EES 227: Paleobiology

Spring 2004

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Lecture 22:  April 27

Reading:

Web resources for this lecture:

Lecture Notes: Human Evolution

Main events in human evolution:

  1. Evolution of Primates within mammals (55 Ma -> 85 Ma)
  2. Evolution of human-like Primates (bipedal) within Primates ( 4.5-4.0 Ma -> ~7 Ma)
  3. Evolution of 'modern' Homo sapiens within Homo (~40 kyr -> 75 kyr)

All three events recently argued to have occurred earlier than thought until about a few years ago.

Fossil record of humans poor:

Relationships of modern Eutheria (placental mammals): see text book p. 388/403. Primates closely related to bats, probably derived from insectivores.

Primates:

Primate characters:

Primate History and Family

Primate evolution: when split from other mammals? Fossil record: about 55 Ma

Discrepancies might be caused by poor fossil record; recently argued in Nature (from statistical arguments) that this is indeed the cause. But molecular data and latest statistical interpretation do not really take into account that mammal evolution may have varied in rate (see this paper by Mike Benton on discussion of problems in dating origin of mammals and birds).

Hominoid History

Primates subdivided into:

Where we fit within Homininae:

Characters of humans

These characters did not all go together during evolution; upright walking came long before our large brain.

Various human family members. Note that the vertical bars (time range) may indicate either uncertainty in age determination, or ranges of specimens found at different places, or both..

Human ancestors (?): Africa, in and out of Africa, Europe only

Note: clear that during much of this time there were various species that were bipedal primates around in Africa. One or more of these may have been tool users.

First Wave, about 2.0-1.8 Ma: the first to migrate out of Africa was Homo erectus to Asia and Europe.

At various locations in Asia and Europe fossils of both Homo erectus and Homo sapiens were found. How and where was Homo sapiens derived from Homo erectus?

Two views:

Much evidence in favor of the first:

Mitochondrial DNA inherited through egg cytoplasm (only through female line); data from Y chromosome only in male line. Both lines of evidence in support of Out of Africa theory. Mitochondrial data: all humans descended from one woman 'Mitochondrial Eve' who lived in Africa about 170,000 years ago. This does NOT mean that ~ 170 kyr ago only one woman was alive, only that one mitochondrial genotype became dominant (not every woman reproduces or has daughters)

2nd Wave of migration , about 130,000 kyr (?): by modern humans. Reached Australia about 50-60 kyr, the Americas by about 12 kyr (in large numbers).

Since about 170,000-160,000 years skeleton not distinguishable from these of modern people. But were these humans modern in their way of thinking (use of symbols?)

When did humans become 'human' (use of symbols)?

Until recently: signs of culture (art) in Europe, ~ 40 kyr ago

In 2001: patterned scratches on ochre rocks in cave in South Africa, dated at about 77-70 kyr: suggestive that human symbolic thinking evolved in Africa as well. Just this year (2004): discovery of ostrich-shell beads in Kenya (>45 kyr), snail beads in Blombos cave where ochre was also found in 2001.

And what about Homo neanderthalensis?