Download 10.2 Darwin`s Observations

10.2 Darwin’s Observations
KEY CONCEPT
Darwin’s voyage provided insight on evolution.
10.2 Darwin’s Observations
Darwin observed differences among island species.
• Variation is the difference in a physical trait between individuals .
– Galápagos saddle backed tortoises that live in areas with tall
plants have long necks and legs.
– Domed tortoises that live in wet areas with short plants have
shorter necks and legs.
10.2 Darwin’s Observations
Darwin observed differences among island species.
• Finches are another example.
– Finches with strong, thick beaks live in areas with a lot of
large, hard shell nuts.
– Finches with delicate beaks live in areas where small
insects and fruits are readily available.
10.2 Darwin’s Observations
• An adaptations is a feature that allows an organism to
better survive in its environment.
– Species are able to adapt to their
environment.
– Adaptations can lead to genetic
change in a population.
10.2 Darwin’s Observations
Darwin observed fossil and geologic evidence supporting
an ancient Earth.
• Fossil evidence included:
• Darwin found fossils of extinct animals that resemble modern
animals. (ex: Glyptodon- a giant extinct armadillo, resembled
modern armadillos)
• Darwin found fossil shells from marine organisms high up in
the Andes mountains.
10.2 Darwin’s Observations
• Geologic evidence:
– He saw land
move from
underwater to
above sea level
due to an
earthquake.
– Darwin
extended his
observations to
the evolution of
organisms.
10.2 Darwin’s Observations
Several key insights led to Darwin’s idea for natural
selection.
• Darwin noticed a lot of variation in domesticated plants
and animals.
• Artificial selection is the process by which humans
change a species by breeding it for certain traits.
neck feathers
crop
tail feathers
10.2 Darwin’s Observations
• Natural selection is a mechanism by which individuals
that have inherited beneficial adaptations produce more
offspring on average than do other individuals.
• Heritability is the ability of a trait to be passed down.
• There is a struggle for survival due to overpopulation
and limited resources.
• Darwin proposed that adaptations arose over many
generations.
10.2 Darwin’s Observations
Natural selection explains how evolution can occur.
• There are four main principles to the theory of natural
selection.
• Fitness is the measure of
– variation
survival ability and ability
– overproduction
to produce more offspring.
– adaptation
– descent with modification
ADAPTATION
VARIATION
OVERPRODUCTION
10.2 Darwin’s Observations
Natural selection acts on existing variation.
• Natural selection can act only on traits that already exist.
• Structures take on new functions in addition to their
original function.
five digits
wrist bone