Evolution by Natural Selection

Scientific Theory

An explanation of natural phenomenon supported by a large body of scientific evidence obtained from many different investigations and observations.

Evolution

A gradual change in a species (populations) through adaptations over time.

Adaptation = some phenotypic feature or trait that improves an organism’s likelihood of survival and reproduction.

In Georgia, there is a popular hunting area of forest called the Poopycack forest, where the Poopy Deer lives. This species of deer has 6 ears. How might this adaptation have occurred and how is it

beneficial?

What would you expect to happen to the Poopy Deer population in the next 1000 years?

Charles Darwin “Theory of Evolution by Natural Selection”

Proposed that new species could develop through a process called Natural Selection

During his travels aboard HMS Beagle, made numerous observations and collected evidence that led him to propose a revolutionary hypothesis about the way life changes over time

Darwin’s Voyage Darwin studied animal species in the Galapagos

Islands and found they each had unique adaptations

Darwin’s Studies

Galapagos finches demonstrate different adaptations to eat different kinds of foods

Galapagos tortoises are the biggest in the world

Natural Selection

Acts on Phenotype rather than Genotype

Those better suited for their environment will survive

Those least suited to their environment will die faster, leaving fewer offspring

Genetic variation is essential!

_________ promote genetic variation, which helps ensure a species survival

Like crossing over!

Mutations

How does a great number of species ensure that at least

some organisms survive major changes in the

environment?

Those who are better at adapting will survive major changes in the environment

Natural Selection

A mechanism for change in a population

Natural Selection (NS) is responsible for most evolutionary change by selectively changing genetic variation through differentiated survival and reproduction.

Goal - To be fit enough to survive and reproduce

Three types of NS

Stabilizing Selection

Favors average individuals in a population

Those individuals have a “selective advantage”.

Reduces variation in a population

Directional Selection

Favors one of the extreme variations of a trait

Can lead to rapid evolution of a population

Disruptive Selection

Favors both extreme variations of a trait

Leads to evolution of two new species

Speciation

A process of producing two individual species from one

Members of the population no longer interbreed within their natural environment

Evidence for Evolution: 1. Fossil record

A piece of organism or imprint left behind.

Fossils show that species have changed over time.

2. Vestigial structures Body structures that have shrunken and are not used anymore.

3. Homologous structures Structures that share a common ancestry and look/behave

similarly.

4. Embryology

5. DNA homology, Amino Acid homology, Mitochondrial DNA, Photosynthetic Plant cells

Evidence For Evolution

Fossils

Provide a record of early life and evolutionary history

Geologic Strata (sedimentary layers) and Carbon Dating

Carbon-14 (remember isotopes?) Used to date any

object composed of carbon

Radioactive carbon decays over time check amount of C14

left in sample, enabling you to tell age of object

Defining age of fossils!

Did you know that whales have feet?

Well, sort of….

Fossils help us determine whale evolution

60 million

years ago

50 million

years ago

40 million

years ago

Yesterday

Human tail-bone, wisdom teeth, appendix (they have no purpose)

Snake feet,

Whale feet

Vestigial Structures

Homologous Structures (derived from a common ancestral feature)

Limb adapted to function

means the same!

Analogous Structures-

similar in function but not structure

Evidence For Evolution

Embryology

Similarities among the young embryos suggest evolution from a distant, common ancestor

Biochemistry

Comparing DNA and RNA

How do we know what happened when?

Radiometric dating relies on half-life decay of radioactive elements to allow scientists to date rocks and materials directly

Stratiography provides a sequence of events from which relative dates can be extrapolated

Molecular Clocks allow scientists to use the amount of genetic divergence between organisms to extrapolate backwards to estimate dates.

DNA/Amino Acid Homology

Human 5’A-T-C-T-T-A-C-G-A-A-T-C-A-T-G-C-C-C-T-A-A-C-T-T-C-G-G-C-A-T-T-A-C-G-C-T-A-G-C-3’

Whale 5’A-C-C-T-T-A-C-C-A-A-T-C-A-T-T-C-C-C-T-A-A-C-T-T-A-G-G-C-A-T-T-A-C-G-C-T-A-G-C-3’

Frog 5’A-C-C-A-T-G-C-G-T-G-T-C-A-T-C-C-C-C-G-A-G-C-T-T-C-G-G-T-A-T-T-A-C-G-C-A-A-G-C-3’

Gorilla 5’A-T-C-T-T-A-C-G-A-A-T-C-A-T-G-C-C-C-T-A-A-C-A-T-C-G-G-C-A-T-T-A-C-G-C-T-A-G-C-3’

(Means the same!)

Can you create a cladogram from the information above?

http://www.youtube.com/watch?v=faRlFsYmkeY