Innate Blank Slates
Even the most hardline nativist will agree that not everything that passes before the mind, or exists in it, is innately fixed. In particular, memory contains contents that derive from experience. Memory may be defined as the ability to learn, and animals with memory absorb information from the environment that was not in them at birth. To this extent the mind is a blank slate—a receptacle waiting to be filled by post-natal experience. There may be (there is) a lot that is innate, but not everything is innate: fresh input reaches the mind to be added to its original resources. Does this mean that nativism has to concede a local victory to empiricism? Is it that the mind is partly innately structured and partly formless? Is it well stocked in some departments and entirely empty in others? Is the library of the mind a collection of written texts existing alongside an empty volume waiting for the world to inscribe messages on it? Is the mind partly nativist and partly empiricist? I think this is the wrong way to look at the matter; in fact, the so-called blank slate (memory) is really just another iteration of the nativist doctrine. The mind is genetically determined all the way down—including the blank slate. The blank slate is just another innately fixed biological component of the mind. 
It might not have been so. Consider this theory, conceivably true in some possible world: the blank slate is acquired by experiencing blank slates in the world and copying them inwardly. You observe empty spaces or sheets of white paper or wax tablets and this creates in you a blank mental canvas on which experience can subsequently write. You “abstract” inner blankness from perceptible blank and formless things, and this forms the basis of memory. Thus the blank slate is an acquired characteristic. If this is the entirety of the mind, then the whole thing is acquired. But that is clearly a completely wacky theory, held by exactly no one. For one thing, wouldn’t the mind need an antecedent blank slate in order to acquire one by means of observing external blank slates? And how on earth could the mind “abstract” blankness and then internalize it—wouldn’t that be just an idea of blank slates? No, the reasonable view—and the one held by all empiricists—is that the mind is innately blank. That is its character at birth, its genetically determined nature, its intrinsic essence. So the blank slate is itself an innate component of the mind existing alongside other innate components. Its distinguishing characteristic is its flexibility: it is a receptiveepistemic faculty—it accepts novelty and change. It is modified by experience instead of being oblivious to experience. We might better call it “the receptive slate” in order to emphasize its function and mode of operation. It is genetically fixed and yet malleable, inborn and also plastic. In this respect it is like the perceptual faculties: we are not born already seeing all the things we will ever see (!), yet vision is an innately fixed faculty. The point of vision (and the other senses) is to permit variation in what is seen, i.e. sensitivity to environmental contingencies; but that is quite consistent with a strongly nativist conception of vision. The form is innate and the content is acquired, as we might put it. The perceptual categories might all be innate, but the particular state of affairs perceived is a result of environmental influence. Similarly, memory is innate even though what is remembered results from the impact of the world. There are clearly advantages to such flexibility and receptivity, but in no way does this cast doubt on the innateness of the faculty in question. Even the humble earthworm can sense and learn, but its ability to do so depends on its innate constitution.
Why should we classify the blank slate existing inside every learning organism alongside its other innate characteristics? Why should we deem it biological? Why is it not, say, “cultural”? Why resist a form of dualism about what traits an organism possesses, the blank traits and the non-blank traits? There are several reasons. First, it is genetically determined: there is a gene (or complex of genes) for blankness (flexibility, receptivity). Blankness is certainly not the result of an absence of genes! The genes construct an epistemic organ whose specialization is openness to experience, as opposed to one that already knows all the answers. It is as if the genes constructed an amorphous bodily organ that could be modified by experience—say, a limb that could be molded into a different appendage depending upon environmental demands (a leg, a fin, a wing). That could be a useful adaptation in certain conditions, as a modifiable memory is a useful adaptation. An animal with a gene for blankness will enjoy a selective advantage. Some creatures lack such genes, harboring merely a set of instinctive reflexes, but others contain them, the better to survive in a changing world. So the blank state is as genetically engineered as any physical or mental organ (say, the human language faculty).  Animals are genetically designed that way. They are born to be blank (in part).
