In the 150 years since Charles Darwin hypothesized that humans were from Africa, the number of species in the human family tree has exploded, as has the level of dispute over the early human evolution. Fossil apes are often at the center of the debate, with some scientists dismissing their importance to the origins of human lineage (“hominins”), and others giving them evolutionary roles. A new review published on May 7 in the newspaper Science looks at major discoveries about the origins of hominids since Darwin’s work and argues that fossil apes can inform us about essential aspects of the evolution of apes and humans, including the nature of our last common ancestor .
Humans diverged from apes – in particular, of the chimpanzee lineage – at some point between about 9.3 million and 6.5 million years ago, towards the end of the Miocene era. To understand the origins of hominids, paleoanthropologists aim to reconstruct the physical characteristics, behavior, and environment of the last common ancestor of humans and chimpanzees.
“When you look at the story of the origins of hominids, it’s just a big mess – there’s no consensus,” said Sergio Almécija, senior researcher in the anthropology division of the American Museum of Natural History and author principal of the journal. “People work under completely different paradigms, and that’s something I don’t see happening in other areas of science.”
There are two main approaches to solving the problem of human origins: “top to bottom”, which relies on the analysis of living apes, especially chimpanzees; and “from the bottom up,” which places importance on the largest tree of mostly extinct monkeys. For example, some scientists speculate that hominins originated from an ancestor that walks to the joints of the chimpanzee. Others argue that the human line originated from an ancestor more closely resembling, in some ways, some of the strange Miocene apes.
Reviewing the studies surrounding these divergent approaches, Almécija and her colleagues with expertise ranging from paleontology to functional morphology and phylogenetics discuss the limitations of relying exclusively on one of these opposing approaches to the problem of origins. hominins. “Top-down” studies sometimes ignore the reality that living apes (humans, chimpanzees, gorillas, orangutans, and hylobatids) are only the survivors of a much larger group, and now mostly extinct. On the flip side, studies based on the “bottom-up” approach tend to give individual fossil apes an important evolutionary role that fits with a pre-existing narrative.
“In The Descent of Man in 1871, Darwin hypothesized that humans originated in Africa from a different ancestor from any living species. However, he remained cautious given the scarcity of fossils at the era, “Almécija said. “One hundred and fifty years later, possible hominids – approaching the time of the human-chimpanzee divergence – have been found in East and Central Africa, and some even claim in Europe. In addition, more than 50 genera of fossil apes are now documented across Africa and Eurasia. However, many of these fossils exhibit mosaic combinations of features that do not meet the expectations of ancient representatives of modern apes and human lineages. no scientific consensus on the evolutionary role played by these fossil apes. “
Overall, researchers have found that most human-made stories are incompatible with the fossils we have today.
“Living ape species are specialized species, remnants of a much larger group of now extinct monkeys. When we consider all of the evidence – i.e. living and fossil apes and hominids – it is clear that a history of human evolution based on a few currently living ape species is missing much of the evidence. overview, ”said Ashley Hammond, study co-author, associate curator in the Museum’s Anthropology Division.
Kelsey Pugh, postdoctoral fellow at the Museum and co-author of the study, adds: “The unique and sometimes unexpected characteristics and combinations of characteristics observed in fossil apes, which often differ from those of living apes, are necessary to disentangle hominids. inherited from our monkey. ancestors and who are unique to our lineage. “
Monkeys living alone, the authors conclude, offer insufficient evidence. “Current disparate theories regarding apes and human evolution would be much more informed if, along with the earliest hominins and living apes, Miocene apes were also included in the equation,” Almecija says. “In other words, fossil apes are essential in reconstructing the ‘starting point’ from which humans and chimpanzees evolved.”