Chapter 10
Review
Early Ideas about Evolution

Last week, we investigated some of the
scientists who had contributed to the theory
of evolution

Before Charles Darwin:
– Linnaeus: classification system from kingdom to
species
– Lamarck: environmental change leads to use or
disuse of a structure
– Other scientists:
– thought species shared ancestors rather than arising
separately
– Or that more-complex forms developed from lesscomplex forms
Darwin’s Observations

What is Variation?
 Variation is the difference between physical
traits of an individual from those of other
individuals in the population
 What are some of the variations Darwin
noticed on the Galapagos Islands?
○ Neck length and leg length in tortoises, beak
thickness in finches
Darwin’s Observations

What is an adaptation?
 An adaptation is a feature that allows for an
individual or species to better survive in their
environment
 What are some of the adaptations Darwin noted
on the Galapagos islands?
○ On islands with large hard-shelled nuts, finches
had strong thick beaks. On islands where fruits
and insect were plentiful, finches had more
delicate beaks.
○ On islands with tall plants, tortoises had long
necks and long legs. On islands with mosses and
short plants, tortoises had shorter necks and
shorter legs.
Darwin’s Observations

For each finch above, think
about what foods it can
eat.

The tortoise to the right
has long legs and a long
neck.
Natural Selection
 KEY
CONCEPT
Darwin proposed natural selection as
a mechanism for evolution.
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
select traits through breeding.
Theory of Natural Selection




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.
Theory of Natural Selection
Natural selection helps explain how
evolution can occur
 There are four main principles to the
theory of natural selection

1) Variation
2) Overproduction
3) Adaptation
4) Descent with modification
Theory of Natural Selection





Variation – heritable differences
Overproduction – many offspring raises chances that
some will survive, but increases competition for
resources
Adaptation – a certain variation may allow an
individual to be more competitive
Descent with modification – Over time, natural
selection will result in species with adaptations that
are well suited for survival and reproduction in an
environment
Fitness is the measure of survival ability and ability
to produce more offspring.
Theory of Natural Selection
•
•
Natural selection can act only on traits
that already exist.
Structures take on new functions in
addition to their original function.

Interactive Review, Chapter 10, Natural
Selection

Natural Selection Worksheet