BBB - Interaction of Heredity and Environment Lesson

Learning Targets:

Discuss how heredity and environmental factors influence behavior and mental processes.
Explain how evolutionary psychologists apply natural selection to understand behavioral tendencies.
Explain how behavior genetics accounts for individual variations.
Describe how twin and adoption studies enhance our understanding of the influence and interplay of genetic and environmental factors.
Describe the collaborative role of heredity and the environment in shaping individuals.

Courtesy of the AP psychology course and exam description, effective fall 2024. (n.d.). Links to an external site.

Heredity and the Environment

A significant debate in psychology revolves around the impact of nature versus nurture on human behavior. What influences us more - our genes and heredity (nature) or our experiences (nurture)? By applying the principle of natural selection to behavioral tendencies, evolutionary psychologists address this debate. Psychologists who specialize in biological psychology are particularly interested in the relationship between our biological (genes, neurons, etc.) processes and our psychological processes.

Charles Darwin

Charles Darwin, a British naturalist, made significant contributions to psychology's study of heredity and environment. His theory of evolution by natural selection proposed that species evolve through a process of variation and selection, with those most adapted to their environment having a higher probability of surviving and reproducing.

Darwin's theory had profound implications for studying heredity and environment in psychology. He argued that certain traits are inherited through genes but that environmental factors can also play a role in shaping behavior. This concept is known as nature versus nurture.

Darwin's emphasis on adaptation and survival continues to impact psychology, shedding light on human motivation and decision-making. By scrutinizing the role of evolutionary history in human behavior, evolutionary psychology explores the commonalities rooted in our shared biology. Meanwhile, behavior genetics examines individual differences resulting from unique combinations of genes and environments. In this field, researchers examine the intricate relationship between biological and environmental factors in shaping psychological events, including the predisposition of gender differences and the influence of heredity on intelligence and personality.

Evolutionary Psychology of Human Behavior

We are all born with certain genes that predispose us to be a certain way. They determine our height, weight, facial features, and behavior.

Nature plays a significant role in shaping who we are as individuals. The genetic makeup we inherit from our parents determines our physical characteristics and behavioral tendencies. Everyone is born with a unique genetic pattern, representing just 0.1% of our DNA. This small percentage is crucial in determining various aspects of our personalities, from exceptional achievements to potential challenges like sociopathic behavior.

Evolutionary Psychology

Evolutionary psychology explores how a change in environment over generations influences the development of certain characteristics. By studying how our ancestors overcame challenges, this field seeks to explain universal behaviors. Evolutionary psychologists study how essential traits for survival are passed down through generations based on natural selection. Darwin's theory of natural selection is fundamental to understanding human behavior and mental processes, emphasizing how species adapt to their environment.

Future generations will likely inherit successful traits that enhance reproductive and survival capabilities. Even though we are genetically predisposed to survive, some behaviors are mismatched with the modern world. Our preference for high-calorie foods, once vital for survival, now contributes to contemporary health issues, such as obesity. The study of evolutionary psychology reveals how our biological ancestors' experiences shaped our present-day traits, emphasizing the interplay between nature and nurture in human behavior.

Behavior Genetics

The study of behavior genetics examines the intricate interplay between our genetics and the environment that shapes who we are. Genes, inherited from our parents, are like a recipe book that shapes our individuality. Similarly to a recipe book, which contains different ingredients and instructions for cooking different dishes, our genes, which consist of about 20,000 genes, provide the instructions for creating the features that define us. Like ingredients in a recipe, these genes determine our physical characteristics and behaviors. Genes may be more active in some people, depending on their environment, but the combination of genetic predispositions and environmental factors makes us so uniquely diverse.

Behavior genetics not only illuminates the common behavioral tendencies among individuals, but also highlights how genetic inheritance and environmental influences contribute to our social diversity. Using genetics and environment as tools for understanding human differences, we gain a deeper understanding of what shapes our individuality and how nature and nurture interact to shape us.

Image depicting a cell, which contains a nucleus, which contains a chromosome, which contains DNA

Types of Twins

Identical (Monozygotic) share a placenta and are from one sperm and egg.

