“Environmental factors can be an important source of nongenetic influences on laterality.  Since the effect of a gene is to play a role in some form of chemical reaction, it is not surprising that genetic determination is not absolute.  Every chemical reaction can be modified by alterations in pressure, temperature, pH, light, the presence of other substances, the availability of chemical precursors, and the rate at which products are removed.  With growing sophistication of molecular genetics, it has become increasingly clear that nongenetic effects can play a powerful role; methylation, for example, has been shown to suppress expression of many genes.  We will now consider some of the random effects that might modify lateralization.  One implication of our hypothesis is that even if the genetic endowment of any particular fetus were known precisely, it would not be possible to make predictions concerning the distribution in a population basis.  One of the reasons for this relative freedom from genetic determination is that if hormones do play a role in determining laterality, then the effects of testosterone or related substances on the developing brain will be modified by factors not under the control of the fetal genes.  Androgens are produced not only by fetal testes and the placenta but also by the maternal ovaries, adrenals, and nonglandular tissues.  The fetus can be influenced by the actions of many of the unshared maternal genes.  It is reasonable to expect that if a fertilized ovum were transplanted into the uterus of an unrelated female, the final pattern of the brain would be quite different, because the brain would develop in an environment of hormones and other substances that would certainly differ in many respects.  It might therefore be reasonable to take a different approach than usual to the genetics of many conditions.  One should perhaps consider, not the genes carried by the offspring alone, but rather the genes of that organism existing or active only for the nine months of pregnancy; in other words, one should consider the mother and the fetus as a unit.  This unit contains three groups of different genes: one paternal set present in the fetus, one maternal set present in the mother, and another maternal set present both in the mother and in the fetus.  The situation is even more complex when dizygotic twins are involved, since the maternal-fetal unit will contain another group of paternal genes.  The effects of substances produced by the mother will, however, be diminished by the capacity of the placenta to act as a barrier to some maternal hormones.  The fetus is protected to a great extent from maternal testosterone, which is converted to estradiol by placental aromatase.  Dihydrotestosterone, which is not aromatized and therefore crosses the placenta, is, however, usually present in the mother at much lower levels than testosterone.  The protection from maternal testosterone is not complete, since offspring do show signs of masculinization when mothers are exposed to this hormone.  In addition, progesterone administered to the mother may masculinize female fetuses.  It is clear that the placental barrier is far from complete.  Furthermore, it is likely that there are individual variations in the aromatizing capacity of the placenta.  It is conceivable that some maternal genes not shared by the offspring have greater effects on female fetuses.  Thus, the testosterone to which female fetuses are exposed comes predominantly from maternal tissues, whereas males produce it themselves in high quantities.  In the study of Nichols and Chen (1981) sex hormones given to mothers were associated with a higher rate of hyperactivity in female offspring than in males.”  (Geschwind and Galaburda 1987: 133-134, Cerebral Lateralization)

This long excerpt discusses Geschwind and Galaburda’s 1987 thoughts regarding the yet unnamed evolutionary biological discipline, evolutionary developmental biology.  Neuropsychologists are not often referred to in evolutionary biology.  When neuropsychologists are referencing evolution at all they are usually thinking in terms of natural selection.  Neuropsychologists and evolutionary biologists retain separate journal systems, separate languages, separate conferences.

T. J. Crow is a British theorist who has crossed lines in his explorations of schizophrenia and other mental conditions, bringing in discussions of neoteny to explain cerebral anomalies.  Marion Annett has suggested left-handedness reveals features of an evolutionary forebear.  Bernard Crespi, though focusing on genetics as the cause of schizophrenia and autism, seems to imply evolutionary underpinnings to the conditions.  Connecting the work of these three theorists to an evolutionary developmental interpretation of their work may be useful.  From what I can tell, these kinds of interpretations are rare events.

In the excerpt above, Geschwind and Galaburda are realizing that a person’s genetic heritage as regards something as central as cerebral lateralization has far less to do with an individual’s genes than with the environment that they are located in and possibly the genes of those they are in contact with.  In the model I am playing with, we cannot easily look at a representative of a species, any person, for example, as the source of information regarding the individual’s “genetic heritage.”  We each are part of a larger matrix of genetic information, with genomes located in other individuals, including individuals in other species, informing our personal ontogeny.

The following is the premise I am playing with.  If heterochrony is the study of the rates and timing of maturation, with testosterone levels impacting rate and estrogen levels controlling timing, then those environmental or social structure adjustments that influence levels of testosterone and estrogen determine the speed, timing, features and direction of evolution.

Connected to this premise is a reinterpretation of genetics to be not a “template,” an algorithm or a code, but more a musical score requiring both (1) the input of unique musicians that includes their life history and experience and their interpretation of the score and (2) the influence of the audience on the musicians.

Integral to this interpretation is a complete overhaul of the reductionist or materialist perspective.  Geschwind and Galaburda see clues to a shift in this direction.  Evo Devo advocates can sometimes sense where we are headed.  Consider that Geschwind and Galaburda are noting that if something as central as cerebral lateralization, which I have described as integral to understanding human self awareness, or split consciousness, is heavily influenced by hormones, hormones heavily influenced by environmental factors, then the origin of human consciousness ontologically in each of us individually is directly related to what is happening in the world around us.

I have stated that environmental or social structure adjustments that influence levels of testosterone and estrogen determine the speed, timing, features and direction of evolution.  The emergence of split consciousness was, of course, central to human evolution.  Geschwind and Galaburda are trying to sort out the influence of the hormones on individual cerebral ontogeny.  Their work can also be interpreted to be seeking to untie the knot of understanding of how humans evolved split consciousness originally.  We’re not talking just adjustments in genes, what Annett has described as right shift theory, or tendency to lateralize.  We are talking about the contribution of a whole environment to the origin of human split consciousness both tens of thousands of years ago and right now with the emergence of each new person.

I often read papers by specialists in disciplines and have few clues about what they are trying to communicate.  Works by an evolutionary biologist I seem to get most of.  If the work is by a geneticist or neurologist, I miss much.  I often feel like an outsider trying to grasp some particular subdiscipline’s insight, needing courses in the subdiscipline, a mentor and the kind of personality that is willing to study what I’ve been told to study because it is the convention to do so.  Reading neuropsychology and evolutionary developmental biology, I’m asking myself if these two subdisciplines can even understand each other.  I don’t think my brother-in-law, who is the chair of an economics/finance department, has the background to grasp concepts that my astronomy professor friend Craig would be familiar with, though they both use mathematics.  (I could be wrong.)  I’m starting to wonder if the holistic insights characterized by understanding common concepts among neuropsychology, evolutionary biology and social structure where it integrates with endocrinology are difficult to grasp in no small part because the different disciplines just don’t talk because they can’t.

When I read excerpts like the passage that began this piece, little evolution flags start excitedly waving.  What do academics do when they have those cross-disciplinary gestalt experiences?


This entry was posted on Wednesday, January 6th, 2010 at 8:49 am and is filed under Biology, Ontogeny, Society. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
2 Comments so far

  1. Socrates on January 6, 2010 9:55 am

    “What do academics do when they have those cross-disciplinary gestalt experiences?”

    Usually win Nobel prizes.

    Your ideas clearly deserve a wider audience.

  2. Andrew on January 6, 2010 10:17 am

    Thank you!

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