Punctuated Equilibrium and the EEA for Human Behavioral Adaptations

AUTHOR: Christopher Ryan

SOURCE: Evolutionary Psychology

COMMENTARY: Allen MacNeill

The following question was asked on the Evolutionary Psychology list:

"...[W]e look to the EEA for the origins of the design of the human mind (modules, and so on) precisely because the structures in question change so slowly. If, on the other hand, it is demonstrated that complex physiological (and, presumably, psychological) structures can arise and disappear in as few as twenty generations, then of what relevance is the EEA to our discussions here?...Does Gould's punctuated equilibria theory integrate such rapid evolutionary change? And is it accepted by the folks working in [evolutionary psychology]? If so, why do we spend so much time discussing adaptations that have likely been replaced long ago?"

To which I replied:

Eldredge and Gould, like the vast majority of other evolutionary biologists (beginning with Darwin and including such luminaries as Ernst Mayr) studied animals almost exclusively. It now appears that the equilibrium/stasis pattern that characterizes macroevolution in animals is at least partly an artifact of their developmental biology. Specifically, the hierarchical control of gene regulation in animals via homeotic genes makes possible surprisingly rapid phenotypic change without correspondingly large changes in genotype (i.e. the old "modern synthesis" has been superceded by the new "evo-devo").

Therefore, it is quite possible (indeed, likely) that relatively slight changes in genetic regulation of development have caused the remarkable changes in hominid phylogeny reflected in the fossil record. This has already been shown to be the case for the FOX-2-P gene, and just last month for the HAR-1-F gene (see "And the winner of the fastest gene award..."), slight changes in both of which have been correlated with significant changes in the human phenotype (both in the direction of greater neoteny, by the way).

So, it is quite possible that humans have changed significantly over the past 40,000 years, and perhaps not just via purely cultural means. It is still an open question just how much of our behavior is affected by our underlying genetics, and how quickly such relationships can change (and under what conditions). And, if new research in epigenetics is any indication, such changes may be even more common and rapid than has been heretofore suspected. Nutrition during early development, chronic stress (including chronic stress in utero), and exposure to certain environmental chemicals have all been implicated in altering gene regulation, and some such alterations have been shown to be heritable (shades of Lamarck!), thereby challenging further the "standard social science model" so vilified by Pinker and other EPers.

Therefore, the EEA for some current "modules" may not date to the Pleistocene, but rather to much later periods, including (but not limited to) events in historical times. Indeed, since relative reproductive success, rather than absolute numerical differences, is the basis for natural selection (and therefore adaptation), it may be that such seemingly cultural processes as warfare, migration (including forced migration via slavery), and religious practices involving both celibacy and increased procreation (via religious prohibition of contraception) may all have played significant roles in the shaping of the human behavioral phenotype via correlated alterations in the expression of genes affecting behavior.

In a nutshell, then, the answer is yes: since humans are animals (like those studied by Eldredge and Gould), it is quite possible that punctuated equilibrium theory is applicable to human evolution, including behavioral evolution, and that further investigations into the relationship between gene regulation, development, and human behavior may yield productive, testable hypotheses about such relationships.

At the risk of blowing my own horn, I have attempted to propose such a hypothesis for the evolution of the capacity for religious experience (see: "The Capacity for Religious Experience is an Evolutionary Adaptation to Warfare"):

"The pan-specific qualities of both religious experience and warfare indicate that they are both evolutionary adaptations. There is considerable variation between individuals with respect to their capacity for religious experience and motivation to participate in warfare. Selective advantages for participation in warfare accrue to both winners and losers as long as the benefits of participation exceed the average costs. These selective advantages, primarily in the form of differential reproductive success, accrue to males when they are on the winning side in a war, and often to females no matter which side they are on."

"Recent work on the evolutionary dynamics of religion have converged on a "standard model" in which religions and the supernatural entities which populate them are treated as epiphenomena of human cognitive processes dealing with the detection of and reaction to agents under conditions of stress, anxiety, and perceived threat. Religious experience at the individual level is characterized by depersonalization, coupled with submission to a super-individual force; the same is essentially the case for participation in warfare. The capacities for both religious experience and participation in warfare are adaptations insofar as they evolve by means of natural selection operating primarily at the level of individuals who are members of groups in which both kin selection and reciprocal altruism are also operative. It is likely that the overall patterns of supernatural organization exist as the result of coevolution between the memetic content of religious beliefs and the underlying neurological matrix within which such beliefs are maintained and transmitted in the context of specific ecological subsistence patterns."

--Allen

There's Something Fishy About Human Brain Evolution

AUTHOR: Arnet Sheppard

SOURCE: Eureka Alert

COMMENTARY: Allen MacNeill (following the article)

Forget the textbook story about tool use and language sparking the dramatic evolutionary growth of the human brain. Instead, imagine ancient hominid children chasing frogs. Not for fun, but for food.

According to Dr. Stephen Cunnane it was a rich and secure shore-based diet that fueled and provided the essential nutrients to make our brains what they are today. Controversially, according to Dr. Cunnane our initial brain boost didn't happen by adaptation, but by exaptation, or chance.

