A study published in ‘Molecular Biology and Evolution’ shows that some genetic features associated with Psoriasis, Crohn’s disease and other aspects of human health are ancient, predating the evolution of Neanderthals and Denisovans as also contemporary humans. Scientists at the University at Buffalo have discovered that a genetic susceptibility to these ailments has persisted for hundreds of thousands of years, afflicting our ancient ancestors and us. The discovery highlights the importance of balancing selection, a poorly understood evolution in which duelling forces drive species to retain a diverse set of genetic features. The scientists have discovered that some of humanity’s early ancestors had the tell-tale features called deletions, while others did not, mirroring the variation in modern humans. This genetic diversity may have arisen as far back as a million or more years ago in a common ancestor of humans, Denisovans and Neanderthals. Why this would happen is not clear, but one possibility is that certain traits that made humans susceptible to Crohn’s and Psoriasis may also have afforded an evolutionary benefit to our ancient ancestors.