If I had to describe the mission, the point, the raison d'etre of the entire field of psychology in just one sentence, I would say: Psychology aims to determine the relative extents to which biology and experience determine cognition and behavior." And, as you might expect, there are widely differing schools of thought. Nativists emphasize genetics, biology, and innate mechanisms. By contrast, the empiricists insist that babies are born into the world with no a priori knowledge thereof, and just a powerful statistical associative learning mechanism by which they piece together their understanding of reality. In reality, it is likely that there are some things that are innate and some things that require learning. Other mechanisms are probably innate but require experience or learning to properly "tune" or "sharpen" the system.
Rene Descartes speculated that the self (or more specifically, the mind) perceives its own body due to the senses. However, he was aware that the senses could be fooled, and explained the apparent limits of sensory perception with the wax argument: Consider a piece of wax. You perceive certain characteristics about it, such as shape, texture, size, color, smell, etc. But when you move the wax towards a flame, the perceived characteristics change as the wax begins to melt. You know it is still the same piece of wax, but the senses inform you however that the characteristics have changed. So, Descartes argued, sensory perception is not sufficient to properly understand the nature of the wax; instead, he must use his mind. He wrote "...And so something which I thought I was seeing with my eyes is in fact grasped solely by the faculty of judgment which is in my mind." Descartes thus discarded perception and focused solely on deduction as a useful method by which we can come to know the world.
Later, Descartes modified his initial claims regarding the role of sensory perception. In his third and fifth Meditation, he constructed two different proofs that God was benevolent. And, since God was benevolent, Descartes reasoned, he could have faith in the reality provided to him by his senses, since God provided him with a sensory system that was not designed to deceive him. Out of this argument he established the possibility of acquiring knowledge about the world based both on deduction AND sensory perception.
In 1637, Descartes published the Discourse on the Method, in which he argued that the geometric principles underlying the knowledge of space were innate, and were accessible not only to vision but to any sensory modality. He used a blind man with a stick as an example. For the blind man to discover the shape and position of objects, he had to match up each tactile percept with a mental spatial framework, structured around the principles of Euclidean geometry.
Descartes further argued that any individual, exploring the world through any mode (tactile, visual, auditory, or otherwise) faces the fundamental problem of the blind man, and that he or she must draw on tacit geometrical knowledge to solve that problem. Moreover, Descartes argued that such a mental geometric template must be innate: since such a template structures all perceptual experiences, the template itself cannot be acquired by experience.
The contrast to the nativist tradition of Descartes is the empiricist tradition of George Berkeley. Berkeley, also known as Bishop Berkeley, was a philosopher in Ireland and England in the 1700s, and was born thirty-five years after Descartes died. He was also the namesake of UC Berkeley and the town around it.
Berkeley argued that knowledge of the world could only be obtained through direct perception, and that conscious awareness of those perceptions was required for the perception to exist. He wrote, in Towards a New Theory of Vision, in 1709:
I appeal to any one's experience, whether, upon sight of an object, he computes its distance by the bigness of the angle made by the meeting of the two optic axes? ... In vain shall all the mathematicians in the world tell me, that I perceive certain lines and angles which introduce into my mind the various ideas of distance; so long as I myself am conscious of no such thing.
In this way, Berkeley continued the empiricist tradition (following, for example, John Locke), arguing that there were no innate systems of knowledge; instead, everything could be learned through experience, and all that was required in the mind was a general system for statistical learning.
What would it take to prove that a cognitive system is innate? If the human mind is built upon evolutionarily ancient building blocks that allow us to perceive and reason about the world, then:
(1) Those building blocks should be present at birth.
(2) Those building blocks should be present in other animals.
(3) Those building blocks should be universal across cultures.
(4) Possibly: those building blocks should have distinct neural substrates.
For most of the history of philosophy and psychology, people have assumed the opposite. John Locke wrote, in An Essay Concerning Human Understanding in 1689 (emphasis added):
Let us suppose the mind to be, as we say, white paper [tabula rasa] void of all characters, without any ideas. How comes it to be furnished? Whence comes it by that vast store which the busy and boundless fancy of man has painted on it with an almost endless variety? Whence has it all the materials of reason and knowledge? To this, I answer, in one word, from experience.
Similarly, William James wrote that "the baby, assailed by eyes, ears, nose, skin, and entrails at once, feels it all as one great blooming, buzzing confusion."
The basic argument is that infants come into the world knowing essentially nothing. They are equipped with basic sensory mechanisms and a powerful statistical brain that is highly skilled at detecting and learning associations between different sensory inputs. Throughout development, the argument goes, children learn more and more associations until they have the same kind of mind as human adults do.
The prediction that follows from this is that adults should always be better at cognitive tasks than infants. This, however, is not the case. For example, human adults are far better at distinguishing among human faces than among monkey faces. This is probably due to experience - humans develop expertise in distinguishing human faces because they spend most of their time with humans. But 6-month-old infants, before experience has significantly guided development, are actually able to accurately distinguish among monkey faces as well as among human faces.
This cognitive skill, facial identification, is actually better in infants than in adults, suggesting that there is an innate template for face recognition and for distinguishing among different individuals, and experience simply serves to build expertise. If facial recognition had to be entirely constructed, then you would expect infants not to distinguish among human faces as accurately as adults, let alone among monkey faces.
More and more, we are finding that the infant brain is not a "blooming buzz of confusion." Instead, the infant brain seems born capable of sophisticated reasoning about the world. The key is to figure out the proper way of testing and identifying those abilities.
Pascalis, O. (2002). Is Face Processing Species-Specific During the First Year of Life? Science, 296 (5571), 1321-1323. DOI: 10.1126/science.1070223
Landau B, Gleitman H, & Spelke E (1981). Spatial knowledge and geometric representation in a child blind from birth. Science (New York, N.Y.), 213 (4513), 1275-8. PMID: 7268438