Theory of Natural Selection:

Darwin’s explanation for HOW evolution works.

VOYAGE OF THE HMS BEAGLE : 1831 - 1836

7 Steps to Natural Selection1. Overpopulation

(overproduction)- animals produce more offspring than survive.

2. Variation- animals of the same species are different

3. Change in environment-

a) Biological - food, predators, shelter, etc.

b) Physical…water, oxygen, temp, etc.

4. Struggle for existence- competition for water, food, & shelter

5. Survival of the fittest- the best adapted & strongest tend to survive longer & produce more offspring

6. Inheritance- favored/best fit/selected variations (characteristics) are passed on to offspring.

7. New species arise- “selected” individuals grow in number and become a new species that cannot reproduce with original species

Darwin’s Observation: 13 or so species of finches on different Galapagos islands; these finches resembled the South American (mainland) finches more than say finches in Asia….

Same process for other species!

used the fossil record as evidence proposed a theory of evolution

where organisms became better and better

Mechanism - ”use” and “disuse” leads to:

inheritance of acquired characteristics (you ‘acquire’ a phenotype in your lifetime and pass it on to your kids)

also means environmental influences can be inherited

DON’T BE LAMARCKIAN!

Jean Baptiste Lamarck: the outcaste!

Hugo DeVries & Mutation Theory

• New Characteristics suddenly appear– Mutation

• These can be passed on and may or may not help a species become more fit

• Helped to modify Darwin’s Theory

Evidences for Darwin’s theory

• Fossil record - horse lab

• Homologous Structures

• Vestigial structures

• Artificial selection

Fig. 22.12

• Natural selection in action: the evolution of insecticide-resistance occurs in

nature - individuals with the best fit genes that can resist the insecticide will survive….

B) HOMOLOGIES –

• Similarities in characteristics resulting from common ancestry is known as homology.

• 1) Homologous Structures: Same skeletal elements, but different functions

B) HOMOLOGIES –

HOMOLOGOUS STRUCTURES

Human hand, cat limb, whale flipper, bat wing - they all have the same basic bone structure and design; So they have ALL evolved from a common ancestor with a similar ‘limb design’.

C) Vestigial organs, structures that are not used, but which had important functions in ancestors - still retained in descendents, so evolution/change has occurred.

Some Alleged Vestigial Organs in Man

Tonsils Adenoids

Coccyx (tail bone) Nictitating membrane of eye

Thymus Appendix

Little toe Wisdom teeth

Nipples on males Parathyroid

Nodes on ears "Darwin's points"

Ear muscles for wiggling

Pineal gland Body hair

C) Vestigial organs – spurs in snakes, hind leg bones in whales.

Artificial Selection

• Artificial Selection: The selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits.

• Short period of time needed for Artificial Selection

Heredity: Characteristics that are passed down to offspringMutations: Changes that occur in the hereditary materialMutant: The new form that survives a mutation and passes this trait on to offspringAdaptation: A favorable variation within a species that may help an organism survive

• Natural selection - Predators/famine/space shortage/disease/ environmental changes

Origin of life and Stanley Miller’s Experiment

• Stanely Miller - simulated conditions on early Earth (no oxygen, reducing environment with inorganic gases like H2, CO2, NH3, CH4; lightning/UV with no ozone. Favored the synthesis of organic compounds from inorganicmaterial

Abiotic synthesis of organic monomers

The Miller-Urey experiments produced a variety of amino acids and other organic molecules (monomers).