Biology and Culture : An interactive co-evolution.
Two recent papers published in Science point to a rapid evolution in Humans of two developmental genes known to regulate brain size (2005, vol. 309, p.1717-1722). This rapid evolution, which is different between ecogeographical regions, seems to be initiated along with radical and historical changes in the Human environment, migrations and agriculture. Researchers don't want to speculate about this because, as impressive as they can be, these are preliminary data. They must be confirmed by more investigations focusing on the precise phenotype of these genes, their physiology and more importantly, in my opinion, there must be quantification, with MRI techniques, of the differences these genes introduce in the phenotype of the brain . Moreover, these genes are probably not the only ones involved in regulating brain size. A year ago, researchers published a finding concerning a Myosin gene mutation in the jaw. This mutation relaxes the jaw muscles. It was speculated that this fact might have contributed to the expansion of the cranium and consequently to a larger brain (Nature 428, 415–418, 2004).
These findings are fascinating. They point to a new direction in many research areas in the brain and mind sciences. Indeed, some beliefs related to these sciences will have to adapt to the new findings. One is that there is one direction to evolution, from genes to phenotypes, and that it is reproductive success which ultimately give a direction to evolution. Another is that the structure of the brain is the product of a random gene selection and a third is that genes are selected on the basis of their behavioral outcomes as ultimate phenotypes. These three assumptions are often part of the ideological arsenal of what is usually called evolutionnary psychology which is a radical version of adaptationist thinking. According to evolutionary psychology, the explanation of the rapid evolution of genes controlling brain size during development can go like this: an allele is selected randomly and it becomes dominant in a population because it gives his owner more fitness - based on the outcome of the gene on the behavioral level - accompanied by reproductive advantage.
This kind of thinking, however powerful (and I am not saying true), does not apply to genes involved in developmental regulation of the phenotype. Why ? Because development is a construction based on interactions between genes and environment. Depending on the developmental stage, these interactions have different pathways . In the evolutionary psychology paradigm, they are carried out mainly by the behavioral outcomes of the gene - note that, most of the time, behavioral outcome is not fully displayed in species with a very slow development like Humans. During development, pre and early post natal, interactions between genes and environment are more likely to be carried out by structural constraints related to the whole organism. Starting at the level of the interface of the organism and its environment, they are transmitted to lower levels of structural organisation in the organism. In humans, the body, its sensations, motions and affects are the primary interface for genes/environment interactions. These interactions are mainly translated, in early development, into constraints on the construction of the organism which go down to the structure of genes.
Phenotype regulation during development acts on forms and not on behavioral outcomes since these outcomes are determined later at maturity. This kind of selection is exerted at the level of an individual organism, it is not populational.
The findings above point to a possibility that the environment - including the one that is our own making like migrations and agriculture - introduces structural constraints on the expression of genes in the construction of the organism, playing an active role in the phenotypic outcome at the structural level and thus directing the evolution. The term 'positive selection' used by the researchers to describe the process of the rapid evolution of genes controlling brain size is nothing else than directed - and not random - selection. Selection directed by the environment. Indeed, positive selection occurs when selection favors only one allele increasing its frequency in a population, where random selection operates on more than one allele.
Arguments against directional selection claim that directional selection is actually an instruction and not a selection. This kind of thinking is erroneous since it assumes that the environment 'knows' what it is doing. There is no 'anticipation' of adaptation in the process, there is only a joint effect on the construction of organisms during a developmental period in which organisms are dependant on their environment for their survival, as in the case of slow human brain development. This slow development is even magnified by an increase in the size of the brain which extends the duration of the maturation process.
What does this mean for us as Humans and as a society ? It means that the environment we are changing continually with our cultural artifacts and products and with our social expertises - which are passed on across generations - is contributing to our biological evolution. It means that Culture is irreversibly grounded in Biology. It means also that radical environmental changes of any kind, being physical, cultural or social, have an impact on our destiny as species for generations to come.
However, in the case of Human brain environment, instruction - as knowledge transfer - is an essential part of the interactions between the organism and its environment. But even though it is directional for the behavioral outcome, it 'knows' what to expect, it is not directional when it comes to structural constraints it may place on the organism and the brain at different organisational levels. At the structural level, instruction is a blind and a neutral process, value free. It has however an unanticipated advantage: it produces additional variations in the phenotype, induced by the environment and not included in the initial genetic program inherited from other species. These value free variations are specified in a social context. We are then responsible for the values that will be attached to these variations.
There is a big challenge here. As Humans, we have the knowledge and the moral capacity to judge behavioural outcomes of gene/environement interactions during development. From these behavioural outcomes we must anticipate and construct an ethic of harmony and agreement between Nature - biological nature of Humans - and Nurture in which every generation must take lessons from the past - the impact of past expertises on present behavioral and environmental outcomes (including man made social and ecological changes) - to build a better future for the generation to come. This is a great responsibility that falls upon us, a responsibility in which every man and woman have to become their own god.