Human Evolution Continues, I Just Decided

• Welcome to the BOL Forum on Evolutionary Psychology by John Grohol, 3/19/97
  • About Evolutionary Psychology by Behavior OnLine Editor, 12/28/96
    • Why only hunter-gatherer by John Grassi, 1/8/97
      
      

There are many great thoughts in the "Adapted Mind" (1) and few annoyances. One of the latter devils me; the notion that human evolution stopped 30K years ago in the Pleistocene. There are several steps to that conclusion.

a) 30K years is insignificant in evolutionary time that includes 3.5 eons (3.5 billion years). Therefore, nothing important could have occurred.

b) Evolved Psychological Adaptations (including everything from the hair on top of our heads to that between our toes) exist that allow us to attend efficiently (more than can be attributed to individual training) to the tasks of child care, mating, gathering food, working in coalitions, managing property and exchanges, etc. We seem to have specializations that show themselves even in such annoyances as morning sickness. (2)

c) Given the complexity of Psychological Adaptations and their essential role in our lives, they must be uniform between individuals. Otherwise, the PAs would be disrupted by the genetic recombinations that occur during meiosis as we mate with each other.(3)

d) Natural Selection operates during times of shortage of resources for reproduction. But culture and climatic uniformity have alleviated natural selective pressures for the wink of 30K years.

The outcome for a-d is that evolution has stopped for humanity.

Granted, very long periods of little change (stasis) have occurred before and for many species. However:

a) Some estimates are that even a 1% selective advantage for a genetic trait could achieve complete penetration through a population in a relatively short time. In addition, such effects as Linkage disequilibrium, sexual selection, and imprinting could accelerate the speed with which new traits develop across generations. We are also going through one of the 6-8 great extinction phases on the earth's history. We seem to be the responsible agent for nearly everything else that dies. We seem to be collectively bigger than volcanoes and meteors. Since we have close, intricate biological dependencies on other life forms, we could already have put events into play that will severely limit our own success in the future.

b) We are NOT all the same in our abilities to care for the kids, to find mating partners, or to work effectively in coalitions. Just as various academic skills are systematically missing in some of us and in our relatives, PAs differ between people. It's difficult to assert that "child care" is uniform for all of us in the face of variability between women even in their ability to produce milk. It's hard to claim PA uniformity for complex behaviors when the simpler PA of regulating breathing is impaired in some of us.

c) It could be that our PAs for forming alliances and handling friendships actually increase the amount of variability that is compatible with personal survival and reproduction. Indeed, some PAs may get lost through genetic recombination but our ability to work in groups may soften the outcome. The woman who can't manage children gets her sisters or friends to watch and feed them. The male who is too small to hunt may have other skills to exchange with people who are larger and quicker.

d) If we admit to high variability in PAs, some of it may be associated with the evolutionary age of the skills.(4) Older traits are thought to be more resilient and less easily disrupted. Newer things, whether memories or adaptations, may break easier and if so, would demonstrate greater variability.(5)

e) Coalitions, the prosthesis that makes other impairments tolerable, seems robust, more resistant to physical or social interference. Thus, its foundations may be comparatively old and have more redundant foundations than some of the other things we do. For example, I have 8 good friends, known as ducks. They work in a group of 8 or smaller, stable ones of 2 or 3 depending on circumstance. There are even moments of altruism between them.

f) If there is variability in PAs, there is some reasonable chance that the variability is in synchrony with environmental differences. There may be systematic contrasts between those of us at high altitudes, in isolated mountain cultures and those in equally isolated plains or jungle conditions.

I think, therefore, that evolution in some forms, does continue even with us. Grassi right. We can't shut it off The challenge for all of us is to remain humble; that adaptations that help some of us this season may be fatal in another. And those of us with a different set of adaptations my survive.

NOTES:

1) Barkow J, Cosmides L, & Tooby J. (1992) The Adapted Mind: Evolutionary Psychology and the Generation of Culture. NY: Oxford.

2) Profet M (1992) Pregnancy sickness as adaptation: A deterrent to maternal ingesting of teratogens, In Barkow J, et al., 1992, pp 327-366.

3) There is an implicit ethical dilemma. If uniform set of PAs is characteristic of being human, are those of us without such PAs not human? Surely we are despite our impairments.

4) Identifying such skills represents a substantial challenge. However, it is no different from that offered by physical traits. See Darden L, (1992) "Character: Historical Perspectives" in Keller E & Lloyd E (Eds) Keywords in Evolutionary Biology, Cambridge, MA: Harvard Univ Press, pp 41-44.

5) Pennington B (1991) Diagnosing Learning Disorders, NY: Guilford. There are varied estimates of the extent of reading, math, or spelling disabilities. Restrictive criteria that use 2 standard deviations limit the estimates to about 0- 3% of the population. Using 1 standard deviation difference between IQ and an achievement score increases the rate to 21% for Reading, 38% for Spelling, and 35% for Math. See Barkley R (1990) Attention Deficit Hyperactivity Disorder: A Handbook for Diagnosis and Treatment. NY: Guilford, p. 77 for an explanation of reasons for using one estimate vs. another.

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