Elliott Sober

We explore the evidential relationships that connect two standard claims of modern evolutionary biology. The hypothesis of common ancestry (which says that all organisms now on earth trace back to a single progenitor) and the hypothesis of natural selection (which says that natural selection has been an important influence on the traits exhibited by organisms) are logically independent; however, this leaves open whether testing one requires assumptions about the status of the other. Darwin noted that an extreme version of adaptationism would undercut the possibility of making inferences about common ancestry. Here we develop a converse claim—hypotheses that assert that natural selection has been an important influence on trait values are untestable unless supplemented by suitable background assumptions. The fact of common ancestry and a claim about quantitative genetics together suffice to render such hypotheses testable. Furthermore, we see no plausible alternative to these assumptions; we hypothesize that they are necessary as well as sufficient for adaptive hypotheses to be tested. This point has important implications for biological practice, since biologists standardly assume that adaptive hypotheses predict trait associations among tip species. Another consequence is that adaptive hypotheses cannot be confirmed or disconfirmed by a trait value that is universal within a single species, if that trait value deviates even slightly from the optimum. 1 Two Darwinian hypotheses 2 Logical independence 3 How adaptive hypotheses bear on the tree of life hypothesis 4 How the tree of life hypothesis bears on adaptive hypotheses 5 What do adaptive hypotheses predict? 6 Common ancestry and quantitative genetics to the rescue 7 Conclusion.

Realism and empiricism have always been contradictory tendencies in the philosophy of science. The view I will sketch is a synthesis, which I call Contrastive Empiricism. Realism and empiricism are incompatible, so a synthesis that merely conjoined them would be a contradiction. Rather, I propose to isolate important elements in each and show that they combine harmoniously. I will leave behind what I regard as confusions and excesses. The result, I hope, will be neither contradiction nor mishmash.

In both biology and the human sciences, social groups are sometimes treated as adaptive units whose organization cannot be reduced to individual interactions. This group-level view is opposed by a more individualistic one that treats social organization as a byproduct of self-interest. According to biologists, group-level adaptations can evolve only by a process of natural selection at the group level. Most biologists rejected group selection as an important evolutionary force during the 1960s and 1970s but a positive literature began to grow during the 1970s and is rapidly expanding today. We review this recent literature and its implications for human evolutionary biology. We show that the rejection of group selection was based on a misplaced emphasis on genes as "replicators" which is in fact irrelevant to the question of whether groups can be like individuals in their functional organization. The fundamental question is whether social groups and other higher-level entities can be "vehicles" of selection. When this elementary fact is recognized, group selection emerges as an important force in nature and what seem to be competing theories, such as kin selection and reciprocity, reappear as special cases of group selection. The result is a unified theory of natural selection that operates on a nested hierarchy of units. The vehicle-based theory makes it clear that group selection is an important force to consider in human evolution. Humans can facultatively span the full range from self-interested individuals to "organs" of group-level "organisms." Human behavior not only reflects the balance between levels of selection but it can also alter the balance through the construction of social structures that have the effect of reducing fitness differences within groups, concentrating natural selection (and functional organization) at the group level. These social structures and the cognitive abilities that produce them allow group selection to be important even among large groups of unrelated individuals.

In a recent article, Kim Sterelny and Philip Kitcher5 defend a version of genic selectionism and attempt to refute the criticisms I made of that doctrine. Their defense has two components. First, they find fault with the account I gave of the units-of-selection controversy-an account which uses the idea of probabilistic causality as a tool of explication. Second, they provide a positive account of their own of what that controversy concerns, one which they think allows genic selectionism to emerge as a successful thesis. I believe that the position they sketch is mistaken, both in its general orientation and in its details. I believe that the Sterelny/ Kitcher position misunderstands what the biological question of the units of selection is about and that their criticisms of my own proposal are mistaken as well.

Philosophers have explored objective interpretations of probability mainly by considering empirical probability statements. Because of this focus, it is widely believed that the logical interpretation and the actual-frequency interpretation are unsatisfactory and the hypothetical-frequency interpretation is not much better. Probabilistic assertions in pure mathematics present a new challenge. Mathematicians prove theorems in number theory that assign probabilities. The most natural interpretation of these probabilities is that they describe actual frequencies in finite sets and limits of actual frequencies in infinite sets. This interpretation vindicates part of what the logical interpretation of probability aimed to establish.

Ockham's razor, the principle of parsimony, states that simpler theories are better than theories that are more complex. It has a history dating back to Aristotle and it plays an important role in current physics, biology, and psychology. The razor also gets used outside of science - in everyday life and in philosophy. This book evaluates the principle and discusses its many applications. Fascinating examples from different domains provide a rich basis for contemplating the principle's promises and perils. It is obvious that simpler theories are beautiful and easy to understand; the hard problem is to figure out why the simplicity of a theory should be relevant to saying what the world is like. In this book, the ABCs of probability theory are succinctly developed and put to work to describe two 'parsimony paradigms' within which this problem can be solved.

Adaptationism is a doctrine that has meant different things to different people. In this essay, I want to isolate and discuss a reading of adaptationism that makes it a non-trivial empirical thesis about the history of life. I'll take adaptationism to be the following claim: natural selection has been the only important cause of most of the phenotypic traits found in most species. I won't try to determine whether adaptationism, so defined, is true. Rather, my task will be one of clarification. What does this statement mean, and how is it related to various remarks that biologists have made about adaptationism, pro and con?

Quine has developed two reasons for thinking that our ontology should not include the ontological category of properties. His first point is that the criterion for individuating properties is unclear, and the second is that postulating the existence of properties would not explain anything. In what follows I critically examine these two themes, which I will call the clarity argument and the parsimony argument. Although I will suggest that these two arguments are defective, I also will try to show that certain related arguments on behalf of the existence of properties are likewise flawed. This will set the stage for the discussion in the fourth section of the perspective provided by evolutionary theory on the question of the ontological status of properties. It will emerge that evolutionary theory provides reason for thinking that properties exist, and, additionally, gives an interesting point of view on the epistemological and metaphysical issues that Quine has addressed.

I want to explain some of the gaps I see between the concepts of morality and altruism. Indeed, there are three concepts here that need to be disentangled, not just two. Evolutionists use the terms “altruism” and “selfishness” in a way that differs from the usage found in ordinary parlance. So my goal is to separate evolutionary altruism, psychological altruism, and morality. Morality includes a variety of characteristics. There is more to morality than altruism. If we can avoid the mistake of thinking we have explained the whole when we have explained only the part, we may yet be able to advance our understanding of what morality is and where it came from.

Philosophy of mind is, and for a long while has been, 99% metaphysics and 1% epistemology. But the fundamental question cognitive ethologists face is epistemological: what count as evidence that a creature has a mind, and if the creature does have a mind, what evidence is relevant to deciding which mental state should be attributed to it? The usual answer that cognitive ethologists give is that one’s explanation should be “conservative”. It recommends a two-part plausibility ordering: mindless is preferred to minded, and first-order intentionality is preferred to second-order intentionality. I argue that the principle of conservatism is not a parsimony principle, and it doesn’t have any justification. What is needed is observational test. I also suggest a strategy for designing experiments in the future. What I offered here is a methodological version of naturalism.

This Element analyzes the various forms that design arguments for the existence of God can take, but the main focus is on two such arguments. The first concerns the complex adaptive features that organisms have. Creationists who advance this argument contend that evolution by natural selection cannot be the right explanation. The second design argument - the argument from fine-tuning - begins with the fact that life could not exist in our universe if the constants found in the laws of physics had values that differed more than a little from their actual values. Since probability is the main analytical tool used, the book provides a primer on probability theory.

In our essay ‘What’s Historical About Historical Materialism?’, we drew two contrasts between the Darwinian theory of evolution (ET) and the Marxist theory of historical materialism (HM).1 We described the former as a ‘micro-theory’ and the latter as a ‘macro-theory’. We also argued that, in Darwinian theory, evolution is driven by exogenous forces, specifically, by natural selection induced by environmental factors; whereas historical materialism sees the transformation of a society from feudalism to capitalism and then to socialism as a consequence of an endogenous process, involving ‘contradictions’ between forces and relations of production and class struggle. Nolan has taken issue with both of these contrasts; his view is that the two theories are more similar than our account allows.

Historical sciences like evolutionary biology reconstruct past events by using the traces that the past has bequeathed to the present. Markov chain theory entails that the passage of time reduces the amount of information that the present provides about the past. Here we use a Moran process framework to show that some evolutionary processes destroy information faster than others. Our results connect with Darwin’s principle that adaptive similarities provide scant evidence of common ancestry whereas neutral and deleterious similarities do better. We also describe how the branching in phylogenetic trees affects the information that the present supplies about the past

The design argument for the existence of God took a probabilistic turn in the 17 th and 18 th centuries. Earlier versions, such as Thomas Aquinas' 5 th way, usually embraced the premise that goal-directed systems (things that "act for an end" or have a function) must have been created by an intelligent designer. This idea – which we might express by the slogan "no design without a designer" – survived into the 17 th and 18 th centuries, 1 and it is with us still in the writings of many creationists. The new version of the argument, inspired by the emerging mathematical theory of probability, removed the premise of necessity. It begins with the thought that goal-directed systems might have arisen by intelligent design or by chance; the problem is to discern which hypothesis is more plausible. With the epistemic concept of plausibility characterized in terms of the mathematical concept of probability, the design argument was given a new direction. The new probabilistic perspective did not extinguish the older idea of "no design without a designer." The two conflicting approaches coexisted, often with less than perfect clarity about their fundamental difference. At the same time, the details of how the probabilistic perspective ought to be articulated were slow in emerging. These characteristics of uneven development are exemplified in a debate that took place in the 18 th century among three probabilists – John Arbuthnot, Nicholas Bernoulli, and Abraham DeMoivre – on the proper explanation of human sex ratio. Arbuthnot proposed a probabilistic version of the design argument, claiming that it is intelligent design, not chance, that provides the better explanation of why slightly more boys than girls are born each year. Bernoulli rejected Arbuthnot's argument. DeMoivre defended Arbuthnot against Bernoulli's criticisms. The problem of explaining sex ratio, both in human populations and in the rest of nature, experienced another transformation after 1859 --it became a problem for the theory of evolution by natural selection. Darwin (1871) addressed the question in the first edition of The Descent of Man but withdrew his suggestion in the second (Darwin 1874). Carl Düsing (1884) provided a mathematical model that moved beyond the explanation Darwin offered. Fisher (1930) added the new idea of parental expenditure. Williams (1966) argued that the sex ratios found in nature provide the opportunity to test hypotheses of group selection against hypotheses of individual selection. Hamilton (1967) constructed a model that generalizes Fisher's approach and represents the effects of both group and individual selection. The theory of natural selection gradually developed the ability to predict sex ratios, not just explain them post hoc.

Philosophers frequently extract two lessons from Moliere's joke about the doctor who tried to explain why opium puts people to sleep by claiming that it has a dormative virtue. First, the principle I will call the equivalence thesis: attributions of dispositional properties are equivalent to certain associated subjunctive conditionals. The second is what I will call the reducibility thesis: for a dispositional concept to be nonproblematic, its “physical basis” must be found. In what follows, I will briefly describe three theoretical positions that have been defended in different areas of psychology. Each claims that a certain disposition does not exist, even though the associated subjunctive conditional is not called into question. Besides showing that the equivalence thesis is mistaken, these examples also illustrate how that doctrine in fact conflicts with the requirement of reducibility. Not that that demand can withstand criticism either; both the equivalence claim and the reducibility claim are mistaken.

I consider three theses that are friendly to anthropomorphism. Each makes a claim about what can be inferred about the mental life of chimpanzees from the fact that humans and chimpanzees both have behavioral trait B and humans produce this behavior by having mental trait M. The first thesis asserts that this fact makes it probable that chimpanzees have M. The second says that this fact provides strong evidence that chimpanzees have M. The third claims that the fact is evidence that chimpanzees have M. The third thesis follows from a plausible Reichenbachian model of how a common ancestor is probabilistically related to its descendants. The first two theses do not, and they have no general evolutionary justification

According to information processing models of cognition, such as Chomsky's, the set of well-formed formulae of any natural language must be recursively enumerable (RE), otherwise, human learning language is impossible. I argue that there is nothing unlearnable about languages that are not RE. Insofar as natural languages turn out to be RE, this is to be accounted for on grounds of simplicity and not by appeal to the mistaken claim that nonRE languages are ruled out a priori. A consequence of this position is that grammars will be somewhat depsychologized, and the acquisition of competence will come to be seen as a matter of degree - perhaps admitting of refinement and improvement without end.

Writers like Attneave [I960], Fodor [I968], and Dennett [1978] have argued that explanations of a mental capacity can only avoid the emptiness of Moliere's dormative virtue by decomposing the capacity into a set of components which are more rudimentary. But What is wrong with smart homunculi? I argue that smart homunculi may explain token events, such as why I now see the page in front of me, but they do not explain what seeing is. It is the importance of the latter explanatory problem which explains why homunculi must be so stupid.

Aristotle’s principle that “nature does nothing in vain” (NDNIV) is central to his teleological approach to understanding organisms. First, we argue that James G. Lennox’s influential account of NDNIV is unsuccessful. Second, we propose an alternative account that includes a natural state model. According to a natural state model of development, an organism will develop toward its natural state unless interfering forces prevent that from happening. Third, we argue that this account also fits Aristotle’s discussion in the Generation of Animals and can explain monstrosities in nature that at first sight seem to be counterexamples to NDNIV. Fourth, we take a broader look at NDNIV, arguing that it does not entail that all structures are teleological (since it accommodates the thought that by-products and some neglected items that Aristotle calls “tokens” are nonteleological), that it does not entail that there is only one function per organ, that NDNIV is not an anthropocentric principle, and that, perhaps surprisingly, the teleological structures of an organism can benefit others apart from the organism and its progeny. Finally, we argue that Aristotle endorsed an empirical justification of NDNIV wherein the principle is justified by its many successful applications.

Carl Hempel argued that probabilistic hypotheses are limited in what they can explain. He contended that a hypothesis cannot explain why E is true if the hypothesis says that E has a probability less than 0.5. Wesley Salmon and Richard Jeffrey argued to the contrary, contending that P can explain why E is true even when P says that E’s probability is very low. This debate concerned noncontrastive explananda. Here, a view of contrastive causal explanation is described and defended. It provides a new limit on what probabilistic hypotheses can explain; the limitation is that P cannot explain why E is true rather than A if P assign E a probability that is less than or equal to the probability that P assigns to A. The view entails that a true deterministic theory and a true probabilistic theory that apply to the same explanandum partition are such that the deterministic theory explains all the true contrastive propositions constructable from that partition, whereas the probabilistic theory often fails to do so.

Alexander Rosenberg begins his recent article on the concept of fitness with the remark that "debates about the cognitive status of the Darwinian theory of natural selection should have ended long ago." I agree that this obsession needs to be overcome. But Rosenberg repeats some of the old mis- takes and invents epicycles on others. In this comment I will not be able to circumscribe fully the range of topics that an adequate treatment of this cluster of problems demands. A few critical re marks will indicate what I find wanting in Rosenberg's treatment

In what follows I will discuss an example of the Duhem-Quine problem in which Pr(H A), Pr(A H), and Pr(OI +H& ?A) (where H is the hypothesis, A the auxiliary assumptions, and O the observational prediction) can be construed objectively; however, only some of those quantities are relevant to the analysis that I provide. The example involves medical diagnosis. The goal is to test the hypothesis that someone has tuberculosis; the auxiliary assumptions describe the er- ror characteristics of the test procedure. Although it can make sense to talk about the objective probability that someone (randomly drawn from a given population) has tuberculosis and it also can make sense to talk about the objective probability that a test procedure has a certain set of error characteristics, neither of these quantities will enter into the analysis. The analysis proceeds entirely via likelihoods, what one needs to consider is just the probability of the observations conditional on four conjunctions of the form (?H & +A).' It is a special feature of the example that all four of these conjunctions are simple statistical hypotheses in the technical sense that each unambigu-ously confers a probability on the observations.'o After describing how the likelihood concept applies to the example concerning medical diagnosis, I will show how similar patterns can arise in the context of a second inferential framework-that of H. Akaike's criterion of model selection;" this time the example will involve phylogenetic inference.

In this paper I want to clarify what biologists are talking about when they talk about the evolution of altruism. I’ll begin by saying something about the common sense concept. This familiar idea I’ll call ‘vernacular altruism.’ One point of doing this is to make it devastatingly obvious that the common sense concept is very different from the concept as it’s used in evolutionary theory. After that preliminary, I’ll describe some features of the evolutionary concept. Then I’ll conclude by briefly considering what explanatory relation might obtain between vernacular altruism and evolutionary altruism. Although the points I’ll make are rather elementary ones, their interest is not restricted to those who have never heard of the evolutionary problem. The reason for this is that there is some amount of confusion about evolutionary altruism among evolutionary biologists themselves.