Eytan Avital

‘Lamarckian’ mechanisms in darwinian evolution

Since the Modern Synthesis, evolutionary biologists have assumed that the genetic system is the sole provider of heritable variation, and that the generation of heritable variation is largely independent of environmental changes. However, adaptive mutation, epigenetic inheritance, behavioural inheritance through social learning, and language-based information transmission have properties that allow the inheritance of induced or learnt characters. The role of induced heritable variation in evolution therefore needs to be reconsidered, and the evolution of the systems that produce induced variation needs to be studied.

Adoption, memes and the Oedipus complex: a reply to Hansen

Hansen’s (1996) criticism of our paper (Avital & Jablonka 1994) concentrates on our approach to adoption. He also argues that, unless additional assumptions are made, our suggestion that mothers who induce an Oedipus complex in their sons have an evolutionary advantage is wrong. In addition, he claims that ‘the vernacular of evolutionary theory’ may lead to faulty reasoning and misleading conclusions. We agree with some, but not all, of Hansen’s points. The evolutionary origin of adopting behaviour is not clear. Hansen suggests that adoption is a non-adaptive pleiotropic effect of parental care. This may indeed be the case, but whatever its origins, the maintenance of adopting behaviour at relatively high frequencies in some bird species suggests that it has some advantages for the adopters as well as the adoptees (Choudhury et al. 1993; Redondo et al. 1995). We suggested that one advantage of adoption is that it is a vehicle of transmission of behavioural traits. Unlike genes, memes (representations of behavioural acts in the nervous system) can be transmitted via several parallel channels. A particular meme can be transmitted through parents, through non-parents displaying parental behaviour, through neighbours, through peers, and so on. An adopter can pass on some of its memes to the adopted young, and these memes can subsequently be passed on without adoption, through orthodox parental care. The transmitted meme has no ‘commitment’ to a particular method of social learning and transmission. Adoption may be important only for the initiation of the transmission of a meme in a different lineage, not for its subsequent transmission in this lineage. From the point of view of the transmitted meme, adoption is just one way in which it can perpetuate itself; from the meme’s point of view, the association with this extra transmission channel may often increase its representation in the population. As Hansen points out, and we made clear in our paper, the evolution of the adopting behaviour itself is unlikely to be explained in these terms. We agree with Hansen that when there is a positive correlation between the meme for adoption and the meme transmitted by adoption, the meme for adoption may increase its representation in the population through indirect selection. Indeed, from the point of view of the memes that are potentially transmissible by adoption, such a correlation may be advantageous, so we would expect such positive correlations to have evolved. However, in our paper we discussed the importance of adoption once it is in place, for the evolution of other behaviour patterns. The adopting individual, unlike a non-adopting individual, may transmit many memes through adoption, and subsequently these memes will be transmitted through other channels. The adopting behaviour thus increases the representation of these memes in the population. Hansen’s second criticism refers to our comment on the Oedipus complex. Hansen is right in pointing out that choosing a mate that is phenotypically similar to the mother (i.e. a kind of positive assortative mating), or choosing a mate who induces an Oedipus complex, does not increase the frequency of the memes in the population. In order for a meme to increase in frequency, positive assortative mating must have a selective advantage. However, although positive assortative mating does not increase the frequency of the meme in the population, it does increase its frequency within the maternal lineage. This may have important consequences: for example, it may increase kin recognition within the maternal lineage. However, as Hansen correctly pointed out, without additional assumptions about the Correspondence: E. Jablonka, Cohn Institute for the History and Philosophy of Science, Tel-Aviv University, Tel-Aviv 69978, Israel. E. Avital is at the Department of Natural Sciences, David Yelin Teachers College, P.O.B. 3578, Jerusalem, Israel.