World Oldest Known Child

The remains of a 3-years old female of Australopithecus afarensis in the arid badlands of Afar (Ethiopia) at the Dikika site sandstones are those of the world oldest known child. The area is perhaps best known for turning up "Lucy," the 3.2 million-year-old skeleton of an adult female of the same species. The child, named Selam, lived 3.3 million years ago.

The skull - of a monkey skull size - was spotted from a dusty slope in December 2000. The smooth brow and short canine teeth were typical for a hominid. Selam's discovery is reported in Nature by Zeresenay Alemseged, paleontologist at Max-Planck-Institute for Evolutionary Research in Leipzig, Germany; Fred Spoor, professor of evolutionary anatomy at University College London, and others.

Researchers have spent five painstaking years removing the bones from sandstone, and to finish removing the sandstone from the child's bones will take several more years. Because it is very well preserved, the body may have been buried by sand and gravel in a flood. "It was buried just after it died," Zeresenay said. "That's why we found an almost complete skeleton, so maybe [drowning] could be the cause of its demise."

Researchers hope this skeleton, because of its completeness, can provide much more information on details that Lucy and similar fossils couldn't. "Selam includes the complete skull, including an impression of the brain and the lower jaw, all the vertebrae from the neck to just below the torso, all the ribs, both shoulder blades and both collarbones, the right elbow and part of a hand, both knees and much of both shin and thigh bones. One foot is almost complete, providing the first time scientists have found an afarensis foot with the bones still positioned as they were in life".

The age of death makes the find especially useful, scientists say, providing insights into the growth and development of human ancestors.

"It will teach us how our early ancestors grew up," Spoor said. "The only way you can evolve from one type of species into another is by growing up in a different way, because that's how you change."

For instance, a prolonged, dependent childhood allowed later human species to grow larger brains, which need more time to develop after birth.

While the adult A. afarensis had a brain slightly larger than a chimpanzee's, Selam's brain appears to have been smaller than a chimp's of the same age. This raises the possibility that A. afarensis experienced a more human-like pattern of brain growth.

"For the first time we have insights that they may have grown their brains a little bit slower than your average chimp," Spoor said.

"If you take more time to form your brain, it may well be that you make more intricate connections inside," the researcher added. "Or it may not be a positive thing-perhaps you live on poorer food or are a bit behind."

Spoor favors the latter explanation in the case of these early hominids. "They haven't progressed over great apes at all, they've just changed their locomotion for whatever reason, but they were not necessarily any more clever than chimps were."

"Selam also revealed just the second hyoid bone to be recovered from any human ancestor. This tiny bone, which attaches to the tongue muscles, is very chimp-like in the new specimen", Spoor said.

While that doesn't directly reveal anything about language, it does suggest that whatever sounds afarensis made "would appeal more to a chimpanzee mother than a human mother," Spoor said.

Selam already possessed the characteristics of her species. Scientists are especially interested in traits linked to locomotion. Selam supports the theory that A. afarensis walked upright on two legs, but also that early humans hadn't completely left the trees by that time.

Scientists are excited to see how will Selam's foot look when fully excavated: human-like or chimp-like ?

Scholars agree that A. afarensis was a creature that got around capably on two legs. But in the 1980s started the debate over whether the species was also adapted for life in the trees.

Whereas A. afarensis has clear adaptations to bipedal walking in its lower body, its upper body exhibits a number of ape-like features, as Selam revealed. One camp held that A. afarensis had transitioned fully to terrestrial life, and that the tree-friendly features of the upper body were just evolutionary baggage handed down from an arboreal ancestor.

The other side contended that if A. afarensis had retained those traits for hundreds of thousands of years, then tree-climbing must have still formed an important part of its locomotion. Like adult A. afarensis, Selam had long, curved fingers. But the shoulder blades, previously unknown for this species, are more like those of a gorilla, even if they present some human traits. The balance part of the inner ear is similar to that of the apes. This could indicate that A. afarensis was not as fast and agile on two legs as we modern humans are.

The neck seems short and thick - like a great ape's - rather than the more slender human type. This limited the ability to decouple its head and torso, which play a key role in endurance running in our own species, keeping the head stable while running. "It's not out of the realm of possibility that they were still exploiting some of the arboreal habitats for getting off the ground at night and sleeping up there, or going back to familiar food sources." said Donald C. Johanson, Lucy's discoverer.

C. Owen Lovejoy of Kent State University disputes the assertion that the scapula looks like that of a gorilla. "It's primitive, but it's really more humanlike than gorillalike" says Lovejoy, a leading proponent of the idea that A. afarensis was a dedicated biped.

The discovery of the famed Laetoli footprints in 1978 closed the debate, he states. That trail showed that A. afarensis did not have a grasping big toe. Lacking that prehensile toe, Lovejoy says, A. afarensis could not move about effectively in the trees.

Selam is a " good example of mosaic evolution". " It looks like natural selection is selecting for bipedalism in the lower limb and pelvis first, and things that are not really used in bipedal locomotion, such as arms and shoulders, change at a later stage", says Johanson. The skull also shows a mixture of traits, with its primitive hyoid bone, and human pattern of brain growth.

Once, the region where afarensis lived was much wetter, with lush woods and grasslands with a savanna fauna, as nearby excavated fossils showed.