Natural Selection, Speciation, and Evolution Textbook Reference Chapter 14 & 15

Lamarck’s Early Theory on Evolution Based on 3 ideas 1. Desire (will) to change 2. Use and Disuse 3. Passing on acquired traits (weight lifting) Brought idea of evolution to forefront Knew nothing of genes or genetics

Charles Darwin Observations aboard Beagle Led to his theory of evolution - change in species over time - modern organisms descend from ancient - change in allele frequency in gene pool Darwin’s mechanism: NATURAL SELECTION Wrote On the Origin of Species

Influences that Shaped Darwin’s Theory Charles Lyell, geologist - Earth very old, changed over time Farmers, artificial selection - choose organisms with desireable traits to produce offspring Thomas Malthus, economist - Malthusian Doctrine

Evidence for Evolution Contrasting theories over mechanism for evolution, typically not evolution itself Evidence of Change: 1. Fossil Record 2. Embryonic Development 3. Anatomical Structures 4. Biochemical Similarities All pieces support Darwin’s idea of descent from a common ancestor

Evolution by Natural Selection Darwin’s observations: 1 - wild species show variations 2 - high birthrates & shortage of necessities, causes competition 3 - individuals whose characteristics are well-suited to their environment survive and reproduce, survival of the fittest 4- larger portion of each new generation will have favorable variation 5 – over long periods of time, small changes accumulate, population has adapted and natural selection took place The environment selects which characteristics are advantageous Video Clip

Peppered Moths: Natural Selection in Action Two varieties, population mainly light colored prior to the Industrial Revolution Soot from burning coal coated trunks Dark moths now “fit” the best, better suited to survive, birds can’t spot the moths Relative frequency of alleles for color changed in the gene pool for the population H.B.D. Kettlewell tested the theory

How do Genes Fit In? Darwin did not know about genes and genetics 1. Responsible for variations 2. Genetic variations arise by mutations 3. Not controlled; no goal in mind Phenotypic/Genotypic variation 1. Raw material for natural selection 2. One genotype proves to be advantageous example, sickle cell carrier

Modern Evolutionary Theory Today we define evolutionary fitness as the success an organism has in passing on its genes to the next generation An adaptation is any genetically controlled trait that increases an organism’s fitness Think about the weight lifter- big muscles won’t be inherited but gene for the potential to develop large muscles could be

How do new species evolve?

Speciation Species- individuals that can breed and produce fertile offspring.(share common gene pool) Niche- habitat and role/job of organism, no 2 can occupy same niche, choices: adapt, move, or go extinct. Speciation occurs when populations are separated by some barrier Natural selection can work differently in each group Groups cannot interbreed develop reproductive isolation Each group will become fit to the environment they are in Overtime, two populations cannot breed, new species Example, Darwin’s finches underwent adaptive radiation

Adaptive Radiation

Darwin’s Finches on the Galapagos Islands Islands isolated populations of finches; natural selection occurred independently in each group Relative frequency for certain traits changed in isolated populations

Convergent vs. Divergent Evolution One species gives rise to many species Also known as adaptive radiation Many species with common ancestor Many homologous structures

Convergent vs. Divergent Evolution Similar looking species that do not have a common ancestor Similar behavior and appearance Many analogous structures Video Clip

Evolutionary Theory Continues to Evolve Gene pools can change in absence of natural selection by: 1. Genetic Drift- allele becomes common by chance 2. Genetic drift implies not all characteristics contribute to fitness Gene pools can remain unchanged for long periods of time ex. Horseshoe crab, living fossil Gradual evolutionary change, theory of gradualism Punctuated equilibrium, long stable periods with spurts of change