Transcript 11.6 Patterns in Evolution

11.6 Patterns in Evolution
KEY CONCEPT
Evolution occurs in patterns.
11.6 Patterns in Evolution
Evolution through natural selection is not random.
• Natural selection can have direction.
• The effects of natural selection add up over time.
11.6 Patterns in Evolution
• Convergent evolution
describes evolution toward
similar traits in unrelated
species.
11.6 Patterns in Evolution
• Divergent evolution describes evolution toward different
traits in closely related species.
kit fox
red fox
ancestor
How do convergent and divergent
evolution illustrate the directional
nature of natural selection?
11.6 Patterns in Evolution
Species can shape each other over time.
• Two or more species can evolve together through
coevolution.
– evolutionary paths become connected
– species evolve in response to changes in each other
11.6 Patterns in Evolution
Predation
Rough-Skinned Newt
Did You Know? A single rough-
skinned newt contains enough poison
to kill 100 people. Unfortunately for
the newt, its predator, the common
garter snake, has coevolved resistance
to the toxin.
• Some predatorprey relationships
are examples of
coevolution, the
process by which
two species evolve
in response to
changes in each
other.
11.6 Patterns in Evolution
• Coevolution can occur in beneficial relationships.
11.6 Patterns in Evolution
• Coevolution can occur in competitive relationships,
sometimes called evolutionary.
11.6 Patterns in Evolution
Species can become extinct.
• Extinction is the elimination of a species from Earth.
• Background extinctions occur continuously at a very low
rate.
– occur at roughly the same
rate as speciation
– usually affects a few species
in a small area
– caused by local changes in
environment
11.6 Patterns in Evolution
• Background extinctions occur continuously at a very low
rate.
– occur at roughly the same rate as speciation
– usually affects a few species in a small area
– caused by local changes in environment
One high estimate for the recent background extinction rate for
birds is one species extinction per 400 years. If only this natural
rate of loss affected the number of bird species, no more than a
couple of extinctions should have occurred in the past 800 years.
Scientists estimate that the actual loss during this time period
lies somewhere between 200 and 2,000! The fact that today's
extinction rate vastly exceeds any estimation of the background
extinction rate impels many scientists to conclude that we are
now on the cusp of the so-called Sixth Extinction.
11.6 Patterns in Evolution
• Mass extinctions are rare but much more intense.
– destroy many species at global level
– thought to be caused by catastrophic events
– at least five mass extinctions in last 600 million years
11.6 Patterns in Evolution
Speciation often occurs in patterns.
• A pattern of punctuated equilibrium exists in the fossil
record.
– theory proposed by Eldredge and Gould in 1972
– episodes of speciation occur suddenly in geologic
time
– followed by long periods of little evolutionary change
– revised Darwin’s idea that species arose through
gradual transformations
11.6 Patterns in Evolution
• Many species evolve from one species during adaptive
radiation.
– ancestral species diversifies into many descendent
species
– descendent species
usually adapted to
wide range of
environments