How different are we from Neanderthals? The answer is “not as much as we used to think”. Or, to put it another way, the more we learn about this group of archaic humans, the more similarities we are discovering. This process of discovery has increased significantly since we learnt that some humans have Neanderthal DNA, a genetic fingerprint left behind when ancient humans intermixed with this now-extinct group.
But does this DNA impact how people think? The answer is, it’s complicated and subtle.
The field of palaeogenomics, which studies ancient DNA to reconstruct or analyze the genomes of extinct organisms, is a relatively young discipline. This of course means we should not see any current findings as necessarily concrete, but that doesn’t mean they’re not interesting.
When Neanderthals were first discovered in the first half of the 19th century (first a baby skull was discovered in a Belgian cave in 1829, and then more remains were discovered in Gibraltar in 1848), these hominids were thought to be primitive. Typical prejudicial attitudes of the era conceived of them as brutish and not much more intelligent than modern apes.
Think back to any representation of a “caveman” you’ve seen on TV and you’ll likely get a sense for how this idea has continued in pop culture today.
However, in the last few decades we have learnt more about Neanderthals and just how sophisticated they were. Contrary to what is often assumed, Neanderthals actually shared many of the cognitive abilities we thought were unique to humans (Homo sapiens), albeit to a lesser extent.
Neanderthals made and used tools, produced flour, communicated with symbols and used them in rituals. It seems they even used plant-based medicines.
So if Neanderthals are not the “dumbasses” scientists of they past believed them to be, what does this mean for people who have some of their DNA?
Well, the first thing to point out is that no one has the brain of a Neanderthal, just some hints of this ancestry. The current evidence suggests some people with European ancestry have more elongated brains.
In 2019, Philipp Gunz, a palaeoanthropologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and colleagues found that Neanderthal DNA seems to affect the expression of two genes in a way that makes human skulls slightly less round. These variants are located near genes UBR4 and PHLPP1, which help produce neurons and are involved in myelin formation – the fatty sheaths that cover the axons of neurons and let them communicate.
Potential skull elongation was also associated with Neanderthal variants located near GPR26, a lesser understood gene that may be involve in the regulation of neurons.
Gunz and colleagues did not find any evidence that the Neanderthal DNA variants affected human cognition, just the shape of people’s skulls. But even this would be to such a limited extent that it would be barely perceptible to the naked eye.
In another study, researchers observed some differences in cranial and brain morphology. In particular, people with higher concentrations of Neanderthal DNA tended to have more connectivity in their visual cortex and intraparietal sulcus – part of the brain associated with sensory information and controlling motor responses. They conclude that Neanderthal DNA is actually functional within these people and may impact their neurodevelopment.
A more recent study led by same first author, Michael D. Gregory, suggests that Neanderthals may have depended upon visual processing capabilities at the cost of social cognition, which may have contributed to their eventual extinction – based on the idea that they would have had a reduced ability to maintain culture and had an inability to deal with fluctuating resources.
One important development in the study of Neanderthal/human genomes came with advancements in methods that allowed scientists to scan medical records for comparative data. In particular, in 2016, a team scanned the electronic health records of 28,000 adults of European descent to see whether Neanderthal gene variants can raise the risk of certain conditions.
“We discovered and replicated associations of [Neanderthal] alleles [variations of the sequence of nucleotides at a point in a DNA molecule] with neurological, psychiatric, immunological, and dermatological phenotypes,” the team wrote in their study
“[Neanderthal] alleles together explained a significant fraction of the variation in risk for depression and skin lesions resulting from sun exposure (actinic keratosis), and individual [Neanderthal] alleles were significantly associated with specific human phenotypes, including hypercoagulation and tobacco use.”
The results showed that a number of Neanderthal genes are associated with neurological issues, such as depression, which may be sparked by disturbances to sleep cycles (our circadian rhythms). Other variants were linked to the production of actinic keratoses, which are effectively dry, scaly patches of skin that have been damaged by the Sun. It is likely that Neanderthals were attuned to respond to the sunlight of prehistoric Europe, which may have offered them advantages. However, the gene variants are now maladaptive as we live in a world diffuse with artificial light.
Neanderthal genes may also contribute to the ability of non-African humans to transport thiamine (vitamin B1), which helps convert carbohydrates into energy. Our bodies can’t produce thiamine on its own, so we have to get it from our food. For Neanderthals, this probably came from their meat-rich diets as well as the availability of nuts, but modern humans who eat processed foods may struggle to get enough of it, contributing to malnutrition.
More recent work suggests that some rare Neanderthal gene variants may also predispose people towards autism. When studying Neanderthal DNA in modern humans, researchers look for single points in DNA that vary across a population. These are called single nucleotide polymorphism (SNPs). In this study, the researchers found that autistic people tended to have more rare Neanderthal SNPs than “ethnically matched nonautistic people”.
This is not to suggest that such people are more “Neanderthal” than others, however, as the authors explained in Scientific American: “It’s just that the [Neanderthal] DNA they carry includes more of the rare variants than nonautistic people tend to have.”
The researchers gathered data on Neanderthal-derived polymorphisms in autism across three major ethnic groups – Black non-Hispanic, white Hispanic, and white non-Hispanic people – using three sources, including the Simons Foundation Powering Autism Research (SPARK), Genotype-Tissue Expression (GTEx), and 1,000 Genomes (1000G) databases. They found that the “NeanderScore” – the average of the Neanderthal DNA content within a given person’s genome – was highest among white Hispanic people, followed by white non-Hispanics and then Black non-Hispanics, when compared to the ethnically matched nonautistic control group.
They also found specific clinical associations between variants from Neanderthal DNA and autism-related traits. This included one SNP (rs112406029) in the SLC37A1 gene which was significantly associated with epilepsy in white non-Hispanic autistic people. The variant was more frequent in autistic people with epilepsy than in those without the condition, and was even more frequent in those with a family history of epilepsy.
The team state that the low frequency of some of these SNPs, combined with their clinical associations, suggests they are mildly harmful but are being gradually filtered out over time through natural selection. As such, it is possible that some rare Neanderthal DNA is gradually fading away as it becomes effectively diluted within a larger breeding population.
Research into the influence Neanderthal DNA can have on modern humans is still evolving, but findings like this significantly enrich our understand of specific conditions or traits, and their genetic roots. It also helps us understand how the hybridization of our species shapes the brain development of humans today.
[H/T: Scientific American]