The human family tree is a complex puzzle. Scientists recently found an important piece.
Filling in our family tree. I'm Bob Hirshon and this is Science Update.
A set of 4-million-year-old fossils in Africa has filled in a missing piece of our ancestry. University of California at Berkeley biologist Tim White co-led the team of 60 scientists from 17 countries that discovered and studied them.
The fossils come from the earliest form of Australopithecus anamensis, an ape-like species whose descendants include modern humans. What’s more, nearby rock layers from different eras contain fossils of both earlier and later species of ape-men.
So, here, we have a succession of hominid ancestors, very well dated. This is the best evidence of human evolution.
The new find captures our ancestors just when their teeth grew big enough to broaden their diet, which helped their descendants spread across the globe. I'm Bob Hirshon, for AAAS, the science society.
Making Sense of the Research
New fossils of early humans are constantly being discovered. What makes this find especially significant is where it fits on our evolutionary timeline, and what else was discovered nearby.
First, some clarifications about the species involved. “Ape-man” is a good thumbnail description, because these species share characteristics of modern apes and humans. However, they were neither apes nor humans. They were hominids, a general term for primitive human ancestors. The descendants of hominids include modern humans, Homo sapiens, and other hominid species, like Homo neanderthalensis (Neanderthals), which lived at the same time as Homo sapiens and either interbred with them or simply died out.
A side note: Contrary to popular belief, evolutionary theory does not say that humans evolved from the kind of apes we see today. Rather, it suggests that both modern apes and modern humans shared a common ancestor in the relatively recent past (as recently as 5 to 7 million years ago, compared with the start of life on Earth at least 3.5 billion years ago). To put this in another perspective, there’s a good chance you share a pair of great-great-great-great grandparents with someone from the other side of the world who looks nothing like you (different skin color, body type, ethnicity, etc). The ape-human connection is kind of like this, except on a much larger time scale.
Back to the findings: The new, 4.1 million-year-old fossils are from a species called Australopithecus anamensis. This is the earliest form of Australopithecus, a genus (category) of hominid that came before the genus Homo (Latin for “human”), which includes you. Previously, A. anamensis had been found only in an isolated location in Kenya. But here, in the Ethiopian desert, it was found near other hominids that came immediately before and after. In the older rock layers below, there are fossils of Ardipithecus ramidus, a more primitive hominid that lived about 4.4 million years ago. In younger, overlying rock layers, there are fossils of Australopithecus afarensis, a more advanced form of Australopithecus dating to about 3.5 million years ago.
Before this find, it was suspected that Australopithecus anamensis was the link between Ardipithecus and A. afarensis, but there wasn’t enough evidence to connect the dots. However, the fossils here show a clear progression in both time and anatomy from one to the next. And while White says that it’s possible that Ardipithecus ramidus may have lived at the same time as Australopithecus anamensis, it’s clear that A. anamensis descended from at least some form of Ardipithecus.
One of the big differences between Australopithecus and Ardipithecus is the size of the species’ teeth. This may not seem like a big deal, but it actually may have had a huge impact on human history. White explains that the dig area, which is a desert today, was actually a lush woodland 4 to 6 million years ago (as evidenced by petrified wood and fossils of forest animals dating to that time period). The teeth of Ardipithecus were small, like modern apes’, which would have restricted its diet to easy-to-chew plants in the area. But the larger back teeth of Australopithecus allowed it to eat tougher, more fibrous plants, which means it could explore and survive in previously uncharted territory. That could have set the stage for their descendants to spread to nearly every corner of the Earth.
Now try and answer these questions:
- What’s significant about these findings?
- Why is it important that the fossils of each species were found in different rock layers? What if they were found in the same rock layer? What would that mean?
- Why is the size of the hominid’s teeth important?
- Why study human ancestry in the first place? What’s the value of this sort of research?
You may want to check out the May 19, 2006, Science Update Podcast to hear this Science Update and the other programs for that week. This podcast's topics include: A condition that makes people pointless, preparing for a pandemic, an early apelike ancestor, a hearing aid in glasses, and promising results about avian flu.
The Archaeology.info website provides a forum for information relating to archaeology, human evolution, and human origins.
In the National Geographic Xpeditions lesson Paleo-What? The Life and Work of Emerging Explorer Dr. Zeray Alemseged, students consider how National Geographic Emerging Explorer Dr. Zeray Alemseged chose paleoanthropology as his career as they learn more about the multifaceted field itself.
The National Geographic News article Tooth Study Reveals Diets of Early Humans tells about other efforts to deduce early humans’ diets from their dental records.
Another National Geographic News article, Adolescence Came Late in Human Evolution, discusses tooth records that suggest adolescence has lengthened as humans have evolved.