Two independent studies, both recently published in the American Journal of Human Genetics, have both confirmed the belief that interbreeding between two of our ancestors, namely Neanderthals and Denisovans, has directly contributed to improvements to our immune system but at the expense of increasing our susceptibility to allergies. The two studies were carried out by the Max Planck Institute for Evolutionary Anthropology (Leipzig) and the Institut Pasteur and the CNRS (Paris).
     The team from the Institut Pasteur studied data on modern humans, gleaned from the large amount of data provided by the 1000 Genomes Project (This was a worldwide project, started in 2008, to build up a catalogue of human genetic variation). They compared this data against the genetic makeup of Neanderthals and Denisovans, identifying where and when the genetic modifications occurred.
     The Max Planck team had concentrated on a study of the importance of inherited genes but identified exactly the same genes as the French team. Janet Kelso, from the Max Planck team, is quoted as saying "What has emerged from our study as well as from other work on introgression is that interbreeding with archaic humans does indeed have functional implications for modern humans and that the most obvious consequences have been in shaping our adaptation to our environment - improving how we resist pathogens and metabolize novel foods". She went on to add "Neanderthals, for example, had lived in Europe and Western Asia for around 200,000 years before the arrival of modern humans. They were likely well adapted to the local climate, foods and pathogens. By interbreeding with these archaic humans we modern humans gained these advantageous adaptations".

Edited from Popular Archaeology (7 January 2016)