Nature versus nurture is a long-standing debate in biology and society about the relative influence on human beings of their

genetic inheritance Heredity, also called inheritance or biological inheritance, is the passing on of traits from parents to their offspring; either through asexual reproduction or sexual reproduction, the offspring cells or organisms acquire the genetic inform ...

(nature) and the environmental conditions of their development (

nurture Nurture is usually defined as the process of caring for an organism, as it grows, usually a human. It is often used in debates as the opposite of "nature", whereby nurture means the process of replicating learned cultural information from one min ...

). The

alliterative Alliteration is the repetition of syllable-initial consonant sounds between nearby words, or of syllable-initial vowels if the syllables in question do not start with a consonant. It is often used as a List of narrative techniques#Style, litera ...

expression "nature and nurture" in English has been in use since at least the

Elizabethan period The Elizabethan era is the epoch in the Tudor period of the history of England during the reign of Queen Elizabeth I (1558–1603). Historians often depict it as the Golden age (metaphor), golden age in English history. The Roman symbol of ...

and goes back to

medieval French Old French (, , ; ) was the language spoken in most of the northern half of France approximately between the late 8th

Victorian Victorian or Victorians may refer to: 19th century * Victorian era, British history during Queen Victoria's 19th-century reign ** Victorian architecture ** Victorian house ** Victorian decorative arts ** Victorian fashion ** Victorian literatur ...

polymath Francis Galton, the modern founder of eugenics and

behavioral genetics Behavioural genetics, also referred to as behaviour genetics, is a field of scientific research that uses genetic methods to investigate the nature and origins of individual differences in behaviour. While the name "behavioural genetics" c ...

when he was discussing the influence of heredity and Social environment, environment on social advancement. Galton was influenced by ''

On the Origin of Species ''On the Origin of Species'' (or, more completely, ''On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life'')The book's full original title was ''On the Origin of Species by M ...

'' written by his

half-cousin A cousin is a relative who is the child of a parent's sibling; this is more specifically referred to as a first cousin. A parent of a first cousin is an aunt or uncle. More generally, in the kinship system used in the English-speaking world, c ...

, the evolutionary biologist

Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English Natural history#Before 1900, naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all speci ...

. The view that humans acquire all or almost all their behavioral traits from "nurture" was termed ''

tabula rasa ''Tabula rasa'' (; Latin for "blank slate") is the idea of individuals being born empty of any built-in mental content, so that all knowledge comes from later perceptions or sensory experiences. Proponents typically form the extreme "nurture" ...

'' ('blank tablet, slate') by

John Locke John Locke (; 29 August 1632 (Old Style and New Style dates, O.S.) – 28 October 1704 (Old Style and New Style dates, O.S.)) was an English philosopher and physician, widely regarded as one of the most influential of the Enlightenment thi ...

in 1690. A ''blank slate view'' (sometimes termed ''blank-slatism'') in human

developmental psychology Developmental psychology is the scientific study of how and why humans grow, change, and adapt across the course of their lives. Originally concerned with infants and children, the field has expanded to include adolescence, adult development ...

, which assumes that human behavioral traits develop almost exclusively from environmental influences, was widely held during much of the 20th century. The debate between "blank-slate" denial of the influence of

heritability Heritability is a statistic used in the fields of Animal husbandry, breeding and genetics that estimates the degree of ''variation'' in a phenotypic trait in a population that is due to genetic variation between individuals in that population. T ...

, and the view admitting both environmental and heritable traits, has often been cast in terms of nature ''versus'' nurture. These two conflicting approaches to human development were at the core of an ideological dispute over research agendas throughout the second half of the 20th century. As both "nature" and "nurture" factors were found to contribute substantially, often in an inextricable manner, such views were seen as naive or outdated by most scholars of human development by the 21st century. The strong dichotomy of nature ''versus'' nurture has thus been claimed to have limited relevance in some fields of research. Close

feedback Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause and effect that forms a circuit or loop. The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handle ...

loops have been found in which nature and nurture influence one another constantly, as seen in

self-domestication Self-domestication is a scientific hypothesis that posits the occurrence of a process of artificial selection among human beings, akin to that observed in domesticated animals. This process has been executed by human beings themselves. During the ...

. In

ecology Ecology () is the natural science of the relationships among living organisms and their Natural environment, environment. Ecology considers organisms at the individual, population, community (ecology), community, ecosystem, and biosphere lev ...

and

, researchers think nurture has an essential influence on the nature of an individual. Similarly in other fields, the dividing line between an inherited and an acquired trait becomes unclear, as in

epigenetics In biology, epigenetics is the study of changes in gene expression that happen without changes to the DNA sequence. The Greek prefix ''epi-'' (ἐπι- "over, outside of, around") in ''epigenetics'' implies features that are "on top of" or "in ...

fetal development Prenatal development () involves the development of the embryo and of the fetus during a viviparous animal's gestation. Prenatal development starts with fertilization, in the germinal stage of embryonic development, and continues in fetal deve ...

History of debate

According to ''

Records of the Grand Historian The ''Shiji'', also known as ''Records of the Grand Historian'' or ''The Grand Scribe's Records'', is a Chinese historical text that is the first of the Twenty-Four Histories of imperial China. It was written during the late 2nd and early 1st ce ...

'' (94 BC) by

Sima Qian Sima Qian () was a Chinese historian during the early Han dynasty. He is considered the father of Chinese historiography for the ''Shiji'' (sometimes translated into English as ''Records of the Grand Historian''), a general history of China cov ...

