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Adaptation (biology)

Contributed by: R. McNeill Alexander

Publication year: 2014

A characteristic of an organism that makes it fit for its environment or for its particular way of life.

For example, the Arctic fox ( Alopex lagopus ) is well adapted for living in a very cold climate. Appropriately, it has much thicker fur than similar-sized mammals from warmer places; measurement of heat flow through fur samples demonstrates that the Arctic fox and other arctic mammals have much better heat insulation than tropical species. Consequently, Arctic foxes do not have to raise their metabolic rates as much as tropical mammals do at low temperatures. This is demonstrated by the coati ( Nasua narica ), which lives in Panama and has a body mass similar to Arctic foxes and about the same metabolic rate at comfortable temperatures. When both animals are cooled, however, the coati’s metabolic rate starts to rise steeply as soon as the temperature falls ◦ ◦ ◦ ◦ below 68 F (20 C), while that of the Arctic fox begins to rise only below − 22 F ( − 30 C). The insulation is so ◦ ◦ effective that Arctic foxes can maintain their normal deep-body temperatures of 100 F (38 C) even when the ◦ ◦ temperature of the environment falls to − 112 F ( − 80 C). Thus, thick fur is obviously an adaptation to life in a cold environment. See also: THERMOREGULATION .

In contrast to the clear example above, it is often hard to be sure of the effectiveness of what seems to be an adaptation. For example, tunas seem to be adapted to fast, economical swimming. Their swimming muscles are kept warmer than the environment. The body has an almost ideal streamlined shape, rounded in front and tapering behind to a very narrow caudal peduncle immediately in front of the tail fin. The tail fin itself is tall and narrow, the shape that should enable it to propel the fish at least energy cost. Experiments with young tunas, however, have failed to show that they are faster or more economical than apparently less well adapted relatives.

A structure that evolved as an adaptation for one function may later come to serve a different function. This phenomenon is known as exaptation. For example, feathers seem to have evolved in the ancestors of birds as an adaptation for heat insulation, but in the evolution of wings feathers were exapted for flight. The wings in turn became an exaptation for swimming, when the penguins evolved.

Evolution by natural selection tends to increase fitness, making organisms better adapted to their environment and way of life. It might be inferred that this would ultimately lead to perfect adaptation, but this is not so. It must be remembered that evolution proceeds by small steps. For example, squids do not swim as well as fish.

Fish swim by beating their tails, and squids by jet propulsion. Comparison of the swimming performance of a trout and a similar-sized squid showed that the fish could swim faster and with less energy cost. The squid would be better adapted for swimming if it evolved a fishlike tail instead of its jet propulsion mechanism, but evolution AccessScience from McGraw-Hill Education Page 2 of 2 www.accessscience.com

cannot make that change because it would involve moving down from the lesser adaptive summit before climbing the higher one. See also: ANIMAL EVOLUTION ; ORGANIC EVOLUTION .

R. McNeill Alexander

Bibliography

R. McNeill Alexander, Optima for Animals , 2d ed., 1996

U. Dieckmann et al., Adaptive Speciation , 2004

S. H. Orzack and E. Sober, Adaptationism and Optimality , 2001

D. Schluter, The Ecology of Adaptive Radiation , 2000

T. Shanahan, The Evolution of Darwinism , 2004

E. R. Weibel, C. R. Taylor, and L. Bolis (eds.), Principles of Animal Design , 1998

Additional Readings

M. Doebeli, Adaptive Diversification , Princeton University Press, Princeton, NJ, 2011

S. J. Gould and R. C. Lewontin, The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the

Adaptationist Programme, Proc. Roy. Soc. B , 205:581–598, 1979 DOI: http://doi.org/10.1098/rspb.1979.0086

I. I. Goryanin and A. B. Goryachev (eds.), Advances in Systems Biology , Springer, New York, 2012

R. McNeill Alexander, Apparent adaptation and actual performance, Evol. Biol. , 25:357–373, 1991

R. K. Noyd, J. A. Krueger, and K. M. Hill, Biology: Organisms and Adaptations , Brooks ∕ Cole, Pacific Grove, CA,

2012

G. A. Parker and J. M. Smith, Optimality theory in evolutionary biology, Nature, 348:27–33, 1990

E. I. Svensson and R. Calsbeek (eds.), The Adaptive Landscape in Evolutionary Biology , Oxford University Press,

Oxford, UK, 2012