Fraternal (Dizygotic) have separate placentas and are from different sperm and eggs.

Identical vs. Fraternal Twins

By studying twin and adoption patterns, behavioral genetic scientists gain valuable insights into how behavioral traits are passed down and influenced. These studies offer a unique lens through which to explore the impact of different environments on our development. Identical twins, or monozygotic twins, develop from a single fertilized egg that splits, making them genetically identical to nature's human clones. They share not only the same genes but also the same conception, uterus, birth date, and often cultural history. Despite this genetic similarity, identical twins may differ in their number of gene copies and brain-wiring structures. Additionally, most identical twins share a placenta during prenatal development, but not all.

Fraternal or dizygotic twins develop from two separate fertilized eggs and are no more genetically similar than regular siblings. Shared genes play a role in shared experiences, such as having a higher risk of a specific medical condition in one twin. For instance, compared to fraternal twins, identical twins show more similarities in their interests, hobbies, and even the age at which they may start certain behaviors or habits. An example of this could be two identical twins, both excelling in sports or both having a love for cooking, demonstrating the influence of genetics on shared behaviors and interests.

Please take a moment to watch this video regarding twin studies. Twin studies have been proven to be a useful tool when examining the nature vs. nurture debate. (Watching the video should take approximately 15 minutes)

Watch the video on Twin Studies and Adoption below.

Video Credit: Twin Studies Video https://www.khanacademy.org/embed_video?v=usnv1_xRCvs (Video is licensed under Creative Commons and is attributed to Khan Academy)

How Heredity and Environment Shape Individuals

As a species, humans have an incredible capacity for adaptation. Across different environments, some traits develop similarly, while others are only exhibited under certain conditions. Adaptation involves changing in response to the surrounding environment. This process involves both genes and experiences, which interact rather than act independently. Epigenetics studies the molecular mechanisms through which the environment influences gene expression. Genes adjust themselves based on input. Epigenetic marks are left on genes by life experiences, instructing them to either activate or deactivate certain genes. Gene activity can be affected by external factors like diet, medication, and stress.

Explore each section in the activity below to learn more information on how each factor influences behavior.

Parents

How much credit or blame do parents really deserve in shaping behavior? Freudian psychologists would say a lot! According to Freud we are prisoners of our past and our behaviors and attitudes are a direct reflection of our relationship with our parents.

However, more recent research suggests that parents are not as influential as previously thought. Studies show that parents are very influential in establishing our beliefs and values, but not much more. This can be illustrated by siblings who were raised by the same parents, but developed very different personalities.

Prenatal Environment

Our prenatal environment is where nuture begins. We will discuss this more in the development unit, but what our mother exposes us to during pregnancy can influence who we become. What foods she eats, the environmental conditions, exposure to teratogens all influence our development. This is another great area in which to examine twins. Rarely, identical twins will have separate placentas. In this case the babies are genetically the same but start out being exposed to different environments or placentas. One twin may receive better nutrition thus explaining differences later on.

Experience

Experience and environmental interaction helps develop the brain's neural connections. Experience or exposure to reading, for example, helps prepare our brains for language. Studies with rats have shown the difference in neural connections between a rat raised in an impoverished environment vs. a rat who had rich experiences. The same is true for children who are raised in impoverished vs. enriched environments. Typically by adolescence there are marked differences in intellectual abilities on intelligence scores by adolescence.

Culture

Culture is another environmental factor that influences behavior. Culture is defined as the beliefs, values, and behaviors that are accepted within a group and that are passed down from one generation to the next.

We generally don't recognize the influence of our culture on behavior unless we go against it or travel to places in which the culture is different. Culture also tends to vary over time. What was normal fifty years ago may not be so today.

Gender

Gender roles are a set of expected behaviors for males and females. From the moment a baby i born, we begin treating him/her according to these roles. We dress little girls in pink and little boys in blue and begin buying them gender-specific toys.

Some of the pros associated with having gender roles is that it provides us with a script of what to do in certain social situations. However, if we deviate from these roles, it can cause anxiety.

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