Did Neanderthals Give Us Autism?
Ancient Interbreeding Led to Complex Changes in Our DNA
Unraveling Ancient DNA
Our genetic makeup tells a story of our evolutionary past, revealing intricate connections between us and the species that preceded modern humans. One of those is our relationship with Neanderthals — not ancestors but close cousins to Homo sapiens. Recent research has unearthed an astonishing link between these ancient relatives and autism spectrum disorder (ASD) — a condition that affects how people interact, communicate, and behave. By exploring the genetic threads woven into our DNA by Neanderthals, scientists are discovering potential factors contributing to ASD development in modern humans today.
Humans have a diverse and intricate evolutionary history that includes various now-extinct species closely related to us. Alongside Homo sapiens, Neanderthals (a branch of the genus Homo) were one such species inhabiting Earth approximately until approximately 40,000 years ago. They are not our direct ancestors but rather close cousins with whom we shared a common genetic heritage through interbreeding during the Middle/Upper Paleolithic age.
Another significant player in human evolution was the Denisovans, another branch of Homo that lived alongside Neanderthals and modern humans. While less is known about them, researchers have found evidence of their existence based on DNA extracted from fossils discovered at the Denisova Cave in Siberia. Like Neanderthals, they interbred with early human populations, leaving a genetic imprint that persists within certain modern populations today.
The Denisovans are thought to have lived alongside and sometimes even co-existed with Neanderthals, but their presence has been less prominent in the fossil record than their cousins. However, recent advances in genomic research have revealed a significant amount of Denisovan DNA within present-day Melanesian populations as well as other Asian groups — suggesting that they played an important role in shaping our genetic makeup too.
Shared Geographies: Where Humans and Neanderthals Converged
The intermingling between Homo sapiens and Neanderthals, our ancient cousins from the genus Homo, led to fascinating genetic exchanges that still exist within modern human populations today. These interbreeding events took place in various parts of the world, with some locations exhibiting greater levels of integration than others. The geographical areas where humans and Neanderthals interacted most frequently offer valuable insights into understanding which contemporary populations carry the highest share of Neanderthal DNA within their genetic makeup.
Most notably, these encounters occurred in Eurasia — particularly Europe and western Asia — where both species cohabited for extended periods before Homo sapiens migrated outward to other regions. As a result of the substantial overlap between human and Neanderthal territories, modern humans living in Eurasia today show significant traces of their ancient relatives within their DNA. Because interbreeding only took place in Eurasia, modern Africans have the lowest share of Neanderthal DNA, most having none at all.
Populations originating from Europe possess one of the largest shares of Neanderthal ancestry among contemporary Homo sapiens groups worldwide. On average, individuals with European heritage can account for approximately 2–4% of their genome as Neanderthal DNA. The most substantial contributions to this legacy are found in Western Europeans, who carry higher percentages compared to Eastern Europeans.
Differences in Our Inherited DNA: Neanderthal Contributions to ASD Susceptibility
The research team, led by scientists Rini Pauly, Layla Johnson, F. Alex Feltus, and Emily L. Casanova from Molecular Psychiatry (2024), used data obtained through the Simons Foundation Powering Autism Research (SPARK) program as well as Genotype-Tissue Expression (GTEx) and 1000 Genomes Project (1000G). By analyzing Neanderthal single nucleotide polymorphisms (SNPs) in diverse ethnic populations, the researchers investigated how these genetic variations may contribute to ASD susceptibility.
Their findings indicate that rare variants — those present only in a small portion of individuals — are significantly more common in autistic probands compared to race-matched controls from black non-Hispanic, white Hispanic, and white non-Hispanic populations. This suggests that Neanderthal-derived DNA plays an essential role in the susceptibility to ASD across major US populations.
Furthermore, 25 rare and common SNPs were identified as significantly enriched among individuals with autism on different ethnic backgrounds. Some of these variants show significant clinical associations — meaning they may contribute directly or indirectly to the development of specific traits observed in ASD (such as intellectual disability, epilepsy, and language regression). While not all SNPs are enriched for autism specifically, their presence may still influence comorbid phenotype expression.
Unlocking Ancient Genetic Mysteries to Better Understand Autism Spectrum Disorder
This exciting research sheds light on the significant role Neanderthal-derived DNA plays in autism susceptibility across major populations within the United States. By examining how ancient genetic variations impact our lives today, scientists hope to better understand and potentially treat ASD — a complex disorder with diverse manifestations.
As we continue unraveling the secrets of our extended family tree, researchers must consider other extinct hominids like Denisovans, who have contributed their genetic legacy to present-day humans. By understanding how various ancient species influenced our evolutionary journey and susceptibility to modern conditions such as ASD, we may unlock new insights into the complex interplay between our DNA and environment — ultimately improving health outcomes for generations to come.
