LECTURE 9: Evidence for Evolution

Abandoned The Idea That Species Were Perfect & Unchanging Observed Significant Variation in All Species Observed Observed Farmers Use Variation To Improve Crops & Livestock Called Selective Breeding 2 2

What is the difference between natural variation and Artificial Selection? Differences Among Individuals Of A Species Artificial Selection Selective Breeding To Enhance Desired Traits Among Stock or Crops 3 3

Natural Variation and Artificial Selection Key Concept: In Artificial Selection, Nature Provided The Variation Among Different Organisms, And Humans Selected Those Variations That They Found Useful 4 4

Major Problem in Darwin’s Theory No mechanism to explain natural selection How could favorable variations be transmitted to later generations? With the rediscovery of Mendel’s work in the first half of the 20th century, the missing link in evolutionary theory was found . 5 5

What is the Evidence of Evolution? Darwin Argued That Living Things Have Been Evolving On Earth For Millions of Years. Evidence For This Process Could Be Found In: The Fossil Record The Geographical Distribution of Living Species (BIOGEOGRAPHY) Homologous Structures of Living Organisms Similarities In Early Development 6 6

The Fossil Records The Darwinian view of life predicts that evolutionary transitions should leave signs in the fossil record Paleontologists have discovered fossils of many such transitional forms

Fossil Record Earth is Billions of Years Old Fossils In Different Layers of Rock (sedimentary Rock Strata) Showed Evidence Of Gradual Change Over Time 8 8

Geographic Distribution of Living Species Different Animals On Different Continents But Similar Adaptations To Shared Environments 9 9

LE 22-17 NORTH AMERICA Sugar glider AUSTRALIA Some similar mammals that have adapted to similar environments have evolved independently from different ancestors Flying squirrel 10

Another example: while the sugar glider and flying squirrel have adapted to the same mode of life, they are not closely related, genetically. Instead, the sugar glider from Australia is more closely related to other marsupial mammals from Australia than to the flying squirrel, a placental mammal from North America. The resemblance between them is an example of convergent evolution. Fig. 22.15 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings 11

Evidence for Evolution Evolutionary relationships are determined from shared characteristics between groups of organisms What are these characteristics called? Homologous structures are those that have the same evolutionary origin but may or may not have similar functions— has been modified to best suit its particular function in each species. DIVERGENT EVOLUTION Analogous Structures: perform same function, evolved separately CONVERGENT EVOLUTION

Homologous Structures 13 13

Homologous Body Structures Not All Serve Important Functions Vestigial Organs Appendix In Man Legs On Skinks 14 14

What is Divergent Evolution? Structures That Have Different Mature Forms But Develop From The Same Embryonic Tissues Strong Evidence That All Four-Limbed Animals With Backbones Descended, With Modification, From A Common Ancestor Help Scientist Group Animals 16 16

Convergent Evolution Convergent Evolution: The evolution of species from different ancestors toward a similar form

“New” Evidence for Evolution? Molecular Biology Similarities in DNA sequences Developmental Biology

What are Molecular Homologies? Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor Ex: Homeobox

LE 22-16 Percent of Amino Acids That Are Identical to the Amino Acids in a Human Hemoglobin Polypeptide Species Human 100% Rhesus monkey 95% Mouse 87% Chicken 69% Frog 54% Lamprey 14%

Similarities in DNA Sequence 21 21

Similarities In Early Development Embryonic Structures Of Different Species Show Significant Similarities Embryo – early stages of vertebrate development 22 22

Similarities In Embryonic Development Evidence for Evolution - Comparative Embryology Similarities In Embryonic Development 23 23

Evidence for the Theory of Evolution by Natural Selection Even when homologies are not obvious in adults, they may be quite apparent in embryonic stages Which one is the human? 24

Human Fetus – 5 weeks 25 25

Chicken Turtle Rat 26 26

Evolution of pesticide resistance in response to selection 27 27

Evidence for Evolution – Evolution Observed Evolution of drug-resistance in HIV 28 28