Transcript Evolution by Natural Selection

Evolution by
Natural Selection
Who was Charles Darwin?
 Began as a medical
student but changed
to be a “naturalist,” or
person dedicated to
the study of nature.
 Voyage on The
Beagle to study
various species.
 Upon returning wrote
The Origin of
Species
What did he say?
1. Overpopulation:
Every population is
capable of
producing more
offspring than can
survive. There are
limited resources.
What did he say?
2. Variation: Variation
exists within all
populations. Much
of it is inherited
because it is
created by crossing
over during
meiosis.
What did he say?
 3. Selection: In an environment, having a
particular trait can make individuals more
or less likely to survive and have
successful reproduction. So, some
individuals leave more offspring than
others.
 4. Adaptation: Over time, those traits that
improve survival and reproduction will
become more common.
Popular Misconceptions
1. “Evolution says man came from
monkey” WRONG! Darwin never said
that. Ever. All he said is that we are
related species.
Popular Misconceptions
2. “Evolution says that Earth began with
the Big Bang” WRONG! Darwin never
said that either. Evolution DOES NOT
address how the Earth began. Only
what happened after that.
Darwin =
Big Bang
More Popular
Misconceptions
“Evolution is just a theory” Recall that in science
theories have been tested and proven. Yes
Evolution is a theory and it has been proven.
(More on the proof to follow!)
Did you know… Darwin never even used the
word Evolution in his book? He preferred
“Descent with Modification.” So what does that
mean?
Descent with Modification
 The real definition of the word evolution:
organisms change over time in order to
adapt to a changing environment. This
change can been passed on to the next
generation.
 AKA descent with modification.
 How do they do this? Natural Selection
What is Natural Selection?
 Competition for resources: there isn’t
enough food for everyone, those who are
the best at getting the food survive and
pass on their genes.
 Traits that make them better at getting
food are adaptations.
Natural Selection is Caused
by the Environment
 Pressure from the limited environment
causes individuals to adapt.
 Certain individuals are born with genes
that make them more fitted for their
environment. Those genes are passed
on.
 More favorable traits emerge generation
after generation.
Natural Selection Example 1
 A Gazelle on the African Plains runs
faster than any other Gazelle in the
heard. A Cheetah comes after the heard
for some dinner, who survives? The
Gazelle who runs faster than the others.
The slow ones get eaten.
 The Gazelle does not have to be faster
than the Cheetah, just faster than the guy
next to him.
Natural Selection Example 1
 That Gazelle lives on
to reproduce and
give his offspring the
fast running gene.
This is an adaptation.
 This Gazelle has
better reproductive
fitness. It is more
able to reproduce
and pass on genes.
Natural Selection Example 2
 Male peacocks have bright colorful tails.
These tails enable them to attract female
mates. The males with the biggest and
brightest tails mate with more females.
The females see the tails as a sign of a
healthy male.
Natural Selection Example 2
 Therefore, males who have genes for
those bright tails will have more offspring
and pass on the bright tails to their
offspring. They have adapted.
 This is evolution at work! The key is to
successfully reproduce and pass on your
advantageous genes to as many
offspring as possible.
Variation in Turtles on the
Galapagos Islands
Seed Eater vs. Insect Eater
Peppered Moths