, during

Chen Sheng Wu Guang uprising The Chen Sheng and Wu Guang uprising (), August 209 B.C.– January 208 B.C., was the first uprising against the Qin dynasty following the death of Qin Shi Huang. Led by Chen Sheng and Wu Guang, the uprising was unsuccessful. Name It is also c ...

in 209 B.C.,

Chen Sheng Chen Sheng (died January 208 BC), also known as Chen She ("She" being his courtesy name), posthumously known as King Yin, was the leader of the Dazexiang Uprising, the first rebellion against the Qin dynasty. It occurred during the reign of th ...

asked the rhetorical question as a call to war: "Are kings, generals, and ministers merely born into their kind?" ( zh, 王侯將相寧有種乎). Though Chen was obviously negative to the question, the phrase has often been cited as an early quest into the nature versus nurture problem.

's ''

An Essay Concerning Human Understanding ''An Essay Concerning Human Understanding'' is a work by John Locke concerning the foundation of human knowledge and understanding. It first appeared in 1689 (although dated 1690) with the printed title ''An Essay Concerning Humane Understand ...

'' (1690) is often cited as the foundational document of the ''

blank slate ''Tabula rasa'' (; Latin for "blank slate") is the idea of individuals being born empty of any built-in mental content, so that all knowledge comes from later perceptions or sensory experiences. Proponents typically form the extreme "nurture" ...

'' view. In the ''Essay'', Locke specifically criticizes

René Descartes René Descartes ( , ; ; 31 March 1596 – 11 February 1650) was a French philosopher, scientist, and mathematician, widely considered a seminal figure in the emergence of modern philosophy and Modern science, science. Mathematics was paramou ...

's claim of an

innate idea In the philosophy of mind, innatism is the view that the mind is born with already-formed ideas, knowledge, and beliefs. The opposing doctrine, that the mind is a ''tabula rasa'' (blank slate) at birth and all knowledge is gained from experience ...

God In monotheistic belief systems, God is usually viewed as the supreme being, creator, and principal object of faith. In polytheistic belief systems, a god is "a spirit or being believed to have created, or for controlling some part of the un ...

that is universal to humanity. Locke's view was harshly criticized in his own time.

Anthony Ashley-Cooper, 3rd Earl of Shaftesbury Anthony Ashley Cooper, 3rd Earl of Shaftesbury (26 February 1671 – 16 February 1713) was an English peer, Whig politician, philosopher and writer. Early life He was born at Exeter House in London, the son and first child of the future An ...

, complained that by denying the possibility of any innate ideas, Locke "threw all order and virtue out of the world," leading to total

moral relativism Moral relativism or ethical relativism (often reformulated as relativist ethics or relativist morality) is used to describe several Philosophy, philosophical positions concerned with the differences in Morality, moral judgments across different p ...

. By the 19th century, the predominant perspective was contrary to that of Locke's, tending to focus on "

instinct Instinct is the inherent inclination of a living organism towards a particular complex behaviour, containing innate (inborn) elements. The simplest example of an instinctive behaviour is a fixed action pattern (FAP), in which a very short to me ...

Leda Cosmides Leda Cosmides (born May 1957) is an American psychologist, who, together with anthropologist husband John Tooby, pioneered the field of evolutionary psychology. Biography Cosmides was born into a Greek family. Her parents, George Cosmides and N ...

and

John Tooby John Tooby (July 26, 1952 – November 10, 2023) was an American anthropologist who, together with his psychologist wife Leda Cosmides, pioneered the field of evolutionary psychology. Biography Tooby received his PhD in Biological Anthropology ...

noted that

William James William James (January 11, 1842 – August 26, 1910) was an American philosopher and psychologist. The first educator to offer a psychology course in the United States, he is considered to be one of the leading thinkers of the late 19th c ...

(1842–1910) argued that humans have ''more''

s than animals, and that greater freedom of action is the result of having more

psychological Psychology is the scientific study of mind and behavior. Its subject matter includes the behavior of humans and nonhumans, both consciousness, conscious and Unconscious mind, unconscious phenomena, and mental processes such as thoughts, feel ...

instincts, not fewer. The question of "innate ideas" or "instincts" was of some importance in the discussion of

free will Free will is generally understood as the capacity or ability of people to (a) choice, choose between different possible courses of Action (philosophy), action, (b) exercise control over their actions in a way that is necessary for moral respon ...

moral philosophy Ethics is the philosophical study of moral phenomena. Also called moral philosophy, it investigates normative questions about what people ought to do or which behavior is morally right. Its main branches include normative ethics, applied et ...

. In 18th-century philosophy, this was cast in terms of "innate ideas" establishing the presence of a universal virtue, a prerequisite for objective morals. In the 20th century, this argument was in a way inverted, since some philosophers (

J. L. Mackie John Leslie Mackie (25 August 1917 – 12 December 1981) was an Australian philosopher. He made significant contributions to ethics, the philosophy of religion, metaphysics, and the philosophy of language. Mackie had influential views on meta ...

) now argued that the evolutionary origins of human behavioral traits forces us to concede that there is no foundation for ethics, while others (

Thomas Nagel Thomas Nagel (; born July 4, 1937) is an American philosopher. He is the University Professor of Philosophy and Law Emeritus at New York University, where he taught from 1980 until his retirement in 2016. His main areas of philosophical interest ...

) treated ethics as a field of cognitively valid statements in complete isolation from evolutionary considerations.

Early to mid-20th century

In the early 20th century, there was an increased interest in the role of one's environment, as a reaction to the strong focus on pure heredity in the wake of the triumphal success of Darwin's

theory of evolution Evolution is the change in the heritable characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certai ...

