Humans are the most lethal predators. From primarily vegetarian ancestors, humans might have developed some traits as adaptation to hunting.
When with climate change forests full of fruit and young leaves were replaced by grassland in Africa about three million years ago, some early hominins like robust australopithecines developed large jaws to grind tougher plant foods. They went extinct two million years later for unknown reasons. Homo included more animal foods as a substitute, and the lineage survived.
About two million years ago, they became good endurance runners, but bipedality did not allow them to become better sprinters than quadrupeds, including large predators of that time like sabertooth cats. Human ancestors could not hide from them on trees and needed to move longer distances to find food.
Physiological changes like sweating co-developed as a cooling system to prevent overheating. The upper body physique changed to allow wider movements for activities like throwing, to the detriment of the ability to climb trees. Longer and more flexible waist, side-facing shoulder socket, and less twisted upper arm still distinguish humans from other apes like chimps. Fossil records suggest that the change in shoulders happened about two million years ago in Homo erectus, and the other features even earlier in other hominins. This trait was probably naturally selected to facilitate upright position by walking among other reasons, but later used in activities like hunting. Modern humans can still throw objects well.
Early evidence of butchering animals was found in East Africa and Germany. Remains of large mammals, scavenged or hunted for high-caloric tissues, and wooden spears were dated back about two million years. It is hard to distinguish the skeleton parts of hunted animals and found carcasses, and from those corpses stolen from predators after attack. One suggestion supporting hunting provided by studying the mortality profile of the bones. Carnivores like lions tend to kill older animals of a herd. On one site in Tanzania though, analysis of the large assemblage of carcasses showed that they were at the prime age at time of killing. This pattern resembles the one of the prey of modern Hadza. Homo had not invented projectile weapons like arrows and bows at that stage of evolution, but might have organized ambush hunts. Evidence from Kenya also suggests persistent carnivory along with plant eating in some early Hominins.
Human brains have doubled in size since then. Self-control and division of labor between sexes helped humans to colonize the Earth.
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