# Lecture 12: Homo sapiens

﻿$\star$﻿ ya = years ago

### Anatomically Modern Humans

#### Time and Place

• 200,000ya in Africa
• 120,000ya in Near East/West Asia
• 40,000ya in Europe and East Asia
• 40,000 or 15,000ya in Australia to the present

• Morphological Characteristics ﻿$\rightarrow$﻿ Distinct chin, round skull, flat vertical face, a higher forehead, pyramidal mastoid process, are generally less robust and have thinner brow ridges.

### What is a Species?

• Speciation ﻿$\rightarrow$﻿ The process of separation into a new species, often based on geological isolation.
• Biological species ﻿$\rightarrow$﻿ Populations that can interbreed with each other and produce fertile offspring.
• Paleospecies ﻿$\rightarrow$﻿ Species defined by fossil evidence from a long time ago, who may or may not interbreed. They look so different that we say that they're a different species. They most likely interbred once before.

### What Happened with the Homo line?

• Top model ﻿$\rightarrow$﻿ Shows the gradual process of evolution. There is an early group of Homo, some go extinct. Homo erectus branches out and eventually becomes early Homo heidelbergenis. Neanderthals split off from later heidelbergenis.
• Bottom model ﻿$\rightarrow$﻿ Shows each group as a separate species, where there is a rapid evolutionary change through transitional species which are not yet discovered.

### Transition Models - Process of Evolution from Premoderns to Homo sapiens

#### Regional continuity - multi-regional evolution model

• Only uses fossil evidence, no DNA data.
• An idea that some populations of premoderns in Africa, Asia and Europe all evolved into Homo sapiens.
• There has to have been significant interbreeding between premoderns and moderns, and significant interbreeding across all regions or this model to hold true.
• States that premoderns and moderns are all a single biological species since they can interbreed, so all the groups should be called Homo sapiens. (Archaic and modern Homo sapiens).
• This model doesn't seem to fit, so isn't widely used anymore.

#### Complete replacement model

• Proposes that every species before premoderns arose in Africa, expect neanderthals and modern humans, and that no other evolutionary transitions happen outside of Africa.
• Basically, that Homo sapiens evolve in Africa and migrate out. There was no interbreeding (or very little) between moderns and premoderns, just the replacement of species, so they are completely different species and have no connection.
• This is based on early DNA data which suggested the group went back to Africa.
• This model may hold true in some areas such as China, but current DNA data shows that there had to have been some interbreeding with neanderthals.

#### Partial replacement model

• Suggests that Homo sapiens evolve in Africa and migrate out. There is some interbreeding between premoderns and moderns, both locally and with new populations from Africa.
• Either there was minor interbreeding (mostly replacement of species) or significant interbreeding in some regions.
• Minor because both groups were Paleospecies, interbreeding in some time periods and not others.
• Overall, most of our ancestors are African, but not all of them. Low levels of Neanderthal DNA in modern humans supports this model.

### Types of Evidence

• Morphological/ Anatomical Evidence
• Dating of earliest finds.
• Transitional skeletons (ex. European neanderthals and moderns). Example ﻿$\rightarrow$﻿ Found a hybrid child skeleton, which suggests continued interbreeding of neanderthals and Homo sapiens.
• Dating problems and transitional skeletons in Asia and Australia.

#### Genetic Evidence

• Modern populations ﻿$\rightarrow$﻿ DNA studies: look at the mutation rate of DNA and find out when the populations separated, using mitochondrial DNA (mtDNA) from the mother, and nuclear DNA from both parents. There are problems with the data, since they have to use neutral DNA and have to have a large sample size.
• Ancient populations ﻿$\rightarrow$﻿ DNA studies. Evidence suggests that there was at least once in the past 80-50mya somewhere in the Middle East that these populations interbred. European neanderthals: mtDNA and nuclear.
• Cultural Evidence ﻿$\rightarrow$﻿ Supports that Homo sapiens evolved in Africa, since cultural innovations associated with Homo sapiens were in Africa.

### Summary

• Evolution and spread of Homo sapiens ﻿$\rightarrow$﻿ Homo sapiens evolved in Africa and migrated out, interbreeding a little with Neanderthals over a short period of time before becoming the dominant species.