Not Just a Body


An excerpt from Hooked: The Brain Science on How Casual Sex Affects Human Development 

by Dr. Joe McIlhaney, MD

Editor's note: Dr. McIlhaney will be presenting on the topic of Brain Science and Sex at the 2020 Heartbeat International Annual Conference. You can join him to learn more in his workshop on Wednesday (Day 2) of the Conference. Below is an exerpt from the first chapter of his book on the same subject. 


Now that we have defined sex according to physical activity—according to what our bodies are doing—we’re ready to talk about the rest of the story. In order to truly understand why sex sells and why it is so pervasive in our society, we have to understand that humans are not just sex machines or animals. We, as human beings, are so much more.

If we think of sex as only a physical activity to be engaged in at our pleasure, and only for our pleasure, we will be blindsided by problems produced by the misunderstandings and miscalculations of our human nature. If we think our makeup is limited to satisfying appetites, we’ll conclude that we can engage in sexual activity, enjoy it on a physical level, and totally disassociate these acts from the rest of what we are as human beings—but we’ll be sadly mistaken and be blindsided by what might happen to us.

Going back to the time of sexual awakening, important research into the phenomenon of puberty has yielded some important discoveries. It has been found that teenage boys with high testosterone levels were more likely to engage in sexual behaviors than boys with lower hormone levels.1 In girls, early puberty has been linked to early age of first sexual intercourse.2 Yet research has found that parental relationships had the greatest influence on teen sexual behavior.  

So, what’s the point? It is worth remembering that every child’s body and brain transforms as he or she gets older, and this transformation has a huge physical and psychological impact on all things sexual. An intense fascination and desire for sex often accompanies these changes. Yet simply going through puberty or having a sex hormone coursing through a young person’s bloodstream, or even a specific genetic disposition, does not determine the decisions they make about sex. Beneficial factors, such as home environment and adult guidance, can help shepherd an adolescent through this tumultuous period in life. Negative guidance, if it dominates, from peers or the media can make the journey much more difficult.

Finally, it is clear that the brain is still developing during puberty and will continue to do so far after the external physical changes have reached their conclusion.

A 2017 survey of high school adolescents illustrates that sexual activity has more ramifications beyond the physical. The survey showed that both boys and girls who have had sex are more likely to be depressed than their friends who have not. The survey also asked questions regarding considering making a suicide attempt, making a suicide plan, and actually attempting suicide. Those students who had not had sexual contact consistently had lower percentages than