. During this time, the

social sciences Social science (often rendered in the plural as the social sciences) is one of the branches of science, devoted to the study of society, societies and the Social relation, relationships among members within those societies. The term was former ...

developed as the project of studying the influence of culture in clean isolation from questions related to "biology.

Franz Boas Franz Uri Boas (July 9, 1858 – December 21, 1942) was a German-American anthropologist and ethnomusicologist. He was a pioneer of modern anthropology who has been called the "Father of American Anthropology". His work is associated with the mov ...

's '' The Mind of Primitive Man'' (1911) established a program that would dominate

American anthropology American anthropology has culture as its central and unifying concept. This most commonly refers to the universal human capacity to classify and encode human experiences symbolically, and to communicate symbolically encoded experiences socially. ...

for the next 15 years. In this study, he established that in any given

population Population is a set of humans or other organisms in a given region or area. Governments conduct a census to quantify the resident population size within a given jurisdiction. The term is also applied to non-human animals, microorganisms, and pl ...

biology Biology is the scientific study of life and living organisms. It is a broad natural science that encompasses a wide range of fields and unifying principles that explain the structure, function, growth, History of life, origin, evolution, and ...

language Language is a structured system of communication that consists of grammar and vocabulary. It is the primary means by which humans convey meaning, both in spoken and signed language, signed forms, and may also be conveyed through writing syste ...

material A material is a matter, substance or mixture of substances that constitutes an Physical object, object. Materials can be pure or impure, living or non-living matter. Materials can be classified on the basis of their physical property, physical ...

, and symbolic culture, are

autonomous In developmental psychology and moral, political, and bioethical philosophy, autonomy is the capacity to make an informed, uncoerced decision. Autonomous organizations or institutions are independent or self-governing. Autonomy can also be defi ...

; that each is an equally important dimension of human nature, but that none of these dimensions is reducible to another.

Purist behaviorism

John B. Watson John Broadus Watson (January 9, 1878 – September 25, 1958) was an American psychologist who popularized the scientific theory of behaviorism, establishing it as a List of psychological schools, psychological school.Cohn, Aaron S. 2014.Watson, J ...

in the 1920s and 1930s established the school of ''purist

behaviorism Behaviorism is a systematic approach to understand the behavior of humans and other animals. It assumes that behavior is either a reflex elicited by the pairing of certain antecedent stimuli in the environment, or a consequence of that indivi ...

'' that would become dominant over the following decades. Watson is often said to have been convinced of the complete dominance of cultural influence over anything that heredity might contribute. This is based on the following quote which is frequently repeated without context, as the last sentence is frequently omitted, leading to confusion about Watson's position:During the 1940s to 1960s,

Ashley Montagu Montague Francis Ashley-Montagu (born Israel Ehrenberg; June 28, 1905November 26, 1999) was a British-American anthropologist who popularized the study of topics such as race and gender and their relation to politics and development. He was the ...

was a notable proponent of this purist form of behaviorism which allowed no contribution from heredity whatsoever: In 1951, Calvin Hall suggested that the dichotomy opposing nature to nurture is ultimately fruitless. In ''

African Genesis ''African Genesis: A Personal Investigation into the Animal Origins and Nature of Man'', usually referred to as ''African Genesis'', is a 1961 nonfiction work by the American writer Robert Ardrey. It posited the hypothesis that man evolved on the ...

'' (1961) and ''

The Territorial Imperative ''The Territorial Imperative: A Personal Inquiry Into the Animal Origins of Property and Nations'' is a 1966 nonfiction book by American writer Robert Ardrey. It characterizes an instinct among humans toward Territory (animal), territoriality and ...

'' (1966),

Robert Ardrey Robert Ardrey (October 16, 1908 – January 14, 1980) was an American playwright, screenwriter and science writing, science writer perhaps best known for ''The Territorial Imperative'' (1966). After a Broadway (theatre), Broadway and Cinema of th ...

argues for innate attributes of human nature, especially concerning

territoriality In ethology, territory is the sociographical area that an animal consistently defends against conspecific competition (or, occasionally, against animals of other species) using agonistic behaviors or (less commonly) real physical aggression. ...

Desmond Morris Desmond John Morris FLS ''hon. caus.'' (born 24 January 1928) is an English zoologist, ethologist and surrealist painter, as well as a popular author in human sociobiology. He is known for his 1967 book ''The Naked Ape'', and for his televis ...

in ''

The Naked Ape ''The Naked Ape: A Zoologist's Study of the Human Animal'' is a 1967 book by English Zoology, zoologist and ethology, ethologist Desmond Morris that looks at humans as a species and compares them to other animals. ''The Human Zoo (book), The Hum ...

'' (1967) expresses similar views. Organised opposition to Montagu's kind of purist "blank-slatism" began to pick up in the 1970s, notably led by

E. O. Wilson Edward Osborne Wilson (June 10, 1929 – December 26, 2021) was an American biologist, naturalist, ecologist, and entomologist known for developing the field of sociobiology. Born in Alabama, Wilson found an early interest in nature and frequ ...

('' On Human Nature'', 1979). The tool of

twin studies Twin studies are studies conducted on Identical twin, identical or Fraternal twin, fraternal twins. They aim to reveal the importance of environmental and genetics, genetic influences for traits, phenotypes, and disorders. Twin research is consid ...

was developed as a research design intended to exclude all confounders based on inherited behavioral traits. Such studies are designed to decompose the variability of a given trait in a given population into a genetic and an environmental component. Twin studies established that there was, in many cases, a significant heritable component. These results did not, in any way, point to overwhelming contribution of heritable factors, with

typically ranging around 40% to 50%, so that the controversy may not be cast in terms of ''purist behaviorism'' vs. ''purist

nativism Nativism may refer to: * Nativism (politics), ethnocentric beliefs relating to immigration and nationalism * Nativism (psychology), a concept in psychology and philosophy which asserts certain concepts are "native" or in the brain at birth * Lingu ...

