Evolution Evolutionary Process Human Evolution

Evolution Evolution = change in characteristics of organisms as a result of changes in genetic compositionEvolution = change in characteristics of organisms as a result of changes in genetic composition Two important aspectsTwo important aspects –Descent from a common ancestor –Adaptation to the environment Adaptation = characteristic that makes it more likely that an organism will survive and reproduce in its environmentAdaptation = characteristic that makes it more likely that an organism will survive and reproduce in its environment

Evidence for Common Descent From the Fossil Record Living Organisms resemble extinct fossil forms.

Evidence for Common Descent From the Fossil Record Progressive changes from simpler to more complex organisms can be seen in the fossil record.

Biogeographical Evidence for Common Descent Plants and animals of each continent are distinctive.

Biogeographical 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 Descent Island Populations resemble those on nearby land. The Galapagos finches resembled the grassquit found on the coast of Ecuador. Recent studies suggest that the finch ancestor may have originated from the Caribbean islands.

Anatomical Evidence for Common Descent: Homologous Structures Flying Swimming Running Grasping

Anatomical Evidence: Vestigial Structures Functional hindlimb in salamander Remnants of hindlimb seen in boa and whale

Anatomical Evidence: Vestigial Structures In 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 are lost through cell death and numbers 4-5 are reduced. The coccyx is the remainder of vertebrae 1-5.

Evidence for Common Descent from Developmental Biology

Evidence for Common Descent from Biochemistry

A Flowchart of Evolutionary Reasoning Variations 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 constant resources 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 giraffes to have the most offspring. Due to natural selection, most giraffes now have long necks. Darwin’s proposal Natural Selection as the Mechanism for Evolution

Primate Evolutionary Tree Common ancestor may have resembled a tree shrew ~45 MYA: There was a common ancestor for monkeys, apes and hominids ~15 MYA: There was a common ancestor for all apes and hominids ~7 MYA: There was a common ancestor for African apes and hominids bipedal posture

Adaptations of Primates Opposable thumbOpposable thumb Well-developed brainWell-developed brain Nails instead of clawsNails instead of claws Single birthSingle birth Extended period of parental careExtended period of parental care Emphasis on learned behaviorEmphasis on learned behavior Australopithecus afarensis An early hominid

Hominin Evolution Possible ancestor of both A. africanus and Genus Homo Possible ancestor of modern humans In Asia In Africa

Human Evolution Genus AustralopithecusGenus Australopithecus –walked upright –product of mosaic evolution = different body parts change at different rates Smaller brain resembles apesSmaller brain resembles apes Bipedal locomotion resembles humansBipedal locomotion resembles humans –ancestors of genus Homo (not certain which species led to Homo habilis)

Human Evolution Genus HomoGenus Homo –Homo habilis = “handy man” produced toolsproduced tools teeth supported omnivorous dietteeth supported omnivorous diet enlarged speech area in brainenlarged speech area in brain –Homo ergaster (in Africa) advanced tools, use of fireadvanced tools, use of fire larger brain, taller bodylarger brain, taller body striding gaitstriding gait –early Homo sapiens (based on Cro-Magnon fossils) compound toolscompound tools larger brainlarger brain language and culture, including artlanguage and culture, including art neck of femur femur femur neck is longer than in modern humans Homo ergaster

Two Hypotheses for the Origin of Modern Humans Multiregional continuityOut of Africa

DNA Analyses Related to Human Origins Visit and choose Mitochondrial Control Region Media and Animations Solving the Mystery of the Neanderthals Other Applications of DNA Analysis can be found at Choose Applications, then Human Origins

A Newly-Discovered (but extinct) Species of Genus Homo Homo erectus Homo floresiensis Homo sapiens