chapter 19 human evolution. on the origin of the species sold out in 1 day, had only a small section...

Chapter 19Chapter 19

Human EvolutionHuman Evolution

On the Origin of On the Origin of TheThe Species SpeciesOn the Origin of On the Origin of TheThe Species Species

Sold out in 1 day, had only a small section on the origin of man.

12 years later The descent of Man, and Selection in Relation to Sex.

The last chapter concerns the origin and evolution of our species

Sold out in 1 day, had only a small section on the origin of man.

12 years later The descent of Man, and Selection in Relation to Sex.

The last chapter concerns the origin and evolution of our species

On the Origin of On the Origin of TheThe Species SpeciesOn the Origin of On the Origin of TheThe Species Species

It is a much debated topic with different camps of researchers drawing different conclusions

Scopes Monkey Trial 1925 in TN– Prohibited teaching evolution– 1995 AL state board of education ruled

all textbooks must state Evolution is a theory not fact.

It is a much debated topic with different camps of researchers drawing different conclusions

Scopes Monkey Trial 1925 in TN– Prohibited teaching evolution– 1995 AL state board of education ruled

all textbooks must state Evolution is a theory not fact.

On the Origin of On the Origin of TheThe Species SpeciesOn the Origin of On the Origin of TheThe Species Species

I have taught you that evolution is a process, and this process is occurring around us.

Utilizing evolutionary theory we will examine physical, morphological, molecular, and behavioral evidence to test hypotheses about human origins

I have taught you that evolution is a process, and this process is occurring around us.

Utilizing evolutionary theory we will examine physical, morphological, molecular, and behavioral evidence to test hypotheses about human origins

Relationships of Humans and Relationships of Humans and Extant ApesExtant ApesRelationships of Humans and Relationships of Humans and Extant ApesExtant Apes Order Primates– Suborder Catarrhini = Old World monkeys

and apes• Superfamily Hominoidea = great and lesser apes

– Family Hominidae = great apes and humans • Homo sapiens

Our closest relatives are Pongo pygmaeus, Gorilla gorilla, Pan troglodytes, and Pan paniscus– Orangutan, gorilla, standard chimpanzee,

bonobo

Order Primates– Suborder Catarrhini = Old World monkeys

and apes• Superfamily Hominoidea = great and lesser apes

– Family Hominidae = great apes and humans • Homo sapiens

Our closest relatives are Pongo pygmaeus, Gorilla gorilla, Pan troglodytes, and Pan paniscus– Orangutan, gorilla, standard chimpanzee,

bonobo

Relationships of Humans and Relationships of Humans and Extant ApesExtant ApesRelationships of Humans and Relationships of Humans and Extant ApesExtant ApesThese taxonomic classifications are not

universally acceptedIt is accepted that humans belong to the

same clade as African great apes– Synapomorphies

• Relatively large brain, elongated skulls, enlarged brow ridges, shortened canines, wrist bone fusion, reduced hair, absence of a tail, great flexibility of hips and ankles

Which is our closest relative?– Chimpanzees or gorilla?

These taxonomic classifications are not universally accepted

It is accepted that humans belong to the same clade as African great apes– Synapomorphies

• Relatively large brain, elongated skulls, enlarged brow ridges, shortened canines, wrist bone fusion, reduced hair, absence of a tail, great flexibility of hips and ankles

Which is our closest relative?– Chimpanzees or gorilla?

Relationships of Humans and Relationships of Humans and Extant ApesExtant ApesRelationships of Humans and Relationships of Humans and Extant ApesExtant Apes

Molecular phylogeny of Sarich and Wilson had polytomy of chimpanzees, gorilla, and man

Timeline showed that split between apes and Old World monkeys was 30 Mya

Split between African great apes and humans 5 Mya

Molecular phylogeny of Sarich and Wilson had polytomy of chimpanzees, gorilla, and man

Timeline showed that split between apes and Old World monkeys was 30 Mya

Split between African great apes and humans 5 Mya

Relationships of Humans and Relationships of Humans and African ApesAfrican ApesRelationships of Humans and Relationships of Humans and African ApesAfrican Apes Gorillas and chimpanzees share

knucklewalking which humans lack Humans and two chimpanzees share

features of skull, teeth, limbs, and delayed sexual maturity

Some molecular analyses place humans and gorillas as sister taxa

Conflicting evidence makes interpretation of correct branching order difficult

Gorillas and chimpanzees share knucklewalking which humans lack

Humans and two chimpanzees share features of skull, teeth, limbs, and delayed sexual maturity

