Teleological Explanations: Purposes, Functions, and Goals in Biology

Author: Michael Zerella
Category: Philosophy of Science
Word Count: 1000

When we talk about living things, we often describe their parts as if they have purposes or goals or functions.^[1] Bones exist to support the body. Enzymes work to regulate chemical reactions. The immune system fights infections so that the organism survives. Explanations like these are called teleological: they explain biological features in terms of what they are for.

That may sound natural enough, but it raises a puzzle. Physicists don’t say that rocks exist in order to fall, or that rivers flow so that they can reach the sea. Most sciences explain the world without appealing to purposes or goals. So why is biology different?

This essay explores some of the main attempts to answer these questions and the difficulties each faces.

1. Scientific Explanations

Before the rise of modern science, it was commonly believed that everything in nature had a purpose, and satisfactory explanations for the existence and characteristics of natural objects or phenomena must include their purposes.^[2] Nowadays, scientists typically understand purposes, functions, and goals as requiring a kind of planning or intentionality that does not exist in most natural phenomena, so they are excluded from most scientific explanations.^[3]

For example, while we might speak metaphorically about a river’s goal of getting to the ocean, or its function of draining the land, it’s not like some water wanted to get to the sea and that caused the river to arise and to follow a certain path. So scientific explanations should not include such claims. Instead, scientific explanations say that, given the natural forces involved, a river flowing to the ocean is just something that happened.^[4]

Contrast this with sciences that study humans, like psychology and archeology, whose causal explanations are expected to include purposes, functions, and goals.^[5] Suppose I go to my refrigerator and get food. A psychological explanation for my behavior that leaves out my goal would be inadequate since my behavior is caused, in part, by my goal (purpose, function) of gathering food. Similarly, an archeological explanation for the existence and characteristics of a piece of ancient pottery should include the intended purpose of the humans who made it.

2. Biological Explanations

Like most other natural sciences, and unlike psychology and archeology, biology largely excludes any pre-planning or intentionality in its causal explanations,^[6] yet biology does include talk of purposes, functions, and goals. My heart, we might say, has the goal or function of pumping blood, and that seems to be an important part of any satisfactory explanation for why my heart exists and has the characteristics it has. A similar thing can be said about a variety of biological structures and processes such as bones, skin, internal organs, blood cells, aerobic respiration, and reproduction.

However, unless we appeal to an intelligent being to create them—and most scientists do not—it isn’t clear how purposes, functions, or goals can be part of the causal explanations for such things.^[7] If they’re not part of the causal explanation, then pumping blood is just something my heart does, along with making a thumping sound,^[8] and any talk of purposes, functions, or goals would be merely metaphorical, as it was with the river.^[9]

3. Evolutionary Approaches

The embryonic development of my heart came before my blood even existed, so the pumping of my blood (my heart’s main goal) could not have helped cause my heart’s existence.^[10] Therefore, many authors try to explain the causal influence of biological purposes, functions, and goals in biology by drawing upon the evolutionary past.^[11]

Every organism’s main features came about through its species’ history of adaptive evolution. It is tempting, therefore, to conclude that an adaptive goal was part of the evolutionary cause of each functional trait. However, a fundamental tenet of contemporary biology is that mutations do not occur in order to produce adaptive traits.^[12] Instead, mutations and their resulting traits are just things that happen, so the functional goal of a trait could not have played a role in the original mutation(s) that caused the trait.

A defender of the evolutionary approach may reply that even if original mutations are not goal-directed, it’s still true that the pumping of blood by my ancestors’ hearts helped cause the existence of my heart today: the pumping of blood by my ancestors’ hearts helped them to survive and reproduce, eventually leading to the existence of me and my heart. By contrast, the thumping sounds of those ancestral hearts did not causally contribute to the existence of my heart. Therefore, my heart’s blood-pumping function is part of its causal explanation while sounds are not.

