Natural selection script and answer key
Today I’m talking to Doctor James Smith, who will be discussing the subject of natural selection. Dr. Smith, can you please explain what it’s all about?
Published on: Mar 3, 2016
Transcripts - Natural selection script and answer key
Today I’m talking to doctor James Smith, who will discussing the subject of natural
selection. Dr. Smith, can you please explain what it’s all about?
Natural selection is a central concept of evolution, sometimes called the survival of the
fittest. It was an idea of Charles Darwin and Alfred Russel Wallace. (1) Darwin chose the
name as an analogy with artificial selection (selective breeding).
Natural selection is the process where organisms with favorable traits are more likely to
reproduce. In doing so, they pass on these traits to the next generation. Over time this
process allows organisms to adapt to their environment. This is because the frequency
of genes for favorable traits increases in the population.
(2) Members of a species are not all alike, partly because of differences in heredity
(genetics). This is true even with children of the same parents. Some of these
differences might make one organism better at surviving and reproducing than others in
a particular habitat. When this organism reproduces, it passes along the genes, which
gave it the advantage, to its children. Some adaptations are extremely long-lasting,
useful in many habitats. The evolution of wings in birds is an example. Others are good
only as long as the environment stays the same. If the environment changes enough,
then another organism might do better.
OK, then. Can you give us an overview of what you’ll talk about today?
1 The process
o 2.1 Antibiotic resistance
o 2.2 Camouflage
o 2.3 Mimicry
Right, so I guess you’ll start by talking about the process.
Natural selection explains why living organisms change over time to have the anatomy,
the functions and behaviour that they have. It works like this:
1. All living things have such fertility that their population size could (3)increase
2. We see that the size of populations does not increase to this extent. Mostly,
numbers remain (4)about the same.
3. The food and other resources are limited. Therefore, there is (5)competition for
food and resources.
4. No two individuals are alike. Therefore, they will not have the same chances to
(6)live and reproduce.
5. Much of this variation can be inherited. The parents pass such traits to the
(7)children through their genes.
6. The next generation can only come from those that survive and reproduce. After
many generations of this, the population will have more helpful genetic
differences, and fewer harmful ones. Natural selection is really a process of
(8)elimination. The elimination is being caused by the relative fit between the
individuals, and the environment they live in.
Ok, so that clarifies how it happens. Do you think you could give us some examples
There are now quite a number of examples of natural selection in natural populations.
Resistance to antibiotics is increased by the survival of individuals which are immune to
the effects of the antibiotic. Their offspring inherit the resistance, creating a new
population of resistant bacteria.
A well-known example of natural selection in action is the development of antibiotic
resistance in microorganisms. (9) Since the discovery of penicillin in 1928 by Alexander
Fleming, antibiotics have been used to fight bacterial diseases. Natural populations of
bacteria contain, among their vast numbers of individual members, considerable
variation in their genetic material, as the result of mutations. When exposed to
antibiotics, most bacteria die quickly, but some may have mutations that make them
slightly less susceptible. If the exposure to antibiotics is short, these individuals will
survive the treatment. This selective elimination of maladapted individuals from a
population is natural selection.
Given enough time, and repeated exposure to the antibiotic, a population of antibiotic-
resistant bacteria will emerge. This leads to what is known as an evolutionary arms race,
or co-evolution, in which bacteria continue to develop strains that are less susceptible
to antibiotics, while medical researchers continue to develop new antibiotics that can
kill them. Response strategies typically include the use of different, stronger antibiotics;
however, new strains of MRSA have recently emerged that are resistant even to these
drugs. A similar situation occurs with pesticide resistance in plants and insects, and with
malarial resistance to quinine.
Some day-flying moths were light in colour, and some of the moths were dark. At first,
the light colored moths survived better because they were camouflaged against the
white colour of the nearby trees. This made it hard for birds to see them. (10) When
factories were built, it caused pollution that made all the trees look black. Now the light
colored moths were obvious against the dark bark. The dark colored moths now had the
advantage, after the environment changed. The genes controlling dark colour spread
through the population of moths.
Another example: Some harmless insects mimic other insects which are dangerous, or
which taste foul. (11) Mimicry evolves because the better mimics survive better. They
live to produce more offspring than the less good mimics. The genes of the better
mimics become more common in the species. Over time, mimic species get closer to
their models. This is the process of evolution by natural selection.
Great stuff... Thanks for sharing your knowledge with us today.