Module 1: Evolution MonthDayTopic Aug28History of life on Earth 30Theory of evolution Sept1Timeline construction 4Holiday 6Evidence for evolution 8Mechanisms of evolution I 11Mechanisms of evolution II 13Speciation

Outline 1.History 2.Cultural and scientific context of Darwin’s theory of evolution 3.The theory 4.Modern ideas

Organic evolution The descent of modern organisms with modification from preexisting life-forms

Time Cosmological Geological Evolutionary Ecological Physiological

Hierarchy of scientific information Theory Fact Model Hypothesis

Hypothesis--a limited statement implying cause and effect in certain situations.

Model--a hypothesis that has been shown to have more general validity.

Fact–a highly corroborated hypothesis that has been so repeatedly tested and for which so much reliable evidence exists, that it would be perverse or irrational to deny it.

Theory or Law—unification of facts. A unifying and self-consistent explanation of fundamental natural processes or phenomena that is totally constructed from facts.

Cultural and scientific context of the theory of evolution

Idea of fixed species Ancient Greeks (2500 years bp): –species do not change

Idea of fixed species Ancient Greeks (2500 years bp): –species do not change Judeo-Christian (2000 years bp): –species do not change –each species divinely created –earth ~ 6000 years old

Confounding Evidence Biogeography Comparative anatomy Geologic discoveries

Confounding evidence: Biogeography Size of the known world expanded in the 15th century Discovery of new organisms could not be explained by accepted beliefs –How did species get from center of creation (e.g., garden of Eden) to all these places?

Confounding evidence: comparative morphology Study of similarities and differences in body plans of major groups Puzzling patterns: –Animals as different as humans and dogs have similar bones in forelimbs –Some parts seem to have no function

backbone pelvic girdle coccyx (bones where many other mammals have a tail) small bone attached to pelvic girdle thighbone attached to pelvic girdle

Geological Discoveries Similar rock layers throughout world Certain layers contain fossils Deeper layers contain simpler fossils than shallow layers Some fossils seem to be related to known species

1800s - New Theories Scientists attempt to reconcile evidence of change with traditional belief in a single creation event Two examples –Georges Cuvier ( ) - multiple catastrophes –Jean Lamarck ( ) - inheritance of acquired characteristics

The New Geology Hutton and Lyell (1830s): –Uniformitarianism: the present is the key to the past –Gradualism: slow process over vast periods of time can cause big changes –Earth is seriously old!

Principles of populations Thomas Malthus ( ): –Exponential growth of populations

Principles of populations Thomas Malthus ( ): –Exponential growth of populations –“Positive checks” on population growth War Disease Famine –As populations increase, resources dwindle, the struggle to live intensifies, and conflict increases

Charles Darwin ( ) Collected and examined the species that inhabited the regions the ship visited Started 5 year, round-the- world voyage aboard the Beagle at age 22

The voyage of H.M.S. Beagle

Pleistocene glyptodont Modern armadillo

Evolution: Descent with modification But what causes modification? What is the mechanism?

Galapagos Finches Darwin observed a variety of lifestyles and body forms On his return, he learned that there were 13 species He attempted to correlate variations in their traits with environmental challenges

Darwin’s facts Any species is capable of increasing its population exponentially BUT we rarely see this increase—populations tend to stay within certain limits Conclusion: not all offspring produced survive Conclusion: there is a “struggle for existence” going on in all species

Darwin’s facts Individuals in any species vary Some vary in ways that help them survive and reproduce; others vary in ways that decrease their chances of survival Variation is inherited (somehow) Conclusion: a species will change over time, producing new and different varieties (evolution)

Darwin’s theory –Fact #1: Overproduction and struggle for existence –Fact #2: Heritable individual variation The inescapable conclusion: Differential or unequal reproductive success causes evolution. He called this natural selection.

Artificial selection as an analog of natural selection

Natural selection Charles Darwin ( s): Ruminated on theory, but didn’t publish Alfred Wallace (1850s): Independently developed a theory similar to Darwin’s Darwin and Wallace “co-published” the theory in 1858 Darwin published The Origin of Species in 1859

Evolution: Descent with modification

Evolution: Descent with modification Natural selection: Differential reproductive success

Evolution: Descent with modification

Natural selection: Differential reproductive success

Darwin’s theory –Fact #1: Overproduction and struggle for existence –Fact #2: Heritable individual variation (no clear mechanism yet) The inescapable conclusion: Differential or unequal reproductive success

Ever since Darwin...

Mendel develops theory of heredity (1860s) –Parents pass onto their offspring discrete, heritable factors that are responsible for inherited traits. –Discrete, heritable factors = genes –Genes act in predictable ways

Ever since Darwin... The “Modern Synthesis” (mid-1900s): –Often called “Neo-Darwinism” –Adding in population genetics –Mathematical models of evolution

Ever since Darwin... The molecular era (mid 1900s-present) –Discovery of DNA as the basis of heredity –Adding in a molecular mechanism –Detecting the relationships among species

Ever since Darwin... The era of genomics (1990s-present) –Mapping of genomes –Rapid sequencing of genes –Creation of molecular phylogenies