Download Patterns Of Evolution

Patterns Of Evolution
17.4 Notes
Patterns of Evolution
Large scale evolutionary patterns that occur
over long periods of time are called
macroevolution.
Macro= large Evolution= Change over time
There are six important topics we will talk
about today…
Patterns Of Evolution
1.
2.
3.
4.
5.
6.
Extinction
Adaptive Radiation
Convergent Evolution
Coevolution
Punctuated Equilibrium/Gradualism
Developmental Genes and Body Plans
1. Extinction
More than 99% of all species that have ever
lived are now extinct!
Two reasons for extinctions are
- Competition for resources (food, water, shelter)
- Environmental changes
Some species adapt and survive while others
gradually became extinct in ways that are
often caused by natural selection.
a. Mass Extinctions
Mass extinctions have occurred several times in
Earth’s history. These are probably caused by
many factors but researchers have not yet
determined the precise cause.
???
Effects of Mass Extinction
The disappearance of so many species left
habitats open and provided ecological
support for those organisms that survived.
The result was often a burst of evolution that
produced many new species.
Example: the extinction of dinosaurs cleared
the way for the evolution of modern
mammals and birds.
Adaptive Radiation
A single species or a small group of species has evolved
through natural selection and other processes into
diverse forms that live in different ways.
Example: Darwin’s finches!
There are more than a dozen
species found on islands that
evolved from a single species
from South America.
Convergent Evolution
Convergent evolution is the process whereby unrelated
organisms, independently evolve similar traits as a
result of having to adapt to similar environments or
ecological niches.
This can produce unrelated organisms that looks
remarkably similar to one another. This is called
convergent evolution and it has occurred in plants and
animals.
Convergent Evolution
Example:
Swimming animals involving fish, mammals (dolphins)
and birds (penguins) have similar structures that
look and function similar but do not share a
common evolutionary history. These structures are
called analagous.
Ex. Dolphin’s
fluke and a
fish tail
Coevolution
Sometimes organisms that are closely connected to
one another by ecological interaction evolve
together.
Example: Flowering plants and a specific pollinator
Two species evolve in
response to changes
in each other.
Coevolution
Orchid from Madagascar has a supply of nectar within
its tip that is 40 cm long. The hawk moth of Madagascar
has an equally long feeding tube.
5. Punctuated Equilibrium
A population of organisms can change gradually or
rapidly over time. Some biologists suggest that
most new species are produced by periods of rapid
change. This rapid evolution after long periods of
equilibrium can occur for several reasons…
Punctuated Equilibrium Examples
A. A small population becomes isolated from the
main part of the population. Genetic changes
can spread more quickly among fewer
individuals.
B. A small group of organisms migrates to a new
environment. Example: Galapago’s finches.
• Organisms evolve rapidly to fill available
niches.
C. Mass extinctions
Scientists term punctuated equilibrium to describe
this pattern of long, stable periods interrupted by
brief periods of more rapid change.
The theory of Gradualism involves a slow, steady change
in a particular line of descent. The fossil record
confirms that populations of organisms did change
gradually over time.
The concepts of punctuated equilibrium and gradualism
are still controversial among biologists today.
6. Developmental Genes and Body
Plans
Changes in the expression
of developmental genes
may explain differences
in ancient and modern
body plans. Small
changes in the activity
of control genes can
affect many other genes
to produce large
changes in adult
animals.
Example
Some ancient insects
had wing-like structures on all
body segments while modern
insects have wings only on one
or two segments. Changes in
the activation of this gene could
have enabled many winged
ancestors of modern insects to
evolve into 4 winged and 2
winged forms.