EVOLUTION

Variation The differences between individual members of a population (ex: fur color, eye color, etc.) Can not always be observed Are almost always genetically inherited Results from mutations and recombination

Adaptation An inherited trait that increases the population’s chances of survival and reproduction It can be physical or behavioral

Evolution Defined as “change over time” There were 3 scientists who made important contributions to this field: – Charles Bonnet – Jean-Baptiste Lamarck – Charles Darwin

Charles Bonnet Noticed that fossils didn’t look like modern organisms Theorized that periodic catastrophes affected the entire planet and after each catastrophe life began anew

Jean-Baptiste Lamarck Challenged Bonnet’s views Believed that the fossils of extinct animals were the ancestors of those living today Developed Lamarck’s hypothesis

Lamarck’s Hypothesis 1. Organisms strive to improve themselves 2. Principle of Use and Disuse: the most- used body structures develop, whereas unused structures waste away 3. Principle of Inheritance of Acquired Characteristics: modified structure is inherited by the organism’s offspring** **This 3 rd principle was disproved by August Weismann. Changes in an individual during its lifetime do not affect its reproductive cells or its offspring.

Charles Darwin Scientist who studied plants and animals while on an around-the-world trip After studying several organisms, he developed his theory of evolution—Natural Selection

Natural Selection 1. There is variation within populations 2. Some variations are favorable [favorable variations improve an organism’s ability to function and reproduce in its own particular environment] 3. Not all young produced in each generation can survive 4. Individuals that survive and reproduce are those with favorable variations

Rate of Evolution Gradualism: – states that evolution occurs at a slow, gradual rate – this is what Darwin believed Punctuated Equilibrium: – states that populations remain genetically stable for long periods of time, interrupted by brief periods of rapid genetic change – this new theory was first stated by Stephen Jay Gould and Niles Eldridge

Comparing Anatomy Homologous Structures: – structure or characteristic with similar functions found in different species – thought to be inherited from common ancestors – EX: humans, whales, and bats all have the same number and type of bones in the forelimbs

Comparing Anatomy (cont.) Analogous Structures: – structures that are similar in function, but are not inherited from a common ancestor – EX: wings of insects and wings of birds

Comparing Anatomy (cont.) Vestigial Structures: – structures that are inherited, but reduced in size and often unused – suggest structures of the ancestors of modern organisms – EX: pythons have vestigial hip and leg bones

Types of Evolution There are 5 different types of evolution: – Speciation – Divergent Evolution – Convergent Evolution – Coevolution – Adaptive Radiation

Speciation species new species original species

Divergent Evolution species new species

Convergent Evolution species new species species These 2 new species share many traits. These two succulent plant genera, Euphorbia and Astrophytum, are only distantly related, but have independently converged on a very similar body form.succulent plantEuphorbiaAstrophytum

Coevolution speciesoriginal species with new traits original species with new traits species BumblebeesBumblebees and the flowers they pollinate have coevolved so that both have become dependent on each other for survival flowerspollinate

Adaptive Radiation species new species

Population Genetics Populations are the smallest unit in which evolution takes place Population genetics is the study of genetic traits and changes in populations

Hardy-Weinberg Principle If a population is not evolving, the allele frequencies in the population remain stable The population is said to be in genetic equilibrium

Conditions Required to Maintain Equilibrium 1. No natural selection 2. Random mating 3. No migration 4. No mutation 5. Very large population size

Types of Selection In stabilizing selection, the extreme phenotypes are selected against

Types of Selection (cont.) In directional selection, there is a shift in frequency to an extreme phenotype

Types of Selection (cont.) In disruptive selection, the most common variation in a population is not favored