Our understanding of human evolution changed dramatically in 1973, when the world was introduced to “Lucy”, the fossilized remains of an ancient hominin found in Ethiopia that lived some 3.2 million years ago. Unlike our closely related cousins of the Homo genus– Homo erectus, Homo habilis, and Homo neaderthalensis, “Lucy” was something else entirely, older than any human species by nearly half a million years, and though she walked upright like a human, she possessed a brain more akin to that of apes. Today, we know her as the first discovered fossil of Australopithecus afarensis, a species of hominin that came before any kind of human, serving as part of the “missing link” between apes and Homo sapiens.
For the longest time, scientists thought that all Homo species originated from Australopithecus afarensis, beginning with Homo habilis, and that any kind of diversity amongst hominins came long after the establishment of the Homo genus. Although evidence of other species belonging to the older Australopithecus genus have been found in the years following Lucy’s discovery, until recently the scientific community has remain dubious of the existence of any other species beside Lucy’s, confident in the assumption that A. afarensis was our direct ancestor.
In 2011, a new discovery turned that very assumption on its head. Only 30 miles (50 kilometers) from a prominent Australopithecus afarensis excavation site, scientists unearthed a number of fossils- including teeth, a partial upper jawbone, and two lower jawbones- that undoubtedly belonged to a member of the Australopithecus genome, yet were just different enough to give scientists pause in naming it as another A. afarensis specimen. A thicker lower jaw and thicker tooth enamel suggested a hominin closely related to A. afarensis, yet different enough to warrant being its own species. A few years later, it was dubbed Australopithecus deyiremeda, the first definitive new Australopithecus species since Lucy.
Australopithecus deyirmeda’s close relation to A. afarensis was reflected in it’s name, which means “close relative” in the language of the Afar people, who live near the area in which A. deyirmeda was discovered. Although lacking a full skeleton to study, studies have dated A. deyirmeda’s remains to be around 3.3-3.5 million years old, meaning that it lived alongside, and probably interacted with, A. afarensis during its existence. While today the excavation site of Australopithecus deyirmeda lies in the midst of a desert, three million years ago rivers dominated the land, with A. deyirmeda most likely living in the forests along their banks. Smaller teeth than A. afarensis suggests that A. deyirmeda ate a meatier diet than its cousin.
All in all, A. deyirmeda’s discovery means that, rather than one hominin species dominating a vast swath of what is today east Africa and eventually evolving into the Homo genus, several different species probably existed alongside each other, each filling different niches in the environment according to different dietary and foraging behaviors. This discovery may shed light on the evolutionary significance of other recently discovered hominin species, such as A. bahrelghazali (discovered in Chad) and Kenyanthropus platyops (discovered in Kenya). It also may mean that Lucy’s A. afarensis was not our direct answer- instead, we may have evolved from one of several other members of the Australopithecus genus, a genus with more diversity than we had ever assumed before.
In many ways, the human family tree is beginning to look like a patch of kudzu, and we should expect more discoveries in the near future.
For More Information:
- Another contender for the ancestor of the human lineage– Mashable (May 2015)
- New Species of Human Ancestor Found in Ethiopia– National Geographic (May 2015)
- Haile-Selassie, Yohannes, et al. “New species from Ethiopia further expands Middle Pliocene hominin diversity.” Nature 521.7553 (2015): 483-488.
- Curator Discovers New Human Ancestor Species – Cleveland Museum of Natural History (May 2015)
- Revisiting early human evolution – Ricochet Science (October 2013)
- Lucy : By 120 (own picture worked with photoshop) [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or CC BY 2.5 (http://creativecommons.org/licenses/by/2.5)], via Wikimedia Commons
- Australopithecus deyiremeda teeth: Yohannes Haile-Selassie / Cleveland Museum of Natural History.
Devin Windelspecht is a sophomore at Northeastern University in Boston MA where he majors in international relations and journalism.