Neanderthals (Homo neanderthalensis) is the closest evolutionary cousin to modern humans (Homo sapiens). In fact they are so close there has been some debate about whether or not they are truly a separate species from humans or if they are a subspecies (Homo sapiens neanderthalensis), but it seems the consensus has moved toward the former recently. They are not our ancestors – humans did not evolve from Neanderthals (anymore than we evolved from modern Chimps). Rather, we share a common ancestor with Neanderthals, about 700,000 years ago.

Neanderthals dominated in Europe from about 400,000 to 40,000 years ago, with their close relatives, the Denisovans, in Asia. They existed alongside modern humans for a long time, but then disappeared. There is probably no single simple reason why this occurred. There were likely many factors – some competition, some interbreeding, and independent reasons for Neanderthal decline that perhaps had nothing to do with humans. But as part of this question is the distinct but related one of – are modern humans somehow inherently superior to Neanderthals? Did we outcompete them because we were better?

This is a difficult question to answer from fossil evidence alone. Neanderthals were more robust than humans, and had brains which were as large (for body weight, meaning they were actually a bit bigger). Perhaps the replacement of Neanderthals by humans was a lateral move. Or perhaps Neanderthals were better adapted to the European ice age, and modern humans had the edge in warmer climates.

But there is a more direct question than ultimate evolutionary forces – were modern humans smarter than Neanderthals?  To answer this question we can use biological evidence or cultural evidence. I will get to the biological evidence second, discussing a recent study that may shed significant light on the question. But first let’s look at the cultural evidence.

There is still a lot of controversy here, but we can dispense with the old view of Neanderthals as dumb brutes. They were clearly about as intelligent as modern humans, they used a sophisticated toolkit, and were efficient hunters. The debate is about whether there was any meaningful difference in intelligence, and if this was enough to provide a survival advantage. A lot of attention focused on the different stone tools of early humans and Neanderthals.

Humans did make more slender and intricate stone tools. They were able to make long blades, while Neanderthal cutting tools were mostly disc-shaped. However, the longer blades may not have been more functional, and in fact the stubbier blades may have been more durable. There is one advantage, though, the ability to attach the long blade to a wood shaft to make a spear. Again, there is debate about how significant this would have been in terms of a competitive advantage, but that is separate from the question of whether the more intricate blades represented superior intelligence.

Humans were also more artistic than Neanderthals. At first we thought that Neanderthals did not make any art, but of course that conclusion is based on a lack of evidence. It was changed the moment we discovered Neanderthal art – it appears they drew the first cave paintings. But even still, Homo sapiens produced much more and more varied art than their Neanderthal cousins. Humans, therefore, appear to be craftier than Neanderthals.

Cultural evidence is indirect, however. It’s possible that modern humans were not inherently smarter than Neanderthals but simply hit upon certain cultural innovations that had a positive feedback loop leading ultimately to all of modern society. It seems unlikely, though, that this was purely cultural. Neanderthals had the identical toolkit for over 100,000 years, until they disappeared. They never developed written language or agriculture. Modern humans seemed to be more innovative.

What about the biological evidence? Like I said, Neanderthals actually had bigger brains than humans, although proportional to their larger overall body size. Their brains developed longer in order to achieve this larger size. But brain size does not directly correlate with intelligence, because brains do more than cognition.

A 2013 study, for example, comparing the skulls of humans and Neanderthals, found that more of the Neanderthal brain was dedicated to motor control and sensory processing, leaving less brain tissue dedicated to higher cognitive function. They needed more brain to control their larger bodies, but did not have frontal lobes as large as humans.

We now also have genetic evidence, and this leads us to the new study. Perhaps even more important than total brain size when trying to infer intelligence is neuronal density – how many brain neurons are present within a given volume? The new study looks at versions of the TKTL1 protein. The version found in modern humans results in greater neuronogenesis, especially in the frontal cortex, than the version common in Neanderthals. Therefore humans likely have greater neuronal density in the higher cognitive areas of the brain than their Neanderthal cousins did.

Again, this alone does not answer the evolutionary question, but it probably is not irrelevant to the question. Looking at all the evidence it’s clear that Neanderthals were very smart, and they were not the brutes classically depicted. They had advanced tools and the beginning of art. Also, they clearly mixed their genes with modern humans. But it also does appear that modern humans did have an intellectual edge over the Neanderthals.

It’s interesting to think of what would have happened to Neanderthal culture if they never died out or had to compete with modern humans. Would they still be stuck in the stone age? Perhaps modern humans neurologically evolved just past some critical threshold, enabling the development of a technological culture. Was that inevitable, or at least highly likely, given hominid evolution? Or are there many worlds out there with creatures that have Neanderthal-level intelligence, but never cross the critical threshold to develop a technological civilization?