BIO 7:  Lecture 36 Preview

Charles Darwin brought together many experiences, observations, and ideas.

• sailed around the world, saw species suited to their environments, related species in neighboring environments, fossils of extinct forms
• read economics (Malthus) and geology (Lyell)
• collected seashells and pigeons

Interactions among living things and their environment influence organisms in the present and future.  Living things have changed over time due to interactions with their environment.

Darwin's and Wallace's Theory of Evolution by Natural Selection (1859)

1.        In a population random (both bad and good) heritable variation occurs; individuals differ in some ways that can be passed on to their offspring.

2.        As a population grows the environment limits the number of individuals that can survive and reproduce.

3.        In a specific environment individuals with some heritable variations (adaptations) will survive and reproduce better than others (be fitter). 

Natural Selection

4.        After many generations there will be more individuals with the adaptations; the average characteristics of the population will change.

Microevolution

5.        New species arise when enough differences occur between two groups within one population that the two groups can no longer interbreed.

Macroevolution

Scientific Theories, Laws, Principles = ideas receiving support from many studies and are therefore widely accepted

• Support from Mendel's discovery of genes.  Early weakness in Darwin's idea:  no explanation for source of random heritable variation.

       1860's Mendel discovers genes = sources of heritable variation

Mutations create new forms of heritable information

Meiosis and sexual reproduction create new combinations of heritable information

 Lots of genetic variation (many different combinations of alleles) observed in natural populations. 

 Evolution = change in the average phenotype in a population; change in genotype and allele frequencies

• Support from ecology:  Many  studies show that environments have carrying capacities.

• Microevolution due to natural selection observed directly in organisms with short generation times   

        (What is the adaptation?  What is the selective agent in the environment?)  

          e.g. drug-resistant bacteria and DDT-resistant mosquitoes arise                                        

e.g. Industrial Melanism (example in lab) of peppered moths in Britain

    e.g. Darwin's Finches on the Galapagos Islands studied in the 1970's by Peter and Rosemary Grant

• Support from plant and animal breeding studies:  Artificial Selection:  reproduction of certain types chosen by humans

• Support from population geneticists:  Populations' gene pools can change due to other factors besides natural selection.

Factors changing populations

1. Natural Selection

2. Mutation

3. Non-random mating

4. Migration (Gene flow)

5. Genetic Drift