Arthur Stanley Eddington was an interesting fellow. The English astrophysicist who photographed the solar eclipse that validated Einstein’s theory of general relativity was also a Quaker, a pacifist, and a clever popular writer. In his 1928 book The Nature of the Physical World  he began by noting that he had before him two tables: one of common sense, which was substantial and could change its essential nature if burned, and the table of science, which was insubstantial, mostly empty space, and which if burned changed only its state, not its essence.
Science, Eddington held, undercut common sense. By contrast, a half century earlier, Thomas Henry Huxley, Darwin’s defender and general polymath, wrote that science was "nothing but trained and organized common sense" . What should we think about this? At least one Christian philosopher, Alvin Plantinga , has argued that this means that if evolution is true we should not think evolution is true, because our evolved cognitive capacities did not evolve to deliver us truth, but only fitness.
Darwin himself wrestled with that problem. In a letter to Belfast philosopher William Graham in 1881, not long before his death, he wrote :
But then with me the horrid doubt always arises whether the convictions of man's mind, which has been developed from the mind of the lower animals, are of any value or at all trustworthy. Would any one trust in the convictions of a monkey's mind, if there are any convictions in such a mind?
With philosopher Paul Griffiths , I call this the Darwin’s Monkey Brain Problem: how can we rely upon a cognitive apparatus which had not evolved for finding out about the world, but instead for the purpose of getting primates laid?
Mind, Darwin’s horrid doubt was not about science. Instead his horrid doubt was more transcendental: "Nevertheless you have expressed my inward conviction, though far more vividly and clearly than I could have done, that the Universe is not the result of chance". Unlike Plantinga, Darwin was in doubt about purpose in the universe. Plantinga thinks the exact opposite: that the monkey brain problem leaves us less certain of science and more certain about purpose and God.
The reliability of common sense is an issue for philosophers and cognitive scientists alike. Philosophers debate whether or not ordinary objects, the objects of common sense such as Eddington’s Table 1, can be said to be real or exist.
Famously among philosophers, George E. Moore argued that one could prove that there was a world outside the mind because we all know that we have a hand, and granting that, the world follows . Of course, the existence of that hand itself was at issue. Ordinary objects are something we need to understand .
Philosopher Guy Kahane has addressed this issue in the realm of ethical skepticism, dubbing these sorts of arguments evolutionary debunking arguments or EDAs . They have this structure:
Causal premise. S's belief that p is explained by X
Epistemic premise. X is an off-track process
Therefore, S's belief that p is unjustified
An "off-track" process is a process that fails to track truth. Evolution by natural selection tracks fitness not truth. Kahane rejects this argument against objective value. But does it mean the monkey brain problem still holds for science? Does evolution debunk our common sense and with it science? Are our beliefs about the world at risk?
EDAs can be leveled against belief in moral truths, religious claims and common sense beliefs. A pragmatist philosopher might say that if you can bark your shins on a table, it is real enough, as the saying goes, for jazz (the other common saying here ends "for government work", which should strike fear into the hearts of every bridge user). This amounts, though, to the the claim that so long as our beliefs contribute to our fitness, or at any rate do not detract from it, the reality of the objects we believe exist, the content of our beliefs, is irrelevant. In the end, Kant was right: we only know and make inferences from the appearances of things.
In assessing EDAs, though, it pays to ask what is fitness for – what is it that gives a belief any fitness? In the case of moral values, fitness is clearly at least in part down to our behaviour being acceptable to those around us, so that we do not suffer sanctions, and gain assistance when we need it. We are adapted to interpersonal and social interactions.
In the case of religious claims, as Griffiths and I argue, our beliefs are more likely to be fitness enhancing for much the same reasons as moral beliefs – they avoid our being censured, perhaps even executed as apostates or heretics, and increase our likelihood of receiving aid when we are in dire straits . These are vulnerable to EDAs because our best account of why they enhance fitness has nothing to do with the truth of the content of the beliefs.
But this need not be the case for every belief. It seems likely that some beliefs – let us call them environmental beliefs – gain fitness because they track, if not exactly truth, then satisfactory ecological correlations. Obviously, if you believe there is a cliff in front of you, and there is, then you will tend not to leap over it, and your fitness is thereby enhanced. If you believe that rustling in the undergrowth is a leopard, and take evasive action, you are fitter than the poor thinker who takes a Plantingan line and treats it as a mere Kantian construct. Hume had Cleanthes invite Philo to take his skepticism seriously by leaving via the upper floor window ; an overzealous skeptic would be very unfit indeed.
Willard Van Orman Quine, the famous American philosopher, put it thus:
Creatures inveterately wrong in their inductions have a pathetic, but praiseworthy, tendency to die before reproducing their kind. 
I do not know how praiseworthy it may be, but if you get things wrong, you can end up not reproducing. Environmental beliefs are, as much as anything, truth tracking, but this is no guarantee that the environmental beliefs we do have are therefore true. They merely need not to kill us on average.
Statisticians refer to two kinds of errors: Type I (false positives) and Type II (false negatives). A false positive may not kill us, but there is a cost to every belief, and believing that, for example, that it is bad luck to walk under ladders takes time and extra effort, which can reduce fitness. Believing that the rustle in the undergrowth is a fairy rather than a leopard (a false negative), can have dramatic costs.
We cannot know everything: we are rationally bounded by our computational, memory and time constraints. We are not cognitively omniscient or ever free from error, so we must trade off Type I against Type II errors  and seek to live on that basis.
