Mechanisms of Evolution
1. Describe the following: natural selection, adaptive radiation gradualism,
and punctuated equilibrium
2. Explain how natural selection produced industrial resistance |
Practice Quiz Site
You must log in 1st
Fill-in-the-Blank Practice Test |
Natural Selection
-
Natural selection is the process by which organisms better
suited to their environment reproduce at a faster rate than those not as
well adapted to that environment; "survival of the fittest".
Was
Darwin the first to come up with natural selection?
-
Steps in the process of natural selection:
> variation is the raw material for natural selection
> living things face a constant struggle for existence
> only some individuals survive and reproduce
> natural selection causes genetic change
> species change to fit their environment (called
adaptation).
-
Organisms that are suited to their environment reproduce
faster than those less suited to that environment.
-
Organisms often produce more offspring than can survive.
-
The evolution of the long necks of giraffes is an example
of directional selection (the 'direction' was longer necks).
-
Natural selection could not occur without genetic variation
in species.
-
Natural selection can change the physical appearance and
genetic makeup of a species.
-
Natural selection causes changes in the frequency of certain
alleles in a species population.
-
Balancing variation occurs when two opposing forces affect
the frequency of an allele in a population.
-
People heterozygous for the sickle cell allele are less susceptible
to malaria. This means that they have an advantage for survival if
they live in Africa, but are disadvantaged in they live in the U.S.
-
Genetic variations in species is the raw material for natural
selection.
Adaptive radiation gradualism
-
Adaptive radiation gradualism - different populations
of a species become reproductively isolated from each other by adapting
to different ecological niches and eventually become separate species.
-
In other words, as a species adapts to different ecological
niches and ultimately evolves into different species (phyletic gradualism).
-
You might start off with one species that spreads out geographically.
As the species responds to different conditions in different locations,
differnt forms of the species evolve.
-
For example, you may have had brown bears that spread out
all over Canada. But only the lighter color bears survived in the
Artic regions because they were harder to see (and could sneak up on prey
easier). The darker bears died out because they were easier to see.
The reverse happened for those bears in the forested areas to the south.
The successful ones developed into different shades of brown and black,
but the lighter color ones died out because they could be seen easier.
-
Natural selection is the principle mechanism driving adaptive
radiation. Others include the founder effect, genetic drift,
sexual selection, etc.
Punctuated equilibrium
-
Punctuated equilibrium is a theory that says that evolution
occurs at an irregular rate over time.
-
It was first proposed in the 1972 by Niles Eldredge and Stephen
Jay Gould.
-
It says that things change in big steps instead of gradually.
-
You may have the same species for a long time, but then something
happens quickly* that produces a creature better adapted for survivial.
*quickly in geologic time could still be thousands of years
-
Over time this new form of the original species survives
and replaces the former species, since the new form's descendants are better
suited for survival.
-
Then a long periodic of inactivity in change occurs until
another 'rapid' change occurs that will alter the species.
-
The mechanism that produces a more rapid change than gradualism
may include mechanisms such as the founder effect, natural selection, genetic
drift, sexual selection, etc.
-
Some say that mutations might be one agent for this sudden
change.
How did natural selection produce industrial resistance (melanism)?
The common example used to illustrate
this is the case of peppered moths in England. Here is a simple
explanation. The trees around the factories had been of a lighter
color before the smoke from those factories made them darker. There
were light and dark peppered moths in the area. The light colored
moths had been the more successful species. But after the smoke
from the factories turned the trees darker, the dark colored moths became
more successful. This is because after the trees became darker, the
dark colored moths were then better camouflaged and were better adapted
to survival.
Kettlewell conducted experiments with
peppered moths that showed that moths whose color matched the tree trunks
were more likely to survive. Basically, industry may cause a change
in the environment. If species in that environment adapt to those
changes, they can better survive. Check out this
site for more information on this subject.
|
