A20fiffAnswers
Q2: Explain how selective breeding leads to artificial selection.
A2: Over time, the population resulting from generations of
selective breeding can change significantly, and we can then say
that artificial selection has occurred.
Q3: Name as many organisms as you can whose current
characteristics are due to artificial selection.
A3: Examples include any domesticated animal, including
common pets and agriculturally important animals. All
agricultural plants are also products of artificial selection.
Figure 11.4
Q1: What is natural selection?
A1: Natural selection is the process by which individuals with
genetic characteristics that are advantageous for a particular
environment survive and reproduce at a higher rate than do
individuals that have other, less useful characteristics.
Q2: If heavy rains caused an abundance of small, tender seeds and
fewer large seeds, what do you predict would happen to the average
beak size of the finches?
A2: Average beak size would become smaller, more like the beak of
the bird on the left.
Q3: Compare and contrast artificial selection and natural
selection. Name two ways in which they are similar. How are they
different?
A3: They are similar in that both occur in populations, not
individuals; that there must be a change or changes in the
population; and that they occur over time—usually many, many
generations. They are different in that artificial selection results
from selective breeding performed by human beings, while natural
selection occurs by the breeding of individuals in a population that
survive in a particular environment.
Figure 11.6
Q1: What is the general definition of a fossil?
A1: Fossils are the mineralized remains of formerly living
organisms or the impressions of formerly living organisms.
Q2: How are the ancestors of modern whales different from their
present form?
A2: They became larger, they lost their back limbs, and their front
limbs became proportionally smaller.
Q3: What is meant by the term “intermediate fossil” when
referring to the fossil record?
A3: Intermediate forms or fossils are fossils of species with some
similarities to the known extinct ancestral group and some
similarities to the descendant or currently living species. They can
be thought of as “missing links” in evolution.
Figure 11.9
Q1: Why do water-dwelling animals have thicker bones than land-
dwelling animals?
A1: Thick bone is an adaptation to living in water. Thick bones are
heavier and help water-dwelling animals control their buoyancy
(ability to float).
Q2: Why does this thick-bone adaptation suggest a water-dwelling
lifestyle?A2: Fossil mammals with thick bones are presumed to have been
water dwellers because almost all currently living water-dwelling
mammals have thick bones.Q3: How did this adaptation likely increase survival or
reproduction in Indohyus?A3: Thick bones probably enabled Indohyus to forage on the
bottoms of lakes or ponds more efficiently than could species with
lighter bones that had to work harder to stay submerged. A feeding
advantage could have enabled Indohyus to eat more, live longer,
and have a higher reproductive rate (producing more babies that
survived) than those with lighter bones.Figure 11.11
Q1: What is meant by the term “common ancestor”? Give an
example.A1: A common ancestor is the species from which at least two
currently living species both descended, ancestral species that two
or more new species arose from through a change in the traits of a
population over time.Q2: Why are homologous structures among organisms evidence
for evolution?A2: Homologous structures are parts of an organism that
have changed in size or specific form over time but are easily
determined to be the same structure in the ancestral species from
which the organism evolved. Species with homologous traits are all
related by originally coming from an ancestor with those specific
structures.Q3: Aside from skeletal structural similarities, what other
commonalities among organisms might be considered
homologous?A3: Any traits that are shared by related organisms and also
shared in an ancestor could be homologous traits. Some examples
include mammary glands, egg laying, structures to extract oxygen
from air or water, and the use of DNA as the genetic material.Figure 11.12
Q1: Why are vestigial structures among organisms evidence for
evolution? Give an example of another vestigial structure.A1: Vestigial structures are evidence for evolution because they
are shared among related species that all have a common ancestor.
Goose bumps in humans are one example. In our furry ancestors,
goose bumps fluffed the fur, thereby increasing its insulating
effects and helping the animals to keep warm.Q2: Are vestigial structures also homologous structures? Explain.A2: Yes. Vestigial traits are shared in organisms that have a
common ancestor. For example, all organisms that descended
from a furry ancestor have goose bumps when they are chilled
or cold.Q3: Why do vestigial structures still exist if they are no longer useful?A3: Only traits that harm an organism’s ability to survive and
reproduce disappear from the fossil record, because organisms