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EVIDENCE FOR EVOLUTION

SBI 3U

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Evidence for Evolution

• ‘Theory of evolution by natural selection’ called… “the greatest idea anybody has ever had…”• “Today scientists have as much confidence in evolution as they do in the existence of atoms or that microorganisms cause infectious disease.”

Jerry A. Coyne

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Evidence for Evolution

Topics To Be Discussed:• Fossil record• Radiometric Dating• Transitional forms• Biogeography• Embryonic development• Homologous structures• Vestigial structures• Atavisms• Micro-evolution happening today

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Fossil Record

• Show which species were alive in the past

• provides evidence that living things have evolved

• fossils show how different groups of organisms have changed over time

• Still very incomplete

Archaeopteryx

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Fossil Record

• Fossils in young layers of rock are more similar to today’s species than are older fossils

• Fossils appear in chronological order in rock layers

• Not all organisms appear in the fossil record at the same time

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• Radioisotopes undergo radioactive decay at predictable rates• Each radioisotope decays at its own constant rate (half-life)• By dating the rocks in which a fossil is found, the age of the fossil can be estimated!

Radiometric Dating

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Transitional Forms

• Incorrectly called ‘missing links’

• None when Darwin wrote ‘Origin of Species’

• Show links between groups of organsims

• Hundreds found to date• Eg. Dorudon was an

ancient terrestrial whale (pelvis; short legs)

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• Eg. Atrociraptor was a link between dinosaurs and birds (Archaeopteryx)

• Eg. Tiktaalik roseae show how amphibians may have risen from fish

• Eyes on top like a salamander, ribs, could breathe air

Transitional Forms

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Name these critters

coelurosaurus

archaeopteryx

chicken

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Biogeography

• Past and present distribution of species

• Darwin & Wallace speculated that species evolve in one location and then spread out

• Plants in S. Am. And Africa same

• Marsupial fossils found in Antarctica Southern super-continent Gondwana

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Biogeography

• Geographically close environments are more likely to contain related species than locations that are distant locations that are environmentally similar (eg. Desert in Africa and a desert in Australia)

• Animals found on islands often resemble animals from the closest continent (evolution from mainland migrants)

• Fossils of same species found on the coastline of neighbouring continents (eg. Gondwana)

• Related species almost never found in exactly same location or habitat

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• Marsupials (Australia) birth undeveloped baby; matures in pouch

• Placentals (N. & S. America) give birth to fully developed babies

• Remarkably similar forms

• “Convergent evolution”

Biogeography

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Embryonic Development

• Many species look similar in early stages of development

• Provides evidence of a common ancestry

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Embryonic Development

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Homologous Structures

• Different mature forms that arose from same embryonic tissue

• Eg. Wing of a bat, flipper of a whale, human arm, etc.

Turtle

Alligator

Bird

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Homologous Body Structures

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Vestigial Organs

• Remnants of homologous organs in other species

• Eg. Pelvis and leg bones in whales when they use to live on land

• What we’d expect if nature weeded out useless traits

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Vestigial Organs

• Keys to our primate ancestry

– Tailbone (remnants of tail)

– Appendix (fermenting vessel to digest cellulose)

– Arrector pili muscles (“goosebumps”)

– 3 scalp muscles (ear wiggling)

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Atavisms

• From Latin: ‘ancestor’• Reappearance of old

traits• Eg. One in 500 whales is

born with protruding legs• Eg. Human babies born

with vestigial tails• Eg. Horses born with

more than one toe (splint toes)

• Mutations ‘turn on’ dead genes

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• Is evolution happening right now?

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Micro-evolution

• Microbes can adapt to virtually any laboratory condition (heat, antibiotics, toxins, starvation, predators, etc.)• E.Coli tested in lab over 18 year study:

– Created feast or famine environment– Latest offspring grow 70% faster than original– Scientists identified at least 9 DNA mutations resulting in adaptations

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Antibiotic resistance

• Drugs evolve to thrive in human envt.– Eg. In 1941 penicillin wipes out all Staphylococcus bacteria; by 2009 95% of Staph. strains are resistant to penicillin– Eg. AIDS treatment requires 3-drug cocktail because virus mutates at a rapid pace– Insects resistant to DDT– Plants adapted to herbicides– Many others!

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Are humans evolving?

• Lactose tolerance– not needed after weaning in many regions (no lactase enzyme)– Pastoral areas (raise cows) keep lactase turned on (3000 to 8000 years ago)– Simple DNA mutation

• Amylase gene– Highly duplicated in humans, not so much in lower apes (due to our starchy diets)

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Are humans evolving?

• Conversely, improvements in nutrition, sanitation, and medical care are curbing natural selection• Bad eyesight cured with glasses; bad teeth fixed by dentists• How many of our ancestors with bad eyes and teeth, unable to hunt, would have survived on the African savanna?• De-evolution…possibly?