EVOLUTION BIODIVERSITY Topic 5 1 Evidence for Evolution

EVOLUTION & BIODIVERSITY Topic 5. 1 Evidence for Evolution

Evolution • The cumulative changes in the heritable characteristics of a population.

Measuring Evolution • Measured by change in frequency of alleles in a population • New species arise when members of a population evolve to a point where they can no longer mate and reproduce with members of the old population

• If we accept not only that species can evolve, but also that new species arise by evolution from pre-existing ones, then the whole of life can be seen as unified by its common origins • Variation within our own species is the result of different selection pressures operating in different parts of the world

Evidence for Evolution • 1. The Fossil Record • A fossil is the ancient preserved remains of an organism. • The fossil can be dated from the age of the rock formation. (Relative Dating and Radioactive dating) • Sequences of fossil can show the gradual change of an organism over geological time (the farther down a fossil is buried, the older it is) • Continuous fossil records are rare with most containing large time gaps until subsequent discoveries are made

Fossils

• 2. Selective Breeding (artificial selection) • Man has selectively breed animals and plants for thousands of years. • If an animal posses a characteristic that is considered useful or valuable then this animal is selected for breeding. • The hope then is that this characteristic will be present in the next generation and at a higher frequency than before. • In subsequent generations it may even then be possible to select from an even more advantageous characteristic.

• 3. Homologous structures by adaptive radiation • Same structure evolved for different functions (common ancestor) • These are often referred to as divergent characteristics since they have evolved to suit the habitat of each new organism but maintain similar characteristics. • For example pentydactyl limbs in mammals, bats, birds and amphibians (hand with 5 digits, lower limb with 2 bones and upper limb with one bone) • Suggests evolution from common ancestor that has evolved to adapted environments

Pentydactyl Limbs

NOT Evidence of EVOLUTION!!! • Analogous structures • Same function evolved from different structures (no common ancestor) • Allows organisms to adapt to their environment • Bat, butterfly and bird wings

4. Biochemical Homologies • Comparison of organisms based on DNA samples • More accurate that basing theories on anatomical structures as most fossils are incomplete • Has allowed scientists to find quantitative evidence for evolution.

5. Biogeography • Using our knowledge of plate tectonics and the movement of our continents with our knowledge of the fossil record. • We are able to piece together our continents as we believe they once were and compare the locations of fossils • This is a less commonly used piece of evidence

6. Embryology • The study of organisms during embryo development.

Natural Selection • AKA Survival of the “Fittest” • Populations produce more offspring than can supported • Therefore competition for resources (food, water, space etc. ) • Variation based on behavior and characteristics; due to genetic differences • New alleles can be formed • Beneficial variations help organisms survive

• 3 types of selection • Stabilizing Selection • The most average phenotype for a particular trait is selected for • Directional Selection • One of the extreme versions of a phenotype is selected for • Disruptive Selection • Both extreme versions of a phenotype are selected for

Divergent Evolution or Speciation • the evolutionary process by which new biological species arise • Species become separate and no longer breed • Can evolve to new species • Examples include Darwin’s Finches • IMPORTANT NOTE: Evolution does not always lead to speciation!

Examples of Evolution • Industrial Melanism The peppered Moth • has two phenotypes for wing color: light grey & dark grey • Prior to the mid 1800’s the light grey phenotype was most abundant it could blend in with bark of the trees it lived around (camoflauge) • When the industrial revolution began (mid 1800’s) soot from factories quickly darkened the plant life in surrounding areas

• As a result the light grey wing color was no longer advantageous and the dark grey wing color was selected for • The life span of the peppered moth is only one year so after only a few years the change in frequency of wing color (and therefore alleles) was easy to see

• Antibiotic resistance in staphylococcus aureus This bacteria is associated with skin & lung infections Treated with Methicillin (antibiotic) Methicillin is the environmental selective pressure Over time, usually because a methicillin treatment was not completed, certain members of an s. aureaus colony survived and developed resistance to the drug (through a mutation) • These individuals multiplied to become resistance strains that can not be treated with Methicillin • •