II Theories of Evolution A Development of Theories

II. Theories of Evolution A. Development of Theories

1. Jean-Baptiste Lamarck (1744 -1829) First person to suggest that life evolved a) The law of Use and Disuse b) Inheritance of acquired characteristics

Lamarck believed that giraffes stretched their necks to reach food. Their offspring and later generations inherited the resulting long necks

Charles Darwin

2. Darwin’s Theory: Natural Selection (Based on his observations) a) b) c) d) Variation exists within all species Populations always tend to increase The amount of resources is limited There will be a struggle for the available resources e) Organisms who are most fit will live longer and have more offspring. (The offspring will inherit advantageous traits)

Most giraffes used to have short necks, but some had slightly longer necks. When the food on the lower branches was eaten, many of the giraffes with shorter necks died of starvation, leaving the ones with slightly longer necks to survive and reproduced. Through many generations, the giraffes with longer necks became the most common.

3. Origin of Variation • Genetic Recombination (Sexual reproduction. Meiosis, Crossing over and random fertilization) • Mutation (Produces New Genes)

B. Mechanisms of Evolution 1. Species and Populations • Evolution cannot be seen in an individual because their genes do not change. a) Evolution is a change in the genetic make up of a population b) Gene Pool- all the different alleles (gene forms) in a population 2. Hardy-Weinburg principle Gene Pool

2.

Population Genetics Or Fun with Hardy-Weinburg! The Math! Let P = the frequency of Dominant Genes in a population Let q = the frequency of Recessive genes in a population Therefore: P+q=1 All the dominant genes + all the recessive genes = all the genes

Individuals can be: Genotypes Hardy-Weinburg Notation Homozygous Dominant Heterozygous Homozygous Recessive Therefore: PP or P 2 p Pq + q. P or 2 Pq q qq or q 2 p q P 2 Pq q. P q 2 P 2 + 2 Pq + q 2 =1 All the Homozygous Dominant + All the Heterozygotes + All the Homozygous Recessives = All the Population With these formulas, you can solve all Hardy-Weinburg problems

C. Factors which Change Genetic Equilibrium (ie. Cause Evolution) 1. Natural Selection: Favoring one genotype over another. Ex. H. B. Kettlewell

In England, before the industrial revolution, tree bark was a lighter color and lighter moths out numbered darker moths 9: 1

Coal caused the tree bark to darken during the industrial revolution. The darker moths then numbered the lighter moths 9: 1

Geospiza fortis Study by Peter and Rosemary Grant

Antibiotic Resistant Strains of Bacteria are a Prime Example of Evolution

Types of Selection a) Directional Selectionconstant genetic change of one type. Ie. Giraffe’s necks getting longer. Dinosaur size increasing

Types of Selection b) Stabilizing Selection that favors the average and eliminates the extremes. The population becomes more alike

Types of Selection c) Disruptive selection. Selection that favors the extremes and eliminates the average. Population becomes more different. This can lead to new species

Types of Selection

C. Factors which Change Genetic Equilibrium (ie. Cause Evolution) 2) Gene flow- Movement of organisms in or out of a population 3) Mutation- change in a gene form that is unequal. Ie. Change form gene A to a more than a to A. 4) Genetic Drift- change in gene frequency due to random chance 5) Isolation- separation of a population so it can’t interbreed. Either genetic or geographic

Patterns of Evolution 1. Divergent evolution-Two separate species becoming more different due to different selective pressures in different environments a) Adaptive Radiation- process by which species adapt to a variety of habitats b) Speciation- formation of two separate species from one

2. Convergent Evolution- the process by which distantly related organisms become more similar due to similar selective pressures in similar habitats