 Both of these claims are believed, even by other critics, to be unfair analyses of the views of the sociobiologists, and especially Wilson—for example, Kitcher, one of the strongest critics of sociobiology, takes Gould and the SSG to task on this point (Kitcher, 1985, 22–23). In On Human Nature Wilson describes genes as, essentially, difference makers—he explicitly claims that differences in genes, even for heritable traits, only explain the variance in traits across a population; they are by no means independent causes for any trait in individuals and variation in the environment also accounts for part of the variation in any trait (Wilson, 1978, 19). In at least one paper responding to the SSG Wilson says that, on the question of the relative contributions to the variation in human behavior from variation in genes vs. variation in the environment, his “own views lie closer to the environmentalist than the genetic pole” (Wilson, 1976, 183). Wilson also does seem to be trying to support his claim that there are some human behaviors which are probably highly heritable: he describes a variety of different sorts of evidence that might identify them. This evidence includes cross cultural appearance (e.g. Wilson, 1975, 550; Wilson, 1978, 20, 129); plausible homology with other closely related species (especially chimpanzees) (e.g. 1978, 20, 27, 151); early development of the trait in question (e.g. 1975, 551; 1978, 129); differences between individuals that arise without differences in their developmental environment (e.g. 1978, 128–130); genetic syndromes that cause behavioral differences (e.g. 1978, 43–45); and twin studies (e.g. 1978, 145). Finally, Wilson claims that trying to change human behavior from its heritable form usually fails or causes misery (Wilson, 1978,  20)[6];  he describes the failures of certain attempts to change the features of normal human behavior by massively changing the social environment, such as the persistence of family ties under slavery (Wilson, 1978, 136) and in the Israeli kibbutzim (1978, 134). Of course, whether or not all of the above is good evidence for his claims is very much up for debate (Kitcher, 1985; Sociobiology Study Group of Science for the People, 1976). It is worth bearing in mind that while Wilson thinks the evidence that some human behaviors are heritable is overwhelming (Wilson, 1978, 19) he does see many of his specific proposed evolutionary explanations as preliminary and speculative rather than fully formed (for example, Wilson is explicit that his discussion of homosexuality is preliminary: 1978, 146). For more discussion of the problems relating to heritability when studying the evolution of behavior, see section 4.2. below and the entry on  heritability.