Idea of Evolution Species of living things change over time Under the right circumstances this change can produce new species of living organisms from existing ones

Before Darwin Theology played a major role in thought. Christian Bible accepted as literal truth and was used for knowledge of the natural world. All life, and existence itself, were a simultaneous creation of a supernatural being (God).

Emergence of Evolutionary Thought Sequence of Fossil Types Existence of Rudimentary Organs Evidence of Common Underlying Plan Facts of Animal & Plant Breeding Struggle for Existence Evidence of New Explorations

Sequence of Fossil Types By 18th century fossils recognized as remains of critters that had become extinct or still existed but in different forms. In other words, living things changed.

Rudimentary Organs Non-functional eye bulbs In cave-dwelling salamanders Pelvis & femur in whales Check out the article on whale evolution at: If organisms were created "de novo," why do they retain these vestiges?

Common Underlying Plan All mammals’ forelimbs are constructed on a similar anatomical plan due to a SHARED ANCESTRY.

Animal & Plant Breeding Starting with the ancestral rock pigeon (middle), Darwin produced a wide variety of morphologically distinct types in a few generations by selective breeding.

Struggle for Existence The elephant, one of the slowest breeders in the animal kingdom, could take over the planet if it reproduced unhindered for long enough. Even if after only 500 years, one pair would leave 15 MILLION descendants. So why aren’t there at least 15 million elephants?

Evidence of New Explorations

Ideas That Shaped Darwin’s Thinking Georges-Louis de Buffon ( ): Uniformitarianism James Hutton ( ): Founder of modern geology; geological forces worked very slowly, thus earth very, very old Charles Lyell ( ): Principles of Geology; Formalized uniformitarianism; Stimulated Darwin: if earth changed over time, what about life?

Uniformitarianism Mt Vesuvius C.E. 79; last time 1944 Mt. St. Helens 15 eruptions in last 4000 years SF Quake C.E Pinnacles Began as a volcano that first erupted about 195 miles south of its present location. It has traveled northward along the San Andreas Fault, and currently moves at a rate of about cm/year. Oxbow Lakes

Geological Forces Work Slowly Marine terraces north of Santa Cruz. Coastal uplift: 5 mm/yr Mt. Everest Uplift: 10mm/yr

Pre-Darwin Explanation of Evolution Jean-Baptiste de Lamarck ( ) –Plants / animals adapted to their environments –When environment changes (as the geological record shows), organisms must change if they are to continue to exist –Organisms change because they WANT or FEEL A NEED to change –Inheritance of Acquired Characteristics

Acquired Characteristics

Darwin’s Explanation for Evolution We’re not created equal (variations in phenotypes & genotypes) Limited stuff (finite resources) Produce more offspring than finite resources can support Struggle for existence Favorable vs. unfavorable traits (relative to the environment) Inheritance

Not Created Equal Over the past 200,000 years or so, natural selection favored subtle variants allowing different human populations to adapt to their different environments.

Limited Stuff

Too Many Babies Too Few Resources

Struggle For Survival

Favorable vs. Unfavorable Traits

Variants best adapted to conditions of life are most likely to survive & reproduce

Over time, favorable traits increase, less favorable traits decrease

Darwin’s Conclusions Nature an open-ended process of becoming: life continually evolves Emergence of new species: result of Descent with Modification Evolution NOT a single line of ascent but an irregularly branching tree (adaptive radiation)

Darwin vs. Lamarck

Descent With Modification

The Genetic Code Life has the same underlying genetic code DNA sequences of organisms are similar

Evolution A change in the relative frequencies of alleles in a population from one generation to the next

HOW DOES EVOLUTION WORK? Natural Selection Mutation Genetic Drift Gene Flow