11.6: Where Did They Go? The End of Neanderthals

While MSA specimens were increasingly successful and ultimately transitioned into modern Homo sapiens, Neanderthals disappeared from the fossil record by around 40,000 years ago. What happened to them? We know, based on genetics, that modern humans come largely from the modern people who occupied Africa around 300,000 to 100,000 years ago, at the same time that Neanderthals were living in northern Europe and Asia. As you will learn in Chapter 12, modern humans expanded out of Africa around 150,000 years ago, rapidly entering areas of Europe and Asia inhabited by Neanderthals and other Archaic hominins. Despite intense interest and speculation in fictional works about possible interactions between these two groups, there is very little direct evidence of either peaceful coexistence or aggressive encounters. It is clear, though, that these two closely related hominins shared Europe for thousands of years, and recent DNA evidence suggests that they occasionally interbred (Fu et al. 2015). Geneticists have found traces of Neanderthal DNA (as much as 1% to 4%) in modern humans of European and Asian descent not present in modern humans from sub-Saharan Africa. This is indicative of limited regional interbreeding with Neanderthals.

While some interbreeding likely occurred, as a whole, Neanderthals did not survive. What is the cause for their extinction? This question has fascinated many researchers and several possibilities have been suggested, including:

• At the time that Neanderthals were disappearing from the fossil record, the climate went through both cooling and warming periods—each of which posed challenges for Neanderthal survival (Defleur and Desclaux 2019; Staubwasser et al. 2018). It has been argued that as temperatures warmed, large-bodied animals, well adapted to cold weather, moved farther north to find colder environments or faced extinction. A shifting resource base could have been problematic for continued Neanderthal existence, especially as additional humans, in the form of modern Homo sapiens, began to appear in Europe and compete for a smaller pool of available resources.
• It has been suggested that the eruption of a European volcano 40,000 years ago could have put a strain on available plant resources (Golovanova et al. 2010). The eruption would have greatly affected local microclimates, reducing the overall temperature enough to alter the growing season.
• Possible differences in cognitive development may have limited Neanderthals in terms of their creative problem solving. As much as they were biologically specialized for their environment, the nature of their intelligence might not have offered them the creative problem-solving skills to innovate ways to adapt their culture when faced with a changing environment (Pearce et al. 2013).
• CRISPR gene-editing technology has been used in studies to evaluate potential differences between human and Neanderthal brains, based on differences in the genetic code. Potential differences include a Neanderthal propensity for mutations related to brain development that could account for more rapid brain development, maturation, synapse misfires, and less-orderly neural processes (Mora-Bermúdez et al. 2022; Trujillo et al. 2021). Fundamental differences in brain function at the cellular level may account for the differential survival rates of Neanderthal and modern human populations.
• There is evidence that suggests reproduction may have posed challenges for Neanderthals. Childbirth was thought to have been at least as difficult for female Neanderthals as anatomically modern Homo sapiens (Weaver and Hublin 2009). Female Neanderthals may have become sexually mature at an older age, even older than modern humans. This delayed maturation could have kept the Neanderthal population size small. A recent study has further suggested that male Neanderthals might have had a genetic marker on the Y chromosome that could have caused incompatibility between the fetus and mother during gestation; this would have had severe consequences for birth rate and survival (Mendez et al. 2016). Even a small but continuous decrease in fertility would have been enough to result in the extinction of Neanderthals (Degioanni et al. 2019).
• As mentioned above, the end of Neanderthal existence overlaps with modern human expansion into northern Europe and Asia. There is no conclusive direct evidence to indicate that Neanderthals and modern humans lived peacefully side by side, nor that they engaged in warfare, but by studying modern societies and the tendencies of modern humans, it has been suggested that modern humans may not have warmly embraced their close but slightly odd-looking cousins when they first encountered them (Churchill et al. 2009). Nevertheless, direct competition with modern humans for the same resources may have contributed to the Neanderthals’ decline (Gilpin et al. 2016); it may also have exposed them to new diseases, brought by modern humans (Houldcroft and Underdown 2016), which further decimated their population. Estimates of energy expenditures suggest Neanderthals had slightly higher caloric needs than modern humans (Venner 2018). When competing for similar resources, the slightly greater efficiency of modern humans might have helped them experience greater success in the face of competition—at a cost to Neanderthals.

As Neanderthal populations were fairly small to begin with (estimated between 5,000 and 70,000 individuals; Bocquet-Appel and Degioanni 2013), one or a combination of these factors could have easily led to their demise. As more research is conducted, we will likely get a better picture of exactly what led to Neanderthal extinction.