New research suggests the number of redheads is growing due to natural selection.
The study of nearly 16,000 people by Harvard University also found that coeliac disease and lighter skin tones were becoming more common.
Other human traits flagged as increasing were:
- Immunity to HIV;
- Resistance to leprosy;
- Lower risk of arthritis;
- Lower risk of alcoholism;
- Lower risk of bipolar disorder and schizophrenia.
First author of the study and senior staff scientist in the lab of Harvard, geneticist David Reich, explained that the study of ancient DNA from nearly 16,000 people across more than 10,000 years in West Eurasia reveals that natural selection has shaped modern human genomes far more than previously thought.
“With these new techniques and large amount of ancient genomic data, we can now watch how selection shaped biology in real time,” he said.
“Instead of searching for the scars natural selection leaves in present-day genomes using simple models and assumptions, we can let the data speak for itself.”
“This work allows us to assign place and time to forces that shaped us.”
Before now, studies of ancient human DNA had identified only about 21 instances of directional selection, the type of natural selection that occurs when one version of a gene confers an extreme form of a trait.
Examples include lactose tolerance after infancy, proving advantageous enough for survival and reproduction that it gets passed on to more offspring than less advantageous versions of the gene and rapidly rises in frequency across a population.
Evidence had suggested that directional selection has been rare since modern humans arose in Africa some 300,000 years ago and began to split into different population groups around the world, Harvard University said.
The study, through combining an unprecedented amount of ancient genomic data with novel computational methods, shows instead that directional selection has driven the spread or decline of hundreds of gene variants in West Eurasia since the end of the Ice Age and that selection has actually accelerated since people transitioned from hunting and gathering to farming.
West Eurasia consists of Europe, parts of Central Asia and North Africa, and the Middle East.