"Adaptation is a word too loosely used in ecological
writing. Often to say that a feature of an organism's life or form is
adaptive is to say no more than that the feature appears to be a good thing,
judged on the basis of an anthropomorphic attitude to the problems that the
organism is seen to face. More accurately, adaptations are those features
of an organism that in the past improved the fitness of its ancestors and so
were transmitted to descendants. Adaptation is always retrospective.
Fitness itself is relative - it is defined by the numbers of descendants left by
an individual relative to its fellows. An organism will be more fit if its
activities reduce the number of descendants left by neighbors, even if the
activities do nothing to the number of descendants that it itself leaves.
The point is easily made by considering the evolution of height in plants.
Within a population of plants growing densely and absorbing the larger part of
incident light, success depends on placing leaves high in the canopy and shading
and suppressing neighbours. There is no intrinsic advantage to the
individual from being high (there are some real disadvantages in the amount of
non-reproductive tissue to be supported), only an advantage from being higher
than neighbours. It is being higher, not just high, that pays.
Similarly a genetic change that gave a plant a larger and earlier root system
might bring no advantages to the possessor other than the relative advantage
over the neighbors that it is able to deprive. If an activity of an
organism brings no direct benefit but hinders the chance the neighbors will
leave descendants, the activity will increase fitness - it will be
"adaptive".
This argument may be important in understanding evolutionary
processes. Often the process is seen as in some way optimizing the
behavior of descendants - in some way making them "better" or
"adjusted to the environment". There is in fact nothing innate
in a process that maximizes evolutionary fitness, that necessarily
"optimizes" physiological function. Indeed a genetic change that
resulted in an organism immobilizing mineral nutrients in old tissue until it
died instead of returning them to the cycle within the ecosystem would almost
certainly confer fitess provided that potentially competing neighbors were
deprived of needed nutrients by this activity.
A theory of natural selection that is based on the fitness of
individuals leaves little room for the evolution of populations or species
towards some optimum, such as better use of environmental resources, higher
productivity per area of land, more stable ecosystems, or even for the view that
plants in some way become more efficient than their ancestors Instead,
both the study of evolutionary processes and of the natural behaviour of
populations suggest that the principles of "beggar my neighbor" and
"I'm all right Jack" dominate all and every aspect of evolution.
Nowhere does this conclusion have more force than when man takes populations
that have evolved in nature under criteria of individual fitness, grows them in
culture as populations and then applies quite different criteria of performance -
productivity per unit area of land. Natural selection is about individuals
and it would be surprising if the behavior that favoured one individual against
another was also the behavior that maximized the performance of the population
as whole. For this to happen, selection would have to act on
groups. It is an interesting thought that group selection which is
believed to be extremely rare or absent in nature (Maynard Smith, 1964) may be
the most proper type of selection from improving the productivity of crop and
forest plants. Plant breeding would then be concerned to undo the results
of selection for selfish qualities of individual fitness and focus on the
performance of populations."
J.L. Harper; final section (pp. 776-778) in "Population Biology of Plants (1977)
