Charles Darwin and the theory of natural selection Biology I

I. Before Darwin Jean Baptiste Lamarck: acquired 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 each bird’s diet

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

Misconception 1:“Evolution is a theory about the origin of life.”

Either an organism has genes that enable its survival or it doesn’t. Misconception 2: “Natural selection involves organisms ‘trying’ to adapt.” (Lamarck) Either an organism has genes that enable its survival or it doesn’t.

Misconception 3 : “Natural selection gives organisms what they ‘need A population either has the ‘right’ variation or it doesn’t. If it doesn’t, the population may die out.

Misconception 4: “Evolution is like a climb up a ladder of progress; organisms are always getting better.”

III. Natural Selection 4 Requirements for Natural Selection 1. Variation 2. Differential Reproduction(Selective Pressures) 3. Heredity 4.Lots of Time

III. Natural Selection Four steps 1. Organisms produce more offspring than can survive competition Only the best are going to survive

III. Natural Selection 2. Individuals have variations. Color, size, speed, etc. The variations that natural selection acts on are genetically linked

III. Natural Selection 3. Beneficial variations survive, pass traits to offspring Passed through DNA (Yay Genetics!!)

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 Not this!

IV Evidence for Evolution Adaptations/Biogeography Comparative Anatomy Fossil Record Comparative 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

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

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

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.

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

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 More DNA bases in common the more closely related

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

Humans choose desired traits and manipulate breeding 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: Interbreed Produce Fertile offspring Two species of meadowlark