Charles Darwin and Natural Selection

Charles Darwin and
Natural Selection
His Ideas and What Shaped Them
Chapter 10
Evolution Defined
= change in a population
over time
►Individuals interact with the
environment, but individuals do NOT
 populations evolve as the frequency of
certain traits / genes changes
Charles Darwin
► Proposed
natural selection
as a mechanism for
► Published theory in 1859 –
On the Origin of Species
Video #2 – Who Was Charles Darwin?
Charles Darwin,
► Developed
during his voyage
as a naturalist on
the HMS Beagle –
particularly as a
result of his
observations of
different species
on the Galapagos
Natural Selection
► is
“differential success” in reproduction
(some have more success than others)
► occurs through interactions between the
environment and the variations found
among members of a population
► leads to populations that are adapted to
their environment
Video #4 – “How Does Evolution Really Work?”
Natural Selection - Details
► All
species have genetic variation.
► Variations are heritable (able to be
► Likelihood of survival depends on traits
– and therefore, genes - present
Natural Selection – Details, cont’d
The environment presents challenges to
organisms and their ability to reproduce.
Organisms produce more offspring than
can survive because of:
Competition for resources
Natural Selection – Details, cont’d
better adapted
to their
produce more
offspring than
those less
suited to the
► The
traits of the better adapted individuals tend to
become more common in the population over time.
Natural Selection - Details, cont’d
► Evolution
can only increase or decrease the
frequency of heritable variations
 if the variation is not passed on, then it will not
be affected by evolution / natural selection
Darwin’s Ideas
► Many
of these ideas were developed during
Darwin’s voyage on the HMS Beagle and his
observations of various plant and animal
species (especially those on the Galapagos)
•Darwin observed a lot of variation in beak size / shape among finches
on the Galapagos
•The variations that were more common on certain islands seemed
to be related to the type of food that was available.
Grants’ Finches
► In
the 1970s,
Peter and
Rosemary Grant
studied changes in
finch beak size
► In dry years, when
berries and small
seeds were harder
to find, average
beak depth
Other Scientists
► Darwin
was influenced by other scientists
James Hutton (1785)
► Proposed
gradualism = idea that
major changes to Earth can be
the result of small changes taking
place over long stretches of time
► Concluded that Earth must be
millions of years old – as opposed
to thousands of years old, like
many people thought at the time.
Charles Lyell (1833)
► Proposed
uniformitarianism =
idea that the processes that
happened on Earth in the past are
still happening today
► Felt that scientific explanations for
past events must be based on
observations that can be made in
the present
► Video clip – 3:25
Hutton and Lyell
► Combined,
Hutton and Lyell’s theories
explained how geological features
(mountains, canyons, etc) could be
created over long periods of time
Hutton and Lyell’s
ideas also led to our
understanding of the
rock cycle (at left).
Thomas Malthus (1798)
► Studied
human population growth
► Predicted that, if left unchecked, the human
population would grow so large that there
would not be enough food and space for
Video Clip from “Darwin’s Dangerous Idea” – connection between Malthus’
theory on humans and other animals’ population size.
Thomas Malthus, cont’d
•Felt that the only things “checking” human
population growth were war, famine, and
Jean Baptiste Lamarck (1809)
► Recognized
that living things change over
time, but proposed some explanations for
this that we now know to be incorrect
► Organisms want to become more perfect, so
they can “will” a change that will help them
be more successful
Lamarck, cont’d
Body parts that are used the most grow
larger; body parts that are used less
“Use and disuse”
Acquired traits – changes to an organism’s
body that happened during its lifetime –
can be inherited by offspring.
“Inheritance of acquired characteristics”
► Two
► Lamarck’s
has not been
supported by
► Darwin’s
has been
Alfred Wallace (1858)
► Independently
developed a
theory of natural selection that
matches Darwin’s ideas
► His letter prompted Darwin to
publish his own theory.
► Video clip – 3:50