The search for human origins is full of mistery! How did we adapt? What did we change and what is hardwired ?
The story of human evolution began in Africa about six million years ago and it describes the very long process that our ancestors went through to ultimately become modern humans. This process has been uncovered by studying fossils and understanding the underlying theory of evolution, and while new fossils are uncovered every decade revealing new chapters, scientists agree about the basic story. Evolution means the changes that occur in a population over time. In this definition, a “population” means a group of the same species that share a specific location and habitat. Evolutionary changes always occur on the genetic level. In other words, evolution is a process that results in changes that are passed on or inherited from generation to generation. When successful, these genetic changes or adaptations, which happen when genes mutate and/or combine in different ways during reproduction, help organisms survive, reproduce, and raise offspring. Some individuals inherit characteristics that make them more successful at surviving and having babies. These advantageous characteristics tend to appear more frequently in the population (because those individuals with less advantageous characteristics are more likely to die without reproducing), and over time these changes become common throughout that population, ultimately leading to new species. Since scientists developed the ability to decode the genome and compare the genetic makeup of species, some people have been stunned to learn that about 98.5% of the genes in people and chimpanzees are identical. This finding means chimps are the closest living biological relatives to humans, but it does not mean that humans evolved from chimps. What it does indicate is that humans share a common ancestor with modern African apes (i.e., gorillas and chimpanzees), making us very, very distant cousins. We are therefore related to these other living primates, but we did not descend from them.
Modern humans differ from apes in many significant ways. Human brains are larger and more complex; people have elaborate forms of communication and culture; and people habitually walk upright, can manipulate very small objects, and can speak.
Most scientists believe our common ancestor existed 5 to 8 million years ago. Then two species broke off into separate lineages, one ultimately evolving into gorillas and chimps, the other evolving into early humans called hominids. In the millions of years that followed, at least a dozen different species of humanlike creatures have existed, reflected in the fossil discoveries of paleoanthropologists, although many of these species are close relatives but not actual ancestors of modern humans.
The genus Homo first evolved at least 2.3 million to 2.5 million years ago. The most significant difference between members of this genus and australopiths, with which they overlapped, was their significantly larger brains (about 30 percent larger, though still small compared to modern humans).
The final transition, from the middle to late periods, happened about 200,000 years ago. Late Homo species, including Neanderthals and Homo sapiens, evolved large and complex brains, leading eventually to language, and developed culture as an increasingly important aspect of human life.
Humans have existed for only a tiny fraction of Earth’s history. Scientists believe Earth itself is approximately 4.55 billion years old. The oldest known fossils are about 3.5 billion years old, although some scientists have discovered evidence that life may have begun nearly 4 billion years ago. Dinosaurs walked Earth between 230 and 65 million years ago. The oldest known humanlike fossil has been dated at 4.4 million years old, although another species, not yet confirmed as a hominid, has been dated at about 6 million years old. As mentioned earlier, scientists estimate that the earliest hominid species diverged from the ape lineage between 5 and 8 million years ago. And yet, the species to which we belong, Homo sapiens sapiens, is only about 40,000 years old.