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ust as there are many different species on Earth, there are also many different
ways in which the evolution of species takes place.
Divergent evolution
Darwin’s finches were all descended from one species.
When several species develop from one common
ancestor, but over many generations become less alike
as they adapt to their specific environments, this is
called divergent evolution.
Seahorses, sea dragons, pipe horses and pipefish
all belong to one family (Syngnathidae) and have
undergone divergent evolution from one common
ancestor. Each species varies significantly in colour
and shape so that it is camouflaged in its own local
environment.
These species may look similar in this respect, but they
do not have very similar genes. They are the result
of convergent evolution, by which each species has
separately evolved with similar adaptations in response
to similar environments.
Niche
Placental mammals
Australian marsupials
Anteater
Numbat
Anteater
Wolf
Thylacine
Wolf
Cat
Bobcat
Spotted-tailed quoll
Lemur
Spotted cuscus
Climber
Glider
Flying squirrel
Sugar glider
Burrower
Mole
Marsupial mole
Mouse
Marsupial mouse
Species A
Ancestral
species
Species D
Mouse
Species B
Species C
Many of Australia’s marsupials have features similar to
non-Australian animals, due to convergent evolution.
Divergent evolution is when one
species evolves into more than
one related species.
Ancestral
species A
The leafy sea dragon is well camouflaged in its habitat.
Convergent evolution
The sugar glider and the flying squirrel are both small,
tree-dwelling animals with the unusual adaptation of a
fold of skin running from their front to back legs. This
enables them to glide between trees to a lower position.
These species
are not closely
related and not
very similar.
Species A
These species
are more alike.
Species B
Ancestral
species B
Convergent evolution is when two species that are not closely
related evolve similar adaptations.
196
Science Alive for VELS Level 6
Go to
worksheet 9.4
Coevolution
Coevolution is the evolution of two or more species in response to each
other. Predators and prey sometimes coevolve, as do parasites and their
hosts.
REMEMBER
1 Define divergent evolution,
convergent evolution and
coevolution.
2 How can we tell if two
species that have similar
adaptations are closely related
or are the result of convergent
evolution?
3 What do scientists believe is
most likely to have caused the
mass extinction of 65 million
years ago?
Extinction
Approximately 99% of all species that have ever existed on Earth have
become extinct. The rate of extinction has increased over the last 100 years,
as humans have destroyed many species and their habitats.
There have also been several mass extinctions. The best known
example of mass extinction was the disappearance of the dinosaurs, and
60% of all sea creatures they coexisted with, 65 million years ago. There
are several theories proposed to explain this mass extinction. One is that
a meteor, or shower of meteorites, hit the Earth, throwing up a huge
blanket of dust that blocked out the Sun, causing a drop in temperature.
Other theories include continental drift; a lethal dose of gamma rays
released from an exploding star; and massive volcanic activity.
that the acacia and ant
species have evolved, which
have helped them adapt
to each other. Which are
behavioural and which are
structural?
5 Are the following examples
of convergent evolution,
divergent evolution or
coevolution?
(a) A plant produces a
chemical that makes it
poisonous to a particular
insect species. The insect
species evolves resistance
to the chemical.
(b) There are two different
groups of African
elephant, one lives in
the forest and one in the
savannah. The groups
may be different enough
to be classified as different
species.
(c) The marsupial mouse and
the house mouse live in
similar habitats and eat
similar food, but belong to
different genera.
learning
The bullhorn acacia has large, hollow thorns that provide homes to an ant species, and
produce an oil and protein mix that the ants can eat. The ants aggressively sting animals
that approach, remove caterpillars from the leaves and even ‘weed’ other plants from
around the base of the tree.
THINK
4 List all of the adaptations
I CAN:
describe divergent and
convergent evolution and
coevolution, giving examples
describe some of the changes
in ideas about evolution and
extinction that have occurred.