To the question why humans developed the upright gait, one could give a short answer, loosely borrowing from Clinton: “It’s the evolution, stupid!” But science doesn’t make it that easy, especially since there are no easy answers. It is not known exactly where the upright gait developed in our ancestors, nor when or why. One can only rely on interpretations of isolated skeletal finds and weigh up the theses of experts on early human history.
Until a few years ago, the school of thought was that walking upright was developed by the pre-human Australopithecus. It relied on the skeleton of Lucy, a representative named after the Beatles LSD song “Lucy in the Sky with Diamonds,” who is 3.18 million years old. Her fossilized bones indicated that she walked mostly on two legs, and that she must have fallen from a tree, her bones were so broken.
But in the family tree of early humans – researchers speak of the “family tree” because of the many branches – there are also earlier indications of bipedy. They lead to Greece, where footprints have been found indicating relatively modern foot architecture and predating Lucy by 2.5 million years.
Could walking on two legs occur several times and independently in evolutionary history? It would be possible, albeit “not very likely”, according to a paleoanthropologist Madelaine Boehme from the University of Tübingen says. She and her team pulled off a major coup three years ago, in research jargon: a paradigm shift. Fossils of a previously unknown primate species were discovered during excavations in a stream in the “Hammerschmiede” clay pit in Unterallgäu (Bavaria). The so-called Danuvius guggenmosi lived 11.62 million years ago and probably moved on two legs as well as climbing, according to the report in the journal “Nature”.
The researchers named the possible ancestor of humans and great apes Udo – after the German rock singer Udo Lindenberg, whose songs were played on the radio during the excavation. He is said to have been pleased about it.
what the bones say
How can you tell from old bones whether they were used for upright walking? by their shape. Since the feet now had to carry the entire body weight instead of reaching for branches, they were redesigned as soles with a cushioning arch. The great apes bowed their legs into an X, the pelvis had to be reshaped, and the spine had to form a double S shape to balance the skull. One thesis says that this change in the head made the growth of the brain possible in the first place. But that will only be part of the story, because the increasing use of tools by pre-humans and the development of language probably also contributed to this. But one thing is clear: In the beginning there was walking upright.
Udo, with his calculated live weight of 31 kilograms, will not have discussed the philosophy of the hand ax with his significantly lighter female. The two fed on plants and lived mostly in trees. They already had an S-shaped spine that allowed them to stay upright. According to Böhme’s co-author David Begun of the University of Toronto, “Danuvius combined hind-limb-dominated bipedalism with fore-limb-dominated climbing”.
This puts a thesis on the development of upright gait, which has been neglected up to now, in the spotlight: “bipedalism in adaptation to trees”, as Böhme says: “Up to now, this has not been seriously discussed, which is just beginning to change.”
on the behavior of Orangutans the thesis can be illustrated. When the primates move on thin branches in the tree canopy, they straighten up and relieve the thin branch by grabbing branches above their heads, seemingly walking upright.
So far, the assumption that upright gait developed because human ancestors were forced to climb down from trees and walk on the ground has been favored. This savannah theory assumes that the dense rainforests in the African Rift Valley changed to open grassland with isolated trees due to climate change. How does this fit in with the fact that chimpanzees build their roosting nests in both trees and the ground? The question of either/or is probably the wrong one. And perhaps the thesis that upright walking developed in the many river courses of the former rainforest, as the Berlin evolutionary biologist Carsten Niemitz suspects, also plays a role? Because it makes more sense to walk through nutrient-rich water on two legs than on all fours. Gorillas exhibit this behavior and also often use a stick for support.
Standing up hurts
Wherever the cradle of those who set out to explore the world on two feet stood, and who happened to successfully pass on their genes, people have bought this locomotion at a high price. The advantages of having your hands free for everything – tools or weapons, food and babies – are offset by the disadvantages of narrowing the birth canal, reduced ability to climb, varicose veins and lower back pain.
timeline
- 12 million years ago Udo, a representative of the extinct Danuvius ape genus, performed gymnastics through the treetops of the Allgäu – the bones of his hind legs show features that speak for bipedy.
- 6 million years ago representatives of the earliest human progenitors (Orrorin tugenensis) left 50 footprints on Crete, which became fossilized.
- 3 million years ago Australopithecus Lucy fell from a tree in East Africa and broke many bones. Their skeleton shows a clear expression of the upright gait.
- It’s been 300,000 yearsthat the modern biped (Homo sapiens) in Africa set out to go to Europe – on two legs.
Source: Nachrichten
