Perspectives
Definitions of sex and gender. In today’s society, it is widely accepted that there are more facets to gender than just male and female. How is an individual’s sex defined? Answers from the fields of evolutionary biology and gender research.
I
n biology, an individual’s sex is defined according to its function “mouthbrooding” – might be performed by females only, by in sexual reproduction – in particular, according to the repro- both parents, or only by males. The males of many seahorse ductive cells (gametes) produced in the germ line: Females species, on the other hand, carry the fertilized eggs in a ventral brood pouch for incubation. produce a comparatively small number of Finally, the factors that determine larger reproductive cells (eggs), whereas gonad formation (and consequently an males produce numerous small, usually individual’s sex) also vary widely in nature: highly mobile reproductive cells (sperm). In mammals, it is well known that the sex Sexual reproduction occurs through the of an individual is determined by the confusion between egg and sperm cells. stellation of the two sex chromosomes X In the overwhelming majority of and Y, with the combination XX yielding animals, including humans, gametes are females and the combination XY yielding formed in dedicated reproductive glands, males. Birds too have specific sex chromoor gonads – ovaries in females, and testes somes (W and Z), with females being dein males. However, in many species, the termined by the combination WZ and differences between the two sexes go far males by ZZ. In reptiles, the ambient beyond the presence of either ovaries or temperature an egg is exposed to often testes, and may, for example, be apparent determines whether the individual later in attributes such as body shape, colorbecomes a female or a male, while fish ation or behavior. Walter Salzburger offer examples of virtually every sex deIn other species, the distinction beis Professor of Zoology and termining mechanisms known to date – tween the sexes is less clear-cut, and in Evolutionary Biology at the University from individual sex-determining genes many cases is not possible at all. For inof Basel. His research examines and chromosomal sections to ambient stance, most species of snails, many how animals evolve, adapt to their environment, and diversify. temperature or social behavior within the worms and most plants are hermaphroHe is especially interested in cichlid group. ditic, meaning that a single individual fishes, which he studies in Lake The question of why sexual reproproduces both types of gamete. In the Tanganyika in Africa. duction emerged in the first place has yet case of simultaneous hermaphrodites, to be conclusively resolved. However, it is an individual is both male and female at the same time, which can even lead to self-fertilization. Other widely believed that the reshuffling of the genetic material from species undergo a sex change: Clownfish, for example, always the two parents associated with sexual reproduction plays a key begin their lives as males, with only those that live long enough role. In any case, that so many species rely solely or primarily on and occupy a dominant position in an anemone later becoming sexual reproduction to reproduce, in spite of the efforts involved, leaves no doubt that it is – in evolutionary terms at least – a major females. Incidentally, in the animal kingdom there is no strong link success story. between an individual’s sex and its role in raising offspring. For example, many cichlid fishes incubate the fertilized eggs in their mouth and continue to offer their progeny refuge there after they hatch. Depending on the species, this practice – known as
36
UNI NOVA
139 / 2022
