Unit 3: Understanding Human Nature

Every species has characteristics that distinguish it from every other species. These characteristics include physical traits (including brains) and behaviors, as well as the blueprints for producing these differences, which are genes. In psychology, the science of behavior and mental processes, we are interested in the genes, brains, and behaviors that make up our unique human nature. The subfield of psychology that is most directly concerned with human nature is biopsychology.

Many of the most exciting developments in psychology over the past couple of decades are related to the discovery of the biological underpinnings of human behavior and mental processes. Throughout the 1990s researchers made countless discoveries about the brain; more recently, many important discoveries have been made in genetics. To understand modern psychology, then, you must have a firm grasp of biopsychology (and the biological perspective, the application of biological thinking to any individual topic in psychology).

A 2019 survey published by United Health Services reported that 97% of US respondents agreed that mental illnesses are medical illnesses that can be treated effectively like chronic physical disorders (UHS, 2019). This is a much higher percentage than even 20 years ago, when only 55% of respondents agreed that “depression is a disease and not a ‘state of mind that a person can snap out of.” Now, of course, these are different questions, and there are likely other differences in the survey methods that make it hard to compare these numbers. It is hard to argue against the conclusion that many more people today believe that mental illnesses are medical illnesses, however. Other surveys paint a somewhat different picture, however. The American Psychological Association published a survey reporting that 55% of respondents agreed that mental illnesses are different from serious physical illnesses. So, they might be medical illnesses, but they are apparently not the same type as illnesses like cancer and heart disease, according to many members of the public (APA, 2019).

In order to have any hope of formulating an informed opinion on this question, you would need at least two things. First is some knowledge of the biological workings of “human behavior and mental processes.” That, in a nutshell, is the major goal of this Unit. The second thing you would need you will find near the end of the book: a description of the biological factors involved in depression and other mental illnesses.

But first things first, the basics. We are not saying that you need to be an expert in biology, although that would certainly work. It is simply the case, however, that if you want to understand psychological phenomena and to have informed opinions about issues such as mental illness, your best defense is to learn some details about the biological underpinnings of psychology. What does it mean when researchers report that depression is an imbalance of brain chemicals? If personality is genetic, does that mean that it can never change? If your eyes convert light energy directly into brain activity, how can you be fooled by visual illusions? You can only answer these questions, and many others like them, with a solid understanding of biopsychology.

Many students are surprised to discover the importance of biology to psychology. In fact, psychology majors who intend to go on to graduate school should strongly consider taking the biology sequence that is intended for biology majors. It really is that important. It is not particularly difficult to convince students that biology is important for psychology. One only needs to look at a representative list of recent research articles in psychology to see the profound influence of biology. That does not necessarily make biopsychology easy, though, as many students struggle with it. There are at least two reasons why many students have difficulty understanding the biological perspective. Although the reasons may seem unrelated at first, they are not.

First, there is an extraordinary quantity of biological information. For example, in a typical biopsychology chapter of a General Psychology textbook, a student may be asked to memorize 15 or more divisions or parts of the brain, each with a specific function or two. Then, they have to learn the complex and confusing process by which the individual cells of the nervous system, neurons, generate and transmit electrochemical signals. Suffice it to say that many students find this an overwhelming task.

Second is the matter of what Francis Crick called the “astonishing hypothesis.” As many psychology instructors like to say, all human behavior and mental processes result from the tiny process of electrical particle exchange on the surface of a nerve cell and the chemical transfer of the signal to neighboring nerve cells. To put it mildly, that idea is just weird and very difficult to accept. As Crick, winner of the Nobel Prize with James Watson for their discovery of the structure of DNA, more eloquently put it:

“Your joys and your sorrows, your memories and your ambitions, your sense of personal identity and free will, are in fact no more than the behavior of a vast assembly of nerve cells and their associated molecules. . . This hypothesis is so alien to the ideas of most people alive today that it can truly be called astonishing.” (Crick, 1994)

Because people have difficulty with the very premise that everything we do and are comes from “the behavior of a vast assembly of nerve cells,” the whole enterprise seems unorganized and disconnected. As we explained in Module 5, material for which we do not see the organization is very difficult to remember, precisely because it is difficult to understand. We will address the “astonishing hypothesis” and offer a way to help you accept it in section 10.1 when we describe the behavior of nerve cells.

Unit 3 contains five modules:

Module 10, How Biology and Psychology Are Linked, introduces you to some of the fundamental principles, issues, and controversies associated with biopsychology.

Module 11, Brain and Behavior, leads you through the organization and parts of the nervous system, especially the brain and its most important individual cells, neurons.

Module 12, How the Outside World Gets into the Brain: Sensation, describes the important processes involved in translating stimulus energy from the world into neural signals

Module 13, How the Brain Interprets Sensations: Perception, picks up where Module 12 left off, providing details about how the brain organizes and recognizes those neural signals so that we can make sense out of the input.

Module 14, “Biopsychology: Bringing Human Nature into Focus,” places the subfield in a historical context and wraps up with some current issues and controversies.