|
|
|
|
|
|
|
are initially unsuited structures transformed to (an observed range of) structures suited to a variety of environmental niches e? To attempt a general answer to this question we need a well-developed formal framework. The framework available at this point is insufficient, even for a careful description of a candidate adaptive plan t for genetic systems, unlike the case of the simpler artificial system. A fortiori, questions about such adaptive plans, and critical questions about efficiency, must wait upon further development of the framework. We can explore here some of the requirements an adaptive plan t must meet if it is to be relevant to data about genetics and evolution. |
|
|
|
|
|
|
|
|
In beginning this exploration we can make good use of a concept from mathematical genetics. The action of the environment  upon the phenotype (and thereby upon the genotype  ) is typically summarized in mathematical studies of genetics by a single performance measure µEcalled fitness. Roughly, the fitness of a phenotype is the number of its offspring which survive to reproduce (precise definitions will be given later in connection with the appropriate formal models, see section 3.1). This measure rests upon a universal, and familiar, feature of biological systems: Every individual (phenotype) exists as a member of a population of similar individuals, a population constantly in flux because of the reproduction and death of the individuals comprising it. The fitness of an individual is clearly related to its influence upon the future development of the population. When many offspring of a given individual survive to reproduce, then many members of the resulting population, the "next generation," will carry the alleles of that individual. Genotypes and phenotypes of the next generation will be influenced accordingly. |
|
|
|
|
|
|
|
|
Fitness, viewed as a measure of the genotype's influence upon the future, introduces a concept useful through the whole spectrum of adaptation. A good way to see this concept in wider context is to view the testing of genotypes as a sampling procedure. The sample space in this case is the set of all genotypes  and the outcome of each sample is the performance µEof the corresponding phenotype. The general question associated with fitness, then, is: To what extent does the outcome µE(A)of a sample influence or alter the sampling plan t (the kinds of samples to be taken in the future)? Looking backward instead of forward, we encounter a closely related question: How does the history of the outcomes of previous samples influence the current sampling plan? The answers to these questions go far toward determining the basic character of any adaptive process. |
|
|
|
|
|
|
|
|
We have already seen that the answer to the first question, for genetic systems, is that the future influence of each individual is directly proportional to the sampled performance µE(A). This relation need not be so in general |
|
|
|
|
|