Mechanisms of Evolution

I. Natural Selection & Charles Darwin  Charles Darwin ( ) an English scientist considered the founder of the evolutionary theory  Evolution is often referred to as Darwinism

 Darwin studied many forms of life through the voyage of the Beagle  Galapagos Islands was where Darwin studied a majority of the organism

  Darwin's comparison of the animals of South America and the Galapagos Islands caused him to conclude that adaptation to the environment can cause diversification, including origin of new species

The Galapagos Islands: Darwin notes:  Island species varied from the mainland species, and from island-to- island  Each island had either long or short necked tortoises depending on the island's vegetation

The Galapagos Islands:  Darwin noted:  Finches: Bill shapes are adaptations to different means of gathering food.

  Galapagos finch species varied by nesting site, beak size, and eating habits

The Theory of Evolution: Darwinism  We have discussed the 4 supporting evidences of evolution.  Comparative anatomy  Molecular Biology  Biogeography  Embryology Today we are going to discuss the 4 mechanisms of HOW Evolution occurs…

Outine: 4 Mechanisms of Evolution 1.Natural Selection 2.Mutation 3.Migration 4.Genetic Drift

#1 Natural Selection: Natural Selection – AKA “Survival of the Fittest” A gradual, non-random process by which biological traits become either more or less common in a population   As you can see there is a variation in the phenotype of these beetles: Green or brown

Genetic Variation: Genetic differences within a population. The genetic variation in this scenario are the genes that code for the color of the beetle.

3 Types of Natural Selection that Act on Variation: 1. Stabilizing – natural selection that favors average individuals

3 Types of Natural Selection that Act on Variation: 2. Directional selection – natural selection that favors an extreme form of a trait

3 Types of Natural Selection that Act on Variation: 3. Disruptive selection – individuals w/ either extreme form of a trait

#2 Mutation  Mutation: change in a gene; alteration of a nucleotide sequence. EX: A mutation causes two green beetle parents to have a brown beetle

#3 Migration  Migration: Movement of some individuals to another population Gene Flow – transfer of alleles from one population to another population through immigration of individuals. This disrupts allele frequency.

#4 Genetic Drift  Genetic Drift: some individuals may by chance and not because of “fitness” leave more descendants and therefore pass on their genes.

The Evolution of Species:  Species – organisms that look alike can interbreed to produce fertile offspring  Speciation – evolution of a new species. *NOTE: Organisms within the same species have reproductive success ( ability to pass genes onto the next generation in a way that they too can pass on those genes.) Donkey + Horse = Mule He can not have offspring because his parents are two different species 

So how do new species come about?

1. Geographic Isolation – a physical barrier divides a population Physical Barriers Cause Speciation:

2. Reproductive Isolation – the inability of organisms to mate and breed fertile offspring  Genetic material becomes so different fertilization can not occur  Behavior – mating seasons are different These Bowerbirds have different mating seasons and rituals. These 2 factors contribute to Reproductive Isolation

Does evolution happen fast or slow?

Speciation Rates - the time it takes for evolution to occur. 2 Theories: #1 Gradualism: – idea that species originate through a gradual change of adaptations Both!

 # 2. Punctuated Equilibrium : things staying the same for a period of time then rapidly changing due to a catastrophic event.

There are TWO types of Evolution

#1 Divergent Evolution – accumulation of differences between groups which can lead to the formation of new species

#2 Convergent Evolution – organisms not closely relate, independently evolve similar traits (to adapt to similar environments.)

Genetics Determines Evolution:  Gene Pool – All the alleles in a populations genes. In other words every form of a trait  Allelic Frequency – the % of any specific allele w/in a gene pool

 Genetic Equilibrium – allele frequency remains the same over generations  Populations in genetic equilibrium are not evolving  Factors that affects genes can affect equilibrium 1. Mutations [negative, positive]  Negative more than likely causes death  Positive may be beneficial

Trait Variations – differences in Organisms  Increases or decreases an organisms chance of survival  Inherited and controlled by alleles  Allelic frequencies in a populations gene pool will change due to natural selection

C. Patterns of Evolution 1. Adaptive Radiation – ancestral species evolves into an array of species to fit a particular environment.