''. Rather, it was ''purist behaviorism'' that was gradually replaced by the now-predominant view that both kinds of factors usually contribute to a given trait, anecdotally phrased by

Donald Hebb Donald Olding Hebb (July 22, 1904 – August 20, 1985) was a Canadian psychologist who was influential in the area of neuropsychology, where he sought to understand how the function of neurons contributed to psychological processes such as learn ...

as an answer to the question "which, nature or nurture, contributes more to personality?" by asking in response, "Which contributes more to the area of a rectangle, its length or its width?" In a comparable avenue of research, anthropologist Donald Brown in the 1980s surveyed hundreds of anthropological studies from around the world and collected a set of

cultural universals A cultural universal (also called an anthropological universal or human universal) is an element, pattern, trait, or institution that is common to all known human cultures worldwide. Taken together, the whole body of cultural universals is known ...

. He identified approximately 150 such features, coming to the conclusion there is indeed a "universal human nature", and that these features point to what that universal human nature is.

Determinism

At the height of the controversy, during the 1970s to 1980s, the debate was highly ideologised. In '' Not in Our Genes: Biology, Ideology and Human Nature'' (1984),

Richard Lewontin Richard Charles Lewontin (March 29, 1929 – July 4, 2021) was an American evolutionary biologist, mathematician, geneticist, and social commentator. A leader in developing the mathematical basis of population genetics and evolutionary theory, ...

Steven Rose Steven Peter Russell Rose (born 4 July 1938) is an English neuroscientist, author, and social commentator. He is an emeritus professor of biology and neurobiology at the Open University and Gresham College, London. Early life Born in London, U ...

and

Leon Kamin Leon J. Kamin (December 29, 1927 – December 22, 2017) was an American psychologist known for his contributions to learning theory and his critique of estimates of the heritability of IQ. He studied under Richard Solomon (psychologist), Richard S ...

criticise "

genetic determinism Biological determinism, also known as genetic determinism, is the belief that human behaviour is directly controlled by an individual's genes or some component of their physiology, generally at the expense of the role of the environment, wheth ...

" from a

Marxist Marxism is a political philosophy and method of socioeconomic analysis. It uses a dialectical and materialist interpretation of historical development, better known as historical materialism, to analyse class relations, social conflic ...

framework, arguing that "Science is the ultimate legitimator of bourgeois ideology ... If

biological determinism Biological determinism, also known as genetic determinism, is the belief that human behaviour is directly controlled by an individual's genes or some component of their physiology, generally at the expense of the role of the environment, wheth ...

is a weapon in the struggle between classes, then the universities are weapons factories, and their teaching and research faculties are the engineers, designers, and production workers." The debate thus shifted away from whether heritable traits exist to whether it was

politically Politics () is the set of activities that are associated with making decisions in groups, or other forms of power relations among individuals, such as the distribution of status or resources. The branch of social science that studies poli ...

ethically Ethics is the philosophy, philosophical study of Morality, moral phenomena. Also called moral philosophy, it investigates Normativity, normative questions about what people ought to do or which behavior is morally right. Its main branches inclu ...

permissible to admit their existence. The authors deny this, requesting that evolutionary inclinations be discarded in ethical and political discussions regardless of whether they exist or not.

1990s

Heritability studies became much easier to perform, and hence much more numerous, with the advances of genetic studies during the 1990s. By the late 1990s, an overwhelming amount of evidence had accumulated that amounts to a refutation of the extreme forms of "blank-slatism" advocated by Watson or Montagu. This revised state of affairs was summarized in books aimed at a popular audience from the late 1990s. In '' The Nurture Assumption: Why Children Turn Out the Way They Do'' (1998),

Judith Rich Harris Judith Rich Harris (February 10, 1938 – December 29, 2018) was an American psychology researcher and the author of '' The Nurture Assumption'', a book criticizing the belief that parents are the most important factor in child development, and pr ...

was heralded by

Steven Pinker Steven Arthur Pinker (born September 18, 1954) is a Canadian-American cognitive psychology, cognitive psychologist, psycholinguistics, psycholinguist, popular science author, and public intellectual. He is an advocate of evolutionary psycholo ...

as a book that "will come to be seen as a turning point in the

history of psychology Psychology is defined as "the scientific study of behavior and mental processes". Philosophical interest in the human mind and behavior dates back to the ancient civilizations of Egypt, Persia, Greece, China, and India. Psychology as a field of ...

." However, Harris was criticized for exaggerating the point of "parental upbringing seems to matter less than previously thought" to the implication that "parents do not matter." The situation as it presented itself by the end of the 20th century was summarized in '' The Blank Slate: The Modern Denial of Human Nature'' (2002) by

. The book became a best-seller, and was instrumental in bringing to the attention of a wider public the paradigm shift away from the behaviourist purism of the 1940s to 1970s that had taken place over the preceding decades. Pinker portrays the adherence to pure ''blank-slatism'' as an ideological

dogma Dogma, in its broadest sense, is any belief held definitively and without the possibility of reform. It may be in the form of an official system of principles or doctrines of a religion, such as Judaism, Roman Catholicism, Protestantism, or Islam ...

linked to two other dogmas found in the dominant view of human nature in the 20th century: # "

noble savage In Western anthropology, Western philosophy, philosophy, and European literature, literature, the Myth of the Noble savage refers to a stock character who is uncorrupted by civilization. As such, the "noble" savage symbolizes the innate goodness a ...

