Welcome to Introductory Biology (BIOL 202)

Biology 202: Introductory Biology Unit 1 : Mechanisms of Evolution Unit 2: Evolutionary History of Biological Diversity Unit 3: Plant Form and Function Unit 4: Animal Form and Function Unit 5: Ecology

Overview of Unit I: Mechanisms of Evolution Descent with Modification: A Darwinian View of Life The Evolution of Populations The Origin of Species Tracing Phylogeny

Chapter 22: Descent with Modification Development of ideas that culminated in the theory of evolution Darwin’s research Evidence for Evolution

Darwin’s Conclusions, in a nutshell Evolution happens; species’ characters (traits) change over time and indeed such evolutionary change may result in origin of new species from existing ones Natural selection is the process that drives evolution; evolution is a consequence Diversity of life on earth is the consequence of evolution, and all organisms, ultimately, share a common ancestry

Aristotle’s non-evolutionary concepts, including immutability of species and “Scala Naturae” that were incorporated in Christian Theology and remained the principal model of biological thought for 2000 years – until the 18 th century

World exploration, the renaissance, the protestant reformation…all contributed to a new intellectual atmosphere that led to the advance of scientific empiricism and rationalistic thinking

19 th Century England: The Intellectual Context in which Darwin Developed His Ideas Important concepts, publications that strongly influenced early 19 th century scientific thinking Botanist Carolus Linneaus Systema Naturae Reverend William Paley Natural Theology Ettiene George St. Hillaire Environmentalism Comparative anatomist Cuvier Catastrophism Radical 19 th century geological concepts about the nature and pace of geological processes –age of earth- that influenced Darwin’s thinking during the voyage Geologist Hutton Gradualism Geologist Lyell Uniformitarianism Concept that influenced Darwin’s thinking after the voyage Thomas Malthus An Essay on Population

Course of the HMS Beagle’s World Journey Continental comparisons of floras and faunas Taxa showed continental affinities --even to the point that plants and animals from temperate South America showed a stronger affinity to those of tropical South America than those of temperate Europe

Within-continent comparisons of fossil and living taxa Found fossils of extinct taxa that appeared to be ancestral to living taxa found there – i.e., distinct resemblances to living South American taxa

Unique “species groups” with curious distributions on the Galapagos Islands Found that most species were “endemic”, yet bore resemblance to South American taxa, with unique distribution on the archipelago

Observation 1. All species have potential fertility for exponential population growth Observation 2. Populations tend to remain stable in size Observation 3. Environmental resources are limited Inference 1: More individuals are produced than can survive; struggle for existence leads to survival of a fraction of offspring each generation Observation 4: Individuals within a population vary extensively in their characteristics Observation 5. Much variation is heritable Inference 2. Survival is not random; depends in part on hereditary makeup; individuals with inherited traits best fit to the environment are likely to have more offspring than others Inference 3. Unequal survival and reproduction will lead to gradual change in a population, with favorable characteristics accumulating over generations Darwin’s Line of Reasoning in Support of Descent with Modification (Evolution through Natural Selection)