Download Natural Selection

How do living things vary?
What makes some organisms more likely to live to adulthood?
 What is different about them?
 Could it have something to do with their traits?
Over time, the number of organisms with a trait that helps
them survive or reproduce will increase in a population.
Charles Darwin
Darwin’s observations
led him to develop a
scientific theory that is
known as the theory of
evolution by natural
selection.
Darwin’s Voyage
•
In December 1831, the
British naval ship HMS
Beagle set sail from
England .
• On board was 22-year-old
scientist Charles Darwin.
His mission was to learn
as much as he could about
the living things he
observed on his trip
around the world.
Replica of the HMS Beagle
Darwin’s Observations
Giant Tortoise
Darwin was amazed by
the tremendous diversity,
or variety of living things
he saw on his voyage.
 Argentina
 Galapagos Islands
He wondered why there were so
different from those in England.
Iguana
Armadillo found in Argentina
Armadillo found in Texas
Observations of diversity
Today scientists know that living
things are even more diverse
than Darwin could ever have
imagined.
Scientists have identified more
than 1.7 million species of
organisms on Earth.
A species is a group of similar
organisms that can mate with
each other and produce fertile
offspring.
Hmmm
…
There are more than 35,000 known
species of spiders, including over 800
tarantula species.
Natural Selection
Natural selection is changes in genetic
traits over many generations (the process
by which individuals with favorable traits survive
and reproduce).
Darwin’s theory of natural selection can be described in four
basic steps:
1.
2.
3.
4.
Overproduction
Genetic variation
Struggle to Survive
Successful reproduction
Over production
Organisms often
have more
offspring than
will survive long
enough to
become adults.
Tarantula egg sack
Genetic Variation
No two individuals in a population are exactly alike.
 Every individual has its
own combination of
physical traits.
 Some of these traits
improve survival and
other traits lower the
chances of survival in
it’s environment.
Struggle to survive
Individuals in a population must compete for food,
water, living space, and mates.
 Some individuals may
be killed by predators,
or by diseases.
Tarantula hawk
Successful reproduction
Organisms must reproduce to pass their genes to
the next generation.
Watching Natural Selection happen
Populations are always responding to changes in
their environment.
Whether a new predator moves
into an area or the climate
changes, some individuals will be
better able to adapt than others.
These individuals will be more
likely to pass their traits to future
generations.
Natural Selection
and the
Peppered Moth
England, Early 1800’s
In the early 1800’s scientists found
that most of the peppered moths in
England were light colored. Dark
colored moths were rare.
The bark on the trees in
Europe at the time were
light colored.
The light colored moths
were hard to see.
The dark peppered moths
were easy to see.
Environmental changes alter the
peppered moth population
England
1850’s
During the 1850’s, the environment
in Europe began to change.
Thousands of factories began to
burn coal and fill the air with
smoke and dark soot.
The bark on the trees in
Europe at this time began to
become darker.
Birds began to eat more light colored
moths because they were easy to find.
The dark colored moths
were hard to see.
The light colored moths
were easy to see.
Environmental
Issues
Pollution can affect
human lives as well as the
lives of other living things.
Smog has killed large
numbers of people since
the industrial revolution.
In 1952, nearly 4,000
people were killed when a
heavy smog hung over
London.
Selective Breeding
• the breeding
of parent
organisms by
man to
produce
desires traits
in the next
generation
Selective
breeding
Summary: Human Influence
on characteristics and
behavior.
• Domestic Animals
– Ex: Chickens, Dogs,
Cows
• Plants:
– Ex: Corn, Brasilica, Fruit
hybrids
Evolution of the whale
http://www.pbs.org/wgbh/evolution/library/03/4/l_034_05.html