Some molecular analyses place humans and gorillas as sister taxa

Conflicting evidence makes interpretation of correct branching order difficult

Relationships of Humans and Relationships of Humans and African ApesAfrican ApesRelationships of Humans and Relationships of Humans and African ApesAfrican Apes Difficult to identify which characters are

ancestral or derived Dryopithecus is an extinct European ape 10 My

old Shares many traits with gorillas that humans

and chimps lack If these characters are ancestral and humans

and chimps don’t have them, it is most parsimonious for humans and chimps to be sisters

Difficult to identify which characters are ancestral or derived

Dryopithecus is an extinct European ape 10 My old

Shares many traits with gorillas that humans and chimps lack

If these characters are ancestral and humans and chimps don’t have them, it is most parsimonious for humans and chimps to be sisters

Relationships of Humans and Relationships of Humans and African ApesAfrican ApesRelationships of Humans and Relationships of Humans and African ApesAfrican Apes

Using DNA sequences, researchers attempt to answer human/chimp/ gorilla question

Three different genes gave different tree topologies–mtDNA, Y chromosome, nuclear gene– All trees support humans as sister to

chimpanzees

Using DNA sequences, researchers attempt to answer human/chimp/ gorilla question

Three different genes gave different tree topologies–mtDNA, Y chromosome, nuclear gene– All trees support humans as sister to

chimpanzees

Relationships of Humans and Relationships of Humans and African ApesAfrican ApesRelationships of Humans and Relationships of Humans and African ApesAfrican ApesCriticism of these reconstructions

because they are gene trees and not species trees

If ancestor was genetically variable for a particular locus, the gene tree may not accurately represent the species tree– Ancestor may pass on a subset of its alleles

for a gene to each descendent species • That gene will not give an accurate estimate of

phylogeny

Criticism of these reconstructions because they are gene trees and not species trees

If ancestor was genetically variable for a particular locus, the gene tree may not accurately represent the species tree– Ancestor may pass on a subset of its alleles

for a gene to each descendent species • That gene will not give an accurate estimate of

phylogeny

Gene Tree vs Species TreeGene Tree vs Species TreeGene Tree vs Species TreeGene Tree vs Species Tree

Relationships of Humans and Relationships of Humans and African ApesAfrican ApesRelationships of Humans and Relationships of Humans and African ApesAfrican ApesRuvolo wanted to address this issue

directly– She exhaustively sampled human and ape

individuals

– If the gene tree and species tree is incongruent, individuals of a species would not group together

– They always did group together in her study so it was not a problem for that gene

Ruvolo wanted to address this issue directly– She exhaustively sampled human and ape

individuals

– If the gene tree and species tree is incongruent, individuals of a species would not group together

– They always did group together in her study so it was not a problem for that gene

Relationships of Humans and Relationships of Humans and African ApesAfrican ApesRelationships of Humans and Relationships of Humans and African ApesAfrican ApesAnother way to test this issue is use as

many genes as possible and see which ones are congruent

In 14 independent genes – 11 showed humans and chimps together– 2 showed gorillas and chimps– 1 showed humans and gorillas

Human/chimp relationship most likely

Another way to test this issue is use as many genes as possible and see which ones are congruent

In 14 independent genes – 11 showed humans and chimps together– 2 showed gorillas and chimps– 1 showed humans and gorillas

Human/chimp relationship most likely

Genome ProjectsGenome ProjectsGenome ProjectsGenome Projects

Humans 23 prs of chromosomes while chimps and gorillas have 24

Humans 23 prs of chromosomes while chimps and gorillas have 24

Timing the Split (by an undergrad)Timing the Split (by an undergrad)Timing the Split (by an undergrad)Timing the Split (by an undergrad)

Recent Ancestry of HumansRecent Ancestry of HumansRecent Ancestry of HumansRecent Ancestry of Humans

Humans and chimps last shared a common ancestor 5.4 Mya

Most recent ancestor was a knucklewalker, ate mostly fruit, lived in many habitats, had complex social groups, and made tools

What intermediate ancestors lived between chimp/human ancestor and modern Homo and Pan?

