Bipedalism#Humans

As savanna hypothesis, the assumption is referred to, the evolution of Hominini of ape-like tree dwellers to the upright-walking species of the genus Homo is thus came million years ago, around 7 to 8 in the transition that the then still living in forests, quadrupedal ancestors of modern people moved their habitat in open, treeless savannas and gradually developed there getting around on two legs.

The savanna hypothesis is now regarded as disproved. State of research is that the early Hominini could walk upright in the sense of preadaptation already hundreds of thousands of years before the settlement of savannas.

Another view is reflected in the water monkey theory.

Broad

After this savanna hypothesis (also called " free- hypothesis "), and left the ancestors of today's people for a time dry climate of declining rainforests and went - in terms of their habitat today steppe baboons comparable - to life on the ground over. In this way, ultimately the characteristics of the people would arise:

• Upright gait, in order to have a better overview in the grasslands, similar to the ostrich. In addition, this has freed the hands for carrying.
• High magnification of the brain as a later adaptation to a hunting lifestyle.
• Loss of hair to dissipate heat by sweating better.

History

Already Charles Darwin conducted by comparing the African apes to man - long before the discovery of African Australopithecus fossils - a creation of the people of Africa from. The early human ancestors through changes in lifestyle or the environment less arboreal ( "less arboreal " ) become. This had led to bipedal locomotion, which have facilitated the use of hands for transporting objects and how to use tools.

1925 Raymond Dart described the " Taung Child ", the hitherto oldest specimen of a human ancestors. Because of this locality to Australopithecus africanus fossils belonging after former doctrine for millions of years was not wooded, emerged from this assessment, the savanna hypothesis. During the forest as a habitat, so darts, a simple foraging enabled, the open habitat requires intelligence and skill have.

During the following decades, the savannah hypothesis widespread, especially in the popular scientific literature. A critical scientific work-up was, however was also in anthropology largely consensus on this model.

Objection

The savanna hypothesis was based primarily on the findings of early types of Hominini were made mainly in savanna areas and that the existence of savannas was assumed as a landscape form during the lifetime of the fossils. However, this has turned out to be an error of judgment. In addition, no analog adjustments in other monkey species were detected that inhabit similar habitat: All kinds of monkeys the savannas and other open terrain move on four legs ( quadruped ) on. This is also true for species that feed partly predatory. Mammals of the savanna are also densely hairy in most cases; The only exceptions are rhinos and elephants, but which have a significantly higher body volume compared to the body surface. Therefore, the savannah hypothesis is now considered outdated.

Paleoclimate, South Africa more accurately - From the 1970s the then still living in South Africa, later teaching at Yale University Elisabeth Vrba examined for the first time - in particular with reference to the fossil fauna. She found out that the climate in South Africa dramatically changed before 2.5 to 2 million years ago. Worldwide cooled the climate, Africa became drier. Changes were also recorded for Tanzania, Kenya and Ethiopia. First cooling and drying out are already 5 million years ago to notice at the Miocene - Pliocene boundary. Vrba sees climate change 2.5 million years ago a possible selection pressure for adaptive radiation ( Vrba 1993: explosive radiation ) led. For a falsifiability was the first time possible in the long history of the savanna hypothesis.

Just one year later, in 1994, but showed John D. Kingston, Andrew Hill and Bruno D. Marino ( Yale and Harvard ) based on carbon isotope studies after that it's in the virtues Hills, Kenya, within the last 15 5 million years ago there were no noticeable shifts between C3 plants and C4 plants. As for forests C3 plants are typical, while grasslands are characterized by a higher proportion of C4 plants, there might have been no dramatic change of habitat from forest to savannah. Accordingly, Kingston, Hill and Marino concluded: When the Hominini developed in East Africa in the late Miocene, the environmental conditions were assumed different from the savanna hypothesis.

Recent finds of early Australopithecus fossils were further doubt on the savannah hypothesis arise as associated finds other vertebrate species consistently pointed to a habitat that consisted mainly of open woodland and gallery forests. Thus, discoveries of Australopithecus afarensis from Hadar were in a heavily wooded context in the environment of waters. Australopithecus bahrelghazali, which was discovered at the site KT 12 in Chad, lived in a riparian forest -like habitat. The oldest of 4.4 million years of meaningful findings, Ardipithecus ramidus was together with typical forest-dwelling Slim and colobus monkeys and pollen of a mixed forest habitat found, and even for Sahelanthropus tchadensis of the reference TM 266 was a forested habitat between a sandy desert and a large lake reconstructed.

A reconstruction of the climatic conditions in Africa results, according to Friedemann Schrenk according to current knowledge, the following course of evolution:

• Already million 30 years ago did the first apes in the African rain forests; some populations spread million 15 years ago to Asia and Europe.
• Geological processes associated with the formation of the Rift Valley led, starting about 10 million years ago, to climate change, which resulted in the vast rain forests were replaced by wooded savannah and scrubland.
• Before about 8 million years ago, "when the climatic conditions in the late Miocene by increasing drought continues to deteriorate, some ape populations found themselves on the eastern periphery of the rainforest along the food-rich riparian zones in the rain shadow of the developing Rift Valley. " On edge of the tropical rain forest had then separated the line of development of Hominini from that of other apes.
• The leading to the Hominini individuals have Friedemann Schrenk According to " experimenting with locomotion on the ground"; walking upright had - " with a suitable hand over hand to the body structure " - developed because "the way from tree to tree apparently traveled on the ground" was. Although such behavior in other ( still living ) could be observed apes: " Ardipithecus ramidus was evident here, however the most successful. "
• The of Ardipithecus ramidus known body construction, the associated finds tactics involved a varied landscape of forests, thickets, wetlands and savannah -like areas, so could have been the starting point for the development of bipedal - climbing locomotion of Australopithecus. Just two million years later, when in fact the savannah areas were settled, the already developed in sparse forests bipedalism proved beneficial for the overviews of large areas and for carrying loads.

" Delicate " and " robust" Australopithecus species

The branching of an upright-walking Australopithecus representative of the group, to " gracile " and " robust" Australopithecus species is now interpreted as a consequence of climate change million years ago from 2.5 to 2 in southern Africa and with the then there actually incurred open brought savannah in conjunction.