1. Evolution & Biodiversity
Topic 5.1 Evidence for Evolution

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

3. 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

4. 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

5. 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

6. Fossils

7. 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.

8. 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

9. Pentydactyl Limbs

10. 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

11. 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.

12. 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

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

15. 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

16. 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

17. 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!

18. 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

19. 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

20. 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