Human evolution

Homo sapiens is a special kind of primate, part of the hominid family that also includes the great apes. Over millions of years, humans developed important traits such as walking on two legs, using their hands skillfully, and speaking complex languages. Modern humans interbred with older human types, showing that human evolution did not happen in a straight line but more like a web.

Primates began to diverge from other mammals about million years ago, during a time called the Late Cretaceous period. Over time, different groups of primates evolved, leading to apes and eventually to hominids, which include humans. The lineage that led to humans split from chimpanzees and bonobos several million years ago. The genus Homo, to which modern humans belong, first appeared over two million years ago, with anatomically modern humans showing up in Africa around 300,000 years ago.

Before Homo

Main article: Australopithecus

For evolutionary history before primates, see Evolution of mammals, History of life, and Timeline of human evolution.

The story of primates begins around 65 million years ago. Early primates lived in places like North America, China, and Africa. Over millions of years, these early primates evolved into many different forms. Some moved to Africa and eventually led to the apes and humans we know today.

One important early primate was Plesiadapis, found in North America, and another was Archicebus from China. As time passed, primates spread across the world. Scientists believe that the ancestors of humans and African apes may have lived in Europe or Western Asia before moving to Africa.

Eventually, primates in Africa evolved into many groups, including lemurs, lorises, and the anthropoids, which include monkeys and apes. The earliest known catarrhine, a type of early ape, is Kamoyapithecus, found in Kenya and dating back to 24 million years ago.

Around 4 million years ago, a group of primates called Australopithecus appeared in Africa. These early human relatives walked on two legs and lived across the continent until about 2 million years ago. Different kinds of australopiths existed, such as A. anamensis, A. afarensis, and A. africanus. Some scientists think other species, like P. robustus and P. boisei, might belong to a different group called Paranthropus.

Evolution of genus Homo

Main article: Homo

The earliest known member of the genus Homo is the Ledi jaw, dated between 2.75 and 2.8 million years ago. This discovery shows early humans may have used stone tools. Around this time, the human SRGAP2 gene changed, which may have helped the brain develop faster.

Over the next million years, brain size increased quickly. By the time Homo erectus and Homo ergaster appeared, brain size had doubled. These early humans were the first to use fire and complex tools, and they were the first to leave Africa, spreading across Africa, Asia, and Europe.

Modern humans, Homo sapiens, likely evolved in Africa from earlier human species like H. heidelbergensis. Around 50,000 to 100,000 years ago, they migrated out of Africa. Along the way, they met and interbred with other human species like Neanderthals and Denisovans. This mixing left a small amount of their DNA in modern humans outside of Africa.

Homo sapiens is the only surviving species in the genus Homo. While some extinct Homo species may have been ancestors of modern humans, many were likely distant cousins. Scientists are still learning about how these early human species are related to each other.

Anatomical changes

Since Homo sapiens separated from its last common ancestor shared with chimpanzees, human evolution has included many important changes. These changes are in how the body looks, grows, works, behaves, and lives in the environment. Key adaptations include walking on two legs (bipedalism), a larger brain, longer time spent growing up, and less difference between males and females.

Walking on two legs, or bipedalism, was a major change. Early humans who could walk on two legs first appeared about 6 to 7 million years ago. Bipedalism freed the hands to carry things and allowed better balance and vision. It also changed the shape of the skeleton, including the legs, pelvis, and spine. As humans walked upright, the pelvis changed shape, which made childbirth more challenging due to the smaller birth canal.

Another big change was the increase in brain size. Modern humans have a brain about three times larger than that of a chimpanzee. This growth allowed for better problem-solving, learning, and language. The brain kept growing after birth, which meant human children needed more care and time to develop. This led to longer periods of dependency on parents and changes in how families and societies worked. The shape of the skull also changed to fit the larger brain, with parts of the brain linked to language and decision-making growing especially fast.

Use of tools

The use of tools is a sign of intelligence and may have helped shape human evolution, especially by allowing early humans to get more energy from food. It is thought that using tools put pressure on early humans to grow bigger brains, which use a lot of energy.

The oldest known tools are very simple stone pieces found in Kenya, dating back to about 3.3 million years ago. More advanced stone tools appeared in Ethiopia around 2.6 million years ago, known as Oldowan tools. These tools were likely made and used by early humans, and a special feature in the human hand helps us grip and use tools better than other apes.

See also: Hunting hypothesis

Transition to behavioral modernity

Further information: Behavioral modernity

Around 50,000 years ago, human culture began to change quickly. People started using new tools, making jewelry, and creating art like cave drawings. They began to hunt animals in clever ways and even traveled to new places far from home. These changes show that early humans were becoming more intelligent and creative.

Some scientists think these changes happened all at once, like a big step forward. Others believe they happened slowly over many thousands of years. Either way, this time period was very important for how humans live and think today.

Recent and ongoing human evolution

Main article: Recent human evolution

Human populations continue to evolve due to natural selection and genetic changes. Even today, humans are adapting to new environments and lifestyles. For example, people living at high altitudes, like Tibetans, have developed genetic changes that help them breathe better in thin air.

Evolution also happens because of diseases and changes in what we eat. Some people have genetic changes that protect them from malaria, while others can digest milk as adults due to changes in their genes. Cultural changes, like better healthcare and education, also influence how humans evolve, affecting everything from when people have children to how our brains develop.

History of study

The study of human evolution began with early scientists like Carl Linnaeus, who classified humans within a system that also included other animals. The idea that humans evolved from earlier ape-like ancestors became widely accepted after Charles Darwin published On the Origin of Species in 1859.

Fossil discoveries in the 20th century helped scientists understand the steps in human evolution. Important finds included the Taung Child, which showed traits linking apes and humans, and "Lucy," an early human ancestor from Ethiopia. These discoveries supported the idea that Africa was the birthplace of humanity. Later, genetic studies confirmed that modern humans originated in Africa and later spread around the world, mixing with other ancient human groups along the way.

Evidence

The evidence for human evolution comes from many areas of science. Traditionally, fossils have been the main source, but since the 1970s, studying DNA has become very important too. By looking at how living things develop and change over time, scientists learn about how all life, including humans, evolved.

Humans share close family ties with bonobos, chimpanzees, and gorillas. By comparing DNA, scientists found that human DNA is about 95% to 99% the same as chimpanzee DNA. Genetic tools help estimate when different species split from each other. For example, humans and chimpanzees split around 4 to 8 million years ago.

Fossils show the early steps of human evolution. Early human-like species such as Sahelanthropus and Orrorin lived around 7 million years ago. Later, australopithecines like Australopithecus afarensis (known from the famous “Lucy” fossil) appeared about 4 million years ago. The genus Homo began with Homo habilis around 2.8 million years ago, who made simple stone tools. By about 1.9 million years ago, Homo erectus evolved, with a larger brain, and was the first human-like species to leave Africa.

Modern humans, Homo sapiens, appeared around 300,000 years ago in Africa. As they spread across the world, they met and sometimes interbred with other human species like Neanderthals. Today, most people outside Africa carry a small amount of Neanderthal DNA.

Species list

See also:

This list shows different species of humans in chronological order. Some names are well-known, while others are still being studied, especially within the genus Homo. For more details, you can explore the individual articles.