Organisms have to act, and so they must do so on limited information. The end result is that species with nervous systems like us evolve typical cognitive mechanisms that operate correctly in their usual environments. These have been named as Umwelten, or "sensed environments", by Jacob von Uexküll, an Estonian ethologist . An Umwelt is what aspects of their environment organisms typically respond to. Uexküll used the example of a tick that reacted to gradients of light, butyric acid, and warmth. These things indicated the presence of hosts or opportunities to attach to hosts, and were all that the tick needed to, in our terms, "believe".
The common sense world of ordinary objects like Eddington’s Table 1 is, in effect, the Umwelt we all share. It signals facts about the world we need to have beliefs about that are reliable and which we therefore have some reason to think are true.
In fact, I would say that our Umwelt is the shared Umwelt of all primates, and which is similar to that of many middle-sized vertebrates (ignoring birds that can see in ultraviolet, bats that can echolocate, and magnetotactic animals that use the earth’s magnetic field to navigate). We are primates, and primates evolved to deal with a world of geography, trees, fruit, other organisms and each other. The monkey brain is not so much a problem as it is an environmental truth tracking device.
In short, common sense is the primate Umwelt. The reason why we all share it, or have access to it (if we do not suffer from a cognitive deficit) is that we inherited it from our predecessors, quite literally, because they did not die in the use of it before they reproduced.
But this still doesn’t validate scientific beliefs. Science is not really organized common sense. It is refined, revised and rejiggered common sense. The ordinary objects of common sense, like Eddington’s table of substance, are not the ultimate objects that science tells us exist, even if we do not think that scientific realism is a viable view .
On no construal of common sense can many of the objects of common sense be defended in the light of science. A substantial table relies on a common sense metaphysics, formalized in Aristotle, that the world is comprised of substance that takes up space and is organized into objects by form, a view called hylomorphism from the Greek for matter+form. Modern physics dismisses this metaphysics, although philosophers seem reluctant to follow.
So, how do we get to scientific beliefs from common sense? The answer is to see science as bootstrapping upon common sense. There is enough truth tracking going on in common sense for us to start revising our beliefs and observations without prior theory . Science takes the objects of experience as explicanda, things that stand in need of explanation. Our Umwelt itself stands in need of explanation – why is our sensory world useful enough to help us survive and reproduce? The answer is given above, a sketch of a scientific view.
In the end, beliefs that track truth come in degrees of validity and accuracy. It is not all-or-nothing, and so long as we do not die before reproducing our kind, that may be good enough for government work.
1. Eddington, Arthur Stanley. 1928. The Nature of the Physical World. Cambridge; New York: Cambridge University Press; Macmillan; pages ix–x.
2. Huxley, Thomas H. 1870. On the educational value of the natural history sciences, in Lay sermons, addresses, and reviews. London: Macmillan, page 77.
3. Plantinga, Alvin. 1991. When faith and reason clash: evolution and the Bible. Christian Scholar's Review 21:8-32.
5. Griffiths, P. E. and J. S. Wilkins (In Press). When do evolutionary explanations of belief debunk belief? Darwin in the 21st Century: Nature, Humanity, and God. Ed. P. Sloan. Notre Dame, IN, Notre Dame University Press; Wilkins, J. S. and P. E. Griffiths (In Press). Evolutionary debunking arguments in three domains: Fact, value, and religion. A New Science of Religion. Eds J. Maclaurin and G. Dawes. Chicago, University of Chicago Press.
6. Moore, George E. 1939. Proof of an External World: Annual philosophical lecture, Henriette Hertz Trust. Vol. 25, Proceedings of the British Academy. London: H. Milford. [PDF Excerpt]
7. See, for example, Thomasson, Arnie. 2010. Ordinary Objects. Oxford; NY: Oxford University Press.
9. This is the account of religion as the "honest costly signaling" of commitment and hence community engagement; See Dow, James W. 2006. The evolution of religion: three anthropological approaches. Method and Theory in the Study of Religion 18 (1):67–91; and Sosis, Richard and Candace Alcorta. 2003. Signaling, solidarity and the sacred: The evolution of religious behavior. Evolutionary Anthropology 12:264-274.
10. Hume, David. 1947 . Dialogues concerning natural religion. 2nd ed. with supplement. London: Nelson; Part IV.
11. Quine, Willard Van Orman. 1969. "Natural kinds" in Ontological Relativity and Other Essays. New York: Columbia University Press, page 126.
12. See Godfrey-Smith, Peter. 1991. Signal, decision, action. Journal of Philosophy 88:709-722.
13. Uexküll, Jakob von. 1926. Theoretical biology, International library of psychology, philosophy and scientific method. London: Kegan Paul, Trench, Trubner.
14. Ladyman, James. 2009. Structural Realism. In The Stanford Encyclopedia of Philosophy, edited by E. N. Zalta: http://plato.stanford.edu/archives/sum2009/entries/structural-realism/ .
15. Bogen, James, and James Woodward. 1988. Saving the phenomena. The Philosophical Review 67 (3):303–352.
About the Author: John S. Wilkins has a PhD in the history and philosophy of biology, and is an Associate of the philosophy department at the University of Sydney. He works on evolution, taxonomy and religion, and has a blog, Evolving Thoughts.
The views expressed are those of the author and are not necessarily those of Scientific American.