Humans and chimps last shared a common ancestor 5.4 Mya

Most recent ancestor was a knucklewalker, ate mostly fruit, lived in many habitats, had complex social groups, and made tools

What intermediate ancestors lived between chimp/human ancestor and modern Homo and Pan?

Recent Ancestry of HumansRecent Ancestry of HumansRecent Ancestry of HumansRecent Ancestry of Humans

Fossils provide some answers– Fossil record is incomplete– Scientists disagree on placement of fossils

on hominid tree Sahelanthropus tchadensis

Fossils provide some answers– Fossil record is incomplete– Scientists disagree on placement of fossils

on hominid tree Sahelanthropus tchadensis

Recent Ancestry of HumansRecent Ancestry of HumansRecent Ancestry of HumansRecent Ancestry of Humans

Sahelanthropus older end of window for split. Looks like chip due to brain case but from front looks like Australopithecine.

Australopithecines are one of the earliest humans– Two main body forms• Robust and gracile

– Bipedal like modern humans• Known from limb structure and footprints

Sahelanthropus older end of window for split. Looks like chip due to brain case but from front looks like Australopithecine.

Australopithecines are one of the earliest humans– Two main body forms• Robust and gracile

– Bipedal like modern humans• Known from limb structure and footprints

Recent Ancestry of HumansRecent Ancestry of HumansRecent Ancestry of HumansRecent Ancestry of Humans

Australopithecines were short with small brain cases

Modern human structure more similar to gracile australopithecines

Robust australopithecines had enormous teeth and very strong jaw muscles for biting tree branches (like gorillas do today)

Australopithecines were short with small brain cases

Modern human structure more similar to gracile australopithecines

Robust australopithecines had enormous teeth and very strong jaw muscles for biting tree branches (like gorillas do today)

Gracile australopithecines

Fossil TimelineFossil TimelineFossil TimelineFossil Timeline

Recent Ancestry of HumansRecent Ancestry of HumansRecent Ancestry of HumansRecent Ancestry of Humans

First Homo was H. habilisHomo had larger brain cases and smaller

teeth than AustralopithecusHomo was also taller with less sexual

dimorphism in sizeHomo rudolfensis may be the same species

as H. habilis but have some skeletal differences

H. ergaster is more recent ancestor from Africa

First Homo was H. habilisHomo had larger brain cases and smaller

teeth than AustralopithecusHomo was also taller with less sexual

dimorphism in sizeHomo rudolfensis may be the same species

as H. habilis but have some skeletal differences

H. ergaster is more recent ancestor from Africa

Recent Ancestry of HumansRecent Ancestry of HumansRecent Ancestry of HumansRecent Ancestry of Humans

H. erectus was first human to leave Africa

H. heidelbergenesis is its descendentH. neanderthalensis may be our

ancestor or may have been a sister species that died out

Modern Homo sapiens appeared approximately 100,000 ya

H. erectus was first human to leave Africa

H. heidelbergenesis is its descendentH. neanderthalensis may be our

ancestor or may have been a sister species that died out

Modern Homo sapiens appeared approximately 100,000 ya

Recent Ancestry of HumansRecent Ancestry of HumansRecent Ancestry of HumansRecent Ancestry of Humans

Strait reconstructed a cladogram based on fossils– Such a cladogram is difficult to read

because ancestor-descendent relationships are not adequately depicted

– All species appear as terminal taxa

Strait reconstructed a cladogram based on fossils– Such a cladogram is difficult to read

because ancestor-descendent relationships are not adequately depicted

– All species appear as terminal taxa

Recent Ancestry of HumansRecent Ancestry of HumansRecent Ancestry of HumansRecent Ancestry of Humans

Strait also constructed hypothesis of descendent relationships– Time scale allows testing by fossil

record• New fossils should be found from ages

depicted in correct hypothesis

Strait also constructed hypothesis of descendent relationships– Time scale allows testing by fossil

record• New fossils should be found from ages

depicted in correct hypothesis

Recent Ancestry of HumansRecent Ancestry of HumansRecent Ancestry of HumansRecent Ancestry of Humans

Determining trait polarities is difficult so that deciding on which hypothesis is more likely is difficult

In the past as many as five human species coexisted

We are the sole surviving species of a much larger human radiation

Determining trait polarities is difficult so that deciding on which hypothesis is more likely is difficult

In the past as many as five human species coexisted

We are the sole surviving species of a much larger human radiation