Interbreeding between humans and Neanderthals in Europe may have enhanced modern humans’ ability to ward off infection, but it may also have increased susceptibility to allergies, say two reports published in the American Journal of Human Genetics.
Older genes have proven to improve our immunity to sickness. Interspecies relations resulted in 1-6% of modern Eurasian genomes probably having been inherited from ancient Neanderthals. Infectious diseases have threatened humans throughout history, ravaging populations and causing high infant mortality and short life expectancy, especially before the discovery of hygiene, vaccines, antiseptics and antibiotics.
The human genetic makeup strongly influences an individual’s susceptibility to infectious disease and the chance of recovery; natural selection imposed by pathogens is therefore thought to have profoundly affected the patterns of variability of the human genome.
Lluis Quintana-Murci and colleagues from the Institut Pasteur and the CNRS in Paris, France, examined the evolution of the immune system over time. Using modern data from the 1000 Genomes Project and the genome sequences of ancient hominins, they focused on a list of 1,500 genes known to be active in the immune system.
Next, they analyzed patterns of genetic variation and evolutionary change in the immune system relative to the rest of the genome.
Finally, they estimated the timing of changes in innate immunity and the extent to which variation in those genes were passed down from Neanderthals.
Some immunity genes showed little change over long periods of time, whereas others appear to have been replaced by new variants that rose to prominence, possibly due to environmental shifts or disease. Most of the adaptations are thought to have occurred in the last 6,000-13,000 years, as human populations shifted from hunting and gathering to farming.
Interestingly, immunity genes present a higher average probability of Neanderthal ancestry than the rest of the coding genome. Quintana-Murci says that this shows how important the movement of genes across species may have been in the evolution of the innate immunity system in humans.
Janet Kelso and colleagues of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, set out to investigate the functional importance of genes inherited from archaic humans more broadly, but they reached the same conclusion as Quintana-Murci’s team.
They tested modern-day human genomes to look for similarities with the Neanderthal and Denisovan genomes, then examined the occurrence of those similarities in people from around the world.
They concluded that two of the variants are just like the Neanderthal genome, but the third resembles the Denisovan genome. This resemblance might protect against infection, but it could also make modern-day people more prone to allergies.
According to Kelso,”interbreeding with archaic humans does indeed have functional implications for modern humans,” and the most obvious results have been in shaping our adaptation to our environment. We can resist pathogens and metabolize novel foods more easily.
In conclusion, Neanderthals lived in Europe and Western Asia for around 200,000 years before modern humans appeared. Therefore, they would have been well adapted to the local climate, foods and pathogens. Interbreeding with Neanderthals meant that modern humans gained these advantageous adaptations.
Article by: Ivy Painter