can constitute another evolutionary trap in organisms in which the embryos develop inside the maternal organism (II.8.3) (Fundele & Surani 1994). This phenomenon is known, for example in mammals and plants. This is manifested in that some genes derived from the gametes of the father and gametes of the mother fulfill different functions in the development of the embryo. The copies of a certain gene derived from the sperm can be active in the embryo and, for example, control the production of the growth factor, while a copy of the same gene derived from the egg need not even be transcribed. This strange behaviour of the genes may (but, of course, need not, see e.g. (Skuse & et al. 1997)), be highly useful from the viewpoint of the father or mother; both individuals modify and thus program the genes of their gametes so that, after formation of the embryo, they “defend the interests” of their original carrier, frequently at the expense of the interests of the other parent (Moore & Haig 1991).
In the above case, the male tries to program his genes so that the newly forming embryo is as large as possible, even at the expense of other developing embryos or even at the expense of the overall state of health of the mother. The other embryos could have different fathers, a very frequent phenomenon in mammals, birds and a great many plants. Even a certain damage to the mother during gravidity or parturition is not detrimental from the viewpoint of the father in a great many animals, as he can have future progeny with other females. The female must program her genes so that they compensate the relevant activity of the paternal genes in the embryo. In the above case, she apparently does this in that she programs her genes to synthesize receptor proteins capable of capturing and thus deactivating the growth factor synthesized under the control of the paternal genes. If a similar battle occurs between the paternal and maternal genes in embryogenesis, then it is practically impossible for the species to change from sexual to asexual reproduction and for a viable embryo to be formed, for example, by the combination of two female gametes – production of the growth factor would be missing. The phenomenon of genome imprinting and some of its other consequences were also described in Section II.8.3.