Lecture 3: Evolution Via Natural Selection

biology’s core theme is

evolution

darwinism/evolution

descent with modification is a process that occurs over generations via natural selection

five theories within Darwinism = evolution

perpetual change, common descent, multiplication of species, gradualism, natural selection

one theory of Darwinism is perpetual change

most important theory all of evolution depends on, living world is always changing, not all things that were alive in the past are alive today, evidence is fossils

one theory of darwinism is common descent

all forms of life descended from a common ancestor

homology

similarity in characteristics because of common ancestors, allows us to classify organisms

one theory of Darwinism is multiplication of species

which is because of speciation, evidence is diversification of animals on islands

speciation

a single ancestral population can split to become 2 different species with time, there’s 2 types of speciation

1st type of speciation is geographic isolation

individuals can’t reproduce because of a geographical barrier, broad and based on environment

2nd type of speciation is reproductive isolation

biological barrier doesn’t allow 2 species to produce viable, fertile offspring, based in the individuals more specific

examples of reproductive isolation prezygotic

habitat, temporal, behavioral, mechanical, gametic

examples of reproductive isolation postzygotic

reduced hybrid viability, reduced hybrid fertility, hybrid breakdown

one theory of Darwinism is gradualism

populations accumulate small changes over long periods of time, accumulation of small changes leads to new species, evidence of this is intermediate species

one theory of Darwinism is natural selection

individuals with advantageous traits survive and reproduce at higher rates than those without the traits, explains why organisms seem designed for their environment, accumulate adaptations over long periods of time, survive better reproduce better

adaptation

some individuals survive longer and reproduce more than others due to traits

fitness

number of offspring an individual leaves behind in its lifetime

artificial selection

process where humans select desired traits in crops, domesticated animals, and livestock, works much faster than nature

Darwins postulates

4 main principles of natural selection are variation, overproduction, adaptation, and descent with modification, these things are true to any population for natural selection to occur

1st Darwin postulate is variation

all individuals within a population differ slightly in inherited traits

2nd Darwin postulation is overpopulation

more offspring are produced than those that survive, can create competition for resources

3rd Darwin postulation is adaption

or adapted individuals survive longer and reproduce more than others due to advantageous traits

4th Darwin postulation is descent with modification

traits of individuals that survive and reproduce will become more common in the next population

differential survival

individuals with favorable traits will survive better than individuals with less favorable traits

differential reproduction

individuals with favorable traits will produce more offspring than individuals with less favorable traits

whom or what does natural selection operate on?

operates on individuals, known as survival of the fittest, the less fit aren’t eliminated they just don’t survive or reproduce as well as the more fit.

who or what evolves?

populations evolve

can natural selection fashion the perfect organism?

NO, it can only act on existing variations, evolution is limited to historical constraints, adaptations are often compromises, and chance events can affect evolutionary history of populations

when environment changes, populations either…

adapt, disperse, or go extinct