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EVOLUTION
EVOLUTION is “change over time”. It is how all living
things on this planet became what they are today. But
where did the idea of how things change come from?
There was a scientist named Lamarck who
believed that animals were able to change to
fit their environment, and they could then
pass these changes on to their offspring.
Lamarck was wrong. Charles Darwin came
up with the idea of Natural Selection, and it
has been proven to be the way individuals
change to best survive in their environment.
Charles Darwin (1809 – 1882)
was an English scientist who
had an interest in all living
things. He took a trip to the
Galapagos Islands, and after
spending some time there
observing the wildlife, came
up with the theory of Natural
Selection while observing the
local finches.
Darwin noticed that there were several species of finch that
had beaks that seemed to be perfectly designed for the food
they ate. How is this possible? Darwin thought that the beaks
changed over time to become the perfect shape. But how?
NATURAL SELECTION
This is “survival of the fittest”, except being “fit”
doesn’t mean being in shape. Being “fit” means having
the traits you need to survive in your environment, and
to have healthy children capable of having children of
their own.
Nature “selects” these traits
almost like a process of
elimination, and they get
passed on to future
generations in the population.
Here’s how it works……the ones with the best traits get to
pass them on. The ones that don’t, tend to die off, or there
are nowhere near as many of them.
Some animals have adaptations that help them
survive, like colors or claws or fur. These adaptations
developed over time due to natural selection
“choosing” them. Some of these changes are from
slight mutations!
All life on Earth evolved from a
single common ancestor. A singlecelled organism that lived in the
water.
As time went forward, that
organism changed and evolved and
became different things, depending
on the environment. Groups formed.
One group stayed the same, the
other groups changed and became
different organisms.
This happened over millions and
millions of years, and that’s how we
got all the different forms of life on
Earth.
Fossils provide proof of this. Fossils
are preserved in date-order, and give us
an accurate timeline of what happened,
and in the order it happened.
We even share common structures with other
animals on the planet. These are called
“homologous structures”.
TYPES OF NATURAL SELECTION
STABILIZING SELECTION
In this type of natural selection, the
EXTREME phenotypes are eliminated, and
the population resembles a “middle of the
road” blend between the two extremes.
DIRECTIONAL SELECTION
In this type of natural selection, one of the
extremes of the phenotypes is favored, and the
population moves towards those set of traits.
DISRUPTIVE SELECTION
In this type of natural selection, the extreme
phenotypes both become dominant, and the
common phenotype is eliminated. This usually
occurs as the result of a natural disaster.
SPECIATION
There’s so much differentiation in life on this planet. How do we get new
species? Where do they come from? There are 2 mechanisms we are
going to look at that help explain this a little better.
SPECIATION
First, let’s define what makes something a species.
Two organisms are considered to be the same species when:
1. They are able to successfully produce a healthy offspring
2. The offspring they produce are fertile, and able to have offspring of
their own.
ALLOPATRIC SPECIATION
ALLOPATRIC
SPECIATION occurs when
you have a natural
separation of a single
species. Over time, they
develop different traits, and
can no longer produce
fertile offspring, making
them each a new species!
SYMPATRIC SPECIATION
Couldn’t find a good pic. Gotta draw one.
Ugh. Do the tree/bush thing, that works.
SYMPATRIC
SPECIATION occurs
when you have NO
separation. Over time,
two new species develop
SIDE BY SIDE due to
a difference in
environment that does
not physically separate
them.