Food for thought… Humans share the Earth with millions of other kinds of organisms of every imaginable shape, size, and habitat. This variety of living things is called biological diversity. How did all of these different organisms arise? How are they related?

What do you think the theory of evolution means? Evolution: (change over time) the process by which modern organisms have descended from ancient organisms. Scientific theory: a well-supported testable explanation of phenomena that have occurred in the natural world.

Charles Darwin & the Theory of Evolution Born in England on February 12, 1809 The individual who contributed more to our understanding of evolution than anyone.

H.M.S. Beagle In 1831, shortly after college, he joined the crew of the H.M.S. Beagle and set sail from England for a voyage around the world.

This was to be one of the most important voyages in the history of science. During his travels, Darwin made numerous observations and collected evidence that led him to propose a revolutionary hypothesis about the way life changes over time.

Patterns of Diversity Darwin visited Argentina and Australia which had similar grassland ecosystems. those grasslands were inhabited by very different animals. neither Argentina nor Australia was home to the sorts of animals that lived in European grasslands.

Patterns of Diversity Darwin posed challenging questions: Why were there no rabbits in Australia, despite the presence of habitats that seemed perfect for them? Why were there no kangaroos in England?

Living Organisms and Fossils Darwin collected the preserved remains of ancient organisms, called fossils. Some of those fossils resembled organisms that were still alive today.

Living Organisms and Fossils Others looked completely unlike any creature he had ever seen. As Darwin studied fossils, new questions arose: Why had so many of these species disappeared? How were they related to living species?

The Galapagos Islands The smallest, lowest islands were hot, dry, and nearly barren. Hood Island had sparse vegetation The higher islands had greater rainfall and a different assortment of plants and animals. Isabela Island had rich vegetation.

The Galapagos Islands Darwin was fascinated in particular by the land tortoises and marine iguanas in the Galápagos. Giant tortoises varied in predictable ways from one island to another. The shape of a tortoise's shell could be used to identify which island a particular tortoise inhabited.

Other animals found in the Galapagos Land Tortoises Darwin Finches Blue-Footed Booby Marine Iguanas

The Journey Home While heading home, Darwin spent a great deal of time thinking about his findings. Darwin observed that characteristics of many plants and animals vary greatly among the islands. Hypothesis: Separate species may have arose from an original ancestor.

Ideas that shaped Darwin’s thinking James Hutton: Proposed Theory of Geological change Forces change earth’s surface shape Changes are slow Estimates that Earth is millions-not thousands- of years old

Ideas that shaped Darwin’s thinking Charles Lyell: Published book: Principles of Geography Geographical features can be built up or torn down over long periods of time. Darwin thought if earth changed over time, what about life?

Lamarck’s Theory of Evolution Lamarck proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime. These traits could then be passed on to their offspring. Over time, this led to change in a species. Tendency toward Perfection (Giraffe necks) Use and Disuse (fiddler crabs using front claws ) Inheritance of Acquired Traits

Male crab uses front claw to attract mate and ward off predators. From repeated use, claw grows larger. The acquired characteristic, a larger claw, is passed on to offspring.

Population growth Thomas Malthus: 19th century English economist If population grew (more babies born than die): Insufficient living space Food runs out Darwin applied this theory to animals

Publication of On the Origin of Species Alfred Russel Wallace wrote an essay summarizing evolutionary change from his field work in Malaysia. This gave Darwin the drive to publish his findings.

Variation and Artificial Selection Natural variation: Differences among individuals of a species Artificial selection: Nature provides the variation among different organisms, and humans select those variations they find useful. Domestic animals and crop plants

Evolution by Natural Selection The Struggle for Existence: Members of each species have to compete for food, shelter, and other life necessities. Faster predators will catch more prey, more camouflaged prey will avoid being caught Survival of the Fittest: Some individuals are better suited for the environment and therefore better able to survive and reproduce. Adaptations include anatomical or structural characteristics or behavior

Natural Selection Over time, natural selection results in changes in inherited characteristics of a population. These changes increase a species fitness in its environment.

Descent Descent with Modification-Each living organism has descended, with changes from other species over time Common Descent- were derived from common ancestors

Evidence of Evolution The Fossil Record Geographic Distribution of Living Things Homologous Body Structures Similarities in Early Development

Summary of Darwin’s Theory Individuals in nature differ, and some of this variation is heritable. Organisms in nature produce more offspring than can survive, and many of those who do not survive do not reproduce. Because more organisms are produced than can survive, each species must struggle for resources. Each organism is unique, each has advantages and disadvantages in the struggle for existence.

Summary of Darwin’s Theory Individuals best suited for the environment survive and reproduce most successful Species change over time Species alive today descended with modification from species that lived in the past All organisms on earth are united into a single family tree of life by common descent Galapagos Islands Activity

Evolution of populations In what ways are you like your parents? Which traits do you think you inherited? So, how do inheritable traits evolve in populations?

Genetic Variation Gene pool: consists of all genes, including all different alleles, that are present in a population. Relative frequency: (of an allele) is the number of times that allele occurs in a gene pool, compared with the number of times other alleles for the same gene occur. (percentage) In genetic terms: Evolution is any change in the relative frequency of alleles in a population.

Gene Pool of Fur Color in Mice In a total of 50 alleles: 20 alleles are B (black): relative frequency = 40% 30 alleles are b (brown): relative frequency = 60%

Sources of Genetic Variation Mutations Genetic shuffling that results from sexual reproduction

Sickle Cell Anemia and Malaria Both sickle cell anemia and malaria are especially prevalent in areas of Africa. Sickle cell anemia is caused by two HbS genes. In these areas, carriers of the HbS gene have been naturally selected because the trait presents resistance to malaria. This immunity is a selective advantage, but also a disadvantage because the chances of being born with sickle cell anemia are relatively high.

Single-gene and Polygenic Traits The number of phenotypes produced for a given trait depends on how many genes control the trait. Single-gene trait: Controlled by a single gene that has two alleles Polygenic traits: Each gene has two or more alleles

Evolution as Genetic Change Natural selection never acts directly on genes. Why? It is an entire organism-not a single gene-that either survives and reproduces ( alleles stay in gene pool) or dies without reproducing (alleles do not contribute to gene pool).

Evolution as Genetic Change Recall, evolution is any change over time in the relative frequencies of alleles in a population. It is the population, not individual organisms, that can evolve over time.

Natural Selection on Single-Gene Traits Can lead to changes in allele frequencies and to evolution.

Natural Selection on Polygenic Traits When traits are controlled by more than one gene, the effects of natural selection are more complex. Natural selection can affect the distributions of phenotypes in any of three ways: Directional selection Stabilizing selection Disruptive selection

Directional Selection When individuals at one end of the curve have higher fitness than individuals in the middle or at the other end. The range of phenotypes shifts as some individuals fail to survive and reproduce while others succeed.

Stabilizing Selection When individuals near the center of the curve have higher fitness than individuals at either end of the curve. This keeps the center of the curve at its current position but narrows the overall graph. If medical advances could prevent problems for high birth weight but not low birth weight, how might the curve change?

Disruptive Selection When individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle. Selection acts most strongly against individuals of the intermediate type.

Population Genetics There is MATH to support this!! Sex and The Single Guppy online activity