74 CHAPTER 3What Not To Expect of Natural Selection
Selection at the level of genes and individual organisms is inherently “selfish”: the
gene or genotype with the highest rate of increase spreads at the expense of oth-
ers. The variety of selfish behaviors that organisms inflict on conspecific individu-
als, ranging from territory defense to parasitism and infanticide, is truly stunning.
Indeed, cooperation among organisms requires special explanations, such as kin
selection (see Chapter 12). Natural selection—or simply “nature”—has often been
invoked to justify codes of human behavior that we might agree are admirable and
others that are pernicious. But natural selection is just a name for differences among
organisms or genes in reproductive success. Therefore it cannot be described as moral
or immoral, just or unjust, kind or cruel, any more than wind, erosion, or entropy can.
Hence it cannot be used as a justification or model for human morality or ethics.
Because the principle of kin selection cannot operate across species, “natural
selection cannot possibly produce any modification in a species exclusively for the
good of another species” (Darwin, On the Origin of Species, chapter 6). If a species
exhibits behavior that benefits another species, either the behavior is profitable to
the individuals performing it, as in bees that obtain food from the flowers they
pollinate, or else one species is duped by another, as are insects that copulate with
sexually deceptive orchids (FIGURE 3.23).
The equilibrium we may observe in ecological communities—the so-called bal-
ance of nature—likewise does not reflect any striving for harmony [52]. We observe
coexistence of predators and prey not because predators restrain themselves, but
because prey species are well enough defended to persist, or because the abundance
of predators is limited by some factor other than food supply. Nitrogen and min-
eral nutrients are rapidly and “efficiently” recycled within tropical rainforests not
because ecosystems are selected for or strive for efficiency, but because under com-
petition for sparse nutrients, microorganisms have evolved to decompose litter rap-
idly, while plants have evolved to capture the nutrients released by decomposition.
Selection of individual organisms for their ability to capture nutrients has the effect,
in aggregate, of producing a dynamic that we measure as ecosystem “efficiency.”Futuyma Kirkpatrick Evolution, 4e
Sinauer Associates
Troutt Visual Services
Evolution4e_03.23.ai Date 11-28-2016(A) (B)
FIGURE 3.23 (A) An orchid (Oph-
rys scolopax) that is pollinated by
“pseudocopulation.” (B) Male bees
of certain species are attracted to
the flower by its scent (which mim-
ics a female bee’s sex pheromone)
and color pattern (which imper-
fectly mimics a bee), and “mate”
with it. The male bee shown here
carries the yellow pollen mass of a
previously visited orchid flower on
its forehead.Go to the
Evolution Companion Website
EVoluTioN4E.SiNAuER.CoM
for data analysis and simulation exercises, quizzes, and more.03_EVOL4E_CH03.indd 74 3/22/17 1:19 PM