Evolution appears to follow the path of least resistance, which can lead to suboptimal physical characteristics that do not typically match functional needs, a new analysis has revealed.
Anthropologist Peter Ungar from the University of Arkansas — who did the research with co-author Leslea Hlusko of the University of California Berkeley — said that paleontology usually reconstructs previous behavior based on the assumption that function follows form.
"We need to look at things in a different way and consider the number of genetic steps it takes to get from one anatomy to another,” he said in a press release. “There can be more than one function for a given form and different forms can serve the same function."
Studying teeth from two human ancestors — eastern Africa’s Paranthropus boisei and southern Africa’s Paranthropus robustus — with similar jaw and dental structure, the researchers found that the dental anatomy usually linked to a hard food diet was used to consume mainly plant-derived diets. The two species maintained similar teeth and anatomies, but their diets were not the same.
The two species date back 4.2 million to 1.3 million years ago, and share similar head and tooth anatomy — marked by flat and large teeth, thick enamel, and jaw structures indicating robust chewing muscles.
These traits are usually thought adaptive for eating hard foods, but using existing data on carbon isotopes, the team concluded that the P. robustus focused on a plant-based diet and only occasionally ate hard items like roots or nuts. The findings on the P. boisei’s teeth, on the other hand, showed that it ate softer, tougher and potentially more abrasive edibles such as grass.
Despite similar anatomy, the traces of the food they consumed suggest that the two species had marked differences in their diets, Ungar said. Neither diet, too, matched earlier beliefs that their facial structure and large muscles indicate diets filled with hard and crunchy foods.
These findings suggest that evolution went for suboptimal but still functional workarounds if fewer genetic mutations were entailed. This is dubbed the path of least resistance in the evolutionary process.
An example: flatter molars marked by thicker enamel, such as those sported by modern humans, progressed through the genetic data, unlike more crested molars seen in gorillas that would better tear fibrous plant items.
The jaw and tooth anatomy, Ungar said, is ideal for hominin diets in this case — the less complicated tooth architecture adapted more to a number of dietary challenges with time, which carried on alongside human species development.
The findings are detailed in the journal Science.
Just last month, a Swiss study discovered clues pointing to how different skin appendages — the fur on dogs, scales on snakes and feathers on creatures such as peacocks — may have come from a common ancestor.
Photo: James St. John | Flickr
