I. Phylogeny of HominoidsI. Phylogeny of Hominoids

II. Hominid TransitionsII. Hominid Transitions

Human EvolutionHuman Evolution

Phylogenetics of PrimatesPhylogenetics of Primates

•• Darwin (1871) proposed the following:Darwin (1871) proposed the following:1) 1) Homo sapiensHomo sapiens is sister species of the is sister species of the

chimpanzee.chimpanzee.2) Hominids2) Hominids evolved in Africa.evolved in Africa.

•• CladisticCladistic analysis of morphological and analysis of morphological and molecular data places gorillas, chimps, molecular data places gorillas, chimps, and humans in a monophyletic group.and humans in a monophyletic group.

•• Darwin was probably correct on both Darwin was probably correct on both counts. counts.

A Simplified Phylogeny of Primates

BonoboBonobo ChimpanzeeChimpanzee(Pigmy Chimpanzee)(Pigmy Chimpanzee)

Hominid TransitionsHominid Transitions

•• Larger brainLarger brain

•• Bipedal locomotionBipedal locomotion

•• Flatter face & smaller caninesFlatter face & smaller canines

Bonobo(400 ml)

Human(1450 ml)

Bipedal Locomotion

Bipedal Locomotion

Bipedal Locomotion

Facial & Dental Structure

Human

Chimp

Did hominids come head first or foot first?Did hominids come head first or foot first?

•• Traditionally, scientists embraced Traditionally, scientists embraced the view that an increase in brain the view that an increase in brain size preceded other hominid size preceded other hominid innovations.innovations.

•• Alternatively, bipedal locomotion Alternatively, bipedal locomotion might have evolved prior to large might have evolved prior to large brains.brains.

The Piltdown FraudThe Piltdown Fraud

•• In 1912, a skull was found In 1912, a skull was found in a gravel field at Piltdown in a gravel field at Piltdown in Sussex, England.in Sussex, England.

•• The jaw was apeThe jaw was ape--like and like and the cranium was humanthe cranium was human--like.like.

•• In the 1950In the 1950’’s the specimen was shown to be a fake; s the specimen was shown to be a fake; someone combined an orangutan jaw with a human someone combined an orangutan jaw with a human cranium.cranium.

‘‘LucyLucy’’((Australopithecus Australopithecus afarensisafarensis))

•• In 1974, Don In 1974, Don JohansonJohansonfound a skeleton in Ethiopia found a skeleton in Ethiopia that resolved the controversy that resolved the controversy over which came first (big over which came first (big brains or brains or bipedalitybipedality).).

•• To date, fragments of 300 To date, fragments of 300 individuals have been found.individuals have been found.

•• A. A. afarensisafarensis lived from 4 to 3 lived from 4 to 3 myamya, and may be a direct , and may be a direct ancestor to ancestor to Homo sapiensHomo sapiens.. JohansonJohanson’’ss LucyLucy

Chimpanzee Australopithecus africanus Homo sapiens

A Comparison of Hominid Hips

Lucy was fully bipedal.Lucy was fully bipedal.

Lucy Chimp

•• In 1978, Mary Leakey In 1978, Mary Leakey discovered footprints in discovered footprints in Tanzania that were 3.6 Tanzania that were 3.6 myamya. .

•• The prints are presumably The prints are presumably those of those of A. A. afarensisafarensis, and , and indicate a gait similar to our indicate a gait similar to our own. own.

•• Very likely, hominids walked Very likely, hominids walked the walk well before they the walk well before they talked the talk.talked the talk.

LucyLucy’’s footprint?s footprint?

A Parting of Ways between HominidsA Parting of Ways between Hominids

•• About 2.3 About 2.3 myamya the hominid lineage split into two the hominid lineage split into two major divisions; one lineage became more major divisions; one lineage became more robust whereas the other became more robust whereas the other became more gracilegracile..

•• Six species are known from these two lineages Six species are known from these two lineages (all found only in Africa):(all found only in Africa):

AustralopithecusAustralopithecus

ParanthropusParanthropus

A. A. anamensisanamensisA. A. afarensisafarensisA. A. africanusafricanus

P. P. robustusrobustusP. P. boiseiboiseiP. P. aethiopicusaethiopicus

A Comparison of Hominid Skulls

Homo sapiens A. africanusParanthropus boisei

A. afarensis

“Paranthropus tried to chew his way out of trouble, and Homo thought his way out of trouble.”

Elisabeth Vrba, Yale University

Are we retarded apes?Are we retarded apes?

•• The human skull is The human skull is remarkably similar in form remarkably similar in form to the skull of a juvenile to the skull of a juvenile chimpanzee.chimpanzee.

•• One hypothesis is that our One hypothesis is that our cranial features evolved cranial features evolved by a shift in the timing of by a shift in the timing of development, causing development, causing humans to retain juvenile humans to retain juvenile features. features.

Evolution of Brain SizeEvolution of Brain Size

•• Survival Survival

•• Mating successMating success

•• Social dynamicsSocial dynamicsA A BonoboBonobo chimp yields a weapon.chimp yields a weapon.

Why did Why did Homo sapiensHomo sapiens persist?persist?

•• H. sapiensH. sapiens outsmarted outsmarted its competitorits competitor

-- building better building better tools and weaponstools and weapons

-- managing resourcesmanaging resources

•• H. sapiensH. sapiens hybridized hybridized with its competitorwith its competitor

Homo Homo neanderthaliensisneanderthaliensis