, who was Director of the Medical Sciences Division of Rockefeller Foundation,
…developed a program of “psychobiology” or “mental hygiene” at the Foundation. Gregg viewed mental illness as a fundamental problem in society and believed that there were strong genetic influences. There was a firm belief that the principles to be discovered in nonhuman animals would generalize to humans. Thus, fundamental problems of human behavior might be more conveniently and effectively studied in other species.
The focus on animals turned out to be a very wise decision. For many years it enabled the behavioral geneticists to carry on their work while taking little flak from the high priests of the Blank Slate, whose ire was concentrated on scientists who were less discrete about their interest in humans, in fields such as ethology. Eventually Gregg teamed up with Clarence Little, head of the Jackson Laboratory in Bar Harbor, Maine, and established a program to study mice, rabbits, guinea pigs, and, especially dogs. Gregg wrote papers about selective breeding of dogs for high intelligence and good disposition. However, as his colleagues were aware, another of his goals “was conclusively to demonstrate a high heritability of human intelligence.”
Fast forward to the 60’s. It was a decade in which the Blank Slate hegemony began to slowly crumble under the hammer blows of the likes of Konrad Lorenz, Niko Tinbergen, Robert Trivers, Irenäus Eibl-Eibesfeldt, and especially the outsider and “mere playwright” Robert Ardrey. In 1967 the Institute for Behavioral Genetics (IBG) was established at the University of Colorado by Prof. Jerry McClearn with his colleagues Kurt Schlesinger and Jim Wilson. In the beginning, McClearn et. al. were a bit coy, conducting “harmless” research on the behavior of mice, but by the early 1970’s they had begun to publish papers that were explicitly about human behavior. It finally dawned on the Blank Slaters what they were up to, and they were subjected to the usual “scientific” accusations of fascism, Nazism, and serving as running dogs of the bourgeoisie, but by then it was too late. The Blank Slate had already become a laughing stock among lay people who were able to read and had an ounce of common sense. Only the “experts” in the behavioral sciences would be rash enough to continue futile attempts to breath life back into the corpse.
Would that some competent historian could reconstruct what was going through the minds of McClearn and the rest when they made their bold and potentially career ending decision to defy the Blank Slate and establish the IBG. I believe Jim Wilson is still alive, and no doubt could tell some wonderful stories about this nascent insurgency. In any case, in 1974 Robert Plomin made the very bold decision for a young professor to join the Institute. One of the results of that fortuitous decision was the superb book that is the subject of this post. As noted above, digression into the Blank Slate affair would only have been a distraction from the truly revolutionary developments revealed in his book. However, there is no question that that he was perfectly well aware of what had been going on in the “behavioral sciences” for many years. Consider, for example, the following passage, about why research results in behavioral genetics are so robust and replicate so strongly:
Another reason seems paradoxical: behavioral genetics has been the most controversial topic in psychology during the twentieth century. The controversy and conflict surrounding behavioral genetics raised the bar for the quality and quantity of research needed to convince people of the importance of genetics. This has had the positive effect of motivating bigger and better studies. A single study was not enough. Robust replication across studies tipped the balance of opinion.
As the Germans say, “Was mich nicht umbringt, macht mich stark” (What doesn’t kill me make me strong). If you were looking for a silver lining to the Blank Slate, there you have it. What more can I say. The book is a short 188 pages, but in those pages are concentrated a wealth of knowledge bearing on the critical need of our species to understand itself. If you would know yourself, then by all means, buy the book.