New Fossil Showed Lucy Had a Swinging Cousin

We'd leave them in the dust in the half marathon but they'd kill us on the uneven parallel bars. Scientists announced today they'd found fossil bones from an evolutionary cousin who would have co-existed with the diminutive 3.2 million-year-old Lucy. While Lucy walked like a human being, this new fossil's foot suggests it could walk upright but was more suited to the trees.

Lucy lived just about mid-way between the present day and the time our lineage split from that of chimpanzees. The new bones were dated at 3.4 million years old and were found just 30 miles from the site where Lucy's bones were excavated. The bones show enough humanlike traits to place it on our side of the chimp/human divide, but with an ape-like opposable toe that would have made walking more awkward and climbing trees more natural.

The findings were published in today's Nature and summarized here in the New York Times:

A 3.4-million-year-old fossil foot found in Ethiopia appears to settle the long-disputed question of whether there was only a single line of hominins — species more closely related to humans than to chimpanzees — between four million and three million years ago. The fossil record for that period had been virtually limited to the species Australopithecus afarensis, made famous by the 3.2-million-year-old Lucy skeleton.

Of perhaps more importance, scientists report in the journal Nature, published online Wednesday, the newfound foot not only belonged to a different species but had evolved a distinctive mode of locomotion, which scientists described as "equivocal." It clung to the trees and never adapted to terrestrial mobility outright.

At a pivotal period in prehuman evolution, the discoverers concluded, two lines of hominins practiced contrasting locomotion behavior. Their feet, mostly, told the tale: The divergent, opposable big toe, long digits and other bones of the newfound species did not match the feet of afarensis. Lucy's foot had a strong arch and the big toe was lined up with the other four digits, much like the feet of modern humans and all critical for effective bipedality, while retaining some agility for climbing trees.

Dan Lieberman of Harvard, who wrote a commentary for the journal, pointed out that while our species may have gained in walking ability, we lost in climbing. Lieberman has studied the evolution of long-distance running in our species, which he explained in detail in this Planet-of-the-Apes column.

In his piece, he reminds us that evolution is not necessarily progressive. It gives and it takes away:

"Human evolution is often portrayed as a triumph of bipedalism, but who among us has not occasionally regretted our species' comparative clumsiness in trees?" he wrote. "I, for one, am pleased to know that some hominins retained feet well adapted for arboreality millions of years after we started to walk on two feet."