THEORIES OF EVOLUTION

Theories  Confirmed through tests and observations  Explain a wide variety of data and observations  Can be used to make predictions  Video Video

Section 1: Darwin’s Influences

Who was Darwin?

Charles Darwin ( )

Darwin’s Influences: Geology  Traditional Beliefs of Darwin’s Time:  Earth less than 10,000 years old and unchanging  James Hutton and Charles Lyell (geologists):  Earth is many millions of years old  Changes through processes like volcanism and erosion

Darwin’s Influences: Jean-Babtiste de Lamarck   Related fossil forms to living animals  Species change as they adapt to their environments

Lamarck’s Explanation 1. Acquired traits passed on to offspring  Acquired trait - arises during an organism’s lifetime 2. Use and disuse  Use it  gets bigger  Don’t use it  gets smaller

Examples of Lamarck’s Explanations

Lamarck’s Rejection  Lamarck’s hypotheses were discarded  Acquired traits cannot be inherited  No genetic basis

Darwin’s Influences: Population Growth  Thomas Malthus  Malthus – human populations outgrow resources  leads to suffering  Darwin – applies to all living organisms

Darwin’s Influences: Artificial Selection  Humans select plants and animals to breed  End up with a variety of domesticated animal breeds and plant crops  Nature provides variations, and humans select those they find useful

Darwin’s Journey

Darwin’s Finches  Observed 13 species of finches on the Galapagos Islands  Descended from single South American species  Offspring of original finches adapted to different environments and food sources

Darwin’s Observations  What else did Darwin observe?  Video Video

Darwin’s Observations  What characteristics made Darwin especially well suited for science?  What did Darwin see and do on his five-year voyage aboard the Beagle?  Why was the publication of On the Origin of Species a courageous act?

Section Two – Darwin’s Theory

The Origin of Species (1859)

Darwin’s Theories 1. Descent with Modification  Newer forms appearing in the fossil record are modified descendants of older species  All species descended from one or a few original types of life

Darwin’s Theories 2. Modification by Natural Selection  How evolution occurs a) Variation exists among individuals in a species b) Many of those differences can be passed on to offspring

Darwin’s Theories 2. Modification by Natural Selection c) Competition leads to the death of some individuals while others survive d) Individuals that had advantageous variations are more likely to survive and reproduce

Important Concepts  A population adapts to its environment as the proportion of genes for favorable traits increases Trees Darken

Important Concepts  Do individuals adapt?  Do individuals evolve?  A single organism’s genetic contribution to the next generation is its fitness

Important Concepts  High fitness = well adapted, reproduces more successfully  Does “survival of the fittest” always mean “survival of the strongest”?  Video Video

If YES – How would Darwin explain the evolution of a particular trait? If NO – Why isn’t this an example of natural selection? Natural Selection: Yes or No?

Polar bears developed light fur from darker-colored ancestors. Do you think natural selection was involved?

Many species of finches are found on the Galapagos, each with differently-shaped beaks. They are all related to a finch in South America. Was natural selection involved?

Blue Tits in GB (related out our Chickadees) have learned to open the tops of milk jars to drink the fat. Birds teach their offspring to do the same. Is this an example of natural selection?

Some might argue that kangaroos have small forearms because they don’t use them much. Is this an example of natural selection?

These stick bugs are very hard to see. Do you think natural selection was involved?

Cactus spines are just modified leaves. Do you think natural selection was involved?

Why is Evolution Controversial  Or is it?  Video Video