"Anthropologists and evolutionary biologists usually point to things like the rise of language and tool making to explain the massive expansion of early hominid brains. But this is a Catch-22. Something had to start the process of brain expansion and I think it was early humans eating clams, frogs, bird eggs and fish from shoreline environments. This is what created the necessary physiological conditions for explosive brain growth," says Dr. Cunnane, a metabolic physiologist at the University of Sherbrooke in Sherbrooke, Quebec.

The evolutionary growth in hominid brain size remains a mystery and a major point of contention among anthropologists. Our brains weigh roughly twice as much as our similarly sized earliest human relative, Homo habilis two million years ago. The big question is which came first – the bigger brain or the social, linguistic and tool-making skills we associate with it?

But, Dr. Cunnane argues that most anthropologists are ignorant or dismissive of the key missing link to help answer this question: the metabolic constraints that are critical for healthy human brain development today, and for its evolution.

Human brains aren't just comparatively big, they're hungry. The average newborn's brain consumes an amazing 75-per cent of an infant's daily energy needs. According to Dr. Cunnane, to fuel this neural demand, human babies are born with a built-in energy reservoir – that cute baby fat. Human infants are the only primate babies born with excess fat. It accounts for about 14 per cent of their birth weight, similar to that of their brains.

It's this baby fat, says Dr. Cunnane, that provided the physiological winning conditions for hominids' evolutionary brain expansion. And how were hominid babies able to pack on the extra pounds? According to Cunnane their moms were dining on shoreline delicacies like clams and catfish.

"The shores gave us food security and higher nutrient density. My hypothesis is that to permit the brain to start to increase in size, the fittest early humans were those with the fattest infants," says Dr. Cunnane, author of the book Survival of the Fattest, published in 2005.

Unlike the prehistoric savannahs or forests, argues Dr. Cunnane, ancient shoreline environments provided a year-round, accessible and rich food supply. Such an environment was found in the wetlands and river and lake shorelines that dominated east Africa's prehistoric Rift Valley in which early humans evolved.

Dr. Cunnane points to the table scrap fossil evidence collected by his symposium co-organizer Dr. Kathy Stewart from the Canadian Museum of Nature, in Ottawa. Her study of fossil material excavated from numerous Homo habilis sites in eastern Africa revealed a bevy of chewed fish bones, particularly catfish.

More than just filling the larder, shorelines provided essential brain boosting nutrients and minerals that launched Homo sapiens brains past their primate peers, says Dr. Cunnane, the Canada Research Chair in Brain Metabolism and Aging.

Brain development and function requires ample supplies of a particular polyunsaturated fatty acid: docosahexaenoic acid (DHA). DHA is critical to proper neuron function. Human baby fat provides both an energy source for the rapidly growing infant grey matter, and also, says Dr. Cunnane, a greater concentration of DHA per pound than at any other time in life.

Aquatic foods are also rich in iodine, a key brain nutrient. Iodine is present in much lower amounts from terrestrial food sources such as mammals and plants.

It was this combination of abundant shoreline food and the "brain selective nutrients" that sparked the growth of the human brain, he says.

"Initially there wasn't selection for a larger brain," argues Dr. Cunnane. "The genetic possibility was there, but it remained silent until it was catalyzed by this shore-based diet."

Dr. Cunnane acknowledges that for the past 20 years he's been swimming upstream when it comes to convincing anthropologists of his position, especially that initial hominid brain expansion happened by chance rather than adaptation.

But, he says, the evidence of the importance of key shoreline nutrients to brain development is still with us – painfully so. Iodine deficiency is the world's leading nutrient deficiency. It affects more than a 1.5 billion people, mostly in inland areas, and causes sub-optimal brain function. Iodine is legally required to be added to salt in more than 100 countries.

Says Dr. Cunnane: "We've created an artificial shore-based food supply in our salt."

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AUTHOR'S BIOGRAPHICAL & CONTACT INFORMATION:

Contact:
Dr. Stephen Cunnane
(819) 821-1170, ext. 2670 (office)
stephen.cunnane@usherbrooke.ca
Natural Sciences and Engineering Research Council
http://www.nserc.gc.ca/index.htm

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COMMENTARY:

Several decades ago, Elaine Morgan ignited a controversy among anthropologists and paleontologists by writing The Aquatic Ape and The Descent of Woman, in which she popularized the theories of Sir Alistair Hardy, who proposed that the evolution of humans from our primate ancestors could best be explained by the assumption that seashores, not savannahs, are our "ancestral" habitat. At the time, both Morgan and Hardy were, like Lynn Margulis and Peter Mitchell, considered to be "crackpots" and "nut cases."

However, recent research into human evolutionary biogeography has lent convincing support to the "aquatic ape hypothesis. As you can see in this website, the biogeographical distribution of marker DNA sequences in our phylogenetic clade closely mirrors the archaeological and paleontological evidence for hominin migrations out of east Africa. For over a million years, our ancestors hugged the shorelines of the old and new worlds...indeed, as any glance at a world map shows, we still do.

Gotta go; it's time for our family swimming lesson at the YMCA ;-).

--Allen

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ORIGINAL PUBLICATION REFERENCE:

Location Online: Eureka Alert
URL: http://www.eurekalert.org/pub_releases/2006-02/nsae-tsf021706.php

Original posting/publication date timestamp:
Public release date: 18-Feb-2006

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