 We often hear that some scientists identify genes associated with violent crime, depression and other psychological threats. We even hear that if someone is beautiful or intelligent, it is because this person has won the genetic lottery. Today, it is very common to attribute many unexplained phenomena to our DNA. While some researchers aim at discovering genes for cancer, heart disease or schizophrenia, we should keep in mind that the reality is highly complex and genetics cannot explain everything. My name is Robin Wallast, I'm a doctor in psychology and in this video we will discuss a popular debate that centers around the effect innate attributes have on human behavior as opposed to the influences that social environments might have. This is the timeless debate of nature versus nurture. Nature refers to all innate biological forces that influence who we are such as genes and hereditary factors. Nature is expressed through a height or skin and eye color. Nature manifests also in genetic disorders like Down syndrome or cystic fibrosis. On the other hand, nurture refers to all the environmental variables such as life experiences and learning. Nurture manifests in how we were raised or social relationships and or surrounding culture. So are we a project of nature or nurture? In 1874, Galton, one of the pioneers of the use of twin studies, introduced the term nature, nurture. And argued that personality traits such as criminality and intelligence are hereditary and he promotes eugenic programs encouraging more intelligent and less criminal people to marry and breed more together. The rationale developed by Galton totally opposed the ideas of philosopher John Locke who thought we had no innate ideas. According to his theory of tabula rasa, Locke suggested that human minds are blank slates upon which experience writes. For him, nurture is everything whereas nature is nothing. In the early 20th century, the main schools of thought analyzing human behavior were behaviorism and psychoanalysis. Although very different, these two approaches share the same view and consider the role of experience and environment, or nurture, as prevalent factors to understanding the behavior of humans. Since the 1970s, the emergence of genetics which adopts a nature perspective on human behavior suggests that our genes play an important role in the way we behave, think and feel. Importantly, scholars demonstrated that opposing nature and nurture is misleading because genes combined with the environment are key components to understanding how complex human physical and psychological traits are established. During this period, scientists conducted twin studies that allowed them to pull apart and examine genetic and environmental influences. Studying monozygotic or identical twins became so crucial because these siblings shared the same DNA, offering a possibility to decipher to what extent similarity is caused by genes and how much of it is due to a shared environment. The main conclusion from these numerous twin studies is that both genetic and environmental components equally influence human behaviors in terms of magnitude, and it is extremely difficult for scientists to disentangle whether nature or nurture is a primary driver for human behavior. Although these are great advances, experts often consider both nature and nurture independently, especially in the context of the treatments of mental health disorders. For instance, endogenous depression, such as melancholia would be caused only by genetic and biological factors. The term endogenous is defined in psychiatry as a disease which is not attributable to any external or environmental factor. Endogenous depression is therefore cured mainly or exclusively with chemical treatments, while other types of depression result from psychological causes will be treated with different methods associated with nurture, such as psychotherapy or parenting guidance. In sum, considering genetic and psychological causes independently is a fatal flaw because it can lead to overmedication and negation of certain facets of the human mind. To overcome this limitation, scientists propose an interdisciplinary model to better capture people's subjective experience. This is the bio-psycho-social model interacting biological, psychological and social factors affecting an individual. Recently, scientific discoveries revolutionized the nature versus nurture debate and came to the conclusion that both nature and nurture are interwoven with one another. As we have seen, genes have an influence on the environments we experience in the way we perceive, think and feel about the world. At the same time, an emerging area of research called epigenetics describes how environmental influences, such as childhood experiences, affect the expression of our genes. This means that a person's environment and experience can directly generate DNA modifications and regulation. These chemical modifications to single genes due to environmental influences are known as epigenetic changes. What does that mean? Well, let me show you a study on rats. A team of researchers led by Michael Meny compared two groups of rat mothers. The first group contained rat mothers who often licked, groomed and nursed their rat babies where the second group contained rat mothers who seemed to ignore their babies. Rat babies who had been highly nurtured tend to be relaxed adults, while rat babies who were ignored tend to be anxious adults. The researchers found that when rat babies became adults, they reproduced the same pattern of behavior as their mother had and started nurturing or ignoring their own babies which in turn passed it on the next generation and so on. To go further, the researchers wondered if this transmission of behavior was purely genetic. To test these assumptions, the researchers simply interchanged babies from low-nurturing mothers with babies from high-nurturing mothers. Interestingly, they found that babies who were raised by high-nurturing mothers became a high-nurture too, regardless of the genes of their biological mothers. So, is the transmission of behavior only related to the environment, to nurture, and so genes have nothing to do with it? To answer this question, the researchers looked directly into the DNA of rats and found significant differences between high-nurture versus low-nurture mothers. The nurturing behavior of rat mothers during the first week of life altered her baby's epigenomes and this evolved epigenetic pattern persisted into adulthood. Specifically, researchers demonstrated that among newborns rat-raised by low-nurturing mothers, certain chemical marks such as metal groups silenced the genes while these marks disappeared among newborn rat-raised by high-nurturing mothers. In other words, through her maternal behavior, a mother rat can write information onto her baby's DNA. Doing so, she gives her baby information about the world they will grow up in and programs their DNA in a way that they will make them more likely to adapt themselves. But what about humans? What about us? Psychologists evidence that early experiences such as abuse, family strife and emotional neglect can increase depression, anxiety and other forms of disorders. These early experiences could leave marks on people's DNA and influence their behavior. Moreover, these marks stacked on the genome can be passed down from generation to generation. However, through epigenetic mechanisms, your lifestyle can positively shape your biology through developing good eating attitudes, exercising, practicing meditation, engaging in psychotherapy and avoiding bad habits like smoking and drinking. These good habits can be observed at the DNA level. To summarize, you cannot help who you are but you can decide what you become. Thank you for watching. Leave a positive mark on your DNA by subscribing to my channel for more content like this. Stay safe and healthy. Bye.