Evolution

The theory that organisms have

changed gradually over time.

Evidence to support the Theory of Evolution

• Fossil Record - Law of Superposition• Comparative Anatomy:

– Homologous Structures– Analogous Body Structures– Vestigial Body Structures

• Comparative Embryology• Comparative Biochemistry (genes/proteins) • Direct Observation

Fossil Record

• Evidence of change over time

• Relative age of extinct organisms

• Age of the Earth

Law of Superposition: Older fossils in bottom layers; younger ones in upper layers

Sedimentary Rock Layers

Fossil Evidence:• Once living

remains of organisms

• Limited:

1. Type of material preserved (bone, shell, impressions, amber)

2. Incomplete record

3. Easily disrupted

Comparative Anatomy

• Compares structures of different organisms living today

1. Homologous Structures – Parts on different organisms that are similar in structure (and sometimes function) and seem to indicate common origin – common ancestor.

Indicate divergent evolution – things becoming more different.

• 2. Analogous Structures – similar in function and appearance, but not in origin. – Illustrate convergent evolution – things becoming more

similar.

Fly wing

Bird Wing

Analogous Structures

3. Vestigial Organs - traces of homologous structures; no apparent use.

Comparative Embryology

Comparative Embryology

• shows early developmental stages in embryos of different vertebrate species is very similar

• Inherited same basic body plan from a common ancestor

• Become distinct at later stages

Genetic Evidence

• Each new generation of organisms in a population shows some change or variation as a result of:– Mutations– Meiosis & fertilization

Comparative Biochemistry

Similar organic compounds (proteins, etc.)

Humans and chimp DNA – 98% similar

Humans and other mammals – 80% similar

Direct Observation

Rapid evolution1. Antibiotic resistant bacteria

2. Resistance of insects to pesticides

3. HIV strains

How does evolution occur?Lamarckism vs. Darwinism

• Jean Baptist Lamarck (1744 – 1829)– “Acquired Characteristics” develop and are

passed on to offspring.– Experimentation failed to support Lamarckism

• Charles Darwin (1809-1882)

Influences on Darwin

• 1. Worked as naturalist on HMS Beagle for 5 year voyage– Collected fossils and specimens– Noted tremendous biodiversity– Galapagos organisms unique yet similar to

species elsewhere– Formulated his idea of “Descent with

Modification” (changes occur from one group of descendants to the next)

Descent with Modification

Voyage of the Beagle

2. Studied Charles Lyell – Geologist who said,

“The present is the key to the past.” The same forces acting on earth in the past are

continuing today.

3. Studied work of Thomas Malthus - 1798

• Human population growing faster than food supply - creates competition• Darwin extended idea to other organisms.

4. Observed that organisms produce more offspring than can survive

5. Observed the Struggle for Existence - Competition

                                                                                                                                                                                                                                                                                                 

                                                                                                                                                                                             

6. Noted Artificial Selection

• Farmers and breeders practice selective breeding to produce preferred offspring.

• Darwin questioned – Is there a force in nature that simulates artificial

selection???

Adaptations are physical or behavioral traits that make an organism better able to survive

in its environment.

Tartan Hawkfish

Cryptic Frog

Walking Stick

www.howstuffworks.com

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Sea Dragonwww.liverpoolmuseum.org/uk

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“On the Origin of Species by Means of Natural Selection”

published in 1859• Summary of Theory of Natural Selection:

1. Overproduction of Offspring (more produced than can survive)

2. Variation within a population

3. Struggle to survive creating competition

4. Successful reproduction - Individuals with better adaptations pass these on to offspring (survival of the fittest)

Darwin envisioned the tree of life

PhylogeneticTree

Sources of Variation

• S – sexual reproduction

• C – crossing over during meiosis

• A – assortment of alleles during meiosis

• M - mutations

Pepper Moths - England

• Original color – 99% white (white bark on trees)

• Industrial Revolution, 1850s – produced smog

• Environment changes - 1890s - 99% black (dark bark on trees)

Each new offspring in a population draws its genes

from the same gene pool.

Which trait was a better adaptation and so selected for?

How did this affect the frequencies of the different alleles?

Gene Pools

Population Genetics

• Natural Selection acts on individuals, BUT

populations evolve

• An individual’s genotype remains constant

• A population’s gene pool (entire collection of genes in a population) evolves as allele frequencies change due to natural selection

History of Earth

• Earth is @ 4.6 billion years old –

• Early earth – – hostile environment – volcanoes, lightning,

meteorites, UV light

– Primitive atmosphere: CH4, NH3, H2, H2O,

• All elements for life present – but no pure oxygen

Origin of Life

Primordial soup hypothesis: Primitive atmosphere filled with carbon, hydrogen, nitrogen, water vapor - bombarded by lightning and uv radiation, producing organic compounds and precursors to first cells, which ended up in oceans

• Stanley Miller’s Experiment1953 – University of Chicago

• After 1 week simple organic compounds including amino acids were present

Origins of Life: Oceans as Nursery Simple compounds

Complex compounds

Primitive precells

Prokaryotes

Prokaryotes to Eukaryotes

• First were heterotrophic prokaryotes which absorbed simple organic compounds.

• Next, chemosynthetic prokaryotes

• Next, photosynthetic autotrophs which produced oxygen

• Led to development of eukaryotes and more complex organisms