Convoluted human evolution: earliest environment (Introduction)

by David Turell , Monday, May 15, 2017, 23:06 (2749 days ago) @ dhw

The earliest Homo fossil, 400,000 years earlier than previous early Homos lived in an unchanging grassy environment:

https://phys.org/news/2017-05-grassy-earliest-homo.html

"Using stable isotopes of fossil teeth, the researchers found that early Homo at Ledi-Geraru was indeed associated with open and arid grassy environments. Results show that almost all animals found with early Homo at Ledi-Geraru fed on grass, including some that consumed substantial amounts of tree leaves prior to 2.8 million years ago.

"The diet of early Homo at Ledi-Geraru, however, appears to be indistinguishable from that of the earlier Australopithecus, implying that a change in diet is not a characteristic of the origins of Homo.

"We weren't necessarily surprised that the diet of early Homo was similar to Australopithecus," said Chris Campisano, research associate with the Institute of Human Origins and associate professor in the School of Human Evolution and Social Change. "But we were surprised that its diet didn't change when those of all the other animals on the landscape did."

"Placing Ledi-Geraru in a regional context indicates that eastern Africa environments at this time were not homogeneous. The ecology of the lower Awash Valley shifted from a wet and wooded environment at the time of the disappearance of Australopithecus around three million years ago to a dry and open landscape at the time of early Homo 2.8 million years ago.

"'Although Lucy's species persisted through many environmental changes in the Hadar sequence," School of Human Evolution and Social Change graduate student John Rowan said, "it seems the species was unable to persist as really open environments spread in the Afar during the late Pliocene."

"Furthermore, these results indicate that the spread of grassy environments at Ledi-Geraru occurred earlier than in the Turkana Basin of Kenya and Ethiopia, which continued to have wooded regions that supported browsers and other mammals that fed on both trees and grasses.

"'By using several different habitat proxies, we were able to refine previous ecosystem reconstructions in each basin so that we were able to identify the details of the spread of grasslands," said Kaye Reed, President's Professor and director of the School of Human Evolution and Social Change. Reed is also a research associate with the Institute of Human Origins. "We are planning to compare other East African hominin sites using these same methodologies.'"

Comment: The common diet between Lucy and the appearance of Homo species indicates a fairly constant environment as it shifted from patches of woods to totaly grassy. Nothing here shows stress to drive brain enlargement. In fact no reason is seen in this study.