," in the sense that people are born good and corrupted by bad influence; and # "

ghost in the machine The "ghost in the machine" is a term originally used to describe and critique the concept of the mind existing alongside and separate from the body. In more recent times, the term has several uses, including the concept that the intellectual part ...

," in the sense that there is a human soul capable of moral choices completely detached from biology. Pinker argues that all three dogmas were held onto for an extended period even in the face of evidence because they were seen as ''desirable'' in the sense that if any human trait is purely conditioned by culture, any undesired trait (such as crime or aggression) may be engineered away by purely cultural (political means). Pinker focuses on reasons he assumes were responsible for unduly repressing evidence to the contrary, notably the fear of (imagined or projected) political or ideological consequences.

Heritability estimates

The term ''heritability'' refers only to the degree of genetic variation between people on a trait. It does not refer to the degree to which a trait of a particular individual is due to environmental or genetic factors. The traits of an individual are always a complex interweaving of both. Pinker, Steven. 2002. '' The Blank Slate: The Modern Denial of Human Nature'' (1st ed.).

Viking Press Viking Press (formally Viking Penguin, also listed as Viking Books) is an American publishing company owned by Penguin Random House. It was founded in New York City on March 1, 1925, by Harold K. Guinzburg and George S. Oppenheimer and then acqu ...

.
Lay summary
For an individual, even strongly genetically influenced, or "obligate" traits, such as eye color, assume the inputs of a typical environment during ontogenetic development (e.g., certain ranges of temperatures, oxygen levels, etc.). In contrast, the "heritability index" statistically quantifies the extent to which variation ''between individuals'' on a trait is due to variation in the genes those individuals carry. In animals where breeding and environments can be controlled experimentally, heritability can be determined relatively easily. Such experiments would be unethical for human research. This problem can be overcome by finding existing populations of humans that reflect the experimental setting the researcher wishes to create. One way to determine the contribution of genes and environment to a trait is to study twins. In one kind of study,

identical twins Twins are two offspring produced by the same pregnancy.MedicineNet > Definition of Twin Last Editorial Review: 19 June 2000 Twins can be either ''monozygotic'' ('identical'), meaning that they develop from one zygote, which splits and forms two e ...

reared apart are compared to randomly selected pairs of people. The twins share identical genes, but different family environments. Twins reared apart are not assigned at random to foster or adoptive parents. In another kind of twin study, identical twins reared together (who share family environment and genes) are compared to

fraternal twins Twins are two offspring produced by the same pregnancy.MedicineNet > Definition of Twin Last Editorial Review: 19 June 2000 Twins can be either ''monozygotic'' ('identical'), meaning that they develop from one zygote, which splits and forms two e ...

reared together (who also share family environment but only share half their genes). Another condition that permits the disassociation of genes and environment is

adoption Adoption is a process whereby a person assumes the parenting of another, usually a child, from that person's biological or legal parent or parents. Legal adoptions permanently transfer all rights and responsibilities, along with filiation, fro ...

. In one kind of

adoption study Adoption studies typically compare pairs of persons, e.g., adopted child and adoptive mother or adopted child and biological mother, to assess genetic and environmental influences on behavior. These studies are one of the classic research methods o ...

, biological siblings reared together (who share the same family environment and half their genes) are compared to adoptive siblings (who share their family environment but none of their genes). In many cases, it has been found that genes make a substantial contribution, including psychological traits such as intelligence and personality. Yet heritability may differ in other circumstances, for instance environmental deprivation. Examples of low, medium, and high heritability traits include: Twin and adoption studies have their methodological limits. For example, both are limited to the range of environments and genes which they sample. Almost all of these studies are conducted in Western countries, and therefore cannot necessarily be extrapolated globally to include non-western populations. Additionally, both types of studies depend on particular assumptions, such as the

equal environments assumption Twin studies are studies conducted on identical or fraternal twins. They aim to reveal the importance of environmental and genetic influences for traits, phenotypes, and disorders. Twin research is considered a key tool in behavioral genetics a ...

in the case of twin studies, and the lack of pre-adoptive effects in the case of adoption studies. Since the definition of "nature" in this context is tied to "heritability", the definition of "nurture" has consequently become very wide, including any type of causality that is not heritable. The term has thus moved away from its original connotation of "cultural influences" to include all effects of the environment, including; indeed, a substantial source of environmental input to

human nature Human nature comprises the fundamental dispositions and characteristics—including ways of Thought, thinking, feeling, and agency (philosophy), acting—that humans are said to have nature (philosophy), naturally. The term is often used to denote ...

may arise from stochastic variations in prenatal development and is thus in no sense of the term "cultural".

Gene–environment interaction

The interactions of genes with environment, called ''gene–environment interactions'', are another component of the nature–nurture debate. A classic example of gene–environment interaction is the ability of a diet low in the amino acid

phenylalanine Phenylalanine (symbol Phe or F) is an essential α-amino acid with the chemical formula, formula . It can be viewed as a benzyl group substituent, substituted for the methyl group of alanine, or a phenyl group in place of a terminal hydrogen of ...

to partially suppress the genetic disease

phenylketonuria Phenylketonuria (PKU) is an inborn error of metabolism that results in decreased metabolism of the amino acid phenylalanine. Untreated PKU can lead to intellectual disability, seizures, behavioral problems, and mental disorders. It may also r ...

