It was published in the journal Science. A huge brain, long legs, the capacity to make tools, and extended maturation periods were supposed to have evolved concurrently at the beginning of the Homo lineage when African grasslands expanded and the Earth's environment grew colder and drier. "These are all features that would have benefited early humans living in tropical climates," says Carbone. "They must have been adapted to some degree by our early ancestors."
But research since then has shown that these traits emerged one after another. The brain size increase happened first, followed by an increase in body size. This means that early humans were not adapted to a particular environment but instead inhabited different regions according to which trait was most important for survival. Brain size increased because it provided a fitness advantage for larger groups to compete more effectively for food and safety. Body size increased because bigger bodies can break down and use nutrients from food faster than smaller ones.
Early humans probably lived in small bands made up of their close relatives. They may have moved around frequently in search of food and protection from other humans or wild animals. There is evidence that some early humans used weapons to kill large animals for meat. But they also might have eaten small animals like mice and insects. As well as food, the environment our ancestors lived in offered protection from predators. If you looked out for big cats, you didn't need to look out for little dogs.
The aridity theory proposes that early hominids adapted to dry temperatures and developed as Africa's dry savannah areas spread. This theory suggests that they would have lived in small groups or even alone, seeking out new territories where they could find food and water. Based on this theory, it would be expected that early humans would have had a limited range of adaptive behaviors because any differences would have been due to individual choices rather than environmental requirements.
The availability theory is based on the idea that large brains are needed for surviving in environments with few resources. It proposes that early humans living in Africa's dry savannahs used their intelligence to find ways to survive, including by moving when conditions weren't favorable for growth or reproduction. According to this theory, there would have been selection for behaviors that helped individuals escape from poor environments but not for different adaptations for different circumstances because people would have used their intelligence to adapt to whatever life gave them.
The containment theory is based on the idea that large brains are required for social interactions. It proposes that early humans lived in communities where the young were protected by adults and where everyone contributed something useful to the group. This theory suggests that there would have been selective pressure to behave in certain ways - for example, not to act aggressively toward others in order to keep communal connections.
Early people were well suited to a variety of climates and flora kinds. And the species under study, Australopithecus afarensis, adapted to these drastic environmental shifts without the benefit of a larger brain or stone tools, which subsequent hominins relied on to adapt to their habitats. Rather, they used their muscles and teeth to obtain food when it was available and appropriate, then left it in the search for more nutritious fare.
They did this by exploring their surroundings with every sense available to them. The ancient landscapes they inhabited offered evidence of past events that could be understood only through observation. Auspicious landmarks might have served as markers for future travel routes, while dangerous obstacles could have been avoided on the way to find foods with more vitamins and minerals.
People also learned how to adapt by listening to their bodies. If one region of land was not suitable for food gathering, people would move on. This is called "geographic mobility" and is still important today in cases where individuals or groups need new opportunities for survival.
Finally, people adapted by copying others who were better at finding food or avoiding danger. They observed the behaviors of those around them and tried to emulate these actions if they found them useful. This is why we see similar types of fossils from different locations all over the world - because early people copied other early people who had done so before them.
Their adaptable diet, which most likely included meat, was facilitated by stone tool-assisted foraging, which allowed our forefathers to utilize a variety of resources. The scientists found that this adaptability likely aided our ancestors' capacity to effectively adapt to uncertain conditions and disperse beyond Africa.
Early humans were not passive observers of their environment; instead, they actively participated in it by foraging for food, avoiding predators, and building shelters. This active involvement with their surroundings led to an effective adaptation to any given situation. For example, when our ancient ancestors came across a new habitat (i.e., one without any natural resources) they would have had to rely on their intelligence to find something worth hunting or gathering. If they failed to do so, they would have perished.
Our early human ancestors were not perfect in their dealings with nature; they made mistakes and sometimes went too far when searching for food or avoiding predators. However, their ability to adapt quickly to changing circumstances enabled them to survive and flourish.
Humans discovered that they could regulate the development and reproduction of some plants and animals. This finding resulted in farming and animal herding, which reshaped Earth's natural landscapes—first locally, then worldwide. Humans were more settled as they engaged more time in food production. They also began to trade with one another and build cities, which increased their impact even further.
People have always needed food, so it makes sense that they would want to grow it themselves instead of going to great lengths to hunt and trap it. With enough effort, you can grow almost anything: fruit, vegetables, grains. And since farmers know which parts of plants are most useful, they can concentrate their efforts on developing those areas. Over time, this leads to greater productivity and less waste.
In addition to growing their own food, people started raising livestock for meat and milk as well. Again, there is a trend toward greater efficiency over time. Farmers learn which animals tend to produce more money per unit of time and feedstuff; they will usually pick these animals and breed them repeatedly until they find ones that produce more income or lower costs per unit of weight or size. This is how cattle, pigs, and goats became smaller but more profitable over time.
Finally, humans began hunting wild animals for sport and practice.