What is the minimum difference a species must show in order to be classed as a new species?
Asked by: Adam King, Huddersfield
This is less straightforward than it seems. The concept of species, as a way of classifying animals and plants, relies on finding some trait that all members of that species share, and which is unique to them. This works pretty well for many organisms, but species are continually being lumped together or split into two as biologists search for the perfect classification system.
There are currently at least 26 different ways to define the concept of a species. Some consider physical or genetic similarity, while others consider whether populations interbreed – or whether they could if they weren’t separated by a geographical barrier, such as a mountain range or ocean. Other definitions of species focus on the evolutionary history of the organism, grouping species according to how recently they shared a common ancestor.
Even if biologists could agree on a single definition of a species, identifying a point at which a new species is created would still be difficult. Theoretically, the minimum difference could be a single mutated gene, marking a fork in the evolutionary tree where one species splits into two.
However, biologists almost certainly wouldn’t recognise the creation of the new species until later, when the genetic mutation manifested as a difference in the way the animal looked or behaved.
The closest we’ve come to this was probably in 2016, when researchers at the Janelia Research Campus in Virginia artificially altered the genome of a species of Drosophila fruit fly. This change to a single gene altered the frequency of the courtship ‘song’ produced by the male fly.
The insects that carried this gene could still mate with the wild population, so they couldn’t be considered a separate species by most definitions. But they preferred to mate with similarly mutated flies, and if this mutation had occurred in the wild, it’s possible that this might have resulted in the evolution of a new species.