Formation of Species
16.3 pp. 309-312
Populations evolve,
individuals do not
evolve.
Speciation = formation of
new species of organisms by
evolving from an ancestor
Morphological Concept:
Morphology = internal &
external structure and
appearance
• Morph = change the look
• Plus: Convenient, works
with extinct species
• Minus: Easy to make
mistakes
Formation of Species
16.3 pp. 309-312
Not this case:
Biological Species concept =
individuals of a population
can successfully interbreed
and cannot interbreed with
other populations
• Offspring are fertile
• Plus: testable for living
species; improved by DNA
analysis
• Minus: can’t apply to nonliving organisms
Formation of Species
16.3 pp. 309-312
Isolation = populations are
separated which may lead to
speciation
Ways to separate:
Geographic isolation =
different places
Temporal isolation = different
times
Reproductive isolation =
don’t mate
Formation of Species
16.3 pp. 309-312
2 categories of Reproductive
Isolation:
1. Prezygotic = before
fertilization (before a zygote)
– Different behavior
– Different times (temporal)
– Different habitats
(geographic)
2. Postzygotic = after
fertilization (after a zygote)
– Mutation
– Infertility of offspring
Formation of Species
16.3 pp. 309-312
Rates of Speciation = how
fast does a new species
evolve
• Rough average is 1 every
million years but this can
vary greatly
• Depends on selection
pressures in the
environment
Formation of Species
16.3 pp. 309-312
Rates of Speciation
1. Gradualism = slowly over
time (~ million years)
– Mutation
– Isolation
2. Punctuated Equilibrium =
periods of sudden evolution
caused by extreme selection
pressures, followed by
periods of no evolution
(~ thousands of years)