Evolution & Darwin

1. Evolution & Darwin Chapter 22

2. Setting for Darwin • Darwin made 2 main points • Many species currently alive are descendents of ancestral species • Ancestral species were different than modern species • Evolution? • Natural selection is the mechanism for this evolution • Certain heritable traits are better suited to the environment • Individuals with these traits leave more offspring • Over generations, population can change

3. Darwin Continued • Natural selection results in evolutionary adaptation • Accumulation of inherited characters that enhance organisms’ ability to survive and reproduce in a specific environment • Evolution • Populations evolve not individuals • Change in genetic composition of a population • May lead to speciation (new species formation)

4. Setting for Darwin • Darwin challenged Young Earth views (1859) • Prevailing belief was that Earth was only few thousand years old • Life forms had all been created at the beginning • Life forms had NOT changed over time • Aristotle – (Scalanaturae) • All species are perfect and permanent • Old Testament • All species were designed by God and therefore perfect

5. Linnaeus • Grouped similar species into increasingly general categories • Grouped according to pattern of their creation • Classify life for the greater glory of God • Taxonomy • Naming and classifying of organisms • Kingdom, Phylum, Class, Order, Family, Genus, Species • Binomial nomenclature • 2-part naming system (Canisfamiliaris)

6. More People • Hutton & Lyell • Uniformitarianism • Geologic processes that shaped the planet have not changed over the course of Earth’s history • The Earth must be millions of years old • Darwin link: He reasoned that if geologic changed occurred slowly over long periods of time, what about animals?

7. Final Non-Darwin Person • Jean-Baptiste de Lamarck • Hypothesized that evolution occurred but was wrong about the mechanism • Use & Disuse • Parts of the body used extensively become larger and stronger, those that aren’t deteriorate • Inheritance of acquired characteristics • Characteristics acquired during an organism’s lifetime can be passed on to the next generation • Governator’s children • Giraffe parents with longer neck = longer neck kids

8. Darwin’s Evolution • Traveled on the HMS Beagle • Mechanism for evolution was natural selection • Lamarck said the mechanism was ??? • Adaptations • Characteristics that enhance organism’s ability to survive and reproduce in specific environments • Natural selection • Individuals with certain inheritable characteristics survive and reproduce at a higher rate than other individuals

9. Darwin’s Evolution (Page 2) • Over time, natural selection increases the fitness of the individual to its environment • Leads to evolution of a population • Darwin used “descent with modification” instead of evolution • Ancestral organisms had descendants that dispersed into environments that were different than ancestral environments • Over millions of years & generations they accumulated adaptations to their environments • Adaptations made them more fit to their specific way of life • Think of how organisms went from South America to the Galapagos and then differentiated (adapted) into their different environments and forms

10. Darwin’s Evolution (Page 3) • Environmental Change = gradual adaptation to these new conditions • May result in speciation • A.R. Wallace • Develops and publishes a theory of natural selection similar to Darwin • Published before Darwin, but gave credit to Darwin

12. Artificial Selection • Human controlled selecting and breeding of organisms to produce desirable traits (for humans) • Selective breeding of domesticated plants and animals influenced Darwin’s thinking • Crop plants and animals often bear little resemblance to their wild ancestors • Artificial selection can change much in a short period of time. Natural selection may be able to do so as well

13. 3 main points about evolution • Natural selection affects individuals through interaction with the environment • Individuals do not evolve • Over time the relative frequencies of traits in a population change = evolution of a population • Natural selection can only amplify or diminish heritable traits • If it cant be inherited, then no evolution • Distinguish between acquired characteristics & inherited adaptations

14. Evolution Main Point • Environmental forces vary from place to place and from time to time • A favorable trait at one time/place, may be selected against at another time/place • Natural selection is always at work, but what constitutes a favored trait may be constantly changing

15. 3 Short Answers 1. How do each of the 3 following phrases: “overreproduction of populations”, “limited resources”, and “heritable variations” relate to Darwinian evolution by natural selection? 2. Why is it incorrect to say that individuals evolve? 3. Explain how antibiotic resistant tuberculosis bacteria have arisen.

16. Evidence for Evolution • Direct observation of Evolutionary change • Antibiotic-resistant bacteria & drug-resistant virus populations • The Fossil Record • Paleontology – study of fossils • Fossils show that evolutionary changes have occurred over time • Punctuated equilibrium instead of gradualism • Long periods of stasis punctuated by brief bursts of evolutionary activity

17. Evidence for Evolution (Page 2) • Homology and Convergent Evolution • Homology – structural similarity resulting from common ancestry • Homologous structures – anatomical signs of evolution • Embryonic homologies • Early stages of animal development reveal many anatomical homologies that are not present in the adult form • In vertebrates, Ontogeny recapitulates Phylogeny

18. Anatomical Homologies

19. Ontogeny recapitulates Phylogeny

20. Evidence for Evolution (Page 3) • Vestigial organs • Structures of dubious utility • Remnants of previously important structures • Appendix (humans) • Limb remnants (snakes)

21. Evidence for Evolution (Page 4) • Molecular homologies • Homologies at the molecular level • Everything uses DNA & RNA • Amino acid sequences in hemoglobin in primates is extremely similar (common ancestor) • Convergent Evolution • Two organisms develop similarities as they adapted to similar environments • Analogous structures result, not homologous

22. Stingrays – were dorsoventrally flattened, so they lie on their belly  Note the midline location of the “backbone” column Flounders – laterally flattened, so they lie on their sides  Note the vertebral column on the right

23. Homology v. Analogy • Homologous structures show evidence of relatedness • Whale fin/Bat wing • Analogous structures show similar solutions to similar problems, but do NOT indicate relatedness • Ray and flounder ventral orientation

24. Biogeography • The geographical distribution of a species • Closely related species tend to be found in the same geographical region • Continental drift – breakup of pangaea • Can explain species similarity in disparate geographic regions • Endemic species • Species found in one geographic location and nowhere else • Example: marine iguanas in Galapagos