The male bluehead wrasse defends his group of yellow females, one of whom has to step-up and take charge if he leaves.
When a male bluehead wrasse is removed from the group he dominates, the largest female changes sex, rapidly transforming ovaries into sperm-producing testes. Molecular research shows how.
Caster Semenya is legally female, was from birth raised as female and identifies as a female.
Jon Connell on flickr
Athlete Caster Semenya will need to take hormone-lowering agents, or have surgery, if she wishes to continue her career in her chosen events. But the decision to ban her is flawed on many grounds.
Chicken or rooster? This bird is both – female on the left (dark feathers), and male on the right (white feathers, with larger comb and physique).
Mike Clinton (Roslin Institute)
Birds have some of the most amazing sex differences of any animal. They can control the sex of offspring, and even produce rare half-male, half-females. And their sex genes and chromosomes are quite different from ours.
In skin, muscle, fat and more tissues, genes behave differently in men and women.
Like it or not, evidence now shows that men and women differ genetically far more profoundly that we previously recognised. An analysis from the 2017 winner of the Prime Minister's Prize for Science.
A baby’s sex determines how they will respond to exposures during pregnancy.
If something goes wrong in pregnancy, a boy baby is more likely to be born malnourished or stillborn than a girl. This may have an evolutionary basis.
There’s a difference in the sex chromosomes between various mammals, such as the platypus compared to humans.
How new species are created is at the core of the theory of evolution. Mammals may be a good example of how sex chromosome change drove major groups apart.
The X-chromosome at some point evolved to be different from all other chromosomes.
Unlike other chromosomes, the X chromosome is inactivated in nearly all cells in women – and genes on it are active in very few tissues.
It’s naive to pretend there are no profound genetic and epigenetic differences between the sexes.
Elephant Gun Studios/Flickr
What produces the differences between men and women? Are they trivial or profound? Are they genetic or environmental, or both? And are men really closer genetically to chimpanzees than to women?