Why Do Survivors Survive?

Jonah Bossewitch

PHI 321

Professor Elgin

March 10, 1993

The theory of natural selection goes far beyond the obvious observation that only the fittest survive. If it did not, then the fact that this statement is nothing more than an empty truism could be made clearer by rephrasing the theory of natural selection as "survivors survive." The theory of natural selection is more than a descriptive theory of evolution. When analyzed carefully it proves to be an explanatory theory that attempts to explain evolution. What it claims to explain is not which species or traits have survived, but rather why they have. It also explains things in such a manner that it can be reasonably argued that the theory of evolution is a law. By defining precisely what we mean when we call something a law, it can be shown that the theory of natural selection fits all of the qualifying criterion.

To accomplish this we first need to define all of the terms that we will use in defining a law. We then need to discuss the different opinions as to what qualifies an explanation as a law. We will also need to distinguish between two types of laws, nomological and statistical. Once we have done this it will be necessary to elaborate on the theory of natural selection so we can talk about specific criterion being satisfied by the theory. Finally, we will restate the theory of natural selection as a statistical law that explains evolution.

Descriptions, by definition, offer no explanation for an event's occurrence. They merely describe an event and nothing more. An explanation, on the other hand serves to explain why an event occurs. As Hempel puts it, "a scientific explanation may be regarded as an answer to a why question", such as "'why is it the case that p?', where the place of 'p' is occupied by an empirical statement specifying the explanandum". (p. 334) Explanations can also be split into nomological explanations and statistical explanations. Both nomological and statistical explanations propose answers to the same type of why-question, the primary difference between the two will be the type of answer they provide. The difference in the type of answers they provide will be clearer after we have defined a law.

Before addressing the issue of what qualifies something as a law, it is necessary to make a distinction between a law and a lawlike statement. A lawlike statement is a statement which is logically identical to a law, however it need not be true. This "trivial" distinction will allow us to treat hypothesis which have not yet been assigned a truth value as if they were law. Apart from this distinction, both definitions will incorporate in them the condition of an explanation as stated above.

According to Goodman a law is an explanation that is capable of sustaining both counterfactuals and subjunctive conditionals. These requirements on a law introduce various difficulties. Goodman himself would be quick to concede the existence of many unresolved philosophical problems that arise in attempting to understand counterfactuals and conditionals. For this reason we will neglect to explore weather the theory of evolution satisfies these conditions. We will look to other criterion, that, if satisfied will implicitly necessitate the satisfaction of the capability of the theory to sustain counterfactuals and subjunctive conditionals. In addition to these requirements, Goodman also asserts that "a law is a true sentence used for making predictions." (p. 20) In his later works, Goodman places predictions in the broader category of projections. He says that projections are guesses of unknown data, while predictions are guesses of unknown data that are unknown because they happen to occur in the future. It is unclear as to whether or not Goodman would have revised his earlier version to read "a law is a true sentence used for making projections."

Hempel claims that Goodmans's criterion are too restrictive since Goodman does not give us a test for a lawlike statement. Hempel's treats a law a subcategory of a lawlike statement, and therefore precedes to give us a definition of a lawlike statement. He skirts the difficulties introduced with the counterfactual and subjunctive conditional, and focuses instead on the notion of generality. According to Hempel, "a lawlike sentence must not be logically limited to a finite number of instances...or, it must be of essentially generalized form...so as to be able to serve in an explanatory role." (pp. 342-343)

A problem that both philosophers encounter is the ability to insure that we do not call an accidental, or a casual relationship an explanation. Restated as a question, this amounts to asking "what makes an explanation a valid one as opposed to a coincidence?" Goodman makes the assertion that "accidental hypothesis seem typically to involve some spacial or temporal restriction, or some reference some particular individual." (p. 77) This is essentially the same way that Hempel defines a lawlike statement. Consequently, Hempel must introduces a more rigorous criterion to separate his laws from casual relations. He does this by defining the concept of a cause. In our context "a 'cause' must be allowed to be a more or less complex set of circumstances and events." (p. 348) What qualifies something as an explanation as opposed to a casual relationship is the existence of an independent correlation between the circumstances and the events in the form of a cause, and a knowledge of the background events surrounding the law.

Whosever criterion we decide to use in classifying our statements as laws, we will still be able to divide all of the statements that qualify as laws into two categories; nomological and statistical laws. These two types of laws differ in that nomological laws provides us with a law whose logical structure is such that true premises applied to the law will yield true conclusions. On the other hand, statistical laws allow us to make no such generalizations about our conclusions. When true premises are applied to a statistical law the only conclusions that we can draw is that there exists a quantifyable probability of that outcome occurring.

