EvolutionEvolutionLesson 1: Lesson 1:

An Introduction to Charles Darwin An Introduction to Charles Darwin and the Nature of Scienceand the Nature of Science

““A scientist, however, gifted, can be A scientist, however, gifted, can be compared with a fly crawling on the inside compared with a fly crawling on the inside wall of a cathedral; if it could draw what it wall of a cathedral; if it could draw what it sees, the fly’s picture of the cathedral would sees, the fly’s picture of the cathedral would be as crude as early maps of the world; if it be as crude as early maps of the world; if it could voice its speculations about the size, could voice its speculations about the size, appearance, and purpose of the cathedral, the appearance, and purpose of the cathedral, the fly’s opinions would be received even more fly’s opinions would be received even more guardedly.”guardedly.”

-- Frederick Aicken, The Nature of Science , pp.29-30

Evolution As An IdeaEvolution As An Idea“ If I were to give an award for the single best idea anyone has ever

had, I’d give it to Darwin, ahead of Newton and Einstein and everyone else. In a single stroke, the idea of evolution by natural selection unifies the realm of life, meaning and purpose with the

realm of space and time, cause and effect, mechanism, and physical law. But it is not just a wonderful idea. It is a dangerous idea.”

Daniel Dennet

Evolution as an IdeaEvolution as an Idea“Evolution is one of the most powerful ideas ever to emerge from science. It is the very foundation of biology and the key to understanding our own human origins. The mechanism of evolution helps determine who lives, who dies, and who gets the opportunity to pass on traits to the next generation. At the same time, evolution ranks as one of the most widely misunderstood scientific principles in America today.”

Richard Hutton, Executive Producer, Evolution WGBHJody Patton, Executive in Charge, Clear Blue Sky

productions

Darwin’s Voyage of DiscoveryDarwin’s Voyage of Discovery

Galapagos IslandsGalapagos Islands

Galapagos IslandsGalapagos Islands

Figure 22.6 Galápagos finches

http://www.cruisesingalapagos.com/wildlife-reptiles4.htm

Darwin and the GalapagosDarwin and the Galapagos

Consider the following:Consider the following:

1. How did the Galapagos Islands get there?2. How did the first plants get there?3. How did the first animals get there?4. What is ecological succession?

Ecological SuccessionEcological Succession

• process in which communities of plants and animal species in a particular area are replaced over time by a series of different and often more complex communities.

• Two stages– Primary succession– Secondary succession

Primary SuccessionPrimary Succession

succession in a bare area (no mature soil) that has never been occupied before

Secondary SuccessionSecondary Succession

succession in an area in which natural vegetation has been removed or destroyed but the soil remains

Ecological SuccessionEcological Succession

Darwin’s Theory of Natural Selection1. Variations exist2. These variations are heritable3. Some variations are advantageous and some are

disadvantageous4. Organisms compete for limited resources5. Organisms with advantageous variations survive and

reproduce most successfully, leafing more organisms like them in the next generation

6. Over time, the population changes to become more like the organisms with advantageous variations

7. Today’s species have descended from past species8. All organisms are related and are members of a single tree

of life

Examples of Natural Selection

English Peppered Moth

Darwin's Finches

Darwin’s Theory of Natural Selection• Individual organisms differ; variation is

heritable• Organisms produce more offspring than can

survive; they compete for limited resources• Some variations are advantageous; individuals

best suited to their environment survive and reproduce successfully

• Species alive today descended with modification from ancestral species that lived in the past

Darwin’s Tree of Life

Evolutionary Classification Using Cladograms• Cladogram – diagram used to show the evolutionary

relationship between organisms• Cladograms are constructed using derived

characteristics– Derived characteristics - characteristics that appear in

recent parts of the lineage but not in older members; new characteristics that evolve over time

– Each branch or junction shows the appearance of a new trait

– Cladograms demonstrate when characteristics first appeared

Cladogram of vertebrates

http://www.emc.maricopa.edu/faculty/farabee/biobk/cladogram_1.gif

http://biology.unm.edu/ccouncil/Biology_203/Summaries/Phylogeny.htm