Download 7th Natural Selection and Survival of the Fittest

Natural Selection and
Survival of the
“FITTEST”
WHO DOES WIN AND WHY?
What is Natural Selection?
Natural selection is the process by which biological (living)
organisms with favorable traits survive and reproduce more
successfully than organisms that do not possess such traits. At the
same time you will find some organisms with deleterious (not so
good) traits survive and reproduce BUT the organisms are not as
successful. This selection process is in response to forces in the
natural world, as opposed to artificial selection, whereby selection is
made by a human being, such as a farmer selecting his breeding
stock to get exactly what he wants. Plants may also be selected to
grow with certain characteristics.
In nature---all animals generally live
where they can survive……right?
It is like when we talked about a polar bear being brought from Antacrtica and
left to live up in our Mountain Green area. How long would the polar bear
survive?
Or….. we take a squirrel from our West Haven area and we ship him off to
Antacrtica, how long will the squirrel survive? Afterall, everything is frozen and
he cannot even dig a snow cave in which to live—let alone find food!
Let’s look a few examples:
Remember--Animals are suited for
their environment or they will not
survive.
So---what makes a fish suitable for the water
so he survives so well in that environment?
Gills
Fins
Streamlined body
Fish scales
Good muscles to swim
What allows a deer to be successful in
it’s environment?
Lightweight
Fast runner
Big ears
Strong muscles
Can jump and leap high
Able to camouflage well
What about survival of a rabbit?
A fast get-away is possible
Strong muscles in back legs
Good hearing
Claws and teeth to try to defend
Meet Charles Darwin
HMS Beagle
HMS Beagle was the British ship that Charles
Darwin was on board to take a five-year trip
around the world.
Darwin was only 22 years old. He became the ship’s
naturalist—a person who studies the natural world. His job?
To learn as much as he could about the living things he saw
on the voyage.
Darwin saw plants and animals he had never seen before
and he wondered why they were so different from those in
England. Darwin’s observations led him to develop on of the
most important scientific theories of all time; THE THEORY
OF EVOLUTION BY NATURAL SELECTION
The importance of Natural Selection:
The Beagle made many stops along the coast of South America and also traveled
to the Galapagos Islands.
Darwin’s important observations included the diversity (variety or not the same)
of living things, ancient organism remains and the different characteristics of the
organisms on the Galapagos Islands.
He found many species (a group of similar organisms that can mate with each
other and produce FERTILE offspring).
He found several types of turtles, iguanas, and finches. They all had different
characteristics which allowed each type to survive. Each of the different
characteristics were why the animals were surviving.
Why was Darwin’s observations about
different characteristics important?
Darwin could tell just by looking at the characteristics, where the animals lived
on the islands. The characteristics were adaptations (a trait that helps an
organism survive and reproduce) that helped keep the animals and plants living.
One example is the beak shape of a finch. The finches’ beaks were shaped to be
able to obtain food in the area of the islands were the finches lived.
Other examples were plants that were poisonous or had a bad taste—insects
and animals would not eat them so they could reproduce.
Some plants had very bright flowers to attract insects to help with the spreading
of pollen for reproduction of the plant. See the next page
Galapagos Island Tortise Types
Finches and different beaks
Darwin’s reasoning:
He reasoned that plants or animals that arrived on
the Galapagos Islands faced conditions that were
different from those on the mainland. Perhaps,
Darwin hypothesized, the species gradually changed
over many generations and became better adapted
to the new conditions. The gradual change in a
species over time is called---you guessed it--EVOLUTION. Please remember—this is a theory only.
Natural Selection:
This is the process by which individuals that are better adapted to their environment are more
likely to survive and reproduce than other members of the same species. The same
characteristics that helped them survive would be passed on to their offspring.
There are some factors that affect natural selection. Those factors are:
Overproduction—this occurs when not many offspring are usually successful in surviving from
birth—example is for insects. Can you imagine if all the eggs from all insects survived? The
whole world would be crowded out by bugs!!! YUCKY!!!
Variations:
Some food is acceptable to some species but not to others.
Some organisms have bright colors and others are not as bright. It can be a protection some
times.
Selection:
Some variations enable individuals better adapted to their environment and so they survive and
can reproduce more successfully. The offspring inherit the characteristics that are helpful.
Because the environment has “selected” organisms with helpful traits, Darwin proposed that
over a long period of time, “natural selection” could/can lead to change. This would aid I the
helpful variations accumulating in a species while the unfavorable ones may disappear.
Environmental Change
If the environment changes that could affect an organism’s ability to survive. This could also lead
to a “selection” process.
If the organisms in the environment could adapt and survive then the traits that helped them
would be passed on. If the animals could not survive then of course all would die and fail to
reproduce so the unhelpful characteristics would be eliminated.
Humans and other predators literally ate the dodo birds until
They were extinct. Their nests were also easy for predators to take
The eggs and any babies so preproduction was a problem. They were
Extinct about 1755. Sad fact.
Genes and Natural Selection:
Without variations, all members of a species would have the
same traits. Natural selection would not occur because all
individuals would have an equal change of surviving and
reproducing.
Darwin could not explain what caused variations or how
they were passed on. Scientists later learned that variations
can result from mutation and the shuffling of alleles during
meiosis. Genes are passed from parents to their offspring.
Because of this, only traits that are inherited, or controlled
by genes, can be acted upon by natural selection.
Now you know. . . . .