Transcript Lecture 19
C. Thomas Malthus (an economist) 1. Essay on the Principles of Population (1798) a. populations of organisms increase geometrically b. rate of reproduction too high to be sustained c. warning against human overpopulation 2. but in nature, this does not seem to occur 3. Darwin’s answer: death (selection) limits population numbers 4. This provided missing link for Darwin D. Alfred Wallace 1. came to same conclusions while in Indonesia 2. published his findings along with Darwin (1858-59) E. Darwin: On the Origin of Species by Means of Natural Selection 1. descent with modification 2. closely related species likely from common ancestor Darwin’s Theory Hypothesis 1: Every organism has the potential to leave more than one offspring. Hypothesis 2: The number of individuals within a species remains fairly constant over time. Prediction A: If 1 and 2 are true, then not all individuals realize their reproductive potential. Hypothesis 3: Individuals within a species vary in terms of their traits. Hypothesis 4: At least some of these traits are inherited. Prediction B: If A, 3, and 4 are true, then some individuals are better suited for their environment, leaving more offspring. Their traits become more common. Darwin’s Theory Better suited individuals have inherited those traits, and they pass them on to their offspring. Survival of the fittest = Reproduction of the fittest. What is the evidence for evolution? Silurian and Devonian fishes (Modified from Fenton and Fenton, 1958) Jurassic and Cretaceous fishes (Modified from Romer, 1966) Radiometric dating (Section 15.5 in the text) Half-life of 14C is 5,730 years (Modified from Bushee and others, 2000) (Modified from Bushee and others, 2000) Biostratigraphy: The science that deals with the distribution of fossils in the rock record and organizes strata into units on the basis of their contained fossils. The oldest layer is on the bottom. Rocks were deposited one layer at a time from the bottom up. (Pojeta and Springer, 2001) The combination of strata and radiometric dating clearly demonstrates progressive change in the fossil record. (Modified from Ward and Blackwelder, 1975) Organisms have evolved in a historical sequence. oldest: prokaryotes next: early eukaryotes next: fish next: amphibians next: reptiles next: mammals next: birds Biogeography 1. geographic distribution of species suggests evolution from common ancestors 2. Galapagos and South America 3. Australian marsupials Comparative Anatomy 1. Homologous structures from common ancestor Comparative Anatomy 1. Homologous structures from common ancestor 2. Analogous structures (15.14) similar structures as the result of separate lineages flippers of dolphins and penguins Comparative Anatomy 3. Vestigial structures non-functional structure inherited from ancestor served a useful purpose in the ancestor Human Appendix Human arrector pili muscles and body hair Human Coccyx Muscles that move the ears Wisdom Teeth Wings on flightless birds Astyanax mexicanus Blind cave-dwelling fish Dandelions have sex organs, but don’t use them. Virgin female whiptail lizards (several species) unisexual: all female will still occasionally “mount” other females Comparative Embryology 1. embryos among some species very similar 2. all vertebrate embryos almost indistinguishable at certain stages Molecular Record 1. as organisms change, so should their genes 2. the more change the more alterations in the nucleotide sequence over time 3. select a gene to study a. organisms more distantly related have greater numbers of differences in their genes b. closer relatives, fewer differences 4. molecular family trees a. support the fossil record b. confirm the “clusters” seen in the fossil record