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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 18th 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
19th Century England: The Intellectual Context in which Darwin
Developed His Ideas
Important concepts, publications that strongly influenced early 19th century
scientific thinking
•Botanist Carolus Linneaus
Systema Naturae
•Reverend William Paley
Natural Theology
•Ettiene George St. Hillaire
Environmentalism
•Comparative anatomist Cuvier
Catastrophism
Radical 19th 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
Darwin’s Line of Reasoning in Support of Descent with
Modification (Evolution through Natural Selection)
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