Charles Darwin and the theory of natural selection Biology I

I. Before Darwin Scientists knew that organisms had evolved Fossil evidence Age of the Earth

I. Before Darwin Lamarck- aquired characteristics Evolve from simple to complex Organisms want to adapt

I. Before Darwin Later disproved

II. Darwin At 21, took a job as a naturalist on the HMS Beagle Collected specimens, took notes of different organisms

His voyage:

II. Darwin Sailed to Galapagos Islands All new species, but similar to those found elsewhere

Finches most famous Had slightly different beaks from island to island Differed by their diet

II. Darwin Darwin 22 years developing theory of natural selection Pressured into publishing by Wallace Published On the Origin of Species by Natural Selection

III. Natural Selection 4 Requirements:Natural Selection 1. Variation 2. Differential Reproduction 3. Heredity 4.Lots of Time

III. Natural Selection 1. Individuals have variations. –Color, size, speed, etc. The variations that natural selection acts on are genetically linked

III. Natural Selection Four steps 2. Organisms produce more offspring than can survive –competition Only the best are going to survive

III. Natural Selection 3. Beneficial variations survive, pass traits to offspring Passed through DNA

III. Natural Selection 4. Over time variations become more frequent in population Results in population being different than ancestors

III. Natural Selection Natural selection usually takes a long time Selection for a particular variation depends on environment

Example of Natural Selection

Evolution Evolution is the change in a population over time

IV Evidence for Evolution Adaptations Anatomy Fossil Record Embryology Biochemistry

Types of Adaptations An Adaptive Trait- variation that is helpful –Thick fur in cold places Maladaptive Trait- variation that is harmful –Poor eyesight

Structural Adaptations Physical traits

Mimicry-An adaptation Enables one species to resemble another species. Ex.-harmless species looks like a harmful one, good tasting vs. bad tasting.

Camouflage-An adaptation A species blends in with its environment to avoid predators. Ex.- peppered moth, leaf frog

Fossils Determine relationships among organisms. Ancestors of whales were probably land-dwelling, doglike animals.

Anatomy- Homologous Structures Common evolutionary origin. Similar in arrangement or function or both. Example: forelimbs of a whale, a crocodile and a bird wing.

Anatomy- Analogous Structures No common evolutionary origin, but similar in function. Wings of a bat and wings of a butterfly.

Anatomy- Vestigial Structures No function now but was probably useful to an ancestor. Ex. A whale has leg bones, a snake has leg bones, we have a tail bone and wisdom teeth.

Embryology Earliest stage of growth and development Embryos of a fish, a chicken, a pig, a cow, a rabbit, and a human are almost identical. They all have gill slits and a tail.

Biochemistry Comparisons of DNA and RNA Now monera is divided into two separate kingdoms based on their biochemistry.

V. Mechanisms of Evolution Genetic Drift Gene Flow Artificial Selection Natural Selection Sexual Selection

Genetic Drift Change in allele frequency by CHANCE

Gene Flow Change in allele frequency as a result of MIGRATION

Artificial Selection Humans choose desired traits and manipulate breeding

Sexual Selection Special case of Natural Selection Variations selected for their ability to attract a mate

Geographic isolation Physical barrier divides a population New selective pressures Two different species

Reproductive isolation No longer able to mate Different genetic information Mating behavior differences

Selective Pressures Environmental Examples: drought, lack of food, extreme temperatures, predation

Sources of Variation GENE FLOW moves genes among populations SEXUAL REPRODUCTION introduces new gene combinations Random MUTATIONS in DNA lead to the formation of new alleles (sound familiar?)

Mutations Can be beneficial, neutral, or harmful for the organism Only mutations in gametes are inherited by offspring

VI. Natural selection affecting populations Three major types of natural selection are: –Stabilizing Selection –Directional Selection –Disruptive Selection

Stabilizing selection Average individual is selected for

Directional selection One extreme trait is selected for

Disruptive Selection Both extremes are selected for Average selected against.

How do we determine a new species? A species is considered a group of organisms that can: 1.Interbreed 2.Produce Fertile offspring Two species of meadowlark