unit vi - evolution ~ a unifying theme of biology ~

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


• 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


• 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• 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


– Embryology• Early similarities may show relation


– Embryology


– Biochemistry• Similar chemicals in most life forms (DNA, ATP)• More similarities in code means closer

relationship


– Anatomy• Homologous structures

– Similar origin, but may now have different function– Shows common ancestry– Ex: bird wing, whale flipper, human arm


– Anatomy• Analogous structures

– Similar function, but very different structure– Shows separate development…not related– Ex: bird wing & butterfly wing


– Anatomy


– 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


• 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


• 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)


• 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,…)


• 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)


• 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


– Convergent evolution• Distantly related organisms end up with similar

traits• Occurs when have similar habitats• Ex: cactus in S. American & African deserts


– 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 – Evolutionfor use with Questions 1 & 2

Quiz – Evolutionfor use with Questions 3-5

Quiz – Evolutionfor use with Question 6

Quiz – Evolutionfor use with Question 7

unit vi - evolution ~ a unifying theme of biology ~

Documents

indirect evidence of

biological evolution

evolutionwhat direct

darwin form ideas

unit vi evolution

variationsdarwins ideahow

timedarwins ideahow

olddarwins ideahow