If naturalism (and more broadly, atheism) is true, then unguided evolution is all that we can appeal to in order to explain how human beings got to be the way we are. The naturalist cannot appeal to a top-down guiding force, since on the view none exist. Some religious apologists argue that such an unguided process would not produce brains and belief-producing mechanisms that were sufficiently aimed at truth; rather the truth-value of our ancestor’s beliefs would have been invisible or inconsequential to the forces of natural selection, and only fitness enhancing behaviors would have been favored. Therefore, says the apologist, our brains would not have been designed to track truth, only to survive. All of this is meant to show that if naturalism were true then rationality would go out the window.

I don’t agree. Here I will present a basic outline of how our brains could have evolved to track truth in the world and how reliable belief-producing mechanisms could exist given unguided evolution. To do this, I will unpack the notions of belief, reference (in language), truth, and design, and offer a brief explanation as to how our central nervous systems were built from the ground up to be reliable (at least enough to survive and lead us to where we are today).

The Evolution of Central Nervous Systems

550 million years ago flatworms developed bilaterally symmetric nerve cords and light sensitive cells (eyes), which led to early fishes with brains inside protected spinal-cord-like structures. 325 million years ago vertebrates began to diversify with spinal cords and well-defined heads and tails, and shortly after amphibians developed forebrains. 200 million years ago mammals evolved with even more complex forebrains. 55 million years ago primates first appeared, and 2.8 million years ago our genus Homo arrived on the scene. And 200,000 years ago modern humans appeared, with brains not differing in kind from our biological relatives, only in degree.

Comparative brains, from the Proceedings of the National Academy of Sciences

Central nervous systems were selected on the basis of their ability to respond appropriately to the environment — otherwise they would have been outcompeted and eliminated. As Darwin noted, a significant percentage of organisms will die before getting a chance to reproduce (e.g. as many as 43% of hunter-gathers died before reaching the age of 15[1]), so selection pressures favored organisms that could better respond to the right stimuli, especially when it came to fighting, fleeing, feeding, and reproducing. Over time, each new generation inherited the most fit genes, and therefore the most fit central nervous systems.

It is from this process that the hominid brain evolved — equipped with information-processing centers and a hard-wired system of survival. Evolution couldn’t have gotten as far as mammals, primates, and hominids if the causal connections between central nervous systems and behavior wasn’t for the most part reliable.

Design from the Bottom-up

Survival wasn’t due to simple blind, dumb luck, but a process of selection that actually favored certain heritable traits. There was a “natural hand” picking and choosing certain traits, in a sense “designing” them. This was Darwin’s revolutionary idea of natural selection. There is a natural filter built into the physical laws such that only the most fit organisms survive, and it is within this evolutionary space that new traits and species emerge.

This type of “design” happens from the bottom-up. It is “unguided” only in the sense that there is no top-down creative force. But this doesn’t suggest that evolution is totally random or without any guiding parameters; to the contrary, the regularities of the laws of physics and chemistry acting within the environment are “natural guides” or “governing regulations” on the mechanisms of evolutionary change. So it is not a matter of sheer chance which organisms survive and reproduce, but rather the environment itself contains factors that predictably determine which will survive, and which will not.

It is in this sense that naturalists can speak of design, as well as function and dysfunction, in biological organisms, including humans.

Truth, and Beliefs that are Aimed at Truth

The truth-value of a belief or proposition is a relational property between what the belief is about and the actual states of affairs that make it the case. It may help to think of the accuracy of beliefs not in strict terms of black and white, but as something like a target for which beliefs are thrown. Some beliefs can be more accurate than others. Accuracy in this sense exists on a continuum, and reliability is the ability of belief-producing mechanisms to form beliefs that can land at least somewhere on the target.

In addition, beliefs are not directly chosen by an agent but rather are caused in them (by factors such as reasons and evidence). I reject a view called direct doxastic voluntarism, which says that people have direct voluntary control over what they believe, in favor of indirect doxastic voluntarism, which says that people have only indirect voluntary control, and must be persuaded or caused to believe because of reasons and evidence.

Consider an example: imagine that a cat suddenly jumped onto your desk. You couldn’t help but think, “There is a cat on the desk” (with the accompanied mental representation of a cat being on the desk) — you couldn’t voluntarily choose to believe, “There is not a cat on the desk.” What follows is that the right account of belief is one in which certain mental states are caused in us, which arise (at least partially) because of external factors. This ability of externally caused mental representations arose naturally out of the centralized information processing centers already hard-wired in our ancestors, and while it doesn’t guarantee true beliefs all the time, it does make it very likely that our belief-producing mechanisms were built from the bottom-up to be causally reliable and (at least minimally) aimed at truth.