. Yet another complication to the nature–nurture debate is the existence of gene–environment correlations. These correlations indicate that individuals with certain genotypes are more likely to find themselves in certain environments. Thus, it appears that genes can shape (the selection or creation of) environments. Even using experiments like those described above, it can be very difficult to determine convincingly the relative contribution of genes and environment. The analogy "genetics loads the gun, but environment pulls the trigger" has been attributed to Judith Stern. Heritability refers to the origins of differences between people. Individual development, even of highly heritable traits, such as eye color, depends on a range of environmental factors, from the other genes in the organism, to physical variables such as temperature, oxygen levels etc. during its development or ontogenesis. The variability of trait can be meaningfully spoken of as being due in certain proportions to genetic differences ("nature"), or environments ("nurture"). For highly penetrant

Mendelian Mendelian inheritance (also known as Mendelism) is a type of biological inheritance following the principles originally proposed by Gregor Mendel in 1865 and 1866, re-discovered in 1900 by Hugo de Vries and Carl Correns, and later popularized ...

genetic disorders such as

Huntington's disease Huntington's disease (HD), also known as Huntington's chorea, is an incurable neurodegenerative disease that is mostly Genetic disorder#Autosomal dominant, inherited. It typically presents as a triad of progressive psychiatric, cognitive, and ...

virtually all the incidence of the disease is due to genetic differences. Huntington's animal models live much longer or shorter lives depending on how they are cared for. At the other extreme, traits such as

native language A first language (L1), native language, native tongue, or mother tongue is the first language a person has been exposed to from birth or within the critical period hypothesis, critical period. In some countries, the term ''native language'' ...

are environmentally determined: linguists have found that any child (if capable of learning a language at all) can learn any human language with equal facility. With virtually all biological and psychological traits, however, genes and environment work in concert, communicating back and forth to create the individual. At a molecular level, genes interact with signals from other genes and from the environment. While there are many thousands of single-gene-locus traits, so-called

complex traits Complex traits are phenotypes that are controlled by two or more genes and do not follow Mendel's Law of Dominance. They may have a range of expression which is typically continuous. Both environmental and genetic factors often impact the variat ...

are due to the additive effects of many (often hundreds) of small gene effects. A good example of this is height, where variance appears to be spread across many hundreds of loci. Extreme genetic or environmental conditions can predominate in rare circumstances—if a child is born mute due to a

genetic mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mitosis ...

, it will not learn to speak any language regardless of the environment; similarly, someone who is practically certain to eventually develop Huntington's disease according to their genotype may die in an unrelated accident (an environmental event) long before the disease will manifest itself. Genes x environment heritability two buckets view diagram

Genes x environment heritability two buckets view diagram

Genes x environment heritability homogenous mudpie view diagram

likewise described several examples:When traits are determined by a complex interaction of

genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...

and environment it is possible to measure the

of a trait within a population. However, many non-scientists who encounter a report of a trait having a certain percentage heritability imagine non-interactional, additive contributions of genes and environment to the trait. As an analogy, some laypeople may think of the degree of a trait being made up of two "buckets," genes and environment, each able to hold a certain capacity of the trait. But even for intermediate heritabilities, a trait is always shaped by both genetic dispositions and the environments in which people develop, merely with greater and lesser plasticities associated with these heritability measures. Heritability measures always refer to the degree of ''variation between individuals in a population''. That is, as these statistics cannot be applied at the level of the individual, it would be incorrect to say that while the heritability index of personality is about 0.6, 60% of one's personality is obtained from one's parents and 40% from the environment. To help to understand this, imagine that all humans were genetic clones. The heritability index for all traits would be zero (all variability between clonal individuals must be due to environmental factors). And, contrary to erroneous interpretations of the heritability index, as societies become more egalitarian (everyone has more similar experiences) the heritability index goes up (as environments become more similar, variability between individuals is due more to genetic factors). One should also take into account the fact that the variables of heritability and environmentality are not precise and vary within a chosen population and across cultures. It would be more accurate to state that the degree of heritability and environmentality is measured in its reference to a particular phenotype in a chosen group of a population in a given period of time. The accuracy of the calculations is further hindered by the number of coefficients taken into consideration, age being one such variable. The display of the influence of heritability and environmentality differs drastically across age groups: the older the studied age is, the more noticeable the heritability factor becomes, the younger the test subjects are, the more likely it is to show signs of strong influence of the environmental factors. For example, one study found no statistically significant difference in self-reported wellbeing between middle-aged

monozygotic Twins are two offspring produced by the same pregnancy.MedicineNet > Definition of Twin Last Editorial Review: 19 June 2000 Twins can be either ''monozygotic'' ('identical'), meaning that they develop from one zygote, which splits and forms two e ...

twins separated at birth and those reared in the same household, suggesting that happiness in middle-aged adults is not based in environmental factors related to family rearing. The same result was also found among middle-aged

dizygotic Twins are two offspring produced by the same pregnancy.MedicineNet > Definition of Twin Last Editorial Review: 19 June 2000 Twins can be either ''monozygotic'' ('identical'), meaning that they develop from one zygote, which splits and forms two e ...

twins. Furthermore, there was significantly more variance in the dizygotic twins' self-reported wellbeing than there was in the monozygotic group. Genetic similarity has thus been estimated to account for around 50% of the variance in adult happiness at a given point in time, and as much as 80% of the variance in long-term happiness stability. Other studies have similarly found the heritability of happiness to be around 0.35–0.50. Some have pointed out that environmental inputs affect the expression of genes. This is one explanation of how environment can influence the extent to which a genetic disposition will actually manifest.

