The interaction between nature and nurture influences human development and behavior and is a subject of study in behavioral genetics. Nature is defined in terms of nativism or innatism philosophy according to which individual's innate qualities such as inheritance, biological background, and genetic material determine human development. Nurture refers to individual experience and learning as the main causes for human knowledge and development.
Simply put, nature is defined as the DNA of the individual, while nurture is their destiny. As a result, the two causes of human development are mutually exclusive because the different behavioral traits are either innate, genetic and internal or acquired, environmental and external. Thus, there is a dichotomy between nature and nurture and nativists and empiricists.The belief that human beings acquire all their knowledge from experience comes from John Locke's notion of tabula rasa, or blank slate, according to which all individuals are born without innate mental capabilities, which are later developed by environmental influences. However, both nature and nurture interact and influence each other and the concept is known as a range of reaction. There is a number of traits which are genetically predetermined but environment and experience determine how much of their potential will be developed. This is the example with height which is more or less genetically predetermined but also influenced by external factors such as nutrition and sport.
The genetic potential of the individual is called genotype, while a phenotype describes the changes resulting from the interaction between nature and nurture. As environment may influence genes so can genetic potentials influence the environment. An innate talent remains only a potential if it is not developed and in this case the genes determine the specific experiences. This proves that nature and nurture interact bidirectionally.
Behavioral genetics studies the interaction between nature and nurture through conducting studies on twins and adopted children. Identical twins are genetically identical but when raised in different family environments they may display different behavioral traits and IQ. Fraternal twins, developed from two separate eggs, are only 50 percent genetically identical but if raised in the same family they may share identical traits. The influence of genes is calculated with a correlation, known as the heritability index. Research shows that identical twins display the highest heritability of up to 70 even when raised separately, while fraternal twins and other siblings have heritability indices below 50.Gene contribution is also studied through adoption cases. Biological siblings who share the same family environment and only half of their genes are compared to adopted children who are raised in the same environment, but possess none of the family's genetic material. In adoption cases experiments show that biological siblings and their parents share similar IQs, while adopted children do not develop an IQ similar to that of their foster parents. In twin studies, identical twins raised separately are more similar in IQ than fraternal twins raised together. This means that genes or nature have a substantial impact on intelligence and personality.
Heritability is defined as the proportion of observed variation in a particular trait attributed to inherited genetic factors in contrast to environmental ones. However, even highly heritable traits, such as eye color, are affected by outside factors such as other genes in the organism or environment-specific conditions. Most traits and capabilities are polygenetic, meaning that more than one gene is responsible for them. Even if low heritability traits, such as specific language and religion, are determined externally by the environment, it is proven that a child can learn with the same ease any language. These findings show that both nature and nurture take part in human development.
The nature versus nurture concept was coined by Francis Galton (1822 to 1911) who was influenced by the book On the Origin of Species written by his cousin Charles Darwin (1809 to 1882). He strongly believed that ability is inherited and supported eugenics, or the strengthening of desirable characteristics using selective mating. Such beliefs were a base for racial theories where whole nations were considered to be superior or inferior by nature. Historically, human nature was thought to be divinely predetermined, but since the late Middle Ages intellectuals began to link differences among humans to socialization or nurture, rather than to innate qualities or nature. Later, during communist times and based on Marx's theory it was believed that human nature was determined by social environment and structure instead of nature.