El nina -> harder seeds -> finches w/ bigger beaks survived better. Avg beak size of surviving indivi + progeny inc. El nino -> smaller seeds ->smaller beaks survive better. Capacity of pop to rsp to changes in env. Traits of indivi w/in pop = continually adjusted to changes in env. Indivi w/ particular makeup prod greater # of offspring. Some variations of genes will be passed on to future generations more freq vs. others. Pop evo + indivi rsps enable species to adapt to cond of its env. Phenotype = outward expression of an indivi"s genotype. Phenotype = outward expression of genotype in indivi"s structure + function. Rendering/expression of genotype in form of an org. Genetic makeup of indivi sets limits on phenotype expression. Phenotypic traits have genetic basis + influenced by variations in env. Behavioral + physiological rsps of indivi to exhibit diff rsps to env. Alleles = diff forms of a particular gene.