How Traits Change Over Time
Cats which are small
and not aggressive
and can play
the piano?
How man has changed
the traits of organisms through
Selective Breeding.
Dogs have been breed to be friendly
Gold-colored fish
Cows to produce
more milk
Horses for speed
If you wished to breed the prettiest
guppies, how would you do it?
By only selecting the most colorful guppies
and those with the longest tails, then
breeding them generation after generation.
Wild guppies
Guppy which has been
selectively bred.
Dog breeders have been selectively
breeding for desirable traits for centuries.
Farmers have cultivated many popular
vegetables from wild mustard,
by artificially selecting for certain attributes.
Selective Breeding
• nature provides variation, humans select
variations of genes that are useful.
• Example - a farmer breeds only his best
livestock
In essence, when humans selectively
breed organisms for certain traits,
they are selecting for certain genes.
Charles Darwin (1809-1882)
Sailed around the world 1831-1836
What did Darwin’s
Travels reveal
• The diversity of living
species was far greater
than anyone had
previously known!!
How did tortoises and birds differ
among the islands of the
Galapagos?
• Each island
had its own
type of
tortoises
and birds
that were
clearly
different
from other
islands
Galapagos
Turtles
Natural
Selection
• The traits that
help an organism
survive in a
particular
environment are
“selected” in
natural selection
He wondered if nature could select
for certain traits in the same way that
man selects for certain traits.
Can you find the animals in the pictures below?
Observations
• Organisms produce many more offspring than
can possibly survive in nature.
• Example- salmon typically lay ~10,000 eggs
• Only a few will survive to adulthood and
reproduce.
Natural Selection
Organisms vary
and
these variations
(genes) are
inherited by
their
offspring.
•As resources become scarce, individuals must
compete with each other to survive.
•Most organisms will not make it to adulthood
•Very few will breed and pass on their genes.
Thousands of frog eggs are laid in clumps in
a fresh water pond. Each clump is laid by
one female. Few will survive to adulthood.
Apple trees produce far more seeds
than could possibly survive to
become full grown trees.
Putting these facts together, Darwin
discovered one of the most important
ideas in biology--
Natural Selection.
• Offspring that do survive are best adapted to
their environment
• They will pass their genes on to their offspring.
• Over time, populations of organisms become
better adapted to their environment by this
process of natural selection.
For example, this species of insect is well
adapted (carries the right genes) to blend into its
environment.
Do you see the walking stick insect?
It received those genes from its parents, whose genes
were successful enough to allow them to survive
long enough to breed.
Another example of natural
selection at work
(click below to watch video clip)
Note: Turn caption on while viewing
Populations are constantly changing
(The Eternal Arms Race)
Click on the video below to see an
interesting case of an evolving arms race.
Evolution means change over time.
Cars have changed over time.
Computers have changed over time.
Video games have changed over time.
pong
Primate
Brain
Capacity
Vestigial Organs
• Traces of homologous organs in other
species
• Organ that serves no useful function
e.g. Appendix , wisdom teeth
Natural Selection (in summary)
1. Organisms vary and these variations (genes)
are inherited by their offspring.
2. Organisms produce more offspring than can
possibly survive in nature.
3. Those offspring that do survive are best
adapted to their environment and will pass
their genes on to their offspring.
The result is, over time, populations of organisms
become better adapted to their environment by this
process of natural selection which increases their
survival rate .