A Rapid Introduction to Cultural Evolution "Cultural traits" ? - behaviors \ - skills | - values | all of these are different phenomena - rules | but each have some commonality - tools | - technologies / To avoid the connotations associated with these terms the collective term, "memes" was suggested by R. Dawkins. But these things are all part of a continuum (they are not distinct entities such as molecules) and they all interact with each other. e.g. Religion is one trait which is also inherited. How does the inheritance and the evolution of culture differ from that of genes? Selection/inheritance acting on Genes ontogeny selection mating Gt Ft Ft' Gt+1 Selection/inheritance acting on Cultural traits cultural cultural transmission selection transmission Ft-1' Ft Ft' mating ontogeny mating ontogeny Gt Gt+1 Hence the evolution of cultural traits adds another conceptual level. How does cultural inheritance differ from genetic inheritance? #1 - "Culture" is inherited from many sources not just your biological parents. This opens the possibility for horizontal inheritance to occur as well as a vertical inheritance. #2 - The "generation length" fro culture is quite variable. For example, grandparents can influence children. Even among primitive peoples the time frame of some traditions can be lengthy with oral traditions passed on for many generations. #3 - "Culture" is acquired slowly over the time span of the individual. #4 - The "culture"/information transmitted is altered by events in the life of the organism. This permits a form of Lamarckian inheritance - the inheritance of acquired traits. Societies themselves will have a large influence. But societies are usually hierarchical and exceedingly complex. Hence the variability in transmission rates and patterns and their inherent complexity make the study of cultural transmission much more difficult and far less precise than genetic transmission. Forces of cultural evolution: There are mutation analogs - #1 - Random variation - our memories and our learning abilities are not perfect. In this case the variation introduced could be random like genetic mutations. #2 - Guided variation - rational calculation can lead to modifications of old behaviors and/or the addition of new ones. In this case the variation introduced would be unlike genetic mutations. There are drift analogs - #3 - If the population of individuals to learn from is small, then chance variations are more likely. Similarly, rarely performed variants might be lost all together. For example, the Tasmanians lack many traits that are common among the Australian aborigines. #4 - Biased transmission - a direct bias; preference for one trait over another. - freq. dep. bias; the tendency of individuals to adopt a trait may depend on the frequency with which the individual encounters that trait. - indirect bias; individuals may adopt a trait because an influential model has this trait (e.g. fads). But this must be uncorrelated with their reason for being an influential or "attractive" model. There are selection analogs - #5 - Natural selection - If the cultural traits influence survival and they are inherited .... A simple example (from R.Boyd and P.J.Richardson 1985). Consider a dichotomous cultural trait - individuals a: like to dance; individuals b: don't like to dance. Consider that this "like"/"dislike" is instilled by three teachers from a previous (and discrete) generation. So to follow our dancing population we need only consider how the frequency of this trait changes from one generation to the next. Assume that a teacher who likes or dislikes dancing will instill the same behavior in the student according to the following rules. Teacher/Model Probability that the student 1 2 3 likes dancing dislikes dancing a a a 1.0 0.0 a a b A1+A2 A3 a b a A1+A3 A2 b a a A2+A3 A1 a b b A1 A2+A3 b a b A2 A1+A3 b b a A3 A1+A2 b b b 0.0 1.0 The only restriction on the influences of the teachers are that they must sum to one (A1+A2+A3=1.0) in order that the above probabilities sum to one (the student at the end must either like or dislike dancing ... there are no intermediates by supposition). To determine the frequency of dancing in the new population we need to know the relative likelihoods of configurations for the teachers. Let's assume that they occur with frequency appropriate to their occurrence in the general populace. Then ... p' = p3(1) + p2(1-p) [ (A1+A2) + (A1+A3) + (A2+A3) ] + p(1-p)2 [ A1 + A2 + A3 ] + (1-p)3(0). But remember that the A's must sum to one, so ... p' = p3 + 2p2(-1p) + p(1-p)2 = p. This can of course be extended and made quite complex. In general, if two conditions are met - #1 the transmission rule of the trait is linear and #2 the choice of teachers/models is random - then it can be shown that transmission of the cultural trait itself does not introduce evolutionary forces. If these conditions are not met ... then the transmission of a cultural trait itself can cause the frequency of the traits to change and cause them to evolve. This makes it very difficult to study such traits.