Four Historical Theories of Organic Change

1. Four Historical Theories of Organic Change • Cuvier, Buffon, Lamarck, and Darwin

2. Georges-Louis LeClerk, Compte de Buffon 1707-1788 • Thought an artificial taxonomy was a waste of time. Naturalists should search for a natural taxonomy, find the order in nature. • Asked by the King to catalog the Royal Garden collection, Buffon decided to catalog everything in nature. • Wrote 36 volume Histoire naturelle, générale et particulière.

3. The Moule Intérieur, said Buffon, was caused by particles inside of an organism. Horses in Europe remain brown and distinctly horse-like because their environment arranges the particles into a horse shape. Move the horses to Africa, and the environment rearranges the particles, especially in the embryos, which reshapes the animals over generations. All animals are affected equally, and over many generations, the particles reshape the horses into zebras.

4. Georges Cuvier 1769-1832 • Supported the “static model” of species — species do not change because they cannot survive changes. • Comparative anatomist: looking for patterns in structure, especially among vertebrate animals. • Set up a natural, non-hierarchical taxonomy of animals based on the nervous system.

5. Jean-Baptiste Pierre Antoine de Monet de Lamarck 1744-1829 • Protegé of Buffon. Interested in natural classification of living organisms. • Background was in Botany, but later studied invertebrates. • Primary questions: Where do you draw the line between species? How do you “rank” species? • Favored a theory of inheritance of acquired characteristics.

6. Woo-hoo, guys, we’re alive! Lamarck’s “Organic Law of Development” • Spontaneous Generation creates new, simple organisms, such as bacteria.

7. Hmm, changes... I need to get organized here. Ooh, a nucleus! Problem solved! Lamarck’s “Organic Law of Development” • Organisms are shaped by their environment.

8. Being an amoeba is the pits. I can’t wait until we all become multicellular. Cool! Tissues! Maybe we’ll get real organs soon. Organs and bilateral symmetry! Yeah! Can’t wait until we turn into mammals! Lamarck’s “Organic Law of Development” • Change is teleological (goal-directed). Organisms have an internal drive to become more complex.

9. I’m not short, I’m vertically challenged. Sure, blame me, when you’re the one who hardly left the barn before he was born. Lamarck says it’s your fault, Stanley, that Junior’s legs are so short. If you weren’t such a couch potato and had gotten some exercise... Lamarck’s “Organic Law of Development” • Use and disuse of parts causes change that is passed on to the next generation.

10. Charles Darwin 1809-1882 • Charles attended boarding school as a boy, where he developed an interest in Natural History. • Father sent him to study medicine in Edinburgh. Turned off by barbaric surgery practices and dull lectures. • Joined Natural History society, read Buffon, Cuvier, Lamarck, others.

11. Darwin left Edinburgh determined not to be a physician. Attended Cambridge, thinking he would be a clergyman. • At Cambridge, he read Herschel (philosophy of science), Humboldt (geological distribution of organisms), Lyell. • After graduation in 1831, Darwin was encouraged by friends to apply to be a captain’s companion and naturalist on board the Beagle. • December 27, 1831: Joins Captain Fitzroy on board the Beagle for a five-year journey.

12. Voyage of the H.M.S. Beagle • Official purpose of the voyage was to survey the South American coast. • During the voyage, Darwin observed a volcanic eruption, an earthquake, and noted geologic features suggesting an ancient earth. • In South America, found fossils of ancient sloths, observed living rheas (ostrich-like birds) and llamas, many other animals not described by naturalists. Collected huge numbers of specimens.

13. The Galapagos • In September of 1835, the Beagle reached the Galapagos Islands. • Fascinated by the giant tortoises. Brought three back alive. • Made detailed observations of finches, mockingbirds. Realized that they resembled birds on the mainland, yet were different. Where did they come from? • Besides the Galapagos, Darwin observed organisms on Tahiti and other Pacific islands. Later developed theories of coral reef building.

14. Darwin’s questions • Why the replacement of species geographically; that is, why are the species on islands not exactly the same as those on the nearby mainland? • Why the replacement of species in time? • Where do species come from in the first place? • Change in species appears to be the answer — but how do species change?

15. Natural Selection • Darwin rejected the idea that all members of a population are shaped equally by the environment and that all change together. Selection does NOT look like this: Generation 1 Generation 100 Generation 200

16. Natural Selection • Rather, selection begins with variation. Some variants in a population may be at an advantage, some at a disadvantage. Those with a strong advantage are more likely to have offspring. • “Fitness” is the ability to survive. • “Success” is passing one’s traits to the next generation.

17. Natural Selection • Natural Selection looks more like this. Suppose in a population of horses, black horses get hotter in the sun and are more likely to die of heat exhaustion. Generation 1 Generation 2

18. Natural Selection • But suppose global climate changes alter the local environment. It becomes cooler and cloudier. Now the black horses have an advantage because their black coats help them stay warmer.

19. Natural Selection • Notice the difference: • Buffon and Lamarck would say, “The horses need to be darker, so they will get blacker and blacker each generation.” • Darwin says, “Black horses are better able survive and reproduce each generation, so there will be more and more black horses each generation.”

20. Darwin’s New Questions • Darwin noted two difficulties in his original theory of Natural Selection: • Where did variation come from in the first place? • How did favorable traits get passed on to the offspring, if traits of each parent are blended in the offspring (as was commonly believed at the time)?

21. In the 20th Century... • Darwin’s questions led other scientists to explore heredity, which led to the science of genetics. • Genetic research in the 20th century supported natural selection as a plausible mechanism, and raised new questions and new possibilities.