NATuRAl SElECTioN ANd AdAPTATioN 57
in Natural Theology [39] that, just as the intricacy of a watch implies an intelligent,
purposeful watchmaker, so every aspect of living nature, such as the human eye,
displays “every indication of contrivance, every manifestation of design, which
exists in the watch,” and must, likewise, have had a designer. When Darwin
offered a purely natural, materialistic alternative to the argument from design, he
not only shook the foundations of theology and philosophy, but also brought every
aspect of the study of life into the realm of science. His alternative to intelligent design
was design by the completely mindless process of natural selection. This process
cannot have a goal, any more than erosion has the goal of forming canyons, for
the future cannot cause material events in the present. Thus the concepts of goals or
purposes have no place in biology (or in any of the other natural sciences), except
in studies of human behavior.
Adaptive biological processes appear to have goals: animals engage in many
adaptive behaviors, and a morphological feature, such as a flower, develops
toward a suitable shape and stops developing when that shape is attained. We
may loosely describe such features by teleological statements, which express goals
(e.g., “She studied in order to pass the exam”; “Wasps sting to defend themselves
from predators”). But no conscious anticipation of the future resides in the cell
divisions that shape a flower or, as far as we can tell, in the behavior of wasps
or birds. Rather, the apparent goal-directedness is caused by the operation of a
program—coded or prearranged information, residing in DNA sequences—that
when activated by external or internal stimuli controls a process [33]. A program
likewise resides in a computer chip, but whereas that program has been shaped by
an intelligent designer, the information in DNA has been
shaped by a historical process of natural selection. Modern
biology views the development, physiology, and behavior
of organisms as the results of purely mechanical processes,
resulting from interactions between programmed instruc-
tions and environmental conditions or triggers.Adaptive Evolution observed
Darwin could not point to any cases in which evolutionary
change of a population or species had actually been observed,
and he supposed that evolution was much too slow for us to
see it in action. But today we can cite hundreds of examples
of adaptive evolution of morphological, physiological, and
behavioral traits that have been directly observed. Adaptive
evolution can be rapid, especially in species that have been
introduced into new regions or subjected to human altera-
tions of their environment [26, 40, 47]. For instance, several
species of insects, such as the soapberry bug (Jadera haema-
toloma) [5, 6], have adapted rapidly to new food plants. The
bug feeds on seeds of plants in the soapberry family (Sapin-
daceae) by piercing the enveloping seedpod with its slender
beak. In the last 50 years, related species of Asian trees have
been so abundantly planted in Texas and Florida that the bug
populations feed mostly on these species. Compared with the
original native host plants, the Asian tree species in Texas has
a larger pod, and the Asian tree species in Florida has a much
smaller pod. Corresponding to this difference, soapberry bug
populations in Texas have evolved a longer beak, and those in
Florida, a shorter beak (FIGURE 3.3).Futuyma Kirkpatrick Evolution, 4e
Sinauer Associates
Troutt Visual Services
Evolution4e_03.03.ai Date 11-30-2016Beak length (mm)2 4 6 8 10 12
Pod radius (mm)TexasFlorida6789IntroducedIntroducedNativeNativeBeakFIGURE 3.3 Soapberry bugs (Jadera haematoloma) and the
seedpods of their native and introduced host plants in Texas and
Florida, drawn to scale. The bug’s beak is the needlelike organ
projecting from the head at a right angle to the body. The average
pod radius of each host species is plotted against the average beak
length of associated Jadera populations. Beak length has evolved
rapidly as an adaptation to the new host plants. (After [5].)03_EVOL4E_CH03.indd 57 3/22/17 1:19 PM