Unit 10: Evolution Ch. 29 Evolution

History of Earth Earth ~4.6 billion years old –early Earth hostile environment –volcanoes, lightning, meteorites, UV light primitive atmosphere –methane, ammonia, hydrogen, water vapor »What’s missing?

Origin of Life Life ~3.5 billion years old Miller & Urey –simulated primitive atmosphere zapped w/ electricity –~1 week amino acids & other simple organic molecules formed (in water) »precursors to 1 st cells

“Heterotroph Hypothesis” or “Primordial Soup Hypothesis” –Started w/ simple compounds  complex compounds  primitive pre-cells  prokaryotes (1 st cells) 1 st cells were heterotrophs –Why heterotrophic? »b/c no O 2 for cellular respiration/photosynthesis –fed on organic material (primordial soup in ocean) »Similar to some present-day bacteria, obtained energy from simple chemical reactions The First Organisms: Heterotrophs

prokaryotic autotrophs followed heterotrophs –What did they release into the atmosphere? oxygen (causing the oxygen revolution!) –Why is this so important? »allowed development of eukaryotes & complex organisms Later Organisms: Autotrophs stromatolites

theory that species have changed gradually over time –individual’s genes stay the same –population’s gene pool (total genes) may change evolves as allele frequencies (%) (how often an allele occurs) change due to natural selection What is Evolution?

Mechanisms of Evolution migration genetic drift mutation natural selection

migration –gene frequencies change as individuals move in or out of the population Mechanisms of Evolution genetic drift –change in gene pool of a small population that takes place strictly by CHANCE

Mechanisms of Evolution mutation –random change in the DNA sequence of a gene can change amino acid sequence & protein coded for –can change the way the trait is expressed not all mutations matter in evolution –must be heritable (in gametes)

natural selection –organisms with variation best suited for environment tend to survive, & reproduce (“survival of the fittest”) more offspring will have favorable adaptation than before –acts on individuals, but causes evolution of population Mechanisms of Evolution Which trait was a better adaptation and selected? How were frequencies of different alleles affected?

Explanations for How Evolution Happens Jean Baptist Lamarck –“Theory of Acquired Characteristics” acquired traits are passed on –leads to changes in species –experimentation failed to support Lamarckism

Charles Darwin –naturalist on HMS Beagle collected fossils & specimens observed tremendous biodiversity Explanations for How Evolution Happens desert large rainfall intermediate shell domed Shell saddle- backed shell Climate varied from island to island.

–concluded, life forms can & do change…. but, questioned how this change occurred… –concluded  evolution or “descent with modification” »still needed to test ideas before explaining how or why such changes happen Explanations for Evolution

–wrote On the Origin of Species by Means of Natural Selection (1859) –Darwin’s Main Points: 1.Overproduction of offspring 2.Struggle to survive –competition 3.Variation within population 4.Successful reproduction –“survival of the fittest”/best adapted organisms are “naturally selected” Video: Who Was Charles Darwin? Darwin’s Explanation: Natural Selection

1.Overproduction of offspring –Why is this necessary? to ensure that at least some will survive long enough to reproduce & pass on genes Video: Darwin & Malthus

2.Struggle to survive –more organisms than resources to go around leads to competition For what? –food, shelter, mates, space, light, water, nutrients, etc. Survivors  –Who are they? –How did they get these traits? –Were these traits a response to their environment? Darwin’s Explanation: Natural Selection

3.variation w/in population –What causes variety? Sexual reproduction Crossing over during meiosis Arrangement of chromosomes during meiosis Mutations –Darwin did NOT have knowledge of genetics Darwin’s Explanation: Natural Selection

variations –can be adaptations –are NOT a response to environment just happen to be “useful” when environment changes camouflage Darwin’s Explanation: Natural Selection

4.successful reproduction –natural selection Those organisms best suited for environment tend to survive, reproduce, & pass on genes (“survival of fittest”) –more offspring have favorable adaptation than before Darwin’s Explanation: Natural Selection Pepper Moth “Game” Principles of Natural Selection "Interactive"

How would Darwin adjust the description given by Lamarck about the length of giraffes necks? Lamarck vs. Darwin

Alfred Wallace (1858) –arrived at same basic explanation as Darwin Darwin usually given credit –but BOTH men should be credited Darwin’s Explanation: Wallace’s Same Conclusion

Evidence to support the Theory of Evolution indirect evidence –fossil record –comparative anatomy –comparative embryology –comparative biochemistry direct evidence –current observations

Indirect Evidence: Fossil Record Fossil Record –Evidence of: change in organisms over time age of the Earth –Limited b/c: decomposition type of material –What fossilizes best? incomplete record –Why? easily disrupted –Why? Which layer is youngest? oldest? Explain… Law of Superposition

Indirect Evidence: Comparative Anatomy comparative anatomy –compares structures of diff. organisms living today 1.homologous structures 2.analogous structures 3.vestigial structures

1.homologous structures similar structure w/ modifications −evidence of common ancestor becoming more different (divergent evolution) Indirect Evidence: Comparative Anatomy

2. analogous structures –similar function, but not structure due to similar environment/use do NOT have common ancestor –becoming more similar (convergent evolution) Indirect Evidence: Comparative Anatomy

3. vestigial structures –structures with reduced size or function often no apparent use anymore –evidence that organism has changed Indirect Evidence: Comparative Anatomy

embryonic development –early stages  very similar later stages  more distinction –inherited same basic body plan from common ancestor greater # similar stages  more closely related Indirect Evidence: Comparative Embryology

Indirect Evidence: Comparative Biochemistry similar organic compounds coded for by similar DNA –ex. proteins

DNA  most reliable form of evidence What is the significance of 2 very different species sharing large amounts of the same DNA? –evidence of common ancestry higher %, more closely related –human & chimpanzees 98% similar –humans & other mammals 80% similar Indirect Evidence: Comparative Biochemistry

Direct Evidence: Observation “rapid” evolution 1.antibiotic- resistant bacteria 2.pesticide- resistant insects