Behavioral Evolution I. 1h 36m Robert Sapolsky video.

This lecture starts exploring how we can deduce all sorts of principles of (human) social behavior from the principles of evolutionary theory. The fields of sociobiology (aka behavioral ecology) and later evolutionary psychology have developed this kind of thinking.

Sapolsky gives a quick review of the theory of evolution by natural selection that was developed by Alfred Russel Wallace and Charles Darwin in the 1800s. This is the theory that heritable traits in populations change over time whenever certain traits (there is an assumption of variability in traits including the possibility of mutations leading to new traits) prove to be more adaptive than others. Adaptability is not "survival of the fittest", but rather reproduction of the fittest. Behaviors are also heritable traits that can have selective or adaptive qualities. More adaptive behaviors will over time tend to become more commonplace. Sapolsky riles against Wynne-Edwards' espousal of group selection (the idea that animals behave for the good of the species). Sapolsky asserts that that is not how it works.

Sapolsky identifies three building blocks of natural selection (at least as far as this lecture goes). They are: 1) individual selection which Sapolsky represents with the expression "sometimes a chicken is an egg's way of making another egg". Another aspect of this is sexual selection (choosing mates) which can conflict with the basic "selfish gene" selection proclivity (witness the peacock's tail). 2) kin selection or "inclusive fitness": since each individual shares 1/2 their genes with their siblings and 1/8 of their genes with their cousins, it can happen that traits supporting an increase in the reproductive success of relatives might increase in the population. This is captured by the expression "I will gladly give my life for 2 brothers or 8 cousins" (attributed to Haldane). So evolution selects for organisms who help their relatives. 3) Reciprocal altruism. In addition to truces or stalemates like rock-paper-scissors, organisms (including bacteria, vampire bats, stickelback fish, and naked mole rats) have actual cooperation with non-kin others. This tends to require memory and cheating detection cognition skills. We, like most social organisms, are much better at detecting cheating than "random acts of kindness".

Sapolsky concludes with a long discussion on the mathematical modelling (game theory) of cooperation (prisoner's dilemna and related games), exceptions to cooperation (and the messiness of the real world), and an exquisite exercise to show how even this most basic of introductory accounts on behavioral evolution can detail an extensive understanding of the social behavior of two species given only a basic knowledge of the extent of sexual dimorphism (different traits between males and females of the same species) based on specimen skulls.

Sapolsky goes into depth on the prisoner's dilemna (http://en.wikipedia.org/wiki/Prisoner%27s_dilemma). I read Robert Axelrod's book in the 1980s and so I'll let you read the details in Wikipedia (or watch the video!!!). The 10,000 foot view is that in computer simulations, the tit-for-tat (TFT) strategy wins because it is nice (always cooperates at first), it is punitive (it retaliates against non-cooperation), it is forgiving, and it is straightforward (not random or probabalistic behavior). But it has a vulnerability if signal noise intervenes. When a mistake or noise turns a C (cooperation) into a D (defection), half of the cooperation can be wiped out. Forgiving TFT (FTFT) does better in these cases because it is more forgiving and builds a sense of trust with partners who have cooperated for a long enough period of time. The strategy named pavlov can exploit FTFT with the rule of doing again whatever won points in the last round, but switching if losing points.

Then biologists searched for strategies used by animals in nature and found many good examples (bacteria, vampire bats, stickelback fish, and naked mole rats). But they also found exceptions: unpunished defectors. With division of labor social organisms can have multiple dimensions of behavior. For example, with the naked mole rats, some large individuals appeared to be cheating. However, it was eventually discovered that they block access to their burrows in the rainy season which "compensates" for doing no work during the rest of the year. Sapolsky warns us that as we delve into behavior more deeply we will find extraordinarily complex behaviors as reputations and complex social roles enter the picture.

Sapolsky asks "how does reciprocal altruism play out in the world of natural selection? In addition to cooperative hunting, he suggests that another good example is given if you and your non-relatives spend an insane amount of time making you both look really good before going to the prom.

Then he does a wonderful exercise wherein he applies the principles of behavioral evolution to deduce the behavioral traits in comparison between a "tournament species" (where there is a large difference in sexual dimorphism, or the physical differences between males and females) and a "pair-bond species". We find that the species with bigger males has more aggression, only a few males father most of the children, the males provide relatively little parental work, the males have shorter lifespans, the females are attracted to bigger males (rather than selecting for males who will help more in childrearing: asking them to bring a worm as part of courtship for some birds), but there is less cuckoldry (females abandoning their children to find a better mate). It is remarkable how much we can accurately deduce about a species from analysis of differences in the skulls of males and females.

Humans are a hybrid species that has some tournament qualities and some pair-bond qualities. So our behavior is particularly complex. Welcome to the wonderful world of Robert Sapolsky's Human Behavioral Biology!

2. Behavioral Evolution