The Nature of Science, Evolution & Creationism part 3 Mike Phillips Geology Professor

Organic Evolution & Natural Selection

Organic Evolution ► changes in life through time ► development of complex life forms ► development of a variety of life forms

Natural Selection ► mechanism responsible for evolution ► through mutation and selection ► survival of the  fittest (for a niche)  luckiest  combination

Scientific Explanations ► must be natural ► must be supported by available data ► must be testable & falsifiable ► subject to revision or refinement or negation ► should be predictive ► OE and NS meet all of these requirements

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

Organic evolution: observations ► sedimentary rocks  deposited in layers  oldest layers are on the bottom  layers may be correlated with layers in other areas ► conclusions  relative time scale  the Earth is very old  confirmed with absolute dating

Organic evolution: observations ► 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)  mitochondrial and plasmid DNA ► separate from nuclear DNA ► similar to some bacteria

Organic evolution: observations ► cladistic analyses  statistical examination using ► anatomy ► DNA ► behavior  indicates strength of affinity between species

Organic evolution: observations ► combining data  cladistic analyses of fossils and living species  time data (relative & absolute)  spatial relationships (where fossils and living populations are found) ► reveals phylogeny (“tree of life through time”)

Organic evolution: conclusions ► the characteristics of populations of living organisms have changed through time  life has become more complex  life has become more diverse  all life is related  this is accepted as a factual observation ► the interpretation of the relationships between organisms is being expanded & refined

Organic evolution: Missing links!!! ► the “link” between two fossil species OR between a fossil species and a living species ► PRESERVATION AS A FOSSIL IS RARE! ► many “links” found (it’s just a matter of time and effort) ► however: each “gap” filled creates two new “gaps”

Question ► What is the mechanism that resulted in the evolution of life?

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

Natural selection: observations ► new genes provided by  mutation  duplication  exchange ► passed to offspring during reproduction

Natural selection: observations ► Symbiosis  Living organisms in close proximity, at least one of the symbionts cannot live without the other ► Symbiotic relationships can become permanent, resulting in new characteristics

Natural selection: observations ► artificial selection  domesticated plants and animals can be bred to favor certain characteristics  ONLY individuals with desired characteristics are allowed to breed  descendant populations of plants and animals are dominated by characteristics that are desired by breeders… …and thus favored their survival

Natural selection: observations ► The natural environment acts as a selective breeder  contains opportunities and stresses for living organisms  selection is enhanced by ► stress on an existing niche ► a new niche

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

Conclusion The variety of conditions in the natural environment results in natural selection of populations which, in turn, is responsible for biological evolution.

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

Natural selection: details ► 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

Natural selection: details ► genetic changes  favorable: more likely to be passed on to offspring  neutral: likely to be passed on to offspring  unfavorable: less likely to be passed on to offspring ► natural selection is not random

Divergence & 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 & speciation

Extinction ► stress on limiting factors destroy a population ► “divergent” evolution into subsequent species (pseudo-extinction)

Convergence ► Characteristics of a habitat favor certain styles of adaptation  e.g. streamlined shape, tooth shape ► Natural selection results in organisms in similar niches having similar forms ► Similar forms resulting from convergence usually do not have similar underlying structures

Homology & Vestigial Organs ► a slightly modified organ or organ system my provide advantage in a niche ► when the modification results in selection generation after generation, the modification may become enhanced ► when compared with closely related species, the organ or organ system will have the same parts used for different functions (homology) and some parts may no longer be in use (vestigial)

Coevolution & Symbiogenisis ► A niche may be associated with another organism ► The characteristics that favor interdependence may be subject to continued selection (coevolution) ► Selection that favors an “organic” niche may result in dependence or interdependence (symbiosis) ► Symbiotic relationships may become permanent due to genetic exchange and/or incorporation (symbiogenesis)

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  needs energy, but no oxygen  simple compounds form(CO2, NH3)  organic compounds form (amino acids, nucleic acids)  organic compounds assemble (microspherules, bubbles, clay particles, ice crystals) ► First life: simple, wall-less, fermenting bacteria ► Where?  deep ocean vents, tidal pools, ice sheet, clay sediment

End point ► Evolution has no end

Complexity ► Nothing is too complex to investigate.