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Contemporary theory recognizes three major steps in the evolution of species. The first is mutation, resulting from alterations in the arrangement of molecules in the genes that jointly determine the forms, colors, functioning, and innate behavior of organisms. Genes are distributed along the strands of deoxyribonucleic acid (DNA),

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which together form the "coil of life." Mutations are demonstrably caused by hard radiations, certain chemicals, and thermal agitation of the molecules. Since their occurrence is random in the sense that they are not related to the needs of the organism, most of them prove to be harmful instead of beneficial.

The second step in the evolution of all organisms that reproduce sexually is recombination. In the formation of a germ cellegg or spermthe gene-bearing chromosomes, present in pairs in each parent's body, are separated randomly to form sets of unpaired chromosomes, thus halving their number. At fertilization, the set formed by the male parent is united with the set from the female parent in the nucleus of the egg cell, replicas of which the new organism will carry in all its tissues. The whole process is reminiscent of dealing out playing cards (Skutch 1985).

The third step in evolution is natural selection, which by agents the most diversemalfunction of organs, climatic extremes, malnutrition, predationeliminates individuals poorly endowed by the foregoing random processes, like unlucky gamblers who receive poor hands of cards. However, natural selection does not consistently remove the poorly adapted and preserve the fittest to survive. Accidents occur; a well-endowed animal may fall prey to a predator, while an inferior individual that happens at the moment to be better concealed escapes it. From first to last, and most strongly in the first two steps, chance enters largely into this schema of evolution.

It is easy to understand how mutation and recombination, continued through long ages, might cause the great diversity of the living world. Natural selection is essentially destruction; it eliminates the poorly endowed, while of promising mutants it takes no special care, such as an intelligent breeder of plants or animals gives to individuals that show improvement in the desired characters. Although an organism may be better equipped to resist the stresses or to profit from the opportunities a natural environment offers, the latter does nothing to favor the superior individual, as we might expect it to do if natural selection resembled the breeder's artificial selection, which is responsible for the misleading term. Although we detect nothing constructive in the orthodox account of evolu-

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tion, when we survey its products, the plants and animals that fill the living world, their great diversity, their marvelous adaptations to the most varied situations, the beauty of many of them, the intelligence of some, we recognize that construction has occurred. Causes must be adequate to produce the results attributed to them. What is lacking in the above synopsis of evolution? Could it be a final cause, or a purpose? To answer this question, we must look closely at final causes, which imply ends.

Aristotle's dictum (Physics, bk. 2, ch. 8) that it is absurd to suppose that purpose is not present because we do not observe the agent deliberating becomes the more convincing the more we reflect upon our personal experiences. Sometimes, after trying through much of a day to find a solution to a perplexing problem, I have fallen asleep without reaching a conclusion. Next morning, I awake with the answer clearly in mind. If we insist that purpose is always a goal or end that we consciously try to attain, then purpose was absent while I slept. Nevertheless, it was then more effective than while I pondered my problem. Evidently, my purpose was not dormant even while I was unaware of it, but it had become implicit rather than explicit.

We are never more acutely conscious of our purpose than when we painfully