Natural Selection

5 types of evolution - Genetic drift, non-random mating, mutation, gene flow, and adaptian by natural selection

evolution - change in the gene pool over time

• Species, not individual

Macroevolution - Large change, change in genetic makeup leading to speciation

• cell → frog, human, or bird

Microevolution - small

• change in the genetic makeup of certain populations

• Affected by environment - environment pressures, ex: predators

Directional selection

• polygenic organisms select the most favorable genes during evolution

Fossils - remains/traces of organisms from the past in layers of sedimentary rock called strata

• laid groundwork for Darwin’s ideas (change over time)

Darwins focus on adaptation - adaption to the environment & origin of new species are closely related processes

• Darwin’s observations:

  • unity of life - water, food, carbon, O2, DNA, cells, glycolysis

  • Diversity of life - millions of insects, each adapted to their own niche

Mutations - neither good nor bad, depend on environment

• changes in the genetic makeup of DNA

1. Genetic variation - Members of a population vary in their inherited traits

• allows species to survive in different “zones”

Zone of tolerance - avg zone, will survive and thrive

• Stress → outside of the zone of tolerance

  • caused by the environment, access to resources, pred-prey relationship

• Outside of stress zone - death

  • causes extinction, too much of the population living in this zone

2. Species can produce more offspring than the environment can support → many fail to survive & reproduce

   • Individuals with higher probability & reproducing traits → make more offspring

   • Unequal ability to survive & reproduce → accumulation of favorable traits in the population over generations.

Natural selection summary - heritable traits survive & reproduce at an higher rate than both individuals → natural selection increases match between organisms and their environment over time → environment changes over time → natural selection results in adaption to new conditions & may give rise to new species

Why natural selection isn’t perfect

1. selection can act on only existing variations

2. evolution is limited by historical constraints

3. adoptions are often compromises

4. Chance, natural selection, and the environment interact

Fitness - measured by an organisms ability to survive & reproduce

• determines genetic contribution to next gen

Biotic factors affect rate of evolution (Living)

• special distribution patterns

• location of food

• proximity to other packs

• predator-prey relationships

  • competitions, causes both populations to fluctuate

Abiotic factors (not living)

• light - distribution patterns of photosynthetic organisms

• Water

  • root size

• Pollution

Evolution vs Natural selection

• Evolution - gradual change e in the inherited traits of a population

  over many generations.

• Natural selection - when the members of a

  population best suited to their environment have the best chance of

  surviving to pass on their genes.

Divergent evolution

• species adapt to different environments (ex: finch)

  • fill different ecological roles, niches

Variation → closely related to the success of an organism

• camouflaged animal → successfully avoids predators

  • BUT it may not attract a mate

Artificial selection & adaption- humans modifying other species by selecting & breeding individuals with desired traits

• directional selection

Gene pool- all of the alleles in a population

genetic drift - reduces variation through loss of alleles

• Founder effect - individuals become isolated from a larger population

• Bottleneck effect - sudden reduction in population size due to a change in environment

  • Small populations

  • allele frequencies change at random

  • loss of genetic variation

  • harmful alleles could become fixed

Gene flow - movement of alleles among populations

• immigration & emigration

reproductive isolation - barriers that impede two species from creating viable fertile offspring

• geographic isolation

  • allopatric speciation - population divided into geographical isolated areas

    • more areas → more species

• hybrids

History of life on Earth

AT first - hot, anoxic, no oxygen

• volcanic activity

• acid rain

Fossil record

• To be fossilized - exist for a long time, abundant & widespread, have hard parts

• Mass extinction - result of disruptive global environmental changes

  • consequences - alters ecological communities & niches available to organisms

Adaptive radiation - is the rapid evolution of diversely adapted

• species from a common ancestor

Two-part names for species and hierarchical classification

• Type: Genus species

• Handwritten: Genus species (must be underlined, first letter capitalized)

Homology vs Analogy

Homology- similarity due to shared ancestry

• same ancestry → different function

Anology - similarity due to convergent evolution

• same function → different ancestry

Convergent vs divergent evolution

Convergent - similar environmental pressures produce similar adaptations in unrelated organisms

divergent - species sharing common ancestry → more distinct because differential selection pressure which gradually leads to speciation

4 factors effecting natural selection

• variety

• adaptation

• differential reproduction

• competetion