Did Bigger Brains or Better Wired Brains Give Rise to Humans?

This skull reconstruction of A. sediba with the computer-generated cranial endocast area shown in green. The yellow section indicates missing elements that were mirror-imaged and the transparent blue highlight on the endocast indicates the anterior portion of the inferior frontal gyrus found in the frontal lobe. Courtesy Indiana University.

Two million years ago, our ancestors were running about Africa trying to scratch a living off of the land. Though they were hominids and were well on their way to becoming the thumb-wielding geniuses of today, they were by no means human. Australopithecus – meaning southern ape – was a genus of four species that predates the modern Homo genus that we belong to.

Of the different species, there are four that stand out: A. anamensis, A. afarensis, A. africanus and A. sediba. Scientists are fairly certain that Homo hominids evolved from one of these species, but exactly which one still remains a mystery. Each species exhibits human-like traits in different parts of their bodies. Some have long legs and big teeth, others have modern faces and smaller teeth. Some have hands that more closely resemble our own while others have thin hips.

As the debate goes on, one of the most compelling arguments for which might have given rise to Homo sapiens comes from the brain. During this point in evolution, the brain truly transformed into what it is today, showing reorganization of neural pathways and an enlargement in its size. It’d be easy to point to the species with the largest brains and say that those must be the ones who became modern humans with our huge noggins.

But not so fast.

Kristian Carlson from the Indiana University Department of Anthropology recently created a virtual map of the skull of one of the few Australopithecus sediba skeletons in our possession. This is the same species that Lucy comes from. A team of scientists took the skull and imaged it using x-rays produced by the European Synchrotron Radiation Facility.

Synchrotron radiation is given off by particles accelerated to extremely high velocities changing direction. Whether being coerced into a circle around a cyclotron or the Large Hadron Collider, or being “wiggled” back and forth by a series of magnets in a straight line, electrons, protons and all the other “ons” give off this type of radiation. When harnessed and focused, amazing science can be done.

In this case, the x-rays were used to create a 3D reconstruction of the inside of the fossilized skull. What Carlson found gives pause to those who would crown the big headed hominids king. Though the skull is smaller than some other species (slightly bigger than a grapefruit), it shows evidence of enlargement in the prefrontal cortex, indicating an advancement in the sifting of complex information and human-like planning—multi-tasking, innovation, reasoning—putting it ahead of other South African australopithecines.

“This is a time when we have huge variation in morphology among the hominins. Some have huge teeth, long legs and larger brains. So when you think big brains, that must mean those are the human ancestors, right? But other specimens have more modern faces and smaller teeth, even though they have small brains,” said Kevin Hunt, anthropology professor in IU’s College of Arts and Sciences, who was Carlson’s Ph.D. advisor. “So do we trust the faces or the brains? Or are they all our ancestors? It’s almost like each fossil has its own separate human-like feature, and we’d have to break them all apart and put them together Frankenstein-like to get a modern human.”

On a side note, this species was discovered by a nine-year-old son of a paleoanthropologist while exploring near his father’s dig site in the dolomitic hills north of Johannesburg. He just happened to stumble on the clavicle and the lower piece of a jaw with a tooth sticking out. A couple of years later, it turns out the kid Matthew has made one of the biggest finds in human evolution history. Talk about getting all the luck!


About bigkingken

A science writer dedicated to proving that the Big Ten - or the Committee on Institutional Cooperation, if you will - is more than athletics.
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