To the editors:
There is much that I agree with in David Lahti’s review of Behaving. However, I do take exception to his general comments about the lack of attention paid to developmental processes and his position on the strength of evolutionary explanations for behavior.
“What Behaving does not offer,” Lahti writes, “is a sense of the bigger picture.” There is indeed a bigger picture and I will offer some comments at the end of this response about the kind of a bigger picture that I think is needed. “In the overall science of behavior,” he continues, “behavioral genetics is a rather technical subfield. Any talk of genes and environment only makes sense in the broader context provided by development and evolution.”
I was perplexed by Lahti’s claim that development was not discussed extensively in Behaving. But, we both see the role that evolutionary explanations can play quite differently. This is not only in terms of behavior, but in biology in general. Lest the reader misconstrue my position, I subscribe to the oft-quoted view of Theodosius Dobzhansky that “Nothing in Biology Makes Sense Except in the Light of Evolution.”1
The primary concern of Behaving’s third and fourth chapters is an analysis of the approach termed developmental systems theory (DST). The contrast between the non-developmentalist and developmentalist views is elaborated in detail. These chapters discuss research on development and behavior using the worm C. elegans. A mixed assessment of the strengths and weaknesses of DST is presented. That analysis, although critical, does not reject a developmental perspective, as indicated in a comment made by a major contributor to DST, Paul Griffiths, who has anointed me as a developmentalist.2 Readers who take the time to work through the complexities of the worm’s development, as reported from the work of Martin Chalfie and others, will see just how much attention is, in fact, paid to the importance of development.
It is likely that developmental issues also play an important role in psychiatric genetics, a topic analyzed in chapters six and seven. Early influences on susceptibility genes for antisocial activity are noted in a review of the controversial work by Avshalom Caspi and Terrie Moffitt. The significance of schizophrenia as a developmental disease is also discussed briefly, along with a detailed footnote that reports on the work of Daniel Weinberger.3 After Behaving went to press, Aswin Sekar et al. published an analysis of a gene in the region responsible for the complement component 4. Their study suggested that overproduction of this C4 protein has a pathological effect on the synaptic pruning that is important in brain development.4
On the topic of evolution, Lahti wrote:
In Behaving, Schaffner laments the absence from biology of predictive explanatory theories like those that can be found in physics. On the contrary, we do have a theoretical framework that makes sense of behavior and explains why organisms do one thing rather than another. This framework is the theory of evolution.
I agree that we do have an important theoretical framework. But what we do not have are any confirmed and specific explanations for human behavior, even though there are at least five different evolutionary approaches. These are typically described as the subdisciplines, or schools, of evolutionary-based human behavior, and include sociobiology, behavioral ecology, evolutionary psychology, cultural evolution, and gene-culture co-evolution (dual inheritance theory). There are also several putative multi-school and integrated explanations for human behavior, including infanticide, war, and propaganda, which are often seen as controversial. Readers are advised to examine the range of approaches and accompanying critical assessments found in Kevin Laland and Gillian Brown’s Sense and Nonsense before subscribing to Lahti’s views on the power of human evolutionary theory.5
A major part of the problem with evolutionary explanations of human behavior is that there is no data preserved in the fossil record. This is true even for relatively recent changes. Comparative animal studies are also compromised by an inability to find valid and matching behaviors. As a result, much of what is presented as evolutionary explanations remains speculative because the available data is deficient. Evolutionary accounts are often criticized as just-so stories.6 They are better than that. But still nowhere near as strong as the accounts behavioral and psychiatric genetics will eventually be able to offer. Twenty-five years ago I analyzed what was then, and may still be, one of the best evolutionary explanations for the changing presence of the alleles that cause sickle cell anemia. I concluded, in common with the major researchers at the time, that even the best evolutionary explanations involving humans “rely on critically incomplete data,” and that “a number of conjectural assumptions must be made to generate an explanation.”7 In relation to behavior, Laland and Brown note that the approaches reviewed in their book are representative of “a young and provisional science.”8 Evolutionary approaches remain underdeveloped. This can be seen in the decision made by the authors of the authoritative textbook Behavioral Genetics to remove a chapter included in previous editions entitled “Evolution and Behavior” because not much is new and there is little in the way of hypothesis testing—due largely to the nature of the theory.9
I began this response by noting that there is a bigger picture. This is clearly true in behavioral genetics and psychiatric genetics. Both are grappling with the complex emerging findings from genome-wide association studies (GWAS). Steven Hyman recently remarked that:
a sobering picture is coming into view; it reveals daunting genetic and phenotypic complexity portending enormous challenges for neurobiology. Successful exploitation of results from genetics will require eschewal of long-successful reductionist approaches to investigation of gene function, a commitment to supplanting much research now conducted in model organisms with human biology, and development of new experimental systems and computational models to analyze polygenic causal influences. In short, psychiatric neuroscience must develop a new scientific map to guide investigation through a polygenic terra incognita.10
In relation to “the mysterious and often troubling matter of free will,” Lahti notes that, in addition to genetic influences, there are also evolutionary, developmental, or environmental influences on behavior. I have embraced the role of developmental influences in my analysis. Readers of the introductory chapters, worm chapters, and the psychiatric chapters of Behaving, will find discussions regarding the role of the environment, for which we do not yet have a clear and guiding theory. Genes, as noted in the book, primarily work through the development of a complex neural system, themselves subject to environmental forces and influenced in ways that we are still struggling to understand. Much more remains to be said about human behavior. With this in mind, a follow-up project is now underway. It is tentatively titled Choosing: What Can We Learn about Choice and Flourishing from Behavioral Neurogenetics.
Kenneth Schaffner
