The Evolution of Humans: Characteristics & Evolutionary History

Summary

Primates are mammals with: Forward-looking eyes Hands and feet that can grasp Large brains Complex social behaviors We looked at a variety of primates, including Old World and New World primates. Old World primates live in Asia and Africa, while New World primates live in South America. The hominoids evolved from Old World primates and include humans, gibbons, and chimpanzees. Humans are different from other primates in that we: Walk on two feet rather than four Are capable of language and symbolic thought Can make and use complex tools Humans have an extensive evolutionary history, and scientists have identified more than twenty different human-like ancestors. We looked at a few specific examples of these ancestors, including: Lucy - an Australopithecus Homo habilis - the first member of our genus Homo Homo erectus - the first human ancestor to move out of Africa Homo sapiens While humans are unique among animals, remember that they too have a vast evolutionary history.

Evolution of Humans

Scientists continue to learn more about the evolution of humans and our hominoid ancestors. Currently, more than twenty different species of extinct hominins closely related to humans have been identified. Hominins are hominoids that are related to humans. The oldest distinct hominin is around 6-7 million years old. We won't look at all of these human ancestors but will rather highlight a few distinctive species. Let's first look at Australopithecus. This hominin lived about two to four million years ago, was bipedal, and had human-like hands and teeth but a small brain. Australopithecus increased the diversity of hominins. You may be familiar with an example of this human ancestor already. The infamous Lucy, discovered in Ethiopia in 1974, is a prime example of Australopithecus. More recent human ancestors belong to our same genus - Homo - indicating a closer genetic relationship. The first known member of our genus was Homo habilis. This ancestor lived 1.6-2.4 million years ago and was called 'handy-man' because of the evidence of advanced tool use. There is some overlap as to when Homo habilis and Homo erectus lived. Homo Erectus and Homo Habilis Homo erectus was the first hominin to move out of Africa and lived 200,000 to 1.8 million years ago. You may have noticed that the time frames between Homo habilis and Homo erectus overlap. This is because of the dating of the fossils and because there is definitive evidence that several human ancestral species lived at the same time. The evolution of humans isn't a straight line from one species to the next, but rather it contains several branches and even some dead ends. One example of an evolutionary dead-end is seen in Neanderthals. These individuals were very similar to humans in both physical and social structure but are genetically different. Neanderthals lived 30,000 to 200,000 years ago but went extinct. Map showing when humans migrated out of Africa to different regions Human Migration Homo sapiens are humans. The oldest human fossils are 160,000-195,000 years old. Our ancestors originated in Africa and then migrated elsewhere around 50,000 years ago. Scientists have specifically studied mutations on the Y chromosome - which all males have - to trace the migration out of Africa and into other specific areas of the world.

Evolution of Primates

The earliest primates lived in trees. They used their hands and feet - both capable of grasping - to move between and among trees using the branches and vines. Some also had tails to help maintain balance. A living organism that most closely resembles these early primates is the lemur. These early primates separated into two groups with distinctively different patterns of evolution. The Old World primates reside in Africa and Asia, while the New World primates reside in South America. Examples of hominoids Hominoid Examples The hominoids, a group of primates including gibbons, orangutans, gorillas, chimpanzees, bonobos, and humans, began to evolve from an Old World ancestor about 20-25 million years ago. Unlike other primates, such as lemurs and spider monkeys, these hominoids have long arms but short legs and do not have tails.

Characteristics of Primates

We humans are a very distinct group of animals. However, there are many characteristics that we share with our primate relatives. Primates are mammals with: Forward-looking eyes Hands and feet capable of grasping Large brains Complex social behaviors The forward-looking eyes, rather than having eyes spaced out to have improved peripheral vision, allow for increased depth perception. The complex social behavior varies greatly within primates, but a common feature among all primates is good prenatal care and care for the young. Another similarity is having fingernails rather than claws such as those that other mammals, like cats and bears, have. All primates also have fingerprints due to small ridges on their fingers.

Characteristics of Humans

We started by looking at the characteristics of primates and a brief overview of their evolution, but let's now specifically look at the characteristics and then the evolution of humans. Humans are bipedal primates that are capable of language, symbolic thought, and both the creation and use of complex tools. 'Bipedal' means 'walking on two feet.' Most of our primate relatives are quadrupeds, meaning they walk on four feet. Humans stand upright and walk on just two feet. One difference between humans and other primates is that humans have smaller jawbones. Human Jaws Humans also have proportionally larger brains than other primates. This increased brain size allows for complex language, symbolism, and creativity. While other primates are capable of using simple tools - such as using a twig to get ants out of an ant hole - humans are able to create and use complex tools, such as cars and computers. Other notable differences between humans and other primates are that humans have drastically smaller jaw bones and jaw muscles due to differences in dietary habits. Humans also have shorter digestive tracts than other primates because of the food that we eat.