Second, the blank slate is not as blank as all that: it is not a featureless nothing, devoid of all inner structure. Consider paper: paper is a highly structured and carefully designed piece of technology, not just a mere absence. It must absorb and retain ink, not blurring or running. It stacks and folds. It can be bound into volumes. It is durable. It took centuries to invent and perfect paper. Paper has a certain intrinsic constitution precisely designed to accept ink. It has as much of an inner nature as the ink that adorns it. And memory must be very similar: memory too took a long time to evolve, and it must be possessed of an inner nature that makes its feats of retention possible. The genes for memory are entrusted with a difficult and intricate job: to construct a system that absorbs and retains information, while letting it to degrade if it is no longer useful. Compare the hard drive of a computer—also an intricate and inventive piece of technology. These are not just empty boxes waiting to have stuff thrown into them. So there is no viable dualism of the structured and the unstructured—the mental plenum versus the mental vacuum. It’s all sophisticated architecture. The blank slate is blank only relative to what may be written on it; in itself it is plenitude, no more vacant than any other natural object. 
Third, the blank slate has a biological function, which may be characterized as follows. The world is divided into general facts and specific facts; it is useful to know both kinds. An individual organism has a specific history and it is useful for the organism to learn from its history—to know the specific facts that aid its survival, such as where food is to be found. So it is adaptive to install an organ that can record particular facts for later use—that is, a memory organ. Thus the blank slate is as functionally adaptive as any non-blank organ of the body or mind. It isn’t just for frivolous “culture” and knowing historical dates to pass examinations; it functions as an adaptive trait, no less biological than digestion or locomotion. The genes design it to perform this function. Animals learn new things so as to get the genes that make them into future generations (fundamentally).
Fourth, and very important, there is not the blank slate, there are many blank slates: that is, each species has its own type of blank slate designed to serve its particular mode of life. Memory is species-specific. Squirrels remember where they have stowed their nuts, birds remember which direction to fly in, social animals remember their conspecifics, humans remember birthdays and to pick up the dry cleaning. Memory faculties vary in their storage capacity and in their contents, with inbuilt biases to remember some things and not others. They are like eyes: they all do the same thing, but they vary in their architecture and acuity. The phenomenology and physiology of memory varies from species to species, as does its functional character. Memory systems are shaped by natural selection like any other trait, and they are as species-specific as other traits of evolved organisms. The metaphor of the blank slate should not be allowed to obscure this fact—as if all forms of blankness were the same (compare different sizes and shapes of paper, or paper and hard drives and vinyl discs). The larynx of different vocal animals serves the purpose of emitting sound for every animal that has a larynx, but larynxes come in different designs and produce different sounds—there is not some universal larynx common to all species.  Just as the larynx of one species will not allow it to make the sounds of another species, so the memory of one species will not allow it to remember what another species remembers. Species-specific means functionally limited. The blank slate of an organism is thus tied to a particular ecological niche, a specific biological set-up.
We can accordingly say that blank slates are genetically determined, intrinsically structured, biologically functional, and species-specific. They are part of an animal’s organic endowment—certainly not a product of environmental contingencies or “culture”. True, they can receive information from experience, but that doesn’t render them non-biological, or introduce a sharp line between the innate and the learned—any more than the varying objects of the senses show the senses to be non-biological. So it isn’t that memory reveals the limits of nativism; nativism, rightly understood, simply includes the blank slate of memory. If there were a “blank limb” capable of assuming one specific form or another depending on environmental demands, then that limb would not thereby cease to be biological. It would simply be innately adaptable instead of innately fixed. The traditional opposition between nativism (rationalism) and empiricism is thus misconceived, since even the empiricist is a (closet) nativist. The only issue is how much of human (and animal) knowledge is due to memory based on experience and how much to what is known at birth (without the use of memory); whatever view you take, the faculties in question are innate and biological. The terminology should really be dropped and replaced by talk of memory knowledge and non-memory knowledge. The question then will be whether specific areas of knowledge are known by memory or otherwise—knowledge of logic, mathematics, morals, language, laws of nature, colors, shapes, historical events, science, geography, etc. It is misleading to speak of nativism versus empiricism, as if empiricism could escape nativism about its preferred model of human knowledge. Talk of a blank slate is really a misleading way to talk about memory. Traditional empiricists claim that all knowledge is based on memory, while traditional nativists claim that much knowledge is not based on memory (though some certainly is). Knowledge based on experience is possible only if experience is remembered; knowledge not based on experience is knowledge not remembered. Do we know mathematics because we remember what we were taught or because we have that knowledge built into our minds before being taught anything? That is the real question, not whether the knowledge is innate or acquired.  