Nature and Nurture in Perception

Probably no other issue has engendered more debate in philosophical and scientific discourse than the nature-nurture dichotomy. This entry describes some of the arguments for each side of the dichotomy and the evidence that developmental outcomes are, in fact, the joint product of the coaction of interdependent processes with neither having priority [Page 611]over the other. The idea of separate processes first arose when Plato and Aristotle asked the ultimate epistemological question: What is the origin of human knowledge? In essence, these two philosophers wondered where our ideas of physical objects, causality, number, and space come from. Plato's answer was that our senses do not provide adequate information to form abstract ideas about our world and his “poverty of the stimulus” argument forced him to conclude that all knowledge was innate. Aristotle rejected Plato's argument and declared that our senses do, in fact, provide all the necessary information to understand our world and, thus, concluded that knowledge is acquired through experience. Centuries later, the rationalist philosophers Rene Descartes and Immanuel Kant followed in Plato's footsteps and also argued that we are endowed with a set of innate abstract ideas (i.e., concepts and principles). For the rationalists, perception also was too impoverished to provide enough information about the world and, thus, they held that we must rely on our abstract ideas together with our faculty of reason to arrive at an understanding of our world. John Locke and David Hume, the British empiricist philosophers, challenged the rationalist argument and, like Aristotle, concluded that perception is sufficient to specify our world. Consequently, Locke and Hume asserted that all human knowledge is acquired through experience.

The philosophical arguments regarding the origins of knowledge are inexorably tied up with questions regarding the nature of individual development and the roots of organic form. Aristotle understood this link and, as a result, studied the development of chicks. He noted that development is initiated by some vital force acting on unformed organic matter. As development progresses, this organic matter becomes gradually differentiated into a complex organism. The process of developmental transformation became known as epigenesis. A contrasting view that was prevalent at that time, and one that was held for many centuries after Aristotle, was preformationism. According to this view, the egg or sperm contained a fully formed adult version of the human being (the homunculus) in miniature form and development consists of its gradual growth into a fully mature organism. Although it is evident today that preformationism is wrong, it was not until the advent of the microscope and the emergence of the field of embryology that this view was discredited. Predeterminism—the notion that organisms pass through qualitatively different stages of organization—replaced preformationism. This was a more nuanced conceptualization of development in that it acknowledged the epigenetic principle of transformation but, nonetheless, retained the notion that all knowledge is innate and present at birth.

Charles Darwin's publication of the theory of evolution in 1859 had important but, it could be argued, contradictory effects on developmental thinking. On one hand, the core assumption underlying evolutionary thinking is that the evolution of organisms—phylogenesis—is driven by a process of transformation. This is the same process that underlies the process of individual development—ontogenesis—and, thus, it would be reasonable to expect that this core assumption might have brought the concept of epigenesis to the fore. It did not, though, because the other core assumption underlying the theory of evolution was that natural selection operates on inherited, species-specific characteristics. Thus, it was natural to conclude that ontogenesis begins with an unformed but fully predetermined organism, and this lent further credence to Plato's, Descartes', and Kant's nativist arguments that human nature and knowledge could be passed down through the generations in the form of inherited characteristics. When this idea was later combined with Gregor Mendel's experimental proof of inheritance, the linking of inheritance with phenotypes (i.e., organic form) by the modern synthesis, and James Watson and Francis Crick's discovery of DNA as the physical basis of inheritance, the stage was set for equating the concept of “nature” with the concept of “genetic.” Thus was born the modern version of the nativist idea that the knowledge that is given at birth is coded in our genetic blueprint, and that the sensory, perceptual, and cognitive skills that emerge in development represent an unfolding of that blueprint. Moreover, this modern nativist idea was combined with the concept of genetic encapsulation—the idea that genes are not subject to external influences—and together this conceptualization of development began to dominate biological and psychological thinking.

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