Download NATURAL SELECTION

EVOLUTION
NATURAL SELECTION
How Does Evolution Work?
On his journey with the HMS
Beagle, Darwin studied many
different living organisms. His
research revealed that species
changed over time.
Back at home in England,
Darwin knew that dogs could be
bred for certain traits the
breeders wanted. Traits are
features passed on from parents
to offspring, like your eye color!
This is called artificial selection
and farmers still use it today!
What trait did breeders select for in
bulldogs?
2. Darwin realized for most organisms, nature was
doing the selecting. The organisms that were best
suited to an environment were the ones most likely to
survive and pass on their traits. In a snowy
environment like the Artic, white foxes are more
successful because they are camouflaged. But in the
woods, a brown fox is more successful. The process
where organisms that are best suited for their
environment survive and go on to produce more
offspring is called natural selection.
3. Natural selection as a process has 4 key points. First is
variation. The members of a species are all similar but they are
not exactly alike. Traits are passed on to you through DNA
from your parents. Some of the traits passed are on by
accidental changes called mutations. If the mutation is helpful
the trait will help the organism to survive, and it can be passed
on to its offspring. Like the panda’s thumb. The extra big wrist
bone helped the panda eat bamboo, and pandas with plenty of
food were most likely to survive, so pandas with big wrist bones
survived and passed on that trait. So part 1 of natural selection
is that you can inherit variation.
OVERPRODUCTION
4. A second point about natural selection is that
organisms overproduce, which means they
produce more offspring than can survive. Fish can
lay millions of little eggs. Many of the eggs never
hatch, some might be eaten by a predator, and
others might not get the nourishment they need to
survive.
5. COMPETITION
 A third key point is that
overproduction leads to
competition.
 Organisms have to have
food, water, and shelter to
survive.
 Organisms also have to find
mates in order to reproduce.
 Since more organisms are
born than there are resources
available, organisms have to
compete for the available
resources.
Why would this fish be a “stronger
competitor?”
6. Natural selection
 The fourth key point is that something in the environment
“selects” which organisms are best fit. Sometimes it’s a
predator, sometimes it’s mating preferences, but it is nature
that is selecting who survives and has offspring. Sometimes
in specific patterns like towards being “stronger” or “faster.”
The important thing is that the population changes over
time. Sometimes the organisms change so much they are
different species. This is called speciation.
What environment would
produce the pattern at the end
“stabilizing selection?
NATURAL SELECTION IN ACTION
Click on one of the below links to watch an
animation of natural selection in peppered
moths. The selecting force here was both
birds choosing which moths to eat and the
industrial pollution staining the trees so that
different moths were camouflaged.
Click to play the peppered moth
game!
http://www.recercaenaccio.cat/agaur_rea
c/AppJava/en/interactiu/20091218betularia.jsp/
Click to watch the interactive tutorial
http://www.techapps.net/interactives
/mothproject.htm
SUMMARY SLIDE
 Natural Selection is the process where organisms best
suited for their environment survive and then go on to
produce more offspring.
 Variation exists in populations.
 This variation can be caused by random mutations and can be
passed down from parents to offspring.
 Overproduction - There are more organisms born than can
live to survive.
 Limited resources in the environment causes Competition
for food, water, shelter, and mates. This results in Survival
of the Fittest - those organisms with the most adaptive
traits live longer and reproduce more.
 This causes the population to change to be more like the
most “fit” organisms – EVOLUTION by NATURAL
SELECTION.