Jash Parikh 2012/10/31
Biology for Sciences I Lecture 15
Why Evolution is True
Hardy-Weinberg also assumes random mating with respect to genotype
o But mating is often non-random
Inbreeding Or interbreeding avoidance
Assortative OR dissassortatative
Assortative mating in snow geese
Dissasortative mating in white-throated sparrows
Non-random mating and evolution?
o If a population begins mating assorative for a certain trait, but all genotypes have
the same fitness, what will happen?
2 alleles, 3 genotypes (AA,Aa,aa)
Each genotype mates assortatively
Non-random mating perturbs HWE, but doesn‟t cause evolution
o Homozygous individuals mate amongst themselves to create whatever amount of
individuals they started with
Population becomes homozygous eventually
250 AA, 500Aa, 250aa
Becomes 375AA, 250Aa, 375aa
Why evolution is true
o “Humans evolved from earlier species of animals”
Survey to the world indicated countries that believe evolution is true
United States and Turkey have the least percentage of individuals
that believe in evolution
Evolution as a fact and a theory
o What do scientists mean by a theory?
o What do we mean by true?
o What is the theory of evolution?
o And what empirical evidence supports this theory?
Evolution is “only a theory”…
o “an assumption based on limited knowledge…a conjecture”
o “a coherent set of testable hypotheses that attempt to explain facts about the
Atomic theory of matter
Germ theory of infectious disease
What do scientists mean when we say something is true?
o “an assertion for which there is so much evidence that I would be perverse to
deny it”-SJ Gould
o Theories „graduate‟ to fact-hood after repeated testing fails to falsify them
o Assertions that cannot possibly be falsified are not scientific
What is the theory of evolution?
o 1. Evolution happens
Change in allele frequencies in a population, between generations BIO1001
Jash Parikh 2012/10/31
May be due to genetic drift, natural selection, etc.
o 2. Most evolution is gradual
Small changes over time gradually evolve into a different organism
Viruses and diseases can go through evolution like this, however may be a
o 3. Speciation happens
Species are placed into different branches; Eukarya, Archaea, Eubacteria
o 4. All life is related through common ancestry
Every species on earth is somewhat related to other species on earth
LUCA and MRCA
o 5. Much of evolutionary change is caused by selection
Darwin first to come up with theory of natural selection
Process by which species become adapted to an environment
o 6. Evolution occurs in populations, not within individuals
Happens between one generation to the next
Populations change but individuals do not adjust in response to selection
Descent(from a common ancestor) with modification
o Intermediates in fossil record
o Earth must be old
o Vestigial traits
o Fossil evidence that species change
o Fossil evidence that lineages split(speciate)
o Direct observation of evolution in real time
Descent: homologies sh