Epistemology has been shaped around the case of adult humans, as if these were the sole epistemic agents. Thus we find invoked such concepts as belief, judgment, reason, reflection, rationality, inference, ratiocination, justification, doubt, certainty, fallibility, and so on. But what about human children, infants, fetuses—don’t they also know things? How should we characterize their epistemic life? And what about the innumerable other species that have a claim to being epistemic agents—isn’t knowledge an extremely widespread phenomenon in the biological world? Think of the cognitive feats of birds and bees as they navigate and congregate. If you jib at applying the concept knowledge to these creatures—not that you should—at least accept that there is a wider natural kind here that needs to be acknowledged. You can use the word “cognize” to denote this wider natural kind if you like, but don’t try to deny that epistemology applies across a very wide domain; yet we philosophers seldom venture into non-human epistemology. I propose to take it to the limit and consider the epistemology of bacteria, which bears a striking resemblance in certain respects to human epistemology—but without the intellectualist concepts listed at the beginning. In bacteria we find proto-epistemology.
Bacteria have receptors on their surface, which are sensitive to the surrounding chemistry of their environment. They also have a motor system (the flagella) that enables them to move toward or away from concentrations of chemicals, depending on whether the sensed chemicals are nutritious or toxic. They can navigate the gradient of chemical concentrations, enabling them to home in on food and avoid toxins. So they have a primitive sensory-motor system. Moreover, they can keep a record of earlier chemical concentrations that enables them to move in the right direction, given the gradient (if it was less concentrated earlier than now, they are moving toward the source not away from it). Let’s give ourselves permission to say that bacteria sense, act, remember, and know: not in the way higher animals do, to be sure, but in primitive form (though adequate for their needs). Then what I want to suggest is that bacteria epistemology has some of the central features of human epistemology—despite the lack of belief, reflection, rationality, and so on. That is, the structure of bacteria epistemology mirrors that of human epistemology (and the same applies to all other species in between).
Suppose a bacteria B knows that there is food in a certain direction by sensing the chemicals diffusing toward it. There is food there, B’s receptors are activated, and the proximate chemical environment indicates food. Can we analyze B’s knowledge by these conditions? It might seem as though the conditions are both necessary and sufficient, but consider the following odd case. Food is present and B senses chemicals at its surface that normally indicate the nearby presence of food, but in fact it is pure chance that this is so: a freak lightning bolt has disturbed the chemical environment in such a way that the sensed chemicals don’t actually come from the food source but from the impact of the lightning. B’s receptors have registered the chemicals and those chemicals usually emanate from a nearby food source, but in this odd case these two things have been severed—it is just an accident that the food happens to be where B’s sensors indicate it to be. The impinging chemicals derive from the lightning not the food in this unusual set-up. If B had a human psychology, we would say that it has a true justified belief, but that this belief is only accidentally true, and hence does not count as knowledge. But B doesn’t have a human psychology, though it can (as we agreed) possess knowledge, and in this case the intuitive upshot is the same—Bdoesn’t know there is food nearby. What we have is a Gettier case for bacteria. B’s evidence for the food is not caused by the food, though there is food there and the evidence is generally reliable. B has the analogue of an accidentally true belief. So even at this primitive cognitive level Gettier cases can arise, despite the lack of the humanlike apparatus of belief and justification. There are analogues of that apparatus, but it is not required that the genuine article be present in order for Gettier cases to be possible. This is what I meant by saying that the same epistemological structure applies across the board. And given that this structure applies, we should be less reluctant to employ the concept of knowledge quite broadly: bacteria have knowledge because they are subject to Gettier cases. Such cases are a sign that the concept of knowledge can be applied broadly. Bacteria detect external facts by means of the traces left by those facts (concentrations of chemicals), so it is possible for there to be cases in which the detection corresponds to the facts and is based on reliable evidence but in which there is no knowledge.
A second structural feature relates to skepticism. Sense experience is not logically sufficient for corresponding external facts, so we have the problem of skepticism concerning knowledge of the external world; but likewise the chemical concentrations around bacteria are not logically sufficient for the presence of the distal facts they are taken to indicate. The bacteria could reflect (were they capable of reflection) that they might actually be “bacteria in a membrane”, that is, the chemical interactions at their surface might be occurring without anything corresponding to them in the wider world. They thus have a skeptical problem analogous to ours: scientists might be producing a simulated bacteria world. The same is true for animals with more advanced senses and sentience: the octopus could coherently wonder whether its beliefs about the external world are really true, given that its inner experiences do not logically imply the truth of those beliefs (maybe it is living in an octopus Matrix). The skeptical problem is not a problem about our knowledge of the external world; it is a problem about every animal’s knowledge of the external world. Russell could have written a book called Animal Knowledge: Its Scope and Limits, with a chapter on bacteria epistemology. 
There is also the problem of induction: all animals rely on induction to cope with their environment (as Hume himself pointed out), so the problem of induction applies to all species. The inductive beliefs or dispositions of animals might all be false. Impressed by this point, one might apply Popper’s view of knowledge to all species: falsification not verification is the way to organize one’s beliefs. Each species is in the business of developing a theory of the world, even if it is simple and superficial, and Popper’s epistemology recommends replacing verification by falsification. The prediction that the sun will rise every morning is never justified by its past risings, but it has withstood the test of attempts at falsification and so may be tentatively accepted. Whether animal expectation takes the form of full-blown belief or just habits of behavior is not central to epistemology; the structure is there even when the psychological elements vary. That structure basically consists of receptivity to evidence combined with commitment to facts that go beyond the evidence; but the structure can have different psychological realizations in different species. There are epistemological universals that exist across species with different kinds of mind, even down to bacteria. Species can vary in what facts are known and in the faculties by which they are known, but what is common is the abstract structure just sketched. Epistemology really began on earth some 4 billion years ago with bacteria, and it has been evolving ever since, with humans at the end of long chain. It is parochial to assume that epistemology begins and ends with humans. Gettier problems, skepticism, and the problem of induction have been around since the earliest origins of life, even if unrecognized; we are just recent examples of these ancient problems.
 He did write a book called Human Knowledge: Its Scope and Limits. Such anthropocentrism!
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