Ancestor

1. Mark  your  confusion.  

2. Show  evidence  of  a  close  reading.  

3. Write  a  1+  page  reflection.  

New Human Ancestor Elicits Awe—and Many Questions

Source: Jamie Shreeve, National Geographic, September 10, 2015

Scientists reacted with a mix of awe and exasperation to the news Thursday of

the discovery of fossils in South Africa that are said to define a new species of human

ancestor, Homo naledi. The awe was inspired mostly by the sheer number of fossils—more than

1,500 bones, all of them from a remote chamber in the cave system called Rising Star, 30 miles

northwest of Johannesburg.

“It’s a stunning collection of bones, unlike any we’ve seen before,” said Carol Ward, a

paleoanthropologist at the School of Medicine at the University of Missouri. Like other

scientists, however, Ward tempered her enthusiasm with frustration at the discovery team’s

decision to publish before more information could be gathered—most importantly, on the age of

the bones.

Homo naledi sports a bizarre mixture of primitive and modern traits. It has a tiny ape-like

brain perched on a body proportioned much like a small modern human; it has ape-like shoulders

and torso, curved fingers for climbing trees—and a remarkably human foot. The mix hints at a

species close to the origin of the genus Homo, between two million and three million years ago.

But dating fossils solely by what they look like is a highly risky business. Traits from a

primitive ancestor can be retained in a skeleton alongside ones that have evolved toward a more

modern form. The fossils could be much younger or—less likely—much older than their

morphology suggests.

In East Africa, datable volcanic ash layers provide “time stamps” that have allowed the

age of famous hominin finds, such as the 3.2-million-year-old Lucy skeleton, to be determined

precisely. In contrast, South African cave finds are notoriously difficult to place in time. Often

the age is estimated from the types of extinct...