New synthesis of research connects changing environment with Homo’s evolutionary adaptability.
Various traits unique to humans were thought to have originated in the genus Homo between 2.4 and 1.8 million years ago in Africa. Even though scientists have recognized these characteristics for a multitude of years, they are now reconsidering the true evolutionary factors that drove them.
A large brain, long legs, the ability to craft tools and prolonged maturation periods were aspects that scientists believed all evolved together at the beginning of the Homo lineage as African grasslands spread and the global climate became cooler and drier. However, new climate and fossil evidence analyzed by a group of researchers, including Smithsonian paleoanthropologist Richard Potts, Susan Antón, professor of anthropology at New York University, and Leslie Aiello, president of the Wenner-Gren Foundation for Anthropological Research, implies that these traits did not arise in one single group. Instead, it is now thought that the several key ingredients, once thought to define Homo evolved in the earlier Australopithecus ancestor between 3 and 4 million years ago, while some others emerged much later.
The research team’s findings takes an pioneering approach to integrating paleoclimate data, newly discovered fossils and understandings of the genus Homo, archaeological remains and biological studies of a vast range of mammals (including humans). The synthesis of this data led the team to conclude that the ability for early humans to adapt to changing conditions ultimately allowed the earliest of Homo to vary, survive and begin spreading from Africa to Eurasia 1.85 million years ago. Further information concerning this study can be found in the July 4 issue of Science.
Potts developed a new climate framework for East African human evolution that depicts most of the era from 2.5 million to 1.5 million years ago as a period that suffered significant climate instability including shifting intensity of annual wet and dry seasons. This framework, based on Earth’s astronomical cycles, provides the core of some of the paper’s key findings, and it implies that multiple coexisting species of Homo that overlapped geographically emerged in highly changing environments.
“Unstable climate conditions favored the evolution of the roots of human flexibility in our ancestors,” said Potts, curator of anthropology and director of the Human Origins Program at the Smithsonian’s National Museum of Natural History. “The narrative of human evolution that arises from our analyses stresses the importance of adaptability to changing environments, rather than adaptation to any one environment, in the early success of the genus Homo.”
The team took time to review the entire body of fossil evidence relevant to the origin of Homo in order to obtain a better understanding of how the human genus evolved. For example, five skulls approximately 1.8 million years old discovered at the site of Dmanisi, Republic of Georgia, expose variations in traits typically seen in Africa H. erectus but differ from the defining traits of other species of early Homo known only in Africa. Newly discovered skeletons of Australopithecus sediba (approximately 1.98 million years old) from Malapa, South Africa, also include some Homo-like features in its teeth and hands, while also containing some unique non-Homo traits in its skull and feet. The comparison of these fossils with the substantial fossil record of East Africa shows that the early diversification of Homo was a period of morphological experimentation. It therefore indicates that multiple species of Homo lived in parallel with each other.
“We can tell the species apart based on differences in the shape of their skulls, especially their face and jaws, but not on the basis of size,” said Antón. “The differences in their skulls suggest early Homo divvied up the environment, each utilizing a slightly different strategy to survive.”
Although all the Homo species had overlapping body, brain and tooth sizes, they also had larger brains and bodies than their potential ancestors, Australopithecus. According to the study, these differences and similarities indicate that the human package of traits evolved separately rather than all together and at one time.
As well as studying climate and fossil data, the research team also reviewed evidence from ancient stone tools, isotopes found in teeth and cut marks found on animal bones in East Africa.
“Taken together, these data suggest that species of early Homo were more flexible in their dietary choices than other species,” said Aiello. “Their flexible diet—probably containing meat—was aided by stone tool-assisted foraging that allowed our ancestors to exploit a range of resources.”
The team found that it is this flexibility that most likely improved the ability of human ancestors to successfully adapt to the unstable environments they were faced with and disperse from Africa. This flexibility continues to be a hallmark of human biology even today, and one that ultimately underpins the ability to occupy a vast variety of habitats throughout all over the globe. Any future research on new fossil and archaeological finds will have to concentrate on identifying specific adaptive features that originated with early Homo, which will create a much greater understanding of human evolution.
Contributing Source: Smithsonian
Header Image Source: WikiPedia
