Why is Sex Change in Animals so Rare?
http://ts-si.org/biological-sciences/3920-why-is-sex-change-in-animals-so-rare.html2/3/09
New Haven, CT, USA. Most animals, like humans, have separate sexes — they are born, live out their lives and reproduce as one sex or the other. However, some animals live as one sex in part of their lifetime and then switch to the other sex, a phenomenon called sequential hermaphroditism. What remains a puzzle is why the phenomenon is so rare, since analysis shows the biological "costs" of changing sexes rarely outweigh the advantages.
A report in The American Naturalist says that while this process is evolutionarily favored, its rarity cannot be explained by an analysis of Sequential hermaphroditism naturally occurs in various organisms from plants to fishes. Following four decades of research that established why sex change is advantageous, the question remained why it is rare among animals.
