REPORT ON ETHICS IN RESEARCH ON HUMAN-BEH AVIOR

Sexually reproducing organisms have alternating haploid and diploid ph ases. Each phase is connected to the other through meiosis and fertili zation or conjugation. This article provides a tentative explanation f or several features of sexual reproduction, and in particular for anis ogamy, i.e. ability to produce gametes of unequal sizes. Chemotropism may be regarded as the driving force which led to acquisition of aniso gamy. A chemotropic system functions optimally if the gametes belong t o two distinct categories. One category of cells is non-motile and sec retes an attractive substance, whilst the other category responds to t he attractive signal by moving towards the emitting cells. Anisogamy i s thought to result from selection of two types of mutations: those in creasing the size of the non-motile gametes, and those reducing the si ze of the motile gametes. Such modifications have clear advantages. La rger and slower cells increase their attractive power and give rise to zygotes with higher survival fitness. Smaller cells gain swimming spe ed and can be produced in larger numbers. This gives them a better cha nce of finding a partner to mate with.