What the question actually asks
Humans did not evolve from chimpanzees. Humans and chimpanzees, along with bonobos, share a common ancestor that lived millions of years ago, and the two lineages have been diverging ever since. Most estimates from genetics and fossils place the split somewhere in the range of roughly six to eight million years ago, though the exact figure is debated and depends on assumptions about mutation rates.
The group that includes modern humans and all of our extinct relatives since that split is called the hominins. Scientists reconstruct their story from two kinds of evidence, which together are far more informative than either alone.
Fossils: bones, teeth and tools
Fossils give direct physical evidence of anatomy: skull shape, brain volume, tooth size, limb proportions and the structure of the pelvis and feet. They are rare, since the conditions that preserve bone are unusual. The details of fossil formation explain why the record is patchy and why many finds come from places where sediments buried remains quickly, such as caves and river basins. Dating methods, including measuring radioactive decay in volcanic layers near a find, add time estimates, usually with margins of error.
Stone tools, butchered animal bones and, much later, art and burials record behavior as well as anatomy.
A sketch of the main chapters
The following is a simplified outline. Dates are approximate, and new finds regularly adjust them.
- Early hominins (perhaps six to seven million years ago and later): A handful of fossils from Africa show features suggesting a shift toward walking upright on two legs, such as the position of the opening at the base of the skull. Interpretations of the very oldest remains are still debated.
- Australopiths (roughly four to two million years ago): These small-brained, upright-walking hominins lived in Africa. Well-known examples include the partial skeleton nicknamed Lucy, from around three million years ago. They may have combined walking on the ground with climbing.
- Early Homo (starting roughly two to three million years ago): Larger brains, smaller teeth and the first clear stone tool traditions appear around this period. Which fossils count as the first member of our genus is debated.
- Homo erectus and relatives (from about two million years ago): With body proportions closer to our own, this group spread out of Africa into parts of Asia and, in some form, Europe. They persisted for a very long time.
- Neanderthals, Denisovans and others: In later periods several human groups lived at once. Neanderthals lived mainly in Europe and western Asia, while Denisovans are known mostly from a small number of fossils and DNA from Asia.
- Homo sapiens: The oldest fossils generally assigned to our species come from Africa, with some dated to roughly 300,000 years ago. Features typical of modern humans appeared gradually rather than all at once, and the details remain under study.
Why it looks more like a bush than a ladder
Popular images show a single line of progress from ape to human. The actual record points to many branches, with several hominin species often living at the same time. Some branches left no descendants. Because the fossil record is sparse, researchers disagree about which species were direct ancestors and which were side branches or cousins.
What genetics added
Comparing DNA across living people and other primates shows how closely related humans are to chimpanzees and helps estimate when lineages split. Methods for recovering DNA from ancient bones have also allowed scientists to compare modern people with Neanderthals and Denisovans.
These studies suggest that people whose ancestry lies outside Africa today typically carry a small percentage of Neanderthal DNA, and some populations also carry DNA from Denisovans. That means our ancestors interbred with these groups. Genetics has also been used to study migrations and to look for genes that changed under natural selection. Modern medical genetics draws on much of the same toolkit, though with different goals.
Genetic dating is not a stopwatch. It depends on estimated mutation rates and generation times, which are themselves refined over time.
Brains, diet and the long view
Brain volume grew substantially over the course of hominin history, though not in a straight line. Researchers link it to factors such as diet, social living and tool use, but the relative importance of each is argued over. The topic of brain size evolution is a large field of its own.
Later, around the end of the last glacial period and afterward, people in several parts of the world began domesticating plants and animals. Early farming changed diets, population sizes and disease patterns, and it is part of the human story too, although it is a very recent chapter in evolutionary terms.
What remains uncertain
Open questions include the identity of the earliest hominins, how many species there were, exactly how Homo sapiens emerged across Africa, and how often different groups met and mixed. Each year, new fossils and new methods tend to refine or overturn parts of the picture. A safe way to read any single date in this field is as the current best estimate, not a final answer.