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CHAPTER 10
Stacie Daer
 Are all features of living organisms
adaptations? How could you determine if a
trait in an organism is a product of
evolution by natural selection?
 An adaptation is a trait that is favored by natural
selection and increases an individual’s fitness in
a particular environment.
 Fitness is the relative survival and reproduction
of one variant compared to others in the same
population.
 Natural Selection is the process by which
individuals with certain traits have greater
survival and reproduction than individuals who
lack these traits, resulting in an increase in the
frequency of successful alleles and a decrease
in the frequency of unsuccessful ones.
Belk and Borden
 “Adaptations can take
many forms: a behavior
that allows better evasion
of predators, a protein
that functions better at
body temperature, or an
anatomical feature that
allows the organism to
access a valuable new
resource — all of these
might be adaptations.
Many of the things that
impress us most in nature
are thought to be
adaptations.”
http://evolution.berkeley.edu/evolibrary
Not all features are adaptations!
 Biologists find it difficult to be certain whether
any particular structure of an organism arose by
selection and hence can be called adaptive or
whether it arose by chance and is selectively
neutral. ( Hair color)
 Sometimes there is no obvious reason for the
presence of a certain trait. This can be because
the utility of a trait is lost and does not appear
adaptive now, the function of a trait is unknown,
or the trait is a result of another trait that is
adaptive.
www.encarta.msn.com,
www.blackwellpublishing.com
Linked Genes
 Genes are located on the same chromosome.
 One gene is passed on as a result of natural
selection, and the linked gene is also passed on
even though it isn’t an adaptation.
 Example) red hair and light skin
Belk and Borden,www.anthro.palomar.edu
Vestigial Structures
 Vestigial structures are features that were
adaptations for an organism’s ancestor,
but now have evolved to serve no function
because the environment changed.
www.images.livescience.com,http://evolution.be
rkeley.edu
 While not all evolutionary changes are a
result of adaptation, all adaptations can be
explained by natural selection.
www.blackwellpublishing.com,http://evolution.be
rkeley.edu
Other Mechanisms of Evolution
 Genetic Drift (luck)
 Change in allele frequency that occurs as
a result of chance.
 Gene Flow (migration)
 Spread of an allele throughout a species
gene pool.
Belk and Borden, www.evolutionl.berkeley.edu