It may sound too bizarre to be true but the Amazon molly (Poecilia formosa), a fish that inhabits rivers, lakes and swamps in Mexico and Texas, exists over much of its range in populations that are 100% female. In 1932, the Amazon molly became the first known vertebrate to reproduce by cloning itself, producing all-female populations. A new genetic study has given scientists insights into the longstanding mystery about how and why this happens.
The proportion of females in the human population is roughly 50%. A few countries such as Maldives (38% female) and Moldova (54% female) diverge from this, but these differences can largely be explained due to male immigration and emigration. However, much more dramatic sex ratios are found in the animal kingdom. Kentish plover bird populations, where males care for offspring, comprise only 14% female, and sea turtle populations, where sex is determined by temperature often exceed 75% female.
