Evolution Review Who’s the man? Charles Darwin

What did Darwin observe on his Journey on the HMS Beagle? Many different species of plant and animal life Fossils of extinct animals

How did Darwin explain the differences in the Galapagos finches?

He proposed that the 13 different finches had come from a… Common ancestor

What is a population? A group of one species of organism in a specific geographical area that can interbreed.

Evolution is a.. Well-accepted theory of how organisms have changed over time by natural selection. Darwin based his ideas on: 1. observations of nature 2. Malthus’s theory about exponential population growth 3. his experience breeding animals

Tenets of Evolution Populations have the potential to grow… exponentially They don’t because.. resources are limited There are differences in individuals (genetic variation) These differences can help some individuals survive better than others Those that survive longer pass more of their genes on to the next generation.

What is Natural Selection? The idea that individuals with traits that make them well-suited to the environment will survive and reproduce, passing on their genes, at a higher rate than less suited individuals. This will cause a change in frequency of alleles in the population

Process of becoming better suited to the environment is called.. Adaptation What does natural selection act on? On populations over many generations.

What is needed for natural selection to occur? Genetic variation (differences) in the individuals must exist Otherwise all members of the population would have the same advantage for survival

What are 4 sources of genetic variation? 1. Mutations- errors in base pairs caused by mutagens, energy exposure, or errors in replication 2. Meiosis- two events occur: Random alignment Crossing over  3. Immigration- new genes come into population  4. Sexual Reproduction- combining the alleles of mother and father

What 4 processes change allelic frequency? 1. Natural Selection- environment determines which traits will survive and be passed on 2. Artificial Selection (breeding)- humans decide which traits will be bred for 3. Gene Flow 4. Genetic Drift

Gene Flow Genes moving in and out of a population Give two examples: 1. immigration– new individuals move in 2. emigration- individuals move out

Genetic Drift This is a ___________change in allelic frequency that is due to chance.. Not environmental pressure. Answer= RANDOM

Gradualism vs Punctuated Equilibrium Hypothesis that evolution occurs in short bursts of rapid change, then periods of no change is… Punctuated equilibrium Hypothesis that evolution occurs gradually at a slow, constant rate is.. Gradualism

What has to happen for a new species to become established? First, Reproductive Isolation from the original group Example: a flock of birds gets separated and blown toward an island by a storm They are now isolated from their original group on another island. Over time, in 2 different environments, they become more and more different

When does speciation occur? When they can no longer interbreed with the original group of birds A speciation event= A new species

When a group of organisms starts a new colony, it is called.. The Founder Effect

What is a genetic bottleneck? This happens when a natural disaster (earthquake, volcano, etc) kills off a group of the original population, and the allelic frequencies change (genes are lost). Now the group has different amounts of the alleles for certain traits.

When 2 species become … More different, it’s called… Divergence (diverse=different) More alike, it’s called… Convergence (converge=coming together)

What are Vestigial structures? Those anatomical features that no longer have a purpose Examples: in whales… They have small back limbs, inherited from an ancestor that moved on land. See next slide.

What are Homologous structures? Similar structures in different species that suggest that they have a common ancestor Example: the forearm of many vertebrates (humans, bats, alligators, etc) have similar bones. See next slide.

Contrast: Scientific theory, law, and hypothesis Theory= an explanation of how a natural phenomenon occurs Law= describes a phenomenon (mathematically) Hypothesis= a prediction based on research and prior knowledge