Human Middle Ear Bones Could Provide New Evolutionary Insight
May 14, 2013

Human Middle Ear Bones Could Provide New Evolutionary Insight

redOrbit Staff & Wire Reports - Your Universe Online

The bones located in the middle of a person´s ear might be the smallest in the entire human body, but they could hold big clues regarding evolution and the development of modern-day men and women, according to research published in the latest edition of the Proceedings of the National Academy of Science (PNAS).

Texas A&M University (TAMU) anthropology professor Darryl de Ruiter and colleagues examined a hominin skull from South Africa that is believed to be approximately 1.9 million years old. They focused on the bones found in the middle ear, including one known as the malleus.

The malleus and other ear bones known as the incus and the stapes combine to show a mixture of both ape-like and human-like features, they explained. The malleus itself appeared to be extremely human-like, while the other two more closely resembled the ear bones of an ape-like or chimpanzee-like creature.

The discovery marks the first time that all three of the ear bones have been found together in one skull, the researchers said. Since the malleus closely resembles those found both in modern humans and their early ancestors, they surmise the change must have occurred early on in mankind´s evolutionary history.

“The discovery is important for two reasons,” de Ruiter said in a statement. “First, ear ossicles are fully formed and adult-sized at birth, and they do not undergo any type of anatomical change in an individual lifetime. Thus, they are a very close representation of genetic expression. Second, these bones show that their hearing ability was different from that of humans — not necessarily better or worse, but certainly different.

“They are among the rarest of fossils that can be recovered,” he added. “Bipedalism (walking on two feet) and a reduction in the size of the canine teeth have long been held to be 'hallmarks of humanity' since they seem to be present in the earliest human fossils recovered to date. Our study suggests that the list may need to be updated to include changes in the malleus as well.”

The Texas A&M anthropologist was joined by researchers from Binghamton University in New York, as well as international colleagues from Italy and Spain. Their work was funded by the National Research Foundation of South Africa and by the Ray A. Rothrock Fellowship at the College Station, Texas-based institution.