Even if it is acquired by means of experience and memory, the knowledge rests on an innate faculty, as biological as anything else about us. And again, the fact that vision “acquires” different objects as the eyes rove around the world doesn’t show that vision is not an innate faculty—just as the different objects you might pick up with your hands doesn’t demonstrate that your hands are not innately determined structures. A nativist who held that which objects you pick up in life is genetically determined would clearly be out to lunch, but that is not required in order to maintain the sensible position that hands themselves are genetically determined. It is the same with memory and the blank slate. The blank slate is empty just in the sense in which the empty hand is empty—neither of which entails a lack of innateness. We could rename the debate “memory-ists versus non-memory-ists”. Even the extreme empiricist who believes that all knowledge is based on memory is committed to the innateness of the faculty of memory, with the four characteristics I listed above; the inner constitution of the mind would still be independent of all experience (learning, environmental impact). There is no way to avoid nativism as the foundation of knowledge.
Let me end with some reflections on knowledge of language in the light of the foregoing observations. We can accept that some knowledge of language is innate, i.e. knowledge of universal grammar—memory plays no role in possessing such knowledge. But in addition to this we also have knowledge of the particular human language that we learn to speak—and here memory indisputably plays a role. Does this mean that biology leaves off where knowledge of a particular language begins? No, because memory is itself a biological endowment programmed into the genes. Human speakers thus exploit two innate endowments in their acquisition of language. But there is a further point to be made: the specific form of memory that is exploited in learning a particular language is likely dedicated to that task. We possess a remarkable memory for linguistic information–phonetic, syntactic, and semantic—and it is plausible that this is specific to language. So we are not just using our general-purpose species-specific form of memory but also a special memory module dedicated to language learning.  Of course, this is an empirical hypothesis, but its distinct possibility allows us to make a conceptual point, namely that we have a genetically fixed and highly specific form of memory that is employed in language acquisition—a third type of innate mechanism. Thus language acquisition employs three levels of innate machinery: an innate knowledge of universal grammar; an innate general memory faculty directed to knowledge of a particular language; and an innate memory module dedicated to linguistic memory of a specific language. So it is just not innateness at the first universal level but also at the levels that deal with learning a specific language. We possess not just a blank slate peculiar to humans but several blank slates devoted to different cognitive tasks—and all are innate. The blank slate might be as modular as the non-blank systems that make up our general knowledge. In any case, the blank slate is not the negation of innateness but a special case of it. 
 I am not the first person to make this point, but I think it is still underappreciated. Even if all ideas are acquired, the thing that acquires them isn’t. The blank slate is as innate as anatomy and eye color.
 It might be that blank slates are more complex genetically than determinate organs, because of the engineering requirements of extreme receptivity; certainly, they require big brains. Empiricism could not then claim biological parsimony.
 Notice that paper is selectively receptive: ink leaves a mark on it but wind doesn’t. There could be a form of “paper” that is receptive to wind but not ink. Thus bias is built in as part of the nature of the thing.
 Of course, innate knowledge is also “acquired” in the sense that organisms come to have it at a certain time by certain processes—by gene activity (and earlier by natural selection). The usual use of “innate” and “acquired” in these debates is quite unsatisfactory.
 Why would anyone think that the blank slate is not a robust biological trait of the organism? Perhaps for epistemological reasons: we can’t perceive or introspect the blank slate (i.e. the memory faculty); we can only apprehend its contents (ideas, concepts). Thus we are inclined to doubt its reality. And something unreal can’t be a biological fact. I won’t take time to dissect the errors in this way of thinking.