Charles Darwin and the Theory of Evolution

Charles Darwin’s Voyage of the Beagle

Galapagos Islands Even though these islands are close together they varied greatly in their climates Amount of rainfall, vegetation differences, different species!

Darwin’s Observations The plants and animals were well-suited to their environment Example: A Cactus is adapted to live in dry areas Species vary in traits and some traits are better suited for different areas

Darwin’s Finches The beaks were different from island to island Beaks were better suited for feeding depending upon location (islands)

Darwin’s Tortoises Due to differences in plant life; Darwin noticed that tortoises had differences in SHELL shape and NECK lengths

15-2 Jean-Baptiste Lamarck One of the first scientists to notice living things have changed over time Proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetimes These traits could then be passed on to their offspring Do you agree with this theory?

Darwin Presents His Case-1859 In this book, Darwin proposed the concept of EVOLUTION by the method of NATURAL SELECTION. Evolution is? Natural Selection is? Speciation is? Explain how these relate?

Evolution by Natural Selection Struggle for Existence Each species will compete for food, space, basic needs Survival of the Fittest/Natural Selection Fitness=able to survive and reproduce! Descent with Modification The “fittest” reproduce thus passing on their GREAT traits!

Adaptations A inherited characteristic that increases an organisms chance of survival. Examples: 1.Anatomical/stuctural- porcupines sharp quills, camouflage, mimicry 2.Behavioral- mating rituals 3.Physiological-plant performing photosynthesis

Evolution occurs in Populations *not individuals* But what is a population? *A group of inter-breeding species

Evolution of Populations Genetic variation is studied in populations (group of same species that interbreed) Gene pool – all genes that are present in a population Relative frequency – number of times an allele occurs in a gene pool, compared with the number of times other alleles for the same gene occur

How do we know when Evolution has occurred? A change in the relative frequency of alleles in a population allele for brown fur allele for black fur 48% heterozygous black 16% homozygous black 36% homozygous brown 60% or 30/50=brown allele

Genetic Variation in Populations Two main sources of genetic variation Mutations Change in a sequence of DNA Gene shuffling Independent movement of chromosomes during meiosis and Crossing-Over

3 Causes of Evolution 1. Genetic Drift: change in the gene pool due to chance (small populations will be greatly affected) A. Bottleneck Effect- over hunting, earthquake, fire etc… *this can lead to endangered species! B. Founder Effect- small group leaves the source population to establish their own Example:Polydactyly in Amish that came to the United States (they carried the allele)

3 Causes of Evolution con’t 2. Gene Flow: Fertile immigrants or emigrants bringing or taking alleles from the population Example: If your 2nd period class has all blue eyed people (bb) and someone comes in that has brown eyes (BB)

3 Causes of Evolution con’t Natural Selection: Well suited organisms increase their chance of surviving thus reproducing to pass on their genes (alleles) to the next generation Example: Peppered Moth example

Single-Gene and Polygenic Traits The number of phenotypes produced for a trait depends on how many genes control the trait Single-gene trait Single gene with two alleles Fewer phenotypes than polygenic traits Ex: widow’s peak Polygenic trait Controlled by two or more genes (each with more than 2 alleles) Many different genotypes and phenotypes Ex: height

Natural Selection acts on Polygenic Traits 3 ways Directional Selection Disruptive Selection Stabilizing Selection

Genetic Equilibrium If a population was to not evolve, or change, the population would reach equilibrium – when allele frequencies stay the same Conditions required to reach equilibrium: Random mating Large population No movement in or out of population No mutations No natural selection

Speciation Isolation prevents interbreeding between populations Behavioral isolation Different courtship rituals or reproductive strategies Geographic isolation Two populations are separated by geographic barriers (rivers, mountains, oceans, etc..) Temporal isolation Species reproduce at different times (winter –vs- spring)