We now turn to the task of describing the theory of natural selection in terms of the vocabulary defined above. First, we have been using the phrase "the theory of natural selection" rather loosely. The theory states that a trait, or a species that is best adapted to its environment will usually be the one to survive. Another way of stating this is that the fittest trait/species will usually survive. There are some important initial observations to make about this theory. First, the theory is meant to be a statistical explanation of evolution. As we know statistical laws are only useful when applied to a large enough sample. In our case, "a large enough sample" not only means a large enough number of subjects evolving, but it also only applies over a long enough period of time. This implies that it is meaningless to look at one individual over one lifetime and expect to have the theory of natural selection to even describe, never mind explain that individuals "evolution." By our definition of a statistical law, "evolution" and equivalently "natural selection" apply only to statistically applicable samples of data.

What is the theory of natural selection explaining? One way of answering this question is by posing a parallel question; Is the only test for its fitness the fact that a trait/species has survived? If the answer is no, then we can see how a scientist might determine weather a trait/species was "fit" independent of the fact that trait/species happened to be the one to have survived. He/she could then use the theory of survival of the fittest to explain why that trait/species survived. It seems reasonable to assume that this test can be passed. In other words, is there any reason why science should not be able to give us some idea of which trait/species are fit? Assuming that induction is a valid form of reasoning, then it is reasonable to look to the past to give us an idea as to what types of traits/species are fit under certain conditions and assume that similar types of traits/species will be fit under similar conditions. When looking at the past it is easy to determine which traits/species are fit since they are the ones that have survived. For example, we know that members of a species (S), weather or not that species are hunters or prey, that have the trait of camouflage (C) will be more fit than those members of S who do not have trait C. Thus, we determined the fitness of the trait C independent of its survival in our group S. If over some period of time we notice that the percentage of members of S with trait C is increasing, we can now explain that increase in terms of the theory of natural selection. Now that we have overcome the barrier of demonstrating that the theory of natural selection explains we still face the formidable challenge of demonstrating that the theory of natural selection can be considered a law.

Is the theory of natural selection a law? Now that we have an idea of what the theory of natural selection explains, and we also have some sense of what constitutes a law, we can examine weather or not the theory of natural selection is a law. By demonstrating that the theory of natural selection can serve as an explanation we have shown that the relationship between the statement and the explanandum is not casual.

The next step is to show that the explanation is general enough for it to be considered lawlike. The theory makes the statistical claim that, a trait or a group that is "fit" will be the one that has the highest probability of surviving and on the average, will be the one that survives. This claim contains absolutely no qualifiers that restrict the types of traits or groups that the theory attempts to explain. Nor does the theory make a reference to a particular time or spacial frame. It does restrict our claims to a large group over a long period of time, however, all statistical laws have similar restrictions so this poses no threat to our assertion that this theory is a statistical law. From the preceding analysis it seems as if Hempel would not have a problem accepting the theory of natural selection as a law. However, Goodman might still hold off classifying it as a law until the issue of predictability/projectability was resolved.

The scientific study of evolution is different from most other scientific disciplines since much of the unknown data consists of things that happened in the past, as opposed to the future. Was there ever a species that scientists now refer to as the missing link? Was there ever a species of Homo Sapiens that used their appendix? Why did the dinosaurs become extinct? The answers to all of these questions lie in new discoveries about the past, perhaps in the form of the discovery of new fossil evidence. The idea of making discoveries about the past is in sharp contrast to the notion of new discoveries necessarily being future events. It seems as if the theory of natural selection, by its statistical nature, is not intended to be a predictor. We simply can not predict enough of the relevant variables that will insure us that the conditions that made a trait/species fit in the past will exist in the future. Either we know the relevant variables now and our statistical law will not hold because the time span it is being applied to is too short, or the time span is long enough to apply our law, but our relevant variables are no longer accurate and can no longer assure us of similar conditions. However, while it may not be able to predict, the theory of natural selection is able to project. We can hypothesize the existence of the missing link based on the law of natural selection and if we later find evidence of the link, our law has been confirmed by accurately projecting a possible outcome. Goodman's acceptance of the theory of natural selection as a law will be contingent upon weather or not he would revise his criterion to include projections. Judging from the way he treats laws in some of his later lectures, it seems as if this is a revision he would be ready to make.

The law of natural selection provides us with an explanation in a general way to an infinite number of possible cases of evolution. Its limitations are due to limitations outside the range of the law and that is the only reason it fails to predict. Thus, our law has satisfied all of the criterion that determine a law, and can now be called the "inductive-statistical law of natural selection." In light of this conclusion, the question "why do survivors survive?" no longer seems as ridiculous as it once did.