Genes from an ancient human ancestor that made them better able to deal with cold weather could be to blame for depression in some modern people, a study suggests.
Scientists detected the mutated gene in some people’s DNA whose origins stem from when humans interbred with Denisovans millennia ago.
The gene, called SLC30A9, is thought to have been beneficial to Denisovans and the early Homo sapiens who mated with them because it made them more resilient to the cold.
However, the gene may have a side effect in modern people who have inherited it as it can lead to faulty signalling in the brain.
Denisovans were a species of ancient humans which were a sister species to Neanderthals that formed around 600,000 years ago.
The cold-weather adaptation was likely to have helped them to survive in their home area around Tibet and Siberia.
They later interbred both with Neanderthals and Homo sapiens before going extinct around 15,000 years ago.
Study of ancient and modern genomes
During these inter-species trysts, a variation of the gene was passed from Denisovans to humans, a study of ancient and modern genomes found.
The Denisovan version of the gene led to more zinc being transported into cells and boosted energy production of the mitochondria, allowing people with this mutated gene to stay warm.
But the same Denisovan gene has been shown to also have psychiatric impacts and make people more prone to schizophrenia and depression.
“Through genomic analysis, we noted that the genetic variant observed came from our interbreeding with archaic humans in the past, possibly the Denisovans”, says Ana Roca-Umbert, co-first author of the study from Pompeu Fabra University in Barcelona.
Cold-weather gene does not exist in the Neanderthals
The gene could not have come from the mating with Neanderthals, they say, as this cold-weather gene does not exist in the Neanderthals.
“Apparently, the change was beneficial and proved a selective advantage for humans,” added Jorge Garcia-Calleja, co-first author of the study.
“As a consequence, this variation in the SLC30A9 gene was selected and has reached current populations.”
But previous studies have linked this gene variant to increased risk of anorexia, hyperactivity disorder, autism, bipolar, depression, OCD and schizophrenia.
The study on zinc’s impact was done on cells in a lab and the team hopes to expand to animal models.
Excitability of the nervous system
Evidence was seen that the mutated form leads to increased excitability of the nervous system and a type of equilibrium of the metal in the brain which is different to that of people with the original gene.
The cold-hardy and depression prone gene is more common in people of Asian heritage, data show, and less common in people of African descent.
This is a result of how the population of people who dispersed out of Africa mingled with those that had inherited the Denisovan gene in Asia.
Denisovans likely had a skull that was wider than that of modern humans or Neanderthals, a 2019 study found.
The existence of Denisovans was only discovered in 2010 when scientists found a small finger bone in a cave in the Altai Mountains in Siberia, named the Denisova Cave.
Svante Pääbo, the pioneering paleogeneticist, first proved the existence of Denisovans and won a Nobel Prize in 2022 for his work, which also provided the first evidence humans and other ancient human species mated.
Scientists have progressively learnt more about the lives, genes and appearance of Denisovans, including what they looked like, their range, and when they likely existed.
The new study is published in the journal PLOS Genetics.
Dr. Thomas Hughes is a UK-based scientist and science communicator who makes complex topics accessible to readers. His articles explore breakthroughs in various scientific disciplines, from space exploration to cutting-edge research.
