Evolution__3rd_Edition

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Generation 3
Generation 2
Generation 1
CHAPTER 1 / The Rise of Evolutionary Biology 5
(a) Population (b) Individual development (c) Ecosystem
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reproduction
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reproduction
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birth a
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individual 1 2 3 4 individual 1 2 species 1 2 3 4
Figure 1.1
Evolution refers to change within a lineage of populations
between generations. (a) Evolution in the strict sense of the
word. Each line represents one individual organism, and the
organisms in one generation are reproduced from the
organisms in the previous generation. The composition of the
population has changed, evolutionarily, through time. The
letter a′ represents a different form of the organism from a.
For instance, a organisms might be smaller in size than
a′ organisms. Evolution has then been in the direction of
. . . and has distinct properties
adult a'
another. Recently, Harrison (2001) defined evolution as “change over time via descent
with modification.”
Evolutionary modification in living things has some further distinctive properties.
Evolution does not proceed along some grand, predictable course. Instead, the details
of evolution depend on the environment that a population happens to live in and the
genetic variants that happen to arise (by almost random processes) in that population.
Moreover, the evolution of life has proceeded in a branching, tree-like pattern. The
modern variety of species has been generated by the repeated splitting of lineages since
the single common ancestor of all life.
Changes that take place in human politics, economics, history, technology, and even
scientific theories, are sometimes loosely described as “evolutionary.” In this sense,
evolutionary means mainly that there has been change through time, and perhaps not
in a preordained direction. Human ideas and institutions can sometimes split during
their history, but their history does not have such a clear-cut, branching, tree-like
structure as does the history of life. Change, and splitting, provide two of the main
themes of evolutionary theory.
1.2 Living things show adaptations
a'
increased body size. (b) Individual developmental change is not
evolution in the strict sense. The composition of the population
has not changed between generations and the developmental
changes (from a to a′) of each organism are not evolutionary.
(c) Change in an ecosystem is not evolution in the strict sense.
Each line represents one species. The average composition
of the ecosystem changes through time: from 2a :1a′ at
generation 1 to 1a :2a′ at generation 3. But within each species
there is no evolution.
Adaptation is another of evolutionary theory’s crucial concepts. Indeed, it is one of the
main aims of modern evolutionary biology to explain the forms of adaptation that we
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