Organic Evolution & Natural Selection

Evolution ► development of complex life forms  through mutation and selection  natural selection - survival of the ► fittest (for a niche) ► luckiest ► combination

Evolution ► species  reproductively isolated group of living organisms ► population  group of organisms consisting of all the members of a species living in an area

Evolutionary Trends ► speciation & extinction ► divergence & convergence ► phyletic gradualism & punctuated equilibrium

Organic evolution: observations ► sedimentary rocks  deposited in layers  oldest layers are on the bottom  layers may be correlated with other sedimentary layers ► fossil record  oldest rocks have only simple fossils  younger rocks have more organisms similar to those living today (at levels from species to kingdom)  fossils record includes appearances and extinctions of many species

Organic evolution: observations ► geographic distribution of organisms  many organisms are similar but unique  they are confined to specific areas (islands, continents, water bodies)  includes modern and fossil organisms  distribution has changed through time

Organic evolution: observations ► anatomy  cell structure is similar in all living organisms  embryology - embryos of mammals, birds, and reptiles are very similar  homologus organs - similar organs, different functions  vestigal organs - no purpose in one, purpose in another

Organic evolution: observations ► genetics  structure of DNA and RNA is the same in all living organisms  similarity in genetic code varies between organisms (some organisms are more similar than others)

Organic evolution: conclusions ► the characteristics of populations of living organisms have changed through time  life has become more complex  life has become more diverse  this is excepted as a factual observation ► all life is related

Organic evolution: observations ► What about “missing links”  the “link” between two fossil species OR between a fossil species and a living species  many found, yet none found  each “gap” filled creates two new “gaps”

Natural selection: observations ► populations of organisms display a variety of characteristics  characteristics may be useful, not useful, or detrimental  the variety is reflected in an organisms genes ► new genes  provide variety  produced by mutation, duplication, or exchange of genes  passed to offspring during reproduction

Natural selection: observations ► artificial selection  domesticated plants and animals can be bred to favor certain characteristics  populations of wild and domestic plants and animals develop characteristics that favor their survival

Natural selection: observations ► the natural environment  provides opportunities and stresses for living organisms  a new niche or stress on an existing niche will enhance selection

Natural selection: observations ► populations of a species may become isolated  by geography or behavior  provides new opportunities and stresses  isolates the population from the larger gene pool

Natural selection: conclusion ► the natural environment provides conditions (opportunities and stresses) that result in evolution through the process of natural selection ► organisms with favorable characteristics for their niche are more likely to thrive and reproduce while organisms with unfavorable characteristics are less likely to thrive and reproduce ► over time, favorable characteristics can accumulate in a population until the members of the population can no longer reproduce with the population from which they became isolated

Evolutionary trends ► speciation & extinction ► divergent & convergent evolution ► phyletic gradualism & punctuated equilibrium

Natural selection: speciation ► a population has a gene pool ► members of the population interbreed ► the population may become isolated from others of a species  development of niches & resource partitioning  migration  development of physical barriers ► populations may be selected  by stress  by opportunity ► isolation may result in genetic divergence

Natural selection: extinction ► stress on limiting factors reduce or destroy a population ► evolution into subsequent species (pseudo-extinction)

Phylogeny ► relationships between organisms can be determined using  genetics  anatomy & physiology  Fossils

Phyletic Gradualism & Punctuated Equilibrium ► gradualism  slow, steady change ► equilibrium & punctuation  long periods with little change  short bursts of rapid change

How did it start? ► Chemical evolution? ► Where?  deep ocean vents?  tidal pools?  ice surface?  clay surface?

Randomness ► evolution is not random ► natural selection is not random ► mutations are random ► favorable mutations survive through reproduction

End point ► Evolution has no end