1. 1. Natural selection can only occur if there is variation among members of the same species. WHY?
Variation in a population results from mutation and the recombination of alleles during meiosis and fertilization.

2. Mutation
New alleles arise from the mutation of existing alleles, usually by changing one or a few base pairs

3. Meiosis:
Crossing over of homologous chromosomes during prophase I results in a recombination of maternal and paternal alleles within chromosomes
Independent assortment as homologous chromosomes randomly orient at metaphase I causing a randomized inheritance of maternal and paternal chromosomes within gametes

4. Fertilization: New combinations of alleles appear during fertilization
As the unique set of haploid alleles in the egg
Combine with the unique set of haploid alleles in the sperm

5.  2. Species tend to produce more offspring than the environment can support. · observation 1: All species have such great potential fertility that their population size would increase exponentially if all individuals that are born reproduced successfully. · observation 2: Populations tend to remain stable in size except for seasonal fluctuations.

6. observation 3: Environmental resources are limited.
3. Individuals that are better adapted tend to survive and produce more offspring while the less well adapted tend to die or produce fewer offspring.
observation 3: Environmental resources are limited.
· inference 1: Production of more individuals than the environment can support leads to a struggle for existence among individuals of a population, with only a fraction of offspring surviving each generation (= struggle for existence).

7. 4. Individuals that reproduce pass on characteristics to their offspring.
Survival in the struggle for existence is not random, but depends in part on the hereditary constitution of the surviving individuals. Those individuals whose inherited characteristics best fit them to their environment are likely to leave more offspring than less-fit individuals (= natural selection).
this unequal ability of individuals to survive and reproduce will lead to a gradual change in a population, with the inheritance of favorable characteristics accumulating over the generations.

8. In other words: Natural selection is differential success in reproduction ( unequal ability of individuals to survive and reproduce).

9. 5. Natural selection increases the frequency of characteristics that make individuals better adapted and decreases the frequency of other characteristics leading to changes within the species.
evolution is the cumulative change in the heritable characteristics of a population, or
the changes in allelic frequencies in the gene pool of a population over time, as a result of natural selection, genetic drift, gene flow, and mutation pressure.

10. 6. Adaptations are characteristics that make an individual suited to its environment and way of life.
Natural selection occurs through an interaction between the environment and the variability inherent among the individual organisms making up a population.
The product of natural selection is the adaptation of populations of organisms to their environment.

11. 7. Application: Changes in beaks of finches on Daphne Major.
yearly variation in rainfall in the Galapagos Islands can be extreme due to the weather cycles known as El Nino
in wetter years, all sizes of seeds are available in large numbers
smaller birds with smaller beak sizes eat more efficiently and have higher rates of surviving and reproducing
smaller beaked birds pass on the trait of smaller beaks to their offspring
as a result, in the following year the average beak size decreases
that is, the frequency of the smaller beak alleles increases over time
in dryer years, smaller seeds are quickly consumed, leaving only larger, harder seeds
larger birds with larger beak sizes eat more efficiently and have higher rates of surviving and reproducing
larger beaked birds pass on the trait of larger beaks to their offspring
as a result, in the following year the average beak size increases
that is, the frequency of the larger beak alleles increases over time
As predicted by evolutionary theory, natural selection produces gradual changes in traits in response to changes in the environment

12. 8. Application: Evolution of antibiotic resistance in bacteria.
shortly after development of antibiotics (e.g. penicillin) nearly all bacteria were killed during an application of antibiotics
some variants of bacteria had a heritable trait that gives them resistance to antibiotics
the resistant bacteria have higher rates of surviving and reproducing
resistant bacteria pass on the trait of antibiotic resistance to their offspring
in each following generation the percentage of antibiotic resistant bacteria increases
that is, the frequency of the antibiotic resistance alleles increases over time
As predicted by evolutionary theory, natural selection produces gradual changes in traits in response to changes in the environment