Obligate vs. facultative adaptations

Traits may be considered to be adaptations (such as the umbilical cord), byproducts of adaptations (the belly button) or due to random variation (convex or concave belly button shape). An alternative to contrasting nature and nurture focuses on "

obligate {{wiktionary, obligate As an adjective, obligate means "by necessity" (antonym '' facultative'') and is used mainly in biology in phrases such as: * Obligate aerobe, an organism that cannot survive without oxygen * Obligate anaerobe, an organism ...

vs. facultative" adaptations. Adaptations may be generally more obligate (robust in the face of typical environmental variation) or more facultative (sensitive to typical environmental variation). For example, the rewarding sweet taste of sugar and the pain of bodily injury are obligate psychological adaptations—typical environmental variability during development does not much affect their operation. On the other hand, facultative adaptations are somewhat like "if-then" statements. An example of a facultative psychological adaptation may be adult

attachment style Attachment theory is a psychological and evolutionary framework, concerning the relationships between humans, particularly the importance of early bonds between infants and their primary caregivers. Developed by psychiatrist and psychoanalys ...

. The attachment style of adults, (for example, a "secure attachment style," the propensity to develop close, trusting bonds with others) is proposed to be conditional on whether an individual's early childhood caregivers could be trusted to provide reliable assistance and attention. An example of a facultative physiological adaptation is tanning of skin on exposure to sunlight (to prevent skin damage). Facultative social adaptation have also been proposed. For example, whether a society is warlike or peaceful has been proposed to be conditional on how much collective threat that society is experiencing.

Advanced techniques

Quantitative studies Quantitative may refer to: * Quantitative research, scientific investigation of quantitative properties * Quantitative analysis (disambiguation) * Quantitative verse, a metrical system in poetry * Statistics, also known as quantitative analysis * ...

of heritable traits throw light on the question. Developmental genetic analysis examines the effects of genes over the course of a human lifespan. Early studies of intelligence, which mostly examined young children, found that

measured 40–50%. Subsequent developmental genetic analyses found that variance attributable to additive environmental effects is less apparent in older individuals, with estimated heritability of IQ increasing in adulthood. Multivariate genetic analysis examines the genetic contribution to several traits that vary together. For example, multivariate genetic analysis has demonstrated that the genetic determinants of all specific cognitive abilities (e.g., memory, spatial reasoning, processing speed) overlap greatly, such that the genes associated with any specific cognitive ability will affect all others. Similarly, multivariate genetic analysis has found that genes that affect scholastic achievement completely overlap with the genes that affect cognitive ability. Extremes analysis examines the link between normal and pathological traits. For example, it is hypothesized that a given behavioral disorder may represent an extreme of a continuous distribution of a normal behavior and hence an extreme of a continuous distribution of genetic and environmental variation. Depression, phobias, and reading disabilities have been examined in this context. For a few highly heritable traits, studies have identified loci associated with variance in that trait, for instance in some individuals with

schizophrenia Schizophrenia () is a mental disorder characterized variously by hallucinations (typically, Auditory hallucination#Schizophrenia, hearing voices), delusions, thought disorder, disorganized thinking and behavior, and Reduced affect display, f ...

. The budding field of epigenetics has conducted research showing that hereditable conditions like schizophrenia, which have an 80% hereditability with only 10% of those who have inherited the trait actually displaying Schizophrenic traits. New research is showing that gene expression can happen in adults due to environmental stimuli. For example, people with schizophrenic gene have a genetic predisposition for this illness but the gene lays dormant in most people. However, if introduced to chronic stress or introducing some amphetamines it caused the methyl groups to stick to hippocampi histones.

Intelligence

Heritability of intelligence

Cognitive functions have a significant genetic component. A 2015 meta-analysis of over 14 million twin pairs found that genetics explained 57% of the variability in cognitive functions. Evidence from

behavioral genetic Behavioural genetics, also referred to as behaviour genetics, is a field of scientific research that uses genetic methods to investigate the nature and origins of individual differences in behaviour. While the name "behavioural genetics" c ...

research suggests that family environmental factors may have an effect upon childhood IQ, accounting for up to a quarter of the variance. The

American Psychological Association The American Psychological Association (APA) is the main professional organization of psychologists in the United States, and the largest psychological association in the world. It has over 170,000 members, including scientists, educators, clin ...

's report " Intelligence: Knowns and Unknowns" (1995) states that there is no doubt that normal child development requires a certain minimum level of responsible care. Here, environment is playing a role in what is believed to be fully genetic (intelligence) but it was found that severely deprived, neglectful, or abusive environments have highly negative effects on many aspects of children's intellect development. Beyond that minimum, however, the role of family experience is in serious dispute. On the other hand, by late adolescence this correlation disappears, such that adoptive siblings no longer have similar IQ scores.Plomin, R., J. C. DeFries, G. E. McClearn, and P. McGuffn. 2008. ''Behavioral Genetics'' (5th ed.). New York: Worth Publishers. Moreover, adoption studies indicate that, by adulthood, adoptive siblings are no more similar in IQ than strangers (IQ correlation near zero), while full siblings show an IQ correlation of 0.6. Twin studies reinforce this pattern: monozygotic (identical) twins raised separately are highly similar in IQ (0.74), more so than dizygotic (fraternal) twins raised together (0.6) and much more than adoptive siblings (≈0.0). Recent adoption studies also found that supportive parents can have a positive effect on the development of their children.

