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Human Origins

Common argument against human evolution… If we evolved from chimpanzees, how are there still chimpanzees!?

Human Characteristics What makes us human? As with all species, humans have a number of evolved characteristics In our own way we have become enormously successful and have come to thrive in many environments

What are some human traits?

Human Characteristics What are some of those traits? High-functioning mental facilities Ability to perform complex reasoning Exceptional ability to learn Use and make sophisticated tools Communicate with complex language

Human Characteristics What are some of those traits? Physical characteristics: Large brain relative to body size Hands capable of fine manipulation and coordination Walk upright, allowing hands to use tools

What about other species? Other species have some of these characteristics But we are unique in two regards We have all, not some, of these traits We have evolved these traits to a higher degree than other species

Primates Humans are members of the primate family Primate: A group of mammals with relatively large-brains, forward-facing eyes, and flexible hands

Primates Other members of the primate family include gorillas, chimanzees, orangutans, monkeys, gibbons, and lemurs All primates share a common ancestor dating 60-70 millions years ago

Human Phylogeny

Human Phylogeny Early on, the prosimians and the anthropoids split Prosimians: A number of relatively small nocturnal members of the primate family, including lemurs Anthropoids: The group of primates including monkeys, apes, and humans

Continental Drift Early primates lived in areas that would become Africa, India, and South America 60-70 million years ago, South America was separating from Africa and India This split led to a division in the early ancestors of monkeys

Human Phylogeny

How are apes different than monkeys? Do not have a tail Divided into 2 branches: Lesser apes Great Apes All are fairly similar genetically

Genetic Similarities All great apes have very similar genetic make-up Chimpanzees are the closest relatives of humans: 98.8% of DNA is shared (identical) Both differ from gorillas by about 1.6%

Planet of the Apes Humans are great apes Both genetically and physically, we share a lot of similarities with other great apes Does this mean that we descended from apes? No. It is more correct to say that we descended from the same ancestors as modern apes

We didn’t evolve from chimpanzees We didn’t evolve from chimpanzees! We evolved from a common ancestor that also gave rise to chimpanzees!

Common Ancestry Our most recent shared ancestor with chimpanzees existed about 6 million years ago Our more recent ancestors form an evolutionary branch known as hominids Hominids: all species descended from the most recent common ancestor of humans and chimpanzees that are on the human side of the lineage

Human Phylogeny

The Hominid Fossil Record Hominid fossils help trace the steps in human evolution Skulls can be measured to determine brain size Leg bones can be examined for evidence of bipedalism

A Map of Our Past

Bipedalism Bipedalism: The ability to walk upright, on two legs The Laetoli footprints provide evidence that out ancestors were bipedal 3.6 million years ago

Tools Hominid tools have also been discovered in the fossil record The first evidence of tool use dates to 3.4 million years ago By 2 million years ago, tools were being used by a more recent ancestor, Homo habilis

Cooking The first evidence of cooking dates comes from hearths dating back to 790 000 years ago This would have reduced the chance of disease from eating raw food

Evidence for Brain Growth We see a large increase in brain size from fossils dating between 800 000 and 200 000 years ago The proposed most recent ancestor of humans, Homo heidelbergensis arose at this time

Homo heidelbergensis Both Homo sapiens and Homo neanderthalensis, or neanderthals, likely descended from this species The first modern humans, Homo sapiens had evolved by about 100 000 years ago in East Africa

The Big Picture The hominid fossil record contains more than 20 species currently Not all are proposed to be ancestors of humans The precise relationships among hominids is still being worked out Each new fossil discovery adds to the story

Neanderthals Homo neanderthalensis Now extinct Lived at the same time as Homo sapiens until they went extinct Homo sapiens and Homo neanderthalensis show only a 0.15% difference in DNA Why did they go extinct?

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