Evolution Evolution

Evolutionary ProcessEvolutionary ProcessHuman EvolutionHuman Evolution

EvolutionEvolution

• Evolution = change in characteristics Evolution = change in characteristics of organisms as a result of changes of organisms as a result of changes in genetic compositionin genetic composition

• Two important aspects Two important aspects – Descent from a common ancestorDescent from a common ancestor

– Adaptation to the environmentAdaptation to the environment• Adaptation = characteristic that makes it Adaptation = characteristic that makes it

more likely that an organism will survive more likely that an organism will survive and reproduce in its environmentand reproduce in its environment

Evidence for Common DescentEvidence for Common DescentFrom the Fossil RecordFrom the Fossil Record

Living Organisms resemble extinct fossil forms.Living Organisms resemble extinct fossil forms.

Evidence for Common DescentEvidence for Common DescentFrom the Fossil RecordFrom the Fossil Record

Progressive changes from simpler to more complex Progressive changes from simpler to more complex organisms can be seen in the fossil record.organisms can be seen in the fossil record.

Biogeographical Evidence Biogeographical Evidence for Common Descentfor Common Descent

Plants and animals of each continent are distinctive.Plants and animals of each continent are distinctive.

Biogeographical Evidence for Common DescentBiogeographical Evidence for Common Descent

Different island species resemble each other.Different island species resemble each other.

Cactus-eater Seed-eater

Insect-eater

Natural Selection led to beak sizes and shapes suitable for different food sources

Biogeographical Evidence for Common DescentBiogeographical Evidence for Common Descent

Island Populations resemble Island Populations resemble those on nearby land.those on nearby land.

The Galapagos finches resembled the The Galapagos finches resembled the grassquit found on the coast of Ecuador.grassquit found on the coast of Ecuador.

Recent studies suggest that the finch ancestor Recent studies suggest that the finch ancestor may have originated from the Caribbean islands.may have originated from the Caribbean islands.

Anatomical Evidence for Common Descent: Homologous Structures

FlyingFlying SwimmingSwimming RunningRunning GraspingGrasping

Anatomical Evidence:Anatomical Evidence: Vestigial Structures Vestigial Structures

Functional hindlimb Functional hindlimb in salamanderin salamander

Remnants of Remnants of hindlimb seen in hindlimb seen in boa and whaleboa and whale

Anatomical Evidence: Vestigial StructuresAnatomical Evidence: Vestigial StructuresIn fish, these pouches form the gill slits. In humans, one of the pouches does not persist past this embryonic stage. Other pouches give rise to structures of the ear, tonsils, parathyroid and thymus.

The tail has 12 vertebrae at this stage. Numbers 6-12 are lost through cell death and numbers 4-5 are reduced. The coccyx is the remainder of vertebrae 1-5.

Evidence for Common DescentEvidence for Common Descent from Developmental Biology from Developmental Biology

Evidence for Common Descent from BiochemistryEvidence for Common Descent from Biochemistry

A Flowchart of Evolutionary ReasoningVariations exist

between members of a population

observations

inferences

Individuals whose inherited traits give a higher probability of

survival and reproduction leave a greater number of

offspring

Relatively constantresources and

population over time

At least some variation is hereditary

More offspring are born than survive and

reproduce

Favorable traits will accumulate in the population

over generations

Formation of new genotypes leads to

phenotypic variation

Adaptations

Originally, giraffe neck length varied.

Competition for resources causes long-necked giraffesto have the most offspring.

Due to natural selection, most giraffes nowhave long necks.

Darwin’s proposal

Natural Selection Natural Selection as the Mechanism as the Mechanism

for Evolutionfor Evolution

Primate Primate Evolutionary Evolutionary

TreeTree

Common ancestor may have resembled a

tree shrew

~45 MYA: There wasa common ancestor for monkeys, apes

and hominids

~15 MYA: There wasa common ancestor

for all apes and hominids

~7 MYA: There wasa common ancestor for African apes and

hominids

bipedal posture

Adaptations of PrimatesAdaptations of Primates

• Opposable thumbOpposable thumb

• Well-developed brainWell-developed brain

• Nails instead of clawsNails instead of claws

• Single birthSingle birth

• Extended period of Extended period of parental careparental care

• Emphasis on learned Emphasis on learned behaviorbehavior

Australopithecus afarensis Australopithecus afarensis An early hominid An early hominid

Hominin EvolutionHominin Evolution

Possible ancestor of both A. africanus and

Genus HomoPossible ancestor of

modern humans

In Asia

In Africa

Human EvolutionHuman Evolution• Genus Genus AustralopithecusAustralopithecus

– walked uprightwalked upright– product of mosaic evolution = different body product of mosaic evolution = different body

parts change at different ratesparts change at different rates• Smaller brain resembles apesSmaller brain resembles apes• Bipedal locomotion resembles humansBipedal locomotion resembles humans

– ancestors of genus ancestors of genus HomoHomo(not certain which species led to(not certain which species led to Homo Homo habilis)habilis)

Human EvolutionHuman Evolution• Genus Genus HomoHomo

– Homo habilisHomo habilis = “handy man” = “handy man”• produced toolsproduced tools• teeth supported omnivorous dietteeth supported omnivorous diet• enlarged speech area in brainenlarged speech area in brain

– Homo ergaster Homo ergaster (in Africa)(in Africa)• advanced tools, use of fire advanced tools, use of fire • larger brain, taller bodylarger brain, taller body• striding gaitstriding gait

– earlyearly Homo sapiens Homo sapiens(based on Cro-Magnon fossils)(based on Cro-Magnon fossils)• compound toolscompound tools• larger brainlarger brain• language and culture, language and culture,

including artincluding art

neck of femur

femur

femur neck is longer than in modern humans

Homo ergaster

Two Hypotheses for the Two Hypotheses for the Origin of Modern HumansOrigin of Modern Humans

Multiregional continuity Out of Africa

DNA Analyses Related to DNA Analyses Related to Human OriginsHuman Origins

Visit Visit http://www.geneticorigins.orghttp://www.geneticorigins.org and choose and choose Mitochondrial Control Region Mitochondrial Control Region Media and Animations Media and Animations Solving the Mystery of the Neanderthals Solving the Mystery of the Neanderthals

Other Applications of DNA Analysis can be Other Applications of DNA Analysis can be found at found at http://www.dnai.orghttp://www.dnai.org Choose Applications, then Human OriginsChoose Applications, then Human Origins

A Newly-Discovered A Newly-Discovered (but extinct)(but extinct)

Species of Genus Species of Genus HomoHomo

Homo erectusHomo floresiensis

Homo sapiens