This view reduces the possibility of certain types of false beliefs; for instance, a prehistoric hominid may see a Tiger and also think it’s a spell-casting witch, but nonetheless the hominid sees the Tiger (which is a belief that is reliably caused in him), and recognizes it rightly as a creature with intentions (and in this case, is a creature to be avoided).[2] While this individual has a false belief, his belief-producing mechanisms are, at least to a minimal degree, aimed at truth, and the true beliefs that he has become a contributing factor in his ability to survive.

Language and Reference

An important feature of human cognition is language, and how words are able to refer. The causal theory of reference (Kripke) proposes that an utterance gets its meaning from the causal connections that exist between the speaker and the object. The same theme is present here: the development and usefulness of language is due in part to there being a reliable causal connection between the speaker and the environment. (And apart from a Cartesian demon systematically fooling us, which no account of reliability can get around, Kripke’s theory of reference is very probably true.)

William Ramsey argues that an important consequence of this view is that a speaker can refer to an object and likely predict truths about it even if they suffer from profound ignorance or false beliefs about the nature of the thing itself.[3] And so again, this view reduces the possibility of certain types of false beliefs; for instance, a prehistoric hominid may see a Tiger, and may also think the creature is a reincarnation of his dead Grandfather, yet when he relays the utterance “Tiger!” to the nearby members of his clan, he is sending them a message that contains certain truths about the immediate environment.

The development of language empowered our ancestors to think in the abstract, which allowed for the sharing of ideas and the development of more advanced problem-solving skills. It is likely that tool-making technologies began to increase with the development of more complex forms of communication, and the two became complementary in the growth of our species evolution.[4]


I have framed an account of how human cognitive faculties can fit within a naturalistic picture of the world, and how, from simple beginnings, brains as complex as our own could come to exist. While this naturalistic account is most certainly incomplete, it is a place to start.

In this process of forming such an account, we must keep in mind what we are giving an account of. First, as I argued in my previous post, it is a mistake to portray human beings as Enlightened Creatures of Reason who are like rational calculators weighing evidence for and against beliefs. Cognitive psychology has revealed that human beings are anything but. We suffer from a wide range of biases and errors in thinking — something has made us less-than-perfect reasoners. (These facts become a major thorn in the side of any theistic hypothesis of an “intelligent designer,” while an evolutionary account actually explains why we have them.)

Second, our recent intellectual advancements have been developed through methods preserved not in our genetics, but in culture. Case in point: if we could somehow transport a newborn to ancient Egypt or the early Roman Empire, it would grow up to adopt many of their same beliefs (e.g. geocentrism and the pantheon of Roman gods), and would have no sense of peer review or double-blind testing, or pretty much anything related to what we would now call the scientific method. When placed in an unfamiliar epistemic environment, our brains do not function as they were designed (think quantum mechanics or theoretical cosmology). Thus, our beliefs beyond our immediate biological needs are to a large degree influenced by factors other than our “stock” cognitive hardware.

Evolution gave us brains that can track truth in our immediate environment. We are the descendants of those who could best fight, flee, find food, and reproduce, and have correspondingly true beliefs. As I’ve argued here, there is good reason to think that this could happen through a process of unguided evolution.

End Notes

  1. Michael Gurven and Hillard Kaplan, “Longevity Among Hunter-Gatherers: A Cross-Cultural Examination,” Population and Development Review, June 2007, pp. 321-365. http://nfs.unipv.it/NFS/MINF/DISPENSE/PATGEN/lectures/files/readings/gurven_2007.pdf
  2. A second point to maker here is that the Tiger reliably sees the hominid, and is most likely thinking, “Lunch.” So evolution has also given Tiger brains the ability to track truth.
  3. William Ramsey, “Naturalism Defended,” Naturalism Defeated? Edited by James Beilby, pp. 26-27.
  4. Michael Balter, “Human language may have evolved to help our ancestors make tools,” AMhttp://www.sciencemag.org/news/2015/01/human-language-may-have-evolved-help-our-ancestors-make-tools
  5. Plantinga, “Respondeo,” p. 342.