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

Charles Darwin “Theory of Evolution by Natural Selection” Proposed that new species could develop by a process of natural selection.

Charles Darwin Natural selection: When better adapted organisms survive to produce a greater number of viable offspring. This has the effect of increasing their proportion in the population so they become more common

Darwin’s studies Studied animal species in the Galapagos Islands and found they each had unique adaptations Galapagos finches demonstrate different adaptations to eat different foods Galapagos turtles are the largest on earth

Natural Selection A mechanism for change in a population Natural Selection (N.S.) 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

How does natural selection produce change in a population How does natural selection produce change in a population? 3 types of natural selection

1. Stabilizing Selection Favors average individuals in a population Those individuals have a “selective advantage” Reduces variation in a population

2. Directional Selection Favors one of the extreme variations of a trait Can lead to rapid evolution of a population

3. 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 2 species no longer interbreed within their natural environment

Evidence for Evolution Structural Adaptations Methods of protection Teeth, claws, thorns Mimicry Camouflage

2. Physiological Adaptations: Changes in an organism’s metabolic processes Resistance to antibiotics or chemicals

Fossils: Provide a record of early life and evolutionary history

4. Anatomy: Structural features with a common evolutionary origin are called homologous structures. The body parts of organisms that do not have common evolutionary origins but are similar in function are called analogous structures. A vestigial structure does not have current function but may have been useful to an ancestor

5. Embryology: Similarities among the young embryos suggest evolution from a distant, common ancestor

6. Biochemistry: Comparing DNA and RNA

How do we know what happened when?  1. Radiometric dating relies on half-life decay of radioactive elements to allow scientists to date rocks and materials directly.  2. Stratigraphy provides a sequence of events from which relative dates can be extrapolated.  3. Molecular clocks allow scientists to use the amount of genetic divergence between organisms to extrapolate backwards to estimate dates.

What’s important from all these notes? V = variation I = inheritance (overproduction) S = selection T = time