Why are humans the only species with a chin?

0 0 3 minutes read

Why are humans the only species with a chin?

https://www.profitableratecpm.com/f4ffsdxe?key=39b1ebce72f3758345b2155c98e6709c

Humans are the only species to possess a chin – a feature absent even in our closest relatives. Indeed, it is such a unique anatomical oddity that it is one of the main traits anthropologists use to identify Homo sapiens remains in the fossil record.

Yet for such a defining characteristic, we know surprisingly little about its evolutionary purpose. So why are we the only species with a chin?

This question is difficult to answer because experts have not agreed on a single definition of chin. Although some researchers say that animals like elephants and manatees have chin-like protrusions, these are not the same T-shaped structures that protrude beyond our own lower teeth. As a result, some scientists have stopped viewing the chin as a single feature, but rather as the collective result of interactions between many different parts of our head and jaw.

Article continues below

Subscribe to our newsletter

(Image credit: Marilyn Perkins / Future)

“So many things about the chin are complicated,” said Scott A. Williamsevolutionary morphologist at New York University. “It cannot be quantified by a single measurement but is instead composed of a constellation of morphological characteristics.”

A better understanding of the function of the chin could in turn help scientists develop a definition. Experts have proposed several possible uses for the chin.

Some have suggested that as the teeth got smaller, the chin seemed to get smaller. strengthen our lower jaw and prevents our teeth from breaking when we chew. Others think the chin might be linked to another unique human trait – our ability to speak – with the chin providing a anchor point for the muscles of our tongue. And still others say the variation in how our chins are pronounced suggests it might be linked to sexual selection.

Instead, it seems that structurally we must have a chin, but not because the chin evolved to have a particular function.
Noreen von Cramon-Taubadel, evolutionary morphologist at the University at Buffalo in New York

Noreen von Cramon-Taubadelan evolutionary morphologist from the University of Buffalo in New York, set out to sort this list by determining whether the chin could have evolved by chance or whether evolution acted directly accordingly.

To do this, von Cramon-Taubadel and his team studied dozens of traits related to the size of the head and mandible, including nine traits associated with the chin. Then, using an evolutionary tree of 15 hominoids – a group that includes humans, their fossil ancestors, gorillas, chimpanzees, orangutans and gibbons – they examined whether these traits changed more or less over time compared to chance. Either result would suggest a role for natural selection in the evolution of the lower jaw.

Compared to other species, “the human skull is more different from that of our ancestors than one would expect given the time that has passed,” she said. However, only three of the nine chin-specific traits appeared to be under direct selection.

Together, the team’s results, published in the journal PLOS Onesuggest that the chin could be what is called a spandrel – a term borrowed from architecture to describe a feature that is a side effect of something else. Invented by evolutionary biologists Stephen Jay Gould and Richard Lewontin in 1979, the spandrel concept was introduced to argue against the idea that every feature must serve a specific, evolved purpose.

“Instead, it seems that structurally we must have a chin, but not because the chin evolved to have a particular function,” von Cramon-Taubadel told Live Science. “More and more studies show that things we thought were terribly important in terms of differences between humans and other apes might actually evolve simply by random drift and gene flow.”

Von Cramon-Taubadel said the group’s findings appear to be more heavily influenced by the major benchmarks known in human evolutionincluding when we started walking upright and developing bigger brains.

Despite these takeaways, von Cramon-Taubadel and Williams agree that the issue is far from settled. It’s unclear, for example, when traits like speech first appeared, so it’s difficult to link them to the evolution of the chin. Even though Williams admits that the chin may not have evolved for a specific purpose, that doesn’t make it arbitrary.

“It is still one of the defining characteristics of our lineage that is present in one form or another in every human being living on the planet today,” he said.