The Story of Life on Earth Unit VI - Evolution The Story of Life on Earth

Introduction to Evolution What does biological “evolution” mean? Change in a population of 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 O2 in air) First photosynthetic cells 2.8 bln yrs ago Increased O2 in atmosphere Led to ozone layer that protects from UV rays = more cells cells could make ATP better with aerobic respiration

Evolutionary Theory Charles Darwin (1809-1882) “father” of evolutionary theory 1831 spent 5 years on HMS Beagle Visited the Galapagos Islands were he made observations that would inspire his work 1859 published “On the Origin of Species by means of Natural Selection”

Darwin’s Big Idea Natural Selection/Survival of the Fittest Organisms best suited for their environment are more likely to survive and reproduce, passing on the characteristics which helped them survive to their offspring. Gradually leading to change in the population over time.

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? Malthus noticed populations grow faster than their food supplies (they produce too many offspring)

Darwin’s Idea How did Darwin form ideas about evolution? Artificial selection (breeding) has brought about many changes or modifications to species

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

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

Darwin’s Ideas What did Darwin conclude about populations? 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 & MRSA

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

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

Evidence for Evolution What direct evidence supports this theory? Physiological changes Ex: drug-resistant bacteria; MRSA 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? Anatomy

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 Vestigial structures A part that no longer serves a purpose Ex: snake hip bones; human wisdom teeth

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 genetic code means closer relationship

Mechanisms of Evolution Can individuals evolve? No!!! An organism is born with the only genes it will ever have. These cannot be changed in that individual. Only populations can evolve. This occurs when there are changes in the gene frequencies (in the population) 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 (due to chance). Genetic drift may cause changes…especially in small isolated populations. Gene flow – immigration/emigration into or out of population Large populations not as affected by these factors

Modes of Selection

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

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

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

Mechanisms of Evolution How do species evolve? Called “speciation” - the development of a new species (members of same species can breed) For speciation to occur…there are a few things that have to happen… 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? After geographic isolation … Reproductive isolation no longer capable of interbreeding (timing, parts, gametes differ,…)

Mechanisms of Evolution How fast can species evolve? Gradualism Speciation occurs over long periods of time with gradual changes (takes millions of years) Punctuated equilibrium Speciation occurs in quick bursts with equilibrium in between (~10,000 years 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 N. American & euphorbias in African deserts

Mechanisms of Evolution Does evolution show patterns? Convergent evolution

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