Mouse teeth help us refine humanity's family tree

Mouse studies conducted at the University of Helsinki have generated a significant tool for studying the beginnings of the humans.

An international group of researchers has developed a model enabling them to predict the size of teeth in a tooth row based on a single tooth. This model is a quantitative tool for paleoanthropologists who are piecing together the evolutionary path of humans, often from isolated fossil teeth.

The new study has revealed that tooth size in human ancestors that lived before 2.5 million years ago tended to follow one pattern, while members of our own group, Homo, tended to follow another pattern. The seed for the loss of the wisdom teeth in modern humans appears to have been laid down at the onset of Homo, when tooth size and proportions got mechanistically coupled.

The model can also be used to address taxonomic controversies. For example, Homo habilis, commonly thought to be the earliest member of the Homo genus, may, in fact, fit better the genus Australopithecus based on its teeth.


Based on research from the University of Helsinki

The model now published in Nature stems from a study published eight years ago on the development of mouse teeth, conducted at the University of Helsinki's Institute of Biotechnology under Academy professor Jukka Jernvall. The study showed experimentally that that tooth size in the mouse is determined by combination of factors inhibiting and activating tooth development. A mathematical extension of the inhibitory cascade provides a developmental baseline or rule that predicts how tooth size and proportions should evolve, with a limited number of evolutionary outcomes. The first author of the new article, Alistair Evans, worked in Jernvall’s group for several years.

“Even though the original study on rodents comes from Helsinki, human evolution is not our specialty. This is why we needed international cooperation. Next we intend to determine the genetic bases of the model by studying teeth that are sufficiently simple, namely, the teeth of the Saimaa ringed seal" says Jukka Jernvall, who leads the Academy of Finland’s Centre of Excellence in Experimental and Computational Developmental Biology.