Unit VI - Evolution ~ a unifying theme of biology ~

Introduction to Evolution What does biological “evolution” mean? –Change in organisms over time How does this relate to the “origin of life”? –It doesn’t…two different topics! –Much more evidence to support evolution –Remember: science deals with natural world, not belief

Introduction to Evolution How could “life” have started? –Old Idea: “spontaneous generation” (abiogenesis)…nonliving matter makes living Disproved by Redi and Pasteur –New Idea: “biogenesis”…life comes from life

Introduction to Evolution So, then where did the first cells come from? –Early earth Very hot; volcanoes; violent storms/lightning –Miller & Urey experiment Under early earth conditions, organic compounds form & group together into “protocells”

Introduction to Evolution But, when did we actually get cells? And how? –Evidence of first cells 3.4 bln yrs ago Most likely anaerobic bacteria (no O 2 in air) –First photosynthetic cells 2.8 bln yrs ago Increased O 2 in atmosphere Led to ozone layer that protects from UV rays = more cells Aerobic cells could now develop

Darwin’s Idea How did Darwin form ideas about evolution? –Fossils showed organisms changed over time

Darwin’s Idea How did Darwin form ideas about evolution? –Geologists showed that earth was very old

Darwin’s Idea How did Darwin form ideas about evolution? –He saw diverse species (ex: finches on Galapagos Islands, all with variations)

Darwin’s Idea How did Darwin form ideas about evolution? –Malthus noticed populations grow faster than their food supplies (they produce too many offspring)

Darwin’s Ideas What did Darwin conclude about species? –He identified that populations change due to “natural selection” (nature selects who goes on)

Darwin’s Ideas What did Darwin conclude about species? –Four assumptions: Populations produce large #’s of offspring (more than can survive with given food) Individuals in population have variations Certain variations are more useful (these will survive better) Over time, “good” genes prevail in the population, while “bad” ones fade out

Evidence for Evolution What direct evidence supports this theory? –Changes in populations over time Ex: peppered moth

Evidence for Evolution What direct evidence supports this theory? –Structural adaptations Ex: mimicry; camouflage

Evidence for Evolution What direct evidence supports this theory? –Physiological changes Ex: drug-resistant bacteria; Ex: pesticide-resistant insects

Evidence for Evolution Is there indirect evidence of evolution? –Fossils show changes through time

Evidence for Evolution Is there indirect evidence of evolution? –Embryology Early similarities may show relation

Evidence for Evolution Is there indirect evidence of evolution? –Embryology Early similarities may show relation

Evidence for Evolution Is there indirect evidence of evolution? –Embryology

Evidence for Evolution Is there indirect evidence of evolution? –Biochemistry Similar chemicals in most life forms (DNA, ATP) More similarities in code means closer relationship

Evidence for Evolution Is there indirect evidence of evolution? –Anatomy Homologous structures –Similar origin, but may now have different function –Shows common ancestry –Ex: bird wing, whale flipper, human arm

Evidence for Evolution Is there indirect evidence of evolution? –Anatomy Analogous structures –Similar function, but very different structure –Shows separate development…not related –Ex: bird wing & butterfly wing

Evidence for Evolution Is there indirect evidence of evolution? –Anatomy

Evidence for Evolution Is there indirect evidence of evolution? –Anatomy Vestigial structures –A part that no longer serves a purpose –Ex: snake hip bones; human wisdom teeth

Mechanisms of Evolution Can individuals evolve? –No! –Genes are genes…cannot alter them* –Only populations can evolve –Gene pool = sum of all genes in population

Mechanisms of Evolution How do populations evolve? –Any factor that affects genes in gene pool may disrupt equilibrium…leads to change (evolution) –Mutations may cause a shift –Smaller populations more affected…higher chance to concentrate recessives –Organisms moving in/out cause changes –Large populations not as affected by these factors

Mechanisms of Evolution How do species evolve? –Called “speciation” (same species can breed) –Geographic isolation keeps individuals apart so cannot interbreed…over time they develop different traits (Ex: finches on islands)

Mechanisms of Evolution How do species evolve? –Called “speciation” (same species can breed) –Geographic isolation

Mechanisms of Evolution How do species evolve? –Called “speciation” (same species can breed) –Reproductive isolation no longer capable of interbreeding (timing, parts, gametes differ,…)

Mechanisms of Evolution How fast can species evolve? –Gradualism Species start up over long time with gradual changes (millions of years) –Punctuated equilibrium Speciation occurs in quick bursts with equilibrium in between (~10,000 yrs or less)

Mechanisms of Evolution How fast can species evolve?

Mechanisms of Evolution Does evolution show patterns? –Divergent evolution Ancestral species evolves into many species that fit different habitats Ex: finches; common on islands

Mechanisms of Evolution Does evolution show patterns? –Convergent evolution Distantly related organisms end up with similar traits Occurs when have similar habitats Ex: cactus in S. American & African deserts

Mechanisms of Evolution Does evolution show patterns? –Convergent evolution

Modes of Selection

Directional Selection Pushes toward ONE extreme or the other Ex: in dry years, beak size pushed to larger

Diversifying Selection Pushes toward both extremes Ex: small beak for soft seeds; large beak for hard seeds; medium beak is bad at both types of seeds so selected against

Stabilizing Selection Pushes to average Ex: cactus with few spines eaten by animals more; cactus with too many spines invaded by more parasites

The End

Quiz – Evolution for use with Questions 1 & 2

Quiz – Evolution for use with Questions 3-5

Quiz – Evolution for use with Question 6

Quiz – Evolution for use with Question 7