Lecture 36—Human Evolution

The lecture gives an overview of the origin of Homo sapiens, the migration out of Africa into the rest of the world, and it evolution into the different “races.”

The human line split from the Chimp/Bonobo line ~ 7MYA, leading to two major lines, the Austalopithicine group and the gracile line which led to Homo habilis, H. erectus, H. neanderthalensis, and H. sapiens.Modern humans and chimpanzees have >98% similar DNA.

Key features of humans include their primate hand, bipedal locomotion, brain enlargement, tool use, fire, language are all important to human domination of the world.

Humans are not the only tool users; others include chimpanzees, crows, and sea otters. Communication via sound is not limited to humans either for chimpanzees and some monkeys have several different vocalizations for different signals. But these are paltry in comparison to human tools use and communication skills.

The origin of humans is in Africa. This is where the earliest fossils are found. This is where the greatest genetic diversity occurs. The earliest hominid to leave Africa was H. erectusin 1.7MYA and they spread over Europe and Asia. Later >450,000 YA a more advanced group of Homo left Africa entering into Europe and the Middle East and became H. neanderthalensis. Still later another group, Homo sapiens,left Africa 40,000 and spread throughout the world. Homo erectusand H. neanderthalensis became extinct during these interactions leaving H. sapiens the sole hominid on earth.

Analysis of DNA suggests that most Europeans have 1-4% Neanderthal genes indicating that H. sapiens and H. neanderthalensis were interbreeding. Another human population, Denisovans, split from the Neanderthals 55,000 YA and lived in Eastern Euro-Asia and interbred with H. sapiens; as modern humans in that region have 4-6% Denisovan DNA.

H. sapiens first traveled from Asia via the Bering Strait into North American ~25,000-30,000 YA. They probably traveled along the western coast into Central and S. America.

“Races:” There are dozens of different human populations today with some anatomical and physiological distinctions. There is no clear cut way to identify such groups since the variety within such groups overlaps many other such groups. To call these groups distinct races seems inappropriate and carries strong negative connotations because of historical biases. Still there we can ask how such differences might arise. Many biologists and anthropologists are convinced that all such differences are adaptations by natural selection to the different environments the populations live in. Others surprisingly like Charles Darwin argue differently. Let’s suggest the possibilities:

  1. Natural Selection
  2. Sexual Selection
  3. Genetic Drift
  4. Pleiotropy

There are few cases of “racial” differences that seem to be an adaptation to the environment. Skin color is one of the few examples with any evidence. People with dark skin are more prevalent in the equatorial areas. Black skin pigment protects against sun burn and skin cancer. But in climates where there is less sunlight, dark skin is a disadvantage because a certain amount of UV radiation is necessary to form vitamin D in the skin. One can argue that as people moved from Africa into Europe with less sunlight, there was a selective pressure to decrease the skin melanin. Vitamin D is necessary for calcium metabolism and proper bone development. The disease Rickets found in inner cities with high pollution is an example of sunlight deficiency. So as human migration occurred to the north, light skin color was favored. That is why northern Europeans are white.

New human fossils are being discovered all of the time. One of the most unusual is a small 3-foot tall species discovered in Indonesia called Homo floresiensis. This dwarf species lived until 50,000 YA. There is great controversy who the ancestors are: H. sapiens? H. erectus?H. habilis?Or….?

Terms/Concepts to Define:

Homo habilis

Homo sapiens

Homo erectus

Homo neanderthalensis

Mitochondria Eve

Y chromosome Adam

Denisovans

Homo floresiensis

Can you answer these questions?

  1. Scientists state that when they compare the DNA of humans and chimpanzees that our genes are 98% similar, yet we really appear to be much more distinct than that—certainly behaviorally. How do we account for our differences?
  2. If humans and chimps are so similar, how do we account for the fact that humans have 46 chromosomes and chimps have 48?
  3. It has been claimed that humans are the only tool using animals. Evaluate this claim.
  4. It has been claimed that humans are the only animal that has a language. Evaluate this claim.
  5. Molecular biologists claim that all living humans have the same maternal ancestor who lived 170 MYA. What is their evidence and reasoning for this claim?
  6. Where did the Neanderthals come from in the evolutionary sequence and where did they go?
  7. Chimpanzees and other apes have white skin under their fur, yet Africans have black skin, how do evolutionists explain this?
  8. How are Denisovans related to other human species?
  9. How do anthropologists now explain how humans got to South America well before 18,500 YA, but Alaska and much of North America was mostly covered I glacial ice blocking their way?
  10. Discuss how anthropologists explain the distribution of skin pigment among humans.
  11. It is often noted that many Asians have different shaped eyes than Europeans. An adaptionist explanation for this is that this eye shape had an advantage in ancestors who lived in dusty conditions and the eye diameter (3-5mm) and epicanthic folds limited the entry of foreign particles. The evidence for this explanation is weak. What other possible non-adaptionist explanations can you give explaining them is some detail.
  12. Is there any evidence that humans left Africa before Homo erectus?