White-throated sparrows show sex in nature is not a simple binary Premium

White-throated sparrows reveal nature's complexity, showcasing a spectrum of sexual identities beyond the traditional binary classification.

There continues to be intense debate worldwide about the definition of biological sex, boosted by some recent executive orders. The official theme of LGBTQ+ History Month (February) this year is ‘Science & Innovation’ and the natural universe is replete with examples of how the simple binary of sexes and genders to which some people would like to fall back on is really a cultural convenience rather than a “natural order”.

A particularly clear example is the white-throated sparrow (Zonotrichia albicollis). Studies of this bird have revealed that nature uses complex genetic systems to create a spectrum of sexual and social roles. With one in 100 individuals having an intersex condition, there is a growing demand to ‘usualise’ the concept of sexual diversity through the lens of biology, and the white-throated sparrow is a good natural metaphor for these social conversations.

The white-throated sparrow is a songbird recognisable by its black-and-white or tan-and-brown striped head, a bright yellow spot above each eye, and a white patch on its throat.

Its secret? It exhibits not two but four distinct sexes, and each sex plays a fundamental role in weaving its intricate social and reproductive behaviours.

Indeed, a growing pile of evidence is pointing to the fact that the conventional idea of two sexes is over-simplified. Geneticists have discovered that sexual identity is a wider spectrum involving more intricate regulations than just the presence or absence of Y chromosomes.

Imagine individuals that straddle the boundary where the sex chromosome or anatomy doesn’t align strictly with ‘male’ or ‘female’. This is called being intersex and is present in about 1% of the population. Modern genome sequencing data have suggested that individuals can be a “patchwork of genetically distinct cells”, meaning an individual can have some cells with sex chromosomes that don’t match the rest of their body. This discovery further blurs what it means to be definitively a male or a female and points to a significant ‘area of overlap’ explaining why some people find it difficult to fit within the binary structure.