Environmental role on IQ

Other studies have focused on environmental factors that may affect IQ. For example, research has shown that factors such as access to education, nutrition, and social support can have a significant impact on IQ. Furthermore, research has suggested that certain experiences during early childhood, such as exposure to lead or other environmental toxins, can have a negative impact on IQ. Studies have consistently shown that environmental factors can have a significant impact on IQ. Access to quality education has been found to have a positive effect on IQ, with one study indicating that access to quality preschool education had a lasting impact on IQ scores up to age 35. Malnutrition in early childhood has been linked to lower IQ scores later in life, while supplementation with certain nutrients such as iron and iodine has been shown to improve IQ scores. Social support is also an important environmental factor that positively affects IQ, with one study indicating that children who received high levels of emotional support from their mothers had higher IQ scores than those who received low levels of emotional support.

Personality traits

Personality Personality is any person's collection of interrelated behavioral, cognitive, and emotional patterns that comprise a person’s unique adjustment to life. These interrelated patterns are relatively stable, but can change over long time per ...

is a frequently cited example of a heritable trait that has been studied in twins and adoptees using

study designs. The most famous categorical organization of heritable personality traits were defined in the 1970s by two research teams led by Paul Costa & Robert R. McCrae and Warren Norman & Lewis Goldberg in which they had people rate their personalities on 1000+ dimensions they then narrowed these down into " ''The Big Five''" factors of personality—openness, conscientiousness, extraversion, agreeableness, and neuroticism. Studies have found that extraversion has a genetic component, with estimates of heritability ranging from 30% to 50%. The close genetic relationship between positive personality traits and, for example, our happiness traits are the mirror images of comorbidity in psychopathology. These personality factors were consistent across cultures, and many studies have also tested the heritability of these traits. Personal agency also factors into this debate. While genetic and environmental factors can shape personality, individuals also have agency in shaping their own personality through their choices, behaviors, and attitudes. For example, one study found that college students who participated in study abroad programs scored higher on measures of openness to experience compared to those who did not participate. Another study found that individuals who lived in diverse neighborhoods were more likely to score higher on openness to experience compared to those who lived in more homogenous neighborhoods. Identical twins reared apart are far more similar in personality than randomly selected pairs of people. Likewise, identical twins are more similar than fraternal twins. Also, biological siblings are more similar in personality than adoptive siblings. Each observation suggests that personality is heritable to a certain extent. A supporting article had focused on the heritability of personality (which is estimated to be around 50% for subjective well-being) in which a study was conducted using a representative sample of 973 twin pairs to test the heritable differences in subjective well-being which were found to be fully accounted for by the genetic model of the Five-Factor Model's personality domains. However, these same study designs allow for the examination of environment as well as genes. Adoption studies also directly measure the strength of shared family effects. Adopted siblings share only family environment. Most adoption studies indicate that by adulthood the personalities of adopted siblings are little or no more similar than random pairs of strangers. This would mean that shared family effects on personality are zero by adulthood. In the case of personality traits, non-shared environmental effects are often found to out-weigh shared environmental effects. That is, environmental effects that are typically thought to be life-shaping (such as family life) may have less of an impact than non-shared effects, which are harder to identify. One possible source of non-shared effects is the environment of pre-natal development. Random variations in the genetic program of development may be a substantial source of non-shared environment. These results suggest that "nurture" may not be the predominant factor in "environment". Environment and our situations, do in fact impact our lives, but not the way in which we would typically react to these environmental factors. We are preset with personality traits that are the basis for how we would react to situations. An example would be how extraverted prisoners become less happy than introverted prisoners and would react to their incarceration more negatively due to their preset extraverted personality. Behavioral genes are somewhat proven to exist when we take a look at fraternal twins. When fraternal twins are reared apart, they show the same similarities in behavior and response as if they have been reared together.

Genetics

The relationship between personality and people's own well-being is influenced and mediated by genes. There has been found to be a stable set point for happiness that is characteristic of the individual (largely determined by the individual's genes). Happiness fluctuates around that setpoint (again, genetically determined) based on whether good things or bad things are happening to us ("nurture"), but only fluctuates in small magnitude in a normal human. The midpoint of these fluctuations is determined by the "great genetic lottery" that people are born with, which leads them to conclude that how happy they may feel at the moment or over time is simply due to the luck of the draw, or gene. This fluctuation was also not due to educational attainment, which only accounted for less than 2% of the variance in well-being for women, and less than 1% of the variance for men. They consider that the individualities measured together with personality tests remain steady throughout an individual's lifespan. They further believe that human beings may refine their forms or personality but can never change them entirely. Darwin's Theory of Evolution steered naturalists such as George Williams and William Hamilton to the concept of personality evolution. They suggested that physical organs and also personality is a product of natural selection. With the advent of gene sequencing, it has become possible to search for and identify specific gene polymorphisms that affect traits such as IQ and personality. These techniques work by tracking the association of differences in a trait of interest with differences in specific molecular markers or functional variants. An example of a visible human trait for which the precise genetic basis of differences are relatively well known is

eye color Eye color is a polygene, polygenic phenotypic trait determined by two factors: the pigmentation of the eye's Iris (anatomy), iris and the frequency-dependence of the scattering of light by the Turbidity, turbid medium in the Stroma of iris, str ...

. In contrast to views developed in 1960s that gender identity is primarily learned (which led to a protocol of surgical sex changes in male infants with injured or malformed genitals, such as

David Reimer David Reimer (born Bruce Peter Reimer; 22 August 1965 – 4 May 2004) was a Canadian man raised as a girl following medical advice and intervention after his penis was severely injured during a botched circumcision in infancy. The psychologis ...

), genomics has provided solid evidence that both sex and gender identities are primarily influenced by genes:

References

External links

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Meta-analysis of twin correlations and heritability
{{Authority control 20th-century controversies Human behavior Human development Personality theories Race and intelligence controversy Biology controversies Dilemmas Human genetics Psychology controversies Evolutionary psychology