That explanation sounds reasonable, but it still has a problem. My heart’s supposed goal is to pump my blood, not my ancestor’s blood. Therefore, even if the pumping of my ancestor’s blood helped cause my heart to exist, that is not the goal of my heart, so we still have not shown that the goal of my heart is part of the causal explanation for my heart.^[13]

4. Present-Focused Approaches

Other approaches claim that presently-existing goals are the cause of every goal-directed feature or action of an organism and its parts.^[14] This approach requires that goals are present in such a way that they could exert the necessary causal influence.

However, it isn’t clear how goals such as circulation or rigid support could be physically encoded into genes or tissues such that the goals could be part of a causal mechanism.^[15] Without such encoding, present-focused approaches have trouble distinguishing the “real” function of a biological feature vs. its mere side-effects, without relying on our human tendency to pick out certain effects as somehow special or important relative to the feature’s other effects.^[16]

5. Conclusion

Organisms and their parts definitely seem to have purposes, functions, and goals, and including them in our biological explanations does make the life sciences much easier to understand, even if it turns out that causal explanations in biology should not include such notions. Consequently, biologists are likely to continue using them, despite their absence in most other sciences.^[17]

Notes

[1] Although they may have subtly different meanings and implications, purposes, functions, and goals are considered together here because they all include, or are directed toward, specific end states. That is, they each imply a state of affairs that would count as success, whether that is fulfillment of a purpose, performance of a function, or achievement of a goal. And so, as we see immediately below, these are all telological concepts: teleology (from the Greek telos, meaning ‘end’ or ‘purpose’) refers to explanations in terms of goals, functions, or ends.

[2] Obviously, many religions have proposed that a divine being or beings designed and created all of nature with certain plans, purposes, functions, or goals in mind. Perhaps the most prominent naturalistic (by which I mean non-religious) theory of nature that includes purposes, functions, and goals, was proposed by Aristotle. He believed that there are four parts to any causal explanation for things found in nature. One of those four was the “final cause” or “telos” of the natural item, which was the function that the item performed. For example, part of the natural explanation for rain might include its function in watering plants. See Falcon (2023) for a good overview of Aristotle’s claims.

[3] See Intentionality by Addison Ellis for further elaboration on the role of conscious planning in causal explanations, especially in archeology.

[4] More specifically, given the local geology, hydrology, rainfall patterns, and topography, water ended up flowing along a course that happened to end at an ocean. No goals or functions are invoked by scientists when providing such explanations.

[5] Most scientific explanations for the existence and specific characteristics of objects, events, or other phenomena include (as much as possible) the physical, causal mechanisms that produce those phenomena. Causal explanations are important because science strives to do more than just discover that something exists or that two things are correlated. Science strives to explain how or why something happened, usually in terms of the interactions between physical objects and forces. Scientists and engineers use those causal explanations to change the resulting phenomena or to develop new technologies. Therefore, this essay assumes that a proper scientific explanation should be a causal explanation.

Although fundamental physics is outside the scope of this essay, it is worth noting that explanations in that field may not always be causal in the way described so far. Explanations in physics sometimes involve basic features of the universe such as the geometry of spacetime as part of their explanations, and those are typically understood to be different from the objects and forces used in most causal explanations. Sometimes physicists even invoke goals or purposes in their explanations, such as when they invoke Fermat’s Principle and other extremal principles in classical dynamics and optics. See Sklar (2012) for more on extremal principles in physics. For a more thorough overview of what is needed for causal explanations involving purposes, functions, and goals to be scientifically accurate, see Wright (1973) or Nissen (1993). For a good introduction to causal mechanisms, see Machamer, Darden, and Craver (2000).

[6] I’m setting aside animal behaviors like foraging, nest-building, and tool use that may be causally explained, in part, by the goal-directed mental states of the animals. See Animal Minds by Tiina Carita Rosenqvist for a discussion of the existence of mental states in nonhuman animals.

