Site hosted by Angelfire.com: Build your free website today!

14-1 Developing a Theory of Evolution

Artificial Selection
Technique used in which the intervention of humans allows only selected organisms to produce offspring.
- farmers only allow best plants/animals to breed to produce better stock
- contributed to the idea of natural selection

14-2 Evolution by Natural Selection

Natural Selection Process in nature that results in most fit organisms producing offspring.
- based on ideas of artificial selection
- Malthus: observed aren't enough resources if natality rate exceeds mortality rate
- plants and animals in constant struggle to survive
- most adapted to environment survive and reproduce
Survival of the Fittest A principle that states that only individuals with characteristics best suited to their environment survive the struggle for existence.
- see also natural selection
- most adapted species survive and reproduces
- in this way helpful characteristics are more likely to be passed on
- ie cheetahs; only fastest cheetahs catch food, gene that helps be fast is passed on to next gen

14-3 Genetics and Evolutionary Theory

Population Collection of individuals of the same species in a given area whose members can breed with one another.
- all of one species within specific area (fish in one pond differenet pop than other pond)
Gene Pool Common group of genes shared by members of a population.
- contains number of alleles including those for recessive traits
- allows for genetic variation
Relative Frequency Number of times an event (allele) occurs compared with the number of times another event (other alleles for the same gene) occurs.
- evolution involves change in the relative frequencies of alleles in the gene pool of a population
- sometimes may change(shift) due to natural/unnatural factors (peppered moths)
- if it shifts new variation may become norm

14-4 The Development of New Species

Speciation The process by which new species evolve from old ones.
- geological barriers seperate the gene pools
- species is a group of organisms that can breed with one another and produce fertile offspring in a natural environment
- example is finches: seperate from main, go to different islands, adapt to needs on islands, cannot interbreed
Niche Combination of an organism's habitat and its role in that habitat.
- no two organisms can occupy the same niche for a long period of time
- any species (or population within a species) that occupies an unoccupied niche more likely to survive
- contributes to the process of speciation
Reproductive Isolation Separation of populations so that they do not interbreed to produce fertile offspring.
- one of most common ways which new species form populations are seperated
- when seperated adaptations appear in one group but not other
- eventually so different unable to breed with other group
Adaptive Radiation Process, a.k.a. divergent evolution, in which one species gives rise to many species that appear different externally but are similar internally.
- see divergent evolution
Divergent Evolution
Pattern of evolution, a.k.a. adaptive radiation, in which one species gives rise to many species that appear different externally but are similar internally.
- see also speciation (example finches)
- see also homologous structures
- species diverge from common ancestral form
- allows species to adapt for different niches
Convergent Evolution Phenomenon in which adaptive radiations among different organisms produce species that are similar in appearance and behavior; opposite of divergent evolution.
- produces analogous structures
Analogous Structures Structures that are similar in appearance and function but have different origins and usually different internal structures.
- produced by process of convergent evolution
- ie bird, bat, butterfly, similar because all have wings, but wings differ in material and build

14-5 Evolutionary Theory Evolves

Genetic Drift
Random change in the frequency of a gene.
- produced by a random event such as earthquakes, volcanic eruptions etc.
- thus evolution can occur with the absence of natural selection
- implies not all characteristics contribute to fitness
- ex rhinoceros, indian has one horn african has two, camels one hump and two
Gradualism Theory that evolutionary change occurs slowly and gradually.
- fossil record shows some species evolved over long periods of time
- evidence shows others did not change much before they went extinct
Equilibrium State in which no net change occurs.
- if equilibrium stays for long time then change, species may evolve rapidly
- some biologists argue this is what creates new species
Mass Extinction Phenomenon in which many species suddenly vanish.
- may be caused by changes in global climates
- species that die leave many unoccupied niches
- species with enough genetic variability can adapt to empy niches
- creates many new species
Punctuated Equilibria Pattern of long stable periods interrupted by brief periods of change.
- still controversial among biologists
- clear though, that evolution occurs at different rates