Scientists explain why monkeys and apes still exist if humans evolved from primates

A widespread public misconception holds that evolution is a single line of progress from "primitive" apes to modern humans, and that modern monkeys should therefore have disappeared. Science rejects that view: humans did not evolve from the species of monkeys and apes alive today, experts say, but share common ancestors from which different lineages diverged millions of years ago.

"Think of the evolutionary process as tree-like. All living species are at the tips of the branches," said Professor Ruth Mace of University College London. "Humans and monkeys are on branches that separated at some point. Both branches still exist." Modern humans' closest living relatives are chimpanzees and bonobos, with which scientists estimate we share roughly 98 to 99 percent of our DNA; that similarity reflects a relatively recent split from a last common ancestor rather than direct descent from those species.

Anthropologists place the divergence between the lineage that led to modern chimpanzees and bonobos and the lineage that led to Homo sapiens at roughly six to 10 million years ago. Since that split, each branch has followed its own evolutionary path shaped by ecological conditions, diet, social organization and chance genetic changes. Many branches on the wider hominin tree, including Neanderthals and other archaic human species, ended without giving rise to modern humans; they represent separate twigs on a branching bush, not earlier rungs on a ladder.

Experts emphasize that natural selection does not aim for a particular end point such as greater intelligence or "human-like" traits. The traits that confer success are those suited to local environments and lifestyles. "If you live in the rainforest in groups of primates that mostly eat plant matter, then the kind of intelligence you need is not necessarily the same kind of intelligence you need if you are a carnivore who needs to hunt large prey in groups on the savannah," Mace said.

Dr. John Rowan, an assistant professor of human evolution at the University of Cambridge, noted that other primates are well adapted to their niches and that human traits are not inherently superior in every context. "Chimpanzees and bonobos do very well in their respective niches," he said, and asked rhetorically why humans have not evolved to be more like bonobos, which show lower levels of large-scale intergroup violence. "It’s often assumed that the human version of a trait must be the ‘best,’ but that’s almost never the case."

The differences in cognitive and social capacities between humans and other primates therefore reflect different evolutionary pressures. Human ancestors experienced selective forces that favored increased cooperation, tool use and complex cultural transmission—traits that proved advantageous in changing climates and open environments. Other primate lineages continued to thrive with adaptations better suited to forested habitats, frugivory or other ecological roles; high cognitive complexity of a human kind would not necessarily improve their fitness.

Scientists also address a common popular question about the future: could monkeys or apes evolve into human-like beings? Some researchers allow that, over very long timescales and under particular environmental pressures, convergent evolution could produce organisms with greater intelligence or social behaviours reminiscent of humans. "Every mutation happens by chance, but if species live in similar environments, there are plenty of examples of convergent evolution," Mace said. Dr. Edwin de Jager of the University of Cambridge cautioned that any such descendants would not be ‘‘humans’’ but rather novel species shaped by different starting conditions: "Evolution doesn’t repeat itself exactly."

The broad timeline of primate and hominin evolution spans tens of millions of years. Primitive primates first appear in the fossil record more than 50 million years ago. The great ape family (Hominidae) diverged later, with gorilla, chimpanzee and human lineages separating at different times. Early hominins such as Ardipithecus and the australopithecines emerged several million years ago, followed by successive Homo species including Homo habilis and Homo erectus. Control of fire, the manufacture of stone tools, and increases in brain size appear at various points over the last two million years, and anatomically modern Homo sapiens are thought to have arisen in Africa roughly 300,000 years ago before spreading beyond the continent tens of thousands of years later.

Scientists say correcting the ladder-of-life perception matters for public understanding of evolution and biodiversity. Viewing evolution as a branching process highlights that many contemporary species are not "left behind" but are successful adaptations to particular environments. That framing also underscores that evolutionary change is driven by context-specific selection pressures rather than a single, directional march toward a human ideal.