Natural Selection

—Charles Darwin from "The Origin of Species" http://evolution.berkeley.edu/evolibrary/home.php http://evolution.berkeley.edu/evolibrary/home.php www.darwinday.org/englishL/life/beagle.html www.darwinday.org/englishL/life/beagle.ht Used by permission of Darwin Day Celebration (at DarwinDay.org), 2006 I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection.   —Charles Darwin from "The Origin of Species" http://evolution.berkeley.edu/evolibrary/home.php Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

CHARLES DARWIN – 1809-1882 English Traveled around the world on the Beagle (ship) Most of trip was among the Galapagos Islands Believed that the earth was 6000 years old and that all plants and animals were unchangeable over time During his travels, he observed many live species, as well as fossils He did not understand why some species survived while others were going extinct These ideas went directly against his beliefs

Darwin’s Observations From island to island, he noticed that the species of mockingbird, finches, and other animals varied. Many of the species Darwin collected had not yet been discovered or classified Darwin took his collections and drawings home and after reading essays and studies by many other scientists (Gould & Mathus), he developed the idea of natural selection

5 Principles of Natural Selection Individuals in a population show variation. Variations can be inherited. Organisms have more offspring that can survive under normal circumstances. Variations that increase reproductive success will have a greater chance of being passed on from generation to generation. A population will slowly change over time in response to the environment.

Darwin… By 1840, Darwin had developed the theory of natural selection. He then published “On the Origin of Species by Means of Natural Selection” On the last page of this book, he called his theory “evolution” Evolution is what the process is called ~ natural selection is HOW evolution happens Another researcher, Wallace, also wrote a similar book at the same time and both books were published and presented to the scientific community.

Evolution Overview: Evidence for Evolution, Types of Natural Selection, & Speciation Biology 1 Dr. Butts

How and why does evolution occur? Individuals are born with random traits inherited from parents Some of these traits might be advantageous Individuals who have more advantage in their environment will survive and reproduce with greater success The advantageous traits will be passed down to offspring

Evidence of Evolution The Fossil Record Provides records of species that lived long ago Shows evolutionary relationships among ancient and current living things

Evidence of Evolution Comparative Anatomy: Homologous Structures: anatomically similar structures that occur in species that come from a common ancestor

Evidence of Evolution Comparative Anatomy Vestigial Structures: structures that are present, but no longer needed

Evidence of Evolution Comparative Anatomy Analogous Structures: structures that are similar in function, but are not in living things that share ancestry

Evidence of Evolution Comparative Embryology Studying of the growth and development of various organisms The more similar the embryonic development of organisms, the more closely related they are

Evidence of Evolution Comparative Biochemistry: comparing DNA and other molecules The more closely related, the more similar the DNA sequences

Evidence of Evolution Geographic Distribution & Biogeography Similar climates and biomes have similar living things because living things evolve to be successful in their environment

CoEvolution Some species evolve in close relationship with other species. The relationship may sometimes become so close that the evolution of one species may affect the other.

Examples of Evidence: Coevolution

Examples of Evidence: Camouflage: blending in with environment Mimicry: nonpoisonous organisms mimicking poisonous ones in order to avoid predators

Camouflage

Mimicry

Evidence of Evolution Antibiotic and Pesticide Resistance Antibiotic: bacteria become resistant to antibiotics over time due to over and misuse Pesticide: Insects and other pests become resistant to pesticides due to overuse

Adaptation & Natural Selection Camouflage: blending in with environment Mimicry: nonpoisonous organisms mimicking poisonous ones in order to avoid predators

Adaptation & Natural Selection Genetic Drift Founder Effect: Pioneer species leaves original colony and begins a new one Bottleneck: a once large population is dramatically decreased due to some bottleneck event (ex. Drought, flood, disease, etc)

Adaptation & Natural Selection Stabilizing Selection most common eliminates extremes, which gets rid of negative traits ex. Birth weights of human babies does not show variation

Adaptation & Natural Selection Directional Selection one extreme selected for ex. Peppered moth (p.435, fig. 15.17)

Adaptation & Natural Selection Disruptive Selection splits a population into 2 groups removes average individuals and selects for extremes Ex. Selection based on habitat (snakes in grasslands vs. rocky mountains)

Adaptation & Natural Selection Sexual Selection mate selection based on physical characteristics Nonrandom Mating mating based on nonrandom factors (proximity, sexual selection, etc)

Speciation What is a species? Groups of organisms that can successfully reproduce with one-another. What is speciation? Process by which new species are formed Populations diverge to the point they can no longer reproduce together (reproductive isolation)

Speciation Allopatric Speciation Physical barrier causes speciation Sympatric Speciation Speciation without a physical barrier

Speciation Adaptive Radiation Rapid evolution due to environmental factor(s) that cause a change in what is advantageous vs. disadvantageous

Speciation Coevolution Species evolve in response to one another Convergent Evolution Similar traits evolve in different parts of the world due to similar climates and geography

Hardy Weinberg Theory that states that if gene frequencies remain stable, the population is said to be in equilibrium (or homeostasis) and thus, not evolving. 5 things must be true: 1. Population is large. 2. No immigration nor emigration 3. Mating is always random. 4. Mutations never occur 5. Natural selection does not occur.

Hardy Weinberg Is it true for humans? You decide… Assumes 5 things to be true: 1. Population is large? 2. No immigration nor emigration? 3. Mating is always random? 4. Mutations never occur? 5. Natural selection does not occur? Are populations ever really NOT evolving then?