Molar teeth study can tell us about our evolutionary ancestors

Posted on February 27, 2016 12:49 am

Australian researchers have discovered that the evolution of human teeth is much simpler contrary to what was thought.Many scientists have long tried to explain the profound size change to dietary and cultural shifts considered to be unique to humans. Fossil teeth are often found in isolation, providing a tantalizing clue to their owner and scientists now have a method to help them extrapolate tooth and jaw size in incomplete fossil finds.New Australian research has discovered an important pattern in mammals and humans the size of a molar is always the average of the two molars to either side of it, which includes the wisdom tooth.According to the study, published in Nature, suggests a default pattern, called the inhibitory cascade, applies to the molars and premolars in all modern humans and their ancestors.It also identifies subtle differences between the genus Homo, which includes modern humans and Neanderthals, and the Australopith genus, which includes Australopithecus afarensis of  the so called Lucy fossil.The research team was led by Dr Alistair Evans from the School of Biological Sciences at Monash University, discovered the pattern after analysing hundreds of fossil teeth from modern and ancient humans, and from great apes including chimpanzees and gorillas.”What we found in hominins is when we look at all of the Australopiths, they all basically have the same pattern where if you’ve got these five teeth in a row, they increase in size from the first, second, third, and fourth teeth, and then the fifth tooth is the same size as fourth,” Dr Evans said.”But when we look at Homo species, we find instead of tooth four being the largest, tooth three ends up being the largest, and that’s what we find in humans, that the middle tooth, the first molar is the largest tooth in our tooth row.”

Researchers conducted a range of measurements of tooth size, including CT scanning the teeth, but in the end found that the most accurate measurement was simply to multiply the width of the tooth by its length to form a rectangle representing the crown size.Dr Evans said the difference in the tooth size pattern between Homo and Australopiths may reflect differences in the toughness of their diet, with harder foods requiring more bite strength.”If you’re trying to bite as hard as you can you often move your food and you bite further back in your mouth, so the bite force may be larger at the back of the mouth,” Dr Evans said.”In the Australopiths the biggest teeth were at the back of the jaw and in Homo species the biggest teeth are closer to the middle of the jaw.”The discovery will help anthropologists to extrapolate tooth and jaw size in incomplete fossil finds.”If you find an isolated tooth or a population of teeth, we can look at the inhibitory cascade pattern in found in all other species, and because the sizes are so constrained we can say that once you get one tooth position, you can predict the sizes of the other four with reasonable accuracy,” Dr Evans said.This approach could help with new hominin fossil finds such as the collection of fossils of Homo naledi recently discovered in a cave in South Africa, and reveal more about the life of ancient humans and other mammals.”Teeth are the sorts of things that survive in the fossil record, so we can tell what the animal was, they’re the things that they use to eat the food so they tell us about what it did in the environment, and they also often tell us about how one animal is related to another.”

Contador Harrison