Neanderthals grew up faster than humans to power brain growth

Baby Neanderthals grew up quicker than their human counterparts to feed their growing brains. 

Researchers investigating fossils found in Croatia found that Neanderthal teeth emerged up to four months earlier than in modern humans. They suggest that this would allow them to start eating a wider range of foods and give them the energy to support an early growth spurt. 

Co-author Professor Helen Liversidge, who researches Dental Anthropology at Queen Mary University and is a scientific associate of the Museum, says, 'The relative development speed of human and Neanderthal teeth is a hot topic. Some say that the latter develop faster, but others argue that they fall within the range of human variation.  

'This is the first time we've had a baby Neanderthal tooth that we can infer from the root growth whether it erupted earlier or not. We found that it looks as if the teeth are growing more quickly and their baby teeth were erupting earlier than in present day humans.' 

The findings of the study, conducted by an international team of researchers, was published in Proceedings B.

Grabbing a bite 

Teeth can tell you a lot about an individual. Forensic scientists can use them to help identify remains, while the phrase 'never look a gift horse in the mouth' refers to the practice of determining a horse's age by looking at its teeth. 

Their high mineral content makes them a good candidate for fossilisation, allowing scientists to find out clues about the distant past. Some ancient animals, like sharks, are only known through the teeth they left behind, while the fossils can also reveal how past environments may have changed over time. 

Comparing these ancient teeth to modern examples allows scientists to infer how development may have changed. Helen has previously worked on Roman and medieval remains to investigate how their teeth developed. 

'Teeth have a history of our development within them,' she says. 'Even our adult teeth, which develop from birth to about the age of 20, tell us a lot about the time you were developing. But the baby teeth begin to develop before birth and during the first three years of life so can tell us that bit more.' 

Previous research has linked the development of teeth to brain growth across modern humans, other hominids and non-human primates like the chimpanzee. Scanning the interior of the teeth allows scientists to estimate how quickly they had grown and emerged, but these processes remain hard to decipher. 

'Eruption and tooth development are two separate processes but they happen at the same time,' Helen says. 'It is quite complex and we still don't really understand the theory even though every child in the world has gone through it.' 

In this study, scientists used teeth from Krapina in Croatia, where the bones of up to 80 Neanderthals have been found. 

The researchers used deciduous, or baby, teeth found at the site to investigate how Neanderthals grew during the earliest part of their development.  

'They grow up so fast' 

The scans showed that certain teeth like the incisor were growing much more rapidly than those of modern humans, while molars grew at a similar rate but formed enamel faster.  

Overall, Neanderthal teeth emerged from the jaw around three months earlier than in modern Europeans. People from other nations around the world, such as Nigeria, can have teeth that emerge significantly later, opening the gap to five months. 

This early emergence suggests that Neanderthals were more rapidly weaned off their mother's milk after birth than Homo sapiens, and moved towards eating a range of solid foods. Neanderthals are known to have eaten a wide range of foods, including a high proportion of red meat alongside seafood, plants and mushrooms. 

This matches up with previous studies which used elements found in food to suggest that young Neanderthals were being weaned at around four months old, about two months earlier than in most humans.  

The extra energy this would give allows the energy demands of the growing brain to be met, with Neanderthals having craniums significantly larger than Homo sapiens. These gradually shrunk over time, as in our ancestors. 

Early development may also have necessary due to the early death of Neanderthals, with 85% of the species estimated to have died by the age of 40. While the reasons for this are unclear, it has been suggested the population faced severe environmental stresses. 

While the findings suggest rapid growth in Neanderthals, debate over the species' rate of development is unlikely to be put to bed. 

'It's very difficult to say if the Krapina samples are representative as we've only got a few teeth,' Helen says. 'Historic samples give us a bit of information on how to interpret these fossil teeth but we would need more samples to produce a clearer picture.' 

The researchers hope to carry out further studies to assess how Neanderthal growth changed over time to find out more about the early years of our close relatives.