Download Evolution by Natural Selection

15-3: Darwin Presents His Case
Part 1
Biology 2
Introduction
• Darwin returned to England is
1836, with lots of information
• Brought back many specimens
of what he studied (plants and
animals)
• Found that every Galapagos
island, and continent, had its
own species
On The
Origin of
Species
• 1859: Published book – On The
Origin of Species
• Proposed natural selection
causes evolution
• Showed evidence that
evolution has been happening
for millions of years-and
continues now
Inherited
Variation
and
Artificial
Selection
• Darwin saw that species
naturally vary
– Example: Some cows give more
milk than others
• Sometimes parents pass these
traits to offspring
• Wild plants and animals vary
• Domestic plants and animals
vary
Inherited
Variation
and
Artificial
Selection
• Darwin said the variation is VERY
important
– Others thought it was an accident, or
something wrong
• Farmers and breeders use variations
to improve crops and livestock
– Example: Only breed fastest horse,
cows that produce more milk, plants
that give bigger food
• ARTIFICIAL SELECTION: selection by
humans for breeding of useful traits
from the natural variation among
different organisms
Evolution by • STRUGGLE FOR EXISTENCE:
Natural
competition among members of a
Selection
species for food, living space, and
the other necessities of life
• Members of same species have to
compete for food, shelter
– Predators that move faster or hunt
better catch more prey
– Prey that hides better, protects
themselves or can avoid being
caught lives longer
Evolution by • Important to struggle for
existence is how well living
Natural
organisms “fit” their environment
Selection
• FITNESS: ability of an organism to
survive and reproduce in its
environment
• ADAPTATION: inherited
characteristic that increases an
organism's chance of survival
• BETTER ADAPTATION = BETTER
FITNESS!
Evolution by
Natural
Selection
• SURVIVAL OF FITTEST: process
by which individuals that are
better suited to their
environment survive and
reproduce most successfully;
also called natural selection
• Living organisms that have
better adaptations have
better fitness
– Better fitness = more offspring!
Evolution by
Natural
Selection
• NATURAL SELECTION: process
by which individuals that are
better suited to their
environment survive and
reproduce most successfully;
also called survival of the fittest
• Only certain individuals can
survive and reproduce
offspring!
Evolution by
Natural
Selection
• In natural selection better
adaptations = better fitness
• Better fitness = more offspring
• More offspring = increase in
population with better
adaptations!
• Causes change in population
– More individuals with better
adaptations increase over time
• More individuals without
adaptations will die and decrease