This diagram shows how many different kinds of fish evolved from a common ancestor.This is not really a true story. This is a simplified illustration of how evolution works.
At first there was only one kind of fish in the ocean, but there were many different environments: tide pools, rocky shores, quiet lagoons, and the deeper water. The one kind of fishes lived in all the different environments.
In each environment, some fishes survived and some were eaten by predators or were unable to find enough food. Over time the fishes best fitted to their environments passed on their characteristics, and their descendents began to develop into fishes that adapted to different environments. Eventually these fishes became different species. (Species are groups of life forms that have descended from a common ancestor but are unable to produce fertile young if they should happen to try to interbreed.)
Notice that groups of these fishes have changed in body form from generalists that could survive fairly well in a number of environments to specialist fishes who are experts at surviving in a particular environment.
are many kinds of living organisms
on earth. Looking at their amazing
and splendid variety, we ask many
did there get to be so many different
kinds of living things?
organisms are closely related to
are some animals and plants alive
today and others extinct?
have tools that help them to answer
these questions. They believe that
life appeared and flourished only
once on earth, and that all living
things are related to one another,
and are possibly the descendants of a
Charles Darwin published his book
The Origin of Species.
In this book he proposed the theory
of Evolution. This theory states that:
organisms compete for resources
(energy, water, light, space.)
organisms differ from one another.
organisms that are well adapted
to the environment have the most
of the fittest.)
adaptations lead to changes in the organisms over the generations.
look at some examples to see how this
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Example One: Unicellular Organisms
The earliest life bearing oceans
were full of all sorts of chemicals.
The first cells were able to use the
chemicals for their life processes.
Over time, the chemicals were used
up and became harder to find. Starvation
loomed. Oh, no! The first crisis!
Some cells adapted by using chlorophyll
so that they could make food from
carbon dioxide, water. and the sun's
energy. (Later these cells moved into
larger cells and are now called chloroplasts.)
This worked: they continue to live
in plant tissues today.
Some cells adapted by ingesting (surrounding
and digesting) other living cells.
Some developed special features to
help them to swim. These adaptations
also worked. Their descendants are
Some cells ingested dead cell material.
This was also successful. These life
forms became our decomposers.
Some cells did not adapt successfully.
They have no descendants.
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Grasses are a
huge family today, but they probably
started out as just a simple little
live where there is not enough rainfall
to support forests. Over millions
of years they have diversified into
a huge family of varied plants, plants
which support many of the life forms
on earth. Corn is a grass. Wheat is
a grass. Rye and barley and rice are
grasses. There are pasture grasses,
such as the tall, vigorous grasses
that covered the prairies. There are
shorter grasses for drier places,
huge grasses like pampas grass, decorative
grasses, alpine grasses, and so on.
All of them have descended from a
have been successful because they
have found niches, which are places
where there are available resources.
There is lots of light where there
are no trees between a plant and the
sun, so the dry areas offered a niche
to plants that did not need so much
water. Grasses have developed strategies
for dealing with these drier habitats.
grow rapidly when moisture is available.
Think of how the hills turn green
here in California when the rains
come! The grasses grow quickly, and
make seeds. Their dense stands allow
for efficient wind pollination. When
the hot summers come, the grass stems
and blades die. Our hills turn golden
brown. The grass remains dormant until
the rains return. In some varieties
the roots remain alive, in others,
new plants will sprout from the seeds.
from the Roots: Grasses
are eaten by many animals. Most plants
grow at the tips of their shoots and
branches, but grasses have developed
the ability to grow from the bottom
of their blades, growing up right
from the roots. In that way, their
growth is not interrupted when animals
eat the tops of the blades.
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Example Three: Birds
have developed from land-dwelling
animals, possibly from a species of
dinosaur. There are many different
kinds of birds: humming birds, eagles,
pelicans, penguins, ducks, sparrows,
flamingos -- each one adapted to a
light skeletons with struts
inside the bones allow for flight.
metabolism (warm bloodedness) allows
rapid energy use in the body. This
keeps the muscles working during sustained
light, strong feathers provide insulation
and decoration. A number of different
kinds of feathers protect the bird's
body, provide protective coloration,
and make flight possible.
and Nest Building It was
the reptiles who developed the egg
that could survive out of water --
a leathery shelled egg. Birds developed
the hard-shelled egg. Live births
are not very practical for animals
that are trying to be lighter and
lighter so that they can fly! (Bats
do it, but with only one baby at a
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living things are descendants
of single celled organisms.
and plants compete for energy sources,
water, nutrients, and space.
reproduction leads to a variety
of individuals in each generation,
individuals who differ from each
organisms which are most successful
at capturing energy and escaping
predators are the parents of the
tend to resemble their parents,
so the species gradually becomes
better and better fitted to the
environment that it lives in.
individuals who are less fit may
have an advantage if circumstances
change -- e.g., climate change,
that you will be developing your plants
and animals from generic starter species
into a diversified group with adaptations
for different niches. This can be
a lot of fun!
to the Universe team. Temperature
of Ocean Water. Boulder,
CO: ©2000-04 University
Corporation of Atmospheric
Research (UCAR), ©1995-1999,
2000 The Regents of the
University of Michigan, Aug
313, 2001. Online.
. Nov. 22, 2003.
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2000, 2002, 2003.
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