Give an example that illustrates the difference between ultimate causation and proximate
Ultimate causation answers questions of why an animal behaves the way it does. Ultimate
causes take into account environmental factors that contribute to why an animal is able to
survive and reproduce. They tie directly into the concepts of Darwinism and natural
selection. Ultimate causation has an end goal in forwarding genes and ensuring survival.
Example: A female songbird is attracted to male songbirds' songs. These songs also warn
other males to stay away from the singer’s territory. Male songbirds that sang in the
spring were naturally selected for; they attracted more mates, reproduced more, and
passed their genes on.
Proximate causation answers questions of how biological traits operate in an animal.
Whereas ultimate causation has long-term implications, proximate causes have more
immediate effects. These causes explain why certain animals have certain appendages, for
example, but are independent of the evolutionary discussion.
Example: Increased light during springtime triggered the male songbirds brain to produce
a sex hormone. These hormones drove the birds to sing.
What is the difference between personal fitness and inclusive fitness?
Inclusive fitness differs from individual fitness by including the ability of an allele in one
individual to promote the survival and/or reproduction of other individuals that share that
allele, in preference to individuals with a different allele.
Individual fitness - Reproductive success measured by the number of direct descendants an
Different types of Natural Selection
Individual selection – differences in fitness, owing to a genetically variable phenotypic
character, among individual organisms within a population
Stabilizing selection – When selective pressures
select against the two extremes of a trait, the
population experiences stabilizing selection. For
example, plant height might be acted on by
stabilizing selection. A plant that is too short may not be able to compete with other plants for sunlight. However, extremely tall plants may be
more susceptible to wind damage. Combined, these two selection pressures select to
maintain plants of medium height. The number of plants of medium height will increase
while the numbers of short and tall plants will decrease.
Directional selection - In directional selection, one extreme of the trait distribution
experiences selection against it. The
result is that the population's trait
distribution shifts toward the other
extreme. In the case of such selection, the
mean of the population graph shifts.
Using the familiar example of giraffe
necks, there was a selection pressure
against short necks, since individuals
with short necks could not reach as many
leaves on which to feed. As a result, the
distribution of neck length shifted to
favor individuals with long necks.
Disruptive Selection - In disruptive
selection, selection pressures act against
individuals in the middle of the trait
distribution. The result is a bimodal, or
two-peaked, curve in which the two
extremes of the curve create their own
smaller curves. For example, imagine a
plant of extremely variable height that is
pollinated by three different pollinators,
one that was attracted to short plants,
another that preferred plants of medium
height and a third that visited only the
tallest plants. If the pollinator that preferred plants of medium height disappeared from an
area, medium height plants would be selected against and the population would tend
toward both short and tall, but not medium height plants. Such a population, in which
multiple distinct forms or morphs exist is said to be polymorphic
Frequency-dependent selection – an evolutionary process where the fitness of
a phenotype is dependent on its frequency relative to other phenotypes in a
- In positive frequency-dependent selection (or purifying frequency-dependent
selection) the fitness of a phenotype increases as it becomes more common.
- In negative frequency-dependent selection (or diversifying frequency-dependent
selection) the fitness of a phenotype increases as it becomes rarer. Negative
frequency-dependent selection is an example of balancing selection Sexual Selection
Darwin considered traits selected according to their role in mating to be separate from those
acted on by natural selection. He considered this a different type of selection that he called
"sexual selection." Sexual selection occurs in two ways: through contests and through
Contest – Contests are competitions between members of the same sex for access to the
other sex. This competition may take many different forms. A common example is direct
combat between males.
Choice – While contests involve direct physical competition between members of the same
sex, choice involves competition for attention from