[7] See Design Argument for the Existence of God by Thomas Metcalf for an overview of the famous proposal that the functional complexity of organisms implies the existence of a divine creator. A recent variant of Creationism is so-called Intelligent Design Theory, which claims that at least some biological structures or processes cannot be explained without appeal to an intelligent force of some kind. See Young and Edis (2004) for a deeper explanation of Intelligent Design Theory, along with a variety of arguments against its use in the biological sciences.

[8] If my heart does have a real function, then the sound it makes is a mere side effect of my heart’s blood-pumping function. If my heart does not have a real function, then its pumping and its sound are just two of the things my heart produces, and the only reason left for saying that pumping is the goal is that we, as intelligent beings with a strong interest in life, consider the pumping effect of a heart to be special. Distinguishing between proper functions and mere side-effects is one of the main challenges faced by any account of goal-directedness, whether in biology or anywhere else. See Wright (1973), Cummins (1975), or Nissen (1993) for a good overview of this issue.

[9] This is important because it seems to admit that purposes, functions, and goals do not really exist in biology, similar to what is assumed in most other natural sciences. Some authors in this area, such as Mayr (1974) and Wuketits (1980), accept this and argue that the use of purposes, functions, and goals in biological explanations is merely metaphorical or, at most, is a weaker form of goal-directedness compared to the goal-directedness found in fields like psychology and archeology. See Philosophy of Archaeology by Indy Smith for more regarding archeological methods.

[10] Nissen (1993) explains that this would be so-called “reverse-causation” in which a thing that only exists at a later time causes an event at an earlier time, before the supposed cause even existed. That kind of reverse-causation is assumed to be impossible in biology.

[11] For some representative examples, see De Laguna (1962), Ayala (1970), or Wright (1976). This backward-looking approach to identifying purposes, functions, and goals is common in archeology, so perhaps it works in biology, too. For example, archeologists sometimes have to decide whether something found at a dig site is just a random feature resulting from natural processes or is a human artifact with a function. The answer typically comes from considering the time before the thing came into being, to see whether its origin involved human planning or was the just result of purposeless natural forces.

[12] Typically, new anatomical or physiological traits are the result of mutations or other changes at the genetic level. Such genetic changes are “blind” in the sense that the causes of the genetic changes do not (and cannot) take the resulting organism’s needs into account. Consequently, most genetic changes have either a neutral or negative effect on the resulting organism’s ability to survive and reproduce. By pure chance, a genetic change may end up actually improving the resulting organism’s chances of survival and reproduction. If that change is sustained over generations, we refer to it as an “adaptation” even though that may be somewhat misleading, as it implies intentionality or planning when used in other contexts. For example, the claim, “My team adapted to the changing circumstances” implies that my team recognized the changing circumstances and the problems they would cause, then formed and implemented a successful plan to solve those problems. There do not appear to be any biomolecular mechanisms that can do a similar thing at the genetic level.

[13] A modified version suggests that it is the general pumping of blood (not specifically my blood or my ancestor’s blood) that is the functional goal of all hearts. The general goal of pumping blood existed before my heart developed, and that general goal seems like part of the reason that any hearts exist, so it may be a good basis for the causal explanation for the existence of all hearts, including mine. See Neander (1991) for a good version of this approach. However, Nissen (1993) argues that such a claim shifts from talking about a specific physical action (pumping my blood or a specific ancestor’s blood), to talking about a type of physical action (the general pumping of blood). Unfortunately, a type is an abstract category, and as such cannot have any causal influence in the way required.

[14] See Falk (1981) and Wuketits (1980) for some representative examples of such approaches.

[15] Remember that in psychology and archeology, goals are assumed to be present in a way that does allow them to have the necessary causal influences. Human brains (and many non-human brains) can do this because they have highly versatile and malleable neural networks capable of forming or representing goals and then initiating the actions needed to achieve those goals. On the other hand, things like bones, muscles, genes, and metabolic pathways do not seem to have the right kind of complexity needed to encode or represent their supposed goals.

