MORE HOMININS

Still more African hominins

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Some terrestrial hominins moved into Africa just prior to the onset of the first glacial maximum or just after it. They did not quite seem to belong to the Homo clade.  But almost.

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Australopithecus sediba

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Australopithecus sediba found their way into places where fruiting trees were abundant.  Their ancestors had needed to climb trees in order to find piles of bones, but in Africa they found trees that fruited throughout the year. Moreover, Australopithecus sediba seldom needed to venture cross-country.  Consequently, they evolved a twisted ankle which was not so good for walking cross-country but helped them to walk on brancheHomo habiliss while they wrapped their very flexible feet around the branches. Their hands, however, gave them away as close relatives of Homo habilis.

Australopithecus sediba and Homo habilis both had very human-like hands, but the two species used their hands differently​.  Even though Australopithecus sediba did not have long, ape-like hands that were suitable for supporting their weight while hanging from branches, they often did partially support their weight by holding onto branches.  The resulting strain on their finger bones caused the phalanges of the forefinger and two other fingers to become thickened by the strain that was imposed on them.  Australopithecus sediba also evolved especially long and powerful thumbs to partially make up for their shorter hands, and they had re-evolve a slight curvature of their finger bones that is similar to what is observed in the hands of other Australopithecines.

Homo habilis, had straighter fingers, and their fossilized hand bones show evidence of loading throughout their lifetimes that was very similar to that of modern humans, who seldom use their hands for climbing trees.

Homo habilis

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Homo habilis were closely related to Australopithecus sediba, and both species seem to have evolved from Australopithecus afarensis.  This is shown by an early Homo habilis rmandible found at the Ledi Geraru site in Ethiopia that retains many features of the Australopithecines.

Homo habilis relied more on what they could salvage from animal carcasses, rather than fruits that they found in trees, so Homo habilis still had to climb trees on occasion, in order to escape from predators or to forage in trees, and they still had shorter legs and longer arms than some later hominins.

Homo habilis had hands that were not well adapted to climbing trees.  Instead, they were better at grasping a rock firmly so as to strike it accurately during rock-chipping operations.  A firm grip was also needed for throwing rocks accurately, so as to deter predators or drive them away from carcasses.

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Although they were generally able to defend themselves against medium-size carnivores, they were not good at stealing carcasses from them, so Homo habilis often had to make do with scraps of skin and bones that were not eaten by carnivores.  They could obtain fresh meat by killing herbivores, but they were probably less successful at it than later members of the Homo clade.

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Some archaeologists have posited that Sediba were ancestral to Habilis, but it was more likely the other way around, or the ancestors of Australopithecus sediba might have come earlier to Africa, while the climate there was wetter, and adapted to those conditions, whereas the ancestors of Homo habilis retained the characteristics of their ancestors.

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Homo rudolfensis

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Other hominins, Homo rudolfensis, were similar to Homo habilis.  They also had human-like hands and most likely used them for similar purposes, but they had even larger molars with flat chewing surfaces, meaning that their teeth were well suited for efficiently chewing tough fibrous plant materials.  Yet they did not have the huge jaws and huge jaw musculature that enabled the Paranthropines to chew on their food all day.in order to extract nutrition from very low-quality foods.  Why not?  The answer is that they had even larger brain cases than their cousins, Homo habilis.

Homo rudolfensis used their enhanced mental capabilities to find higher quality plant materials that hid underground, like roots, bulbs and corms, and to dig them out of the ground with sharpened digging sticks and stone tools.  Moreover, they most likely pounded the tough plant materials and cut them into pieces to make them easier to chew.

Still, Homo rudolfensis as well as the later Homo habilis were a dead-end street of evolution.  They became extinct when the African climate continued to dry and the foods they relied on became unavailable in the places where they lived.  Later members of the Homo clade were better able to cope with the changing climate of Africa, and further evolution of the Homo clade involved evolution of more resilient feet, longer legs and shorter arms, all of which helped their descendants to travel long distances.  Their evolution also involved adaptation of their hands and shoulders that made it easier for their descendants to make and use tools and weapons.  Their brain sizes also increased as controls on proliferation of neurons were loosened.  Surprisingly, molar sizes decreased steadily over the course of the next two million years, even though the early members of the Homo clade often relied on the uncooked starches that they obtained from eating the underground parts of plants.

Bone choppers

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The bones of freshly killed animals presented a special problem for Homo habilis, because the bones were not brittle, like those that their ancestors had found lying about in Eurasia.  And when Homo habilishit a fresh bone with a hammerstone it would splinter badly, and the tiny splinters in the marrow were not good for the stomach.  Homo habilis responded to this problem by inventing bone choppers.

The first bone choppers were probably invented accidentally when Homo habilisremoved chips from one edge of a rock.  As they did this, the edge would be whittled down until it was sharp.  Then, if this sharp edge was struck against a large bone so as to put a dent in it, the bone could then be broken at that point without splintering it badly.

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Later hominins who were more closely related to ourselves than Homo habilis, either copied the design or reinvented bone choppers, and then went on to invent hand axes, which were good for efficiently butchering very large beasts.  This shows that later members of the Homo clade must have at least occasionally claimed carcasses of very large herbivores before the flesh had been completely stripped from the bones.