Outline 21: Human/Hominid Evolution Primate Classification

Order Primates Suborder Prosimii Suborder Anthropoidea Superfamily Hominoidea Family Pongidae: apes Family Hominidae: hominids Prosimians

• Tarsiers • Galagos • Lorises • Lemurs Tarsiers, a primitive Primate (Prosimian) from Southeast Asia. A Galago or bush baby, a primitive Primate (Prosimian) from Africa. A Slow Loris, a primitive Primate (Prosimian) from Southeast Asia. Check out the fingers. Lemurs, primitive Primates (Prosimians) from Madagascar. Anthropoids

• Old World Monkeys • New World Monkeys • Hominoids Monkeys, such as baboons, have tails and are not hominoids. Hominoids

• gibbons, orangutans, chimps, gorillas, humans • Pongidae: orangs, chimps, gorillas • Hominidae: the hominids Ardipethecus, Australopithecus, Paranthropus, Homo Hominoids A lesser ape, the Gibbon from Southeast Asia. The Orangutan, a Great Ape from Southeast Asia. Dogs: Hominoids best friend? Gorillas, Great Apes from Africa.

And Hollywood!

Bipedal Gorilla! Yeah, right. Gorilla Chimp Posture of humans vs. gorillas Chimpanzees, Great I’m cool Apes from Africa. Chimps are simple tool users Human Chimp Oldest Hominoid

Proconsul africanus, 18 MY old from Kenya. Looked like a gibbon. Proconsul, the oldest hominoid, 18 MY The Gibbon is a living hominoid similar to Proconsul. Timing of Lineage Splitting on the way to Humans

• Based on DNA studies • Old World monkeys: 33 MY • gibbons: 22 MY • orangs: 16 MY • gorillas: 8 MY • chimps: 7 MY Genetic Differences

• humans - chimps: 1.2% • humans - gorillas: 1.4% • chimps - gorillas: 1.2% • humans - orangs: 2.2% Origin of Hominids

• What differentiates hominids from apes? This is what evolved first. • Large brain? • Bipedalism? Origin of Hominids

• Early hominid brains were the same size as modern chimps. • Bipedalism evolved before large brains. In fact, it was bipedalism that allowed the evolution of large brains by freeing the hands for tool use. Origin of Bipedalism

• Thought to be associated with climatic change 5 MY ago as spreading glaciers caused global cooling. • Global cooling created a drier Africa with fewer rain forests and more savannahs. Origin of Bipedalism

• Earliest hominids were forced to travel between isolated forests if food was in short supply. • This produced selection pressure for upright walking. Origin of Large Brains

• Associated with selection pressure for tool use. Tools to find more food or defend against predators. • Bipedalism freed the hands for extensive tool use, and for carrying helpless babies. Origin of Large Brains: Neoteny

• Neoteny: an evolutionary/genetic process • A slowing of developmental rates while growth continues normally. • Developmental stages are reached at a later stage or not at all.

Neoteny in Human Evolution. Humans resemble baby apes more than adult apes. Humans are said to be paedomorphic.

Chimp Gorilla Chimp

Human Chimp skull on the left, human skull on the right Chimp

Homo sapiens Consequences of Neoteny

• Helpless babies • Walk later • Extended juvenile period • Prolonged period of learning • Later puberty • Longer life span Human babies are weaker and more helpless than newborn apes. Consequences of Neoteny

• large brain and cranium • small face, jaws, and teeth: impacted wisdom teeth • naked skin, hair mostly on head • form of external ear Consequences of Neoteny Mosaic Evolution

Neoteny does not affect all parts of the body equally. Some parts are like juveniles, others like adult apes. We have retained some juvenile features yet have reached sexual maturity. Hominid Brain Sizes

Chimps: 350 cc Australopithecus afarensis: 400 cc Australopithecus africanus: 450 cc Homo habilis: 800 cc Homo erectus: 1000 cc average Homo sapiens: 1400 cc average