[16] See footnote eleven for an elaboration of this issue. It is a variation on the problem of distinguishing functions vs. side-effects, as discussed in Wright (1973), Cummins (1975), and Nissen (1993).

[17] Mayr (1974) and Wuketits (1980) explain how purposes, functions, and goals provide a very useful heuristic in the life sciences even if they turn out to be fictional. Scientists from a variety of fields employ many such useful fictions in understanding and explaining their fields of study, which is ok as long as we remember that such things are fictional.

References

Ayala, Francisco J. (1970) “Teleological Explanations in Evolutionary Biology.” Philosophy of Science. 37(1) pp. 1-15.

Cummins, R. (1975) “Functional Analysis” Journal of Philosophy, 72(20), 741-765.

De Laguna, Grace. (1962) “The Role of Teleonomy in Evolution.” Philosophy of Science. 29(2). pp. 117-131.

Falcon, Andrea. “Aristotle on Causality”, The Stanford Encyclopedia of Philosophy (Spring 2023 Edition), Edward N. Zalta & Uri Nodelman (eds.).

Falk, Arthur E. (1981) “Purpose, Feedback, and Evolution.” Philosophy of Science. 48 pp.198-217.

Kincaid, Harold (1990) “Molecular Biology and the Unity of Science.” Philosophy of Science. v.57 pp. 575-593.

Machamer, P., Darden, L., Craver, C. (2000) “Thinking About Mechanisms” Philosophy of Science, 67, 1-25.

Mayr, Ernst (1974) “Teleological and Teleonomic: A New Analysis” Boston Studies in the Philosophy of Science. v.14 pp. 91-117.

Neander, Karen (1991) “Functions as Selected Effects: The Conceptual Analyst’s Defense.” Philosophy of Science. v.58 pp.168-184.

Nissen, Lowell (1993) “Four Ways of Eliminating Mind From Teleology.” Studies in the History and Philosophy of Science. 24(1) p. 27-48.

Rudwick, M. J. S. (1964). “The inference of function from structure in fossils.” The British Journal for the Philosophy of Science, 15(57), 27-40..

Sklar, Lawrence. (2012) “Extremal Principles” in Philosophy and the Foundations of Dynamics Ch. 11, pp. 102-109. Cambridge University Press.

Wright, Larry (1973) “Functions.” Philosophical Review. v.82 pp. 139-168.

Wright, Larry (1976) Teleological Explanations: An Etiological Analysis of Goals and Functions. Berkeley: University of California Press.

Wuketits, Franz (1980). “On the Notion of Teleology in Contemporary Life Sciences.” Dialectica. 34(4) p.277-290.

Young, M. and Edis, T. (Eds.). (2004) Why Intelligent Design Fails: A Scientific Critique of the New Creationism. Rutgers University Press.

Related Essays

Animal Minds by Tiina Carita Rosenqvist

Philosophy of Archaeology by Indy Smith

Design Argument for the Existence of God by Thomas Metcalf

Intentionality by Addison Ellis

PDF Download

Download this essay in PDF. 

About the Author

Michael Zerella is a philosophy instructor at the University of Colorado, Boulder. He earned a bachelor’s degree in biology in 1993 and a master’s in biology in 1995. He then taught high school science classes for several years before going back to grad school at the University of Colorado to earn his Ph.D. in philosophy in 2011. Unsurprisingly, he specializes in philosophy of science and philosophy of biology. Mike also enjoys the classic summertime Colorado activities like hiking, biking, camping, gardening, and going to bluegrass music festivals.

Follow 1000-Word Philosophy on Facebook, Bluesky, Instagram, Twitter / X, Threads, and LinkedIn, and subscribe to receive email notifications of new essays at 1000WordPhilosophy.com.