J. DIVERGENT and CONVERGENT EVOLUTION 1. Divergent evolution results from two or more species evolving increasingly different traits as a result of different selective pressures this is what we classically think of as evolution : start with one cat and over time get tigers, lions, leopards, cheetahs, jaguars, pumas, bobcats, ocelots etc.

2. Convergent Evolution results from two unrelated species being subjected to similar selective pressures with the result that they produce similar phenotypes an example is shown on the next slide

streamlined shape streamlined shape dorsal fin for stability dorsal fin for stability pectoral fin for up/down control pectoral fin for up/down control tail fin to power forward tail fin to power forward BUT sharks are a bony fish, dolphins are a mammal but sharks and dolphins both hunt fish in the open ocean as a result, both have a similar body shape and similar type and number of fins

in Australia there never were any placental mammals so all of the niches had to be filled by marsupials, many of whom greatly resemble their placental mammal counterpart

K. NATURAL SELECTION 1. when a new allele arises in a population, one of three fates awaits it a. if it confers an advantage, more of the allele will appear in the population red spheres are selected for, so more are found over time

b. if it conveys a disadvantage, less of the allele b. if it conveys a disadvantage, less of the allele will appear in the population red spheres are selected against, so fewer are found over time

c. if it has no effect on survival, it will remain at c. if it has no effect on survival, it will remain at its current level red spheres are not selected for, so numbers stay the same over time

2. alleles that confer an advantage must affect one of the following: a. increase the number of offspring with this allele that survive until they are of reproductive age

b. increase the survival of grandchildren with this b. increase the survival of grandchildren with this allele even though children may be unaffected

c. increase the survival of relatives with the same c. increase the survival of relatives with the same allele such as nephews or nieces

3. alleles that confer a disadvantage may take several forms a. directly reduce the number of offspring born b. reduce the percentage of offspring that reach reproductive age even while increasing the number born c. keep the allele in a small population such that random chance is more likely to completely eliminate all of those individuals with the allele