Excerpt:  Strategy & Biology, part 6

We paused in our exploration of strategy and biology at the point of some initial observations about anatomy.  How, for instance, left handedness is correlated with environments in which an advantage is gained from being able to win conflicts with surprise.  In gastropods, this left handedness manifests as a means of protection against predator crabs.  Let’s explore one more insight from that most revealing of body parts, our hands.

We’ve written about the shape of human hands and their utility in tool use and conflict.  Prior to that, how finger length may be indicative of risk appetite.  Well, finger-length researchers (yes, it is a specialisation) have published even more findings, connecting the testosterone-finger length correlation observations to the prevalence of autism in families.*

* Manning, J. et al., The 2nd to 4th digit ratio and autism. Developmental Medicine and Child Neurology, Volume 43, Issue 3, March 2001; https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1469-8749.2001.tb00181.x

“The relative sizes of someone's fingers are fixed for life within three months of conception, and the relationship seems to be governed by testosterone. Although the reason is not yet understood, earlier studies have shown that finger-length ratios are a robust marker of how much of that hormone a baby has been exposed to in utero—the more testosterone, the longer the ring finger. Overall, therefore, men tend to have longer ring fingers than index fingers, whereas in women the two fingers are more likely to be of equal length…

“High levels of testosterone in the womb have been linked to several other brain-related phenomena, including left-handedness, dyslexia and female homosexuality. Dr Manning thinks that the families of autistic children are genetically predisposed to produce high levels of testosterone during early development…  While high levels of testosterone may not solve the whole puzzle of autism, Dr Manning thinks levels in utero may be an important piece of it. The finding bolsters what is known as the ‘extreme male brain’ theory of autism.”*

* Anonymous, “Autism: Pointing the finger,” The Economist (March 24 2001): 93

Researchers have begun to complement the genetic aspect of biological determinism (nature) with studies into the epigenetic environments of fetuses and newborns (nurture) in a field known as the fetal origins of adult disease.  Their findings are fascinating, suggesting that, in the absence of outside interventions, fetuses optimise development for the short term (reproductive success) at the expense of the long term (overall longevity and/or susceptibility to chronic diseases).  The researchers argue that what has come to be known as syndrome X (the adult symptoms of children born with low birth weight) is a result of natural selection, with outcomes favouring the growth of the brain and survival in a low nutrient environment.

“There are two prongs to this hypothesis. The first is that a fetus has to cut its coat according to its cloth. Faced with a limited amount of food, it has choices about how to use it. Dr Barker's suggestion is that food will be allocated in ways that give an individual the best chance in early life, at the expense of later years when they will have had children and might, indeed, have died of something else. Above all, the growth of the brain is protected.

“The second prong is that a fetus takes its cue about what it will eat after it is weaned from its mother's physiology, and adapts accordingly. In this case, disease is caused when the prediction is wrong. In particular, individuals adapted for a low-calorie, low-fat environment who find themselves, through improved circumstances, in a high-calorie, high-fat environment, might be expected to have problems.”*

* Anonymous, “The child is father to the patient,” The Economist (June 14 2003): 78-79

The hypotheses are supported by evidence from animal studies comparing relative sizes of brains and other internal organs for newborns in either situations of normal or restricted diets.*  These observations are aligned with human studies both historical (the enlarged heads of people born in the immediate aftermath of World War II) and more recent, with serious implications for later onset of heart disease, diabetes, and obesity.**  The implications for public health strategies are equally noteworthy.

* Ozanne SE, Hales CN. The long-term consequences of intra-uterine protein malnutrition for glucose metabolism. Proceedings of the Nutrition Society. 1999;58(3):615-619. doi:10.1017/S0029665199000804

** Reyes, L. et al., Long-term consequences of low birth weight.  Kidney International. Volume 68, SUPPLEMENT 97, S107-S111, August 2005;  DOI:https://doi.org/10.1111/j.1523-1755.2005.09718.x...