Teleology in biology

Natural selection

Natural selection, introduced in 1859 as the central mechanism of evolution by Charles Darwin, is the differential survival and reproduction of individuals due to differences in phenotype. The mechanism directly implies evolution, a change in heritable traits of a population over time.

Adaptation

A trait which persists in a population is often assumed by biologists to have been selected for in the course of evolution, raising the question of how the trait achieves this. Biologists call any such mechanism the function of the trait, using phrases like "A function of stotting by antelopes is to communicate to predators that they have been detected", or "The primate hand is designed (by natural selection) for grasping."

An adaptation is an observable structure or other feature of an organism (for example, an enzyme) generated by natural selection to serve its current function. A biologist might propose the hypothesis that feathers are adaptations for bird flight. That would require three things: that the trait of having feathers is heritable; that the trait does serve the function of flight; and that the trait increases the fitness of the organisms that have it. Feathers clearly meet these three conditions in living birds. However, there is also a historical question, namely, did the trait arise at the same time as bird flight? Unfortunately for the hypothesis, this seems not to be so: theropod dinosaurs had feathers, but many of them did not fly. Feathers can be described as an exaptation, having been co-opted for flight but having evolved earlier for another purpose such as insulation. Biologists may describe both the co-option and the earlier adaptation in teleological language.

Teleology

Teleology, from Greek τέλος, telos "end, purpose" and -λογία, logia, "a branch of learning", was coined by the philosopher Christian von Wolff in 1728. The concept derives from the ancient Greek philosophy of Aristotle, where the final cause of a thing is its function. However, Aristotle's biology does not envisage evolution by natural selection.

Phrases used by biologists like "a function of ... is to ..." or "is designed for" are teleological. The presence of real or apparent teleology in explanations of natural selection is a controversial aspect of the philosophy of biology.

Reasons for discomfort

Apparent teleology is a recurring issue in evolutionary biology, much to the consternation of some writers, and as an explanatory style it remains controversial. There are various reasons for discomfort with teleology among biologists.

Firstly, the concept of adaptation is itself controversial, as it implies, as the evolutionary biologists Stephen J. Gould and Richard Lewontin argued, that biologists agree with Voltaire's Doctor Pangloss in his 1759 satire Candide that this is "the best of all possible worlds", in other words that every trait is perfectly suited to its functions. However, all that evolutionary biology requires is the weaker claim that one trait is at least slightly better in a certain context than another, and hence is selected for.

Secondly, teleology is linked to the pre-Darwinian idea of natural theology, that the natural world gives evidence of the conscious design and beneficent intentions of a creator. For example, the English parson-naturalist John Ray wrote in order "to illustrate the glory of God in the knowledge of the works of nature or creation"., while William Derham continued Ray's tradition with books such as his 1713 Physico-Theology and his 1714 Astro-Theology. They in turn influenced William Paley who wrote a detailed teleological argument for God in 1802, Natural Theology, or Evidences of the Existence and Attributes of the Deity collected from the Appearances of Nature, starting with the Watchmaker analogy. Such creationism, along with vitalism (implying some kind of life-force), has been rejected by the great majority of biologists.

Thirdly, the teleological explanation of adaptation is uncomfortable because it seems to require backward causation, in which existing traits are explained by future outcomes; because it seems to attribute the action of a conscious mind when none is present; and because, as a result, adaptation looks impossible to test empirically.

Removable teleological shorthand

Statements which imply that nature has goals, for example where a species is said to do something "in order to" achieve survival, appear teleological, and therefore invalid to evolutionary biologists. It is however usually possible to rewrite such sentences to avoid the apparent teleology. Some biology courses have incorporated exercises requiring students to rephrase such sentences so that they do not read teleologically. Nevertheless, biologists still frequently write in a way which can be read as implying teleology, even though that is not their intention. John Reiss argues that evolutionary biology can be purged of apparent teleology by rejecting the pre-Darwinian watchmaker analogy for natural selection; other arguments against this analogy have also been promoted by writers such as the evolutionary biologist Richard Dawkins.

Some philosophers of biology such as James G. Lennox have argued that Darwin was a teleologist, while others like Michael Ghiselin described this claim as a myth promoted by misinterpretations of his discussions, and emphasized the distinction between using teleological metaphors and actually being teleological. Andrew Askland, from the Sandra Day O'Connor College of Law claims that unlike transhumanism, an ideology that aims to improve the human condition, which he asserts is "wholly teleological", Darwinian evolution is not teleological.

Various commentators view the teleological phrases used in modern evolutionary biology as a type of shorthand for describing any function which offers an evolutionary advantage through natural selection. For example, the zoologist S. H. P. Madrell wrote that "the proper but cumbersome way of describing change by evolutionary adaptation [may be] substituted by shorter overtly teleological statements" for the sake of saving space, but that this "should not be taken to imply that evolution proceeds by anything other than from mutations arising by chance, with those that impart an advantage being retained by natural selection."

Irreducible teleology

Other philosophers of biology argue instead that biological teleology is irreducible, and cannot be removed by any simple process of rewording. Francisco Ayala argued that all statements about processes can be trivially translated into teleological statements, and vice versa, but that teleological statements are more explanatory and cannot be disposed of. Karen Neander similarly argued that the modern concept of biological 'function' depends on natural selection. So, for example, it is not possible to say that anything that simply winks into existence without going through a process of selection has functions. We decide whether an appendage has a function by analysing the process of selection that led to it. Therefore, Neander argues, any talk of functions must be posterior to natural selection, function must be defined by reference to the history of a species, and teleology cannot be avoided. The evolutionary biologist Ernst Mayr likewise stated that "adaptedness... is an a posteriori result rather than an a priori goal-seeking."

Angela Breitenbach, looking at the question of teleology in biology from a Kantian perspective, argues that teleology is important as "a heuristic in the search for causal explanations of nature and ... an inevitable analogical perspective on living beings." In her view of Kant, teleology implies something that cannot be explained by science, but only understood through analogy.

The biologist J. B. S. Haldane observed that "Teleology is like a mistress to a biologist: he cannot live without her but he's unwilling to be seen with her in public."