Earliest known genetic condition on the enormous teeth of our close fossil relative
Our new research article describes the earliest known common genetic condition in our evolution, in a 2 million-year-old species called Paranthropus robustus. This species commonly had severe tooth defects caused by a genetic condition, amelogenesis imperfecta, with many teeth covered in pits giving them the appearance of the surface of a golf ball.
Paranthropus robustus was a remarkable member of the human family tree. Individuals had extremely large back teeth as well as massive jaws and cheeks, features thought to have evolved so they could cope with a diet with a lot of tough and fibrous vegetation. In our new study, published in the Journal of Human Evolution, we found over half of primary (baby) molars (back teeth) had pitting defects, as did a quarter of adult molars. The cause of this extremely high rate of genetic defects may relate to Paranthropus evolving extremely large molars in a short period of time, leading to instability in crucial gene(s).
For example, one gene, ENAM, is associated with variation in tooth properties such as enamel thickness. Mutations in this same gene are responsible for many types of genetic conditions affecting teeth. Therefore, genetic changes linked to the evolution of thick enamel and large back teeth in Paranthropus, over a short period, may have created knock-on effects in genes such as ENAM, leading to high rates of pitting defects.
The frequency of specific genetic conditions varies among species and populations, and some can be particularly prevalent in certain groups. This new research highlights the earliest example of a population with significantly higher occurrence of a genetic condition than occurs in people today. The genetic condition, amelogenesis imperfecta, affects about 1 in 1,000 people today, whereas about 1 in 3 P. robustus individuals had this condition. This genetic condition likely impacted diet and behaviour in Paranthropus, as pitting defects can lead to extreme tooth wear and dental cavities.
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