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Speciation Notes
• Speciation - the
evolutionary formation
of new biological
species, usually by the
division of a single
species into two or
more genetically
distinct ones.
• Species - members of
the population that
interbreed to produce
fertile offspring
Three Causes of Speciation
a. Geographic isolation
b. Reproductive isolation
Organisms may look different
and yet be the same species.
These two ants are sisters—two
ants of the species Pheidole
barbata, fulfilling different roles
in the same colony.
Organisms may appear to
be alike and be different
species. These
meadowlarks look almost
identical, yet do not
interbreed with each
other—thus, they are
separate species.
c. Change in chromosome number
Polyploid species result from nondisjunction
(chromosomes fail to separate properly) during
meiosis or mitosis.
So, how long does it
take for a new species
to evolve?
Rates in Speciation
a. Polyploid speciation only takes one
b. Gradualism- the idea that species
evolve at a slow, steady rate, with
small, adaptive changes gradually
accumulating over time.
c. Punctuated Equilibrium - argues that
speciation occurs quickly, in rapid
bursts, with long periods of genetic
equilibrium in between.
Caused by changes in the environment,
which rapidly change a population’s gene
i.e. Raise in temperatures, introduction
of competitive species, reproductive
Do patterns of evolution
always look the same?
Why might they be different?
What causes the evolution of new
Patterns of Evolution
a. Divergent Evolutionwhen species that
were once similar
diverge (become more
and more different)
b. Adaptive RadiationWhen one species
evolves into an array
of different species to
fit environmental
c. Convergent Evolution when species that were
unrelated evolve similar
Occurs when unrelated
species occupy similar
environmental habitats in
different areas of the world.
Similar environmental
pressures and similar natural
selection pressures allows
different species to look