SC State Science Education Standard B-5 Indicator 5.5

1. SC State Science Education Standard B-5 Indicator 5.5 The Evidence for Evolution

2. Indicator B-5.5 • Exemplify scientific evidence in the fields of anatomy, embryology, biochemistry, and paleontology that underlies the theory of biological evolution. • This is a crucial indicator! • Science is based on evidence, not beliefs. • Why do scientists conclude that evolution happens? • Why did Darwin reach this conclusion ~150 years ago? • Why did some scientists propose evolutionary ideas even before Darwin? • Paleontology – Lamarck, 1809 • Comparative anatomy – Buffon, 1760

3. Paleontology: The study of fossils

4. A brief historical aside:Why was evolution “discovered” by European scientists in the 1800’s, and not sooner? • Hint: What major sociological upheaval was happening in 19th-Century Europe? • The Industrial Revolution! • What fueled the industrial revolution? • Coal! • What is coal and where do you find it? • It’s a FOSSIL fuel and you find it underground. • What else do you find along with it? • Lots and lots of other fossils, in the coal itself and in the sedimentary rocks above and below it. • The Victorians were fascinated by FOSSILS!

5. Formation of fossils • There are many kinds of fossils. • Replacement fossils and casts – body parts are replaced by minerals (dinosaur bones, petrified wood) • Compression fossils – chemically-altered organic matter left in the rocks (fern leaves, coal) • Trace fossils – tracks, eggs, feces • Microfossils – bacteria & other microbes • The fossil record is extensive, but has many gaps. • Most things don’t fossilize when they die. They ROT! • Soft body parts rarely fossilize. • Fossils form under certain peculiar climatic conditions.

6. What do fossils tell us? • Life long ago was very different from today. • Species that once lived on earth are now extinct. • Just as importantly, species that now are common once did not exist. • So life on earth has changed – evolved! • There are patterns in the fossil record. • The farther back you go, the more “different” it gets. • This basic fact is incredibly important. It sometimes gets forgotten in a rush to memorize details from all the eras and periods. • For some groups, we have excellent series of transitional fossils, despite those gaps in the fossil record.

7. The Geologic Time-Scale A wealth of detail, but don’t lose track of the most basic thing that it shows – a pattern of transition from unfamiliar floras and faunas to those that are progressively more similar to today

8. Transitional fossil series • There are many examples – • Hominids • Horses • Mollusks • Birds • And many others! • Understand the limitations of the fossil record – • We can’t see the transition minute-by-minute. • Transitions can seem abrupt. That’s because the evolution may have happened somewhere else, and then the newer form migrates in.

9. Comparative Anatomy • Patterns of similarity among living species suggest common ancestry. • Similarity of limb bones in vertebrates:

10. Two types of similarity • Analogous structures – similarity due to functional necessity (it must be structured that way or it won’t work). • Analogous similarity is NOT evidence for evolution.

11. Homologous structures • Homologous structures are similar regardless of (and sometimes in spite of) differences in function. • Homology results from common ancestry. Grasping Walking Paddling Flying

12. Another example of homology: structure of eukaryotic cilia and flagella

13. Homologies include vestigial organs, which have lost their original function • Vestigial leg bones in whales • Vestigial hind limbs in pythons • Vestigial human traits • Arrector pili muscle (causes goosebumps) • Tailbone (coccyx) • Appendix has lost its original digestive function, though it does act as part of the lymphatic system.

14. Embryological similarities • Homologies may be more obvious in early embryonic stages than in adults. • Why? Evolution often works by changing developmental processes. Embryos more clearly show the ancestral body plan.

15. Chordate Embryology • All chordate embryos share certain features: • Post-anal tail • Pharyngeal pouches (These develop into gills in fish, facial features in mammals; they used to be called “gill slits” but that name is misleading.) • Don’t confuse this with the discredited idea of “ontogeny recapitulates phylogeny” • E. Haeckel proposed in 1874 that embryo development “re-plays” the evolutionary history of the species. • His drawings of embryos were distorted in order to provide better support for his own hypothesis. • Haeckel was discredited in his own lifetime. • This doesn’t deny the fact that embryos are very similar.

16. Biochemical homologies • Certain molecules, especially proteins, are common across all living things. • The three-dimensional structures of cytochrome c (electron transportprotein) are shown at right for afish and a plant. • Overall structure and function are very similar, but amino acid sequences vary slightly.

17. Amino acid sequence variations in cytochrome c from various organisms

18. Differences in amino acids plotted against time since divergence, as estimated from the fossil record. • Conclusion: • The longer ago two groups diverged, the more different their cytochrome c molecules will be.

19. The most striking homology of all: The universal genetic code