Darwin’s insights on evolutionary forces grew from his exceptional knowledge of natural history, yet two key topics – sex and reproductive genetics – remained poorly understood in Darwin’s Victorian era. That situation changed dramatically in the latter half of the 20th century with societal awakenings about sexuality that happened to coincide with the introduction of molecular parentage analyses that unveiled a plethora of formerly hidden ‘sexcapades’ throughout the biological world. The 2012 Thomas Henry Huxley Review, published in the January issue of Journal of Zoology, summarizes some of the evolutionary revelations that have emerged from selection theory as applied to genetic and phylogenetic information on clonality, hermaphroditism, and pregnancy, three procreative phenomena that are relatively rare in vertebrate animals and thus offer alternative evolutionary perspectives on standard reproductive modes. Collectively, these three peculiarities of nature illustrate how the abnormal in biology can enlighten evolutionary thought about the norm.
This essay encapsulates some of the many novel perspectives on evolution offered by animal species that display various forms of clonality, hermaphroditism and pregnancy and describes the ways in which exceptions to biological norms can prove, challenge or otherwise clarify evolutionary ‘ground rules’.