送交者: AI 于 2005-5-11, 15:21:46:
回答: 怀孕期间，子宫内的激素平衡影响了基因的表达。 由 Latino2 于 2005-5-11, 14:44:50:
Based on theory of evolution, all species are evolved from creatures of single cell. Single cell has too re-product on its own. Then, even if male and female sexes are separated, some of the species can still change sex depending on needs. It means every species carry the gene for both sexes.