Semi-identical or sesquizygotic twins occur when two sperm fertilise one egg. A boy and a girl in Brisbane are only the second set of semi-identical twins known in the world.
New research is pinpointing how much genes influence the stability of educational achievement.
Horror loves evil twins and doubles because of concepts like the uncanny and otherness. They also provide memorable images for movie makers.
A podcast on twins, including why stereotypes about their relationship are so damaging, and why they are so useful to scientists.
What might first seem unarguable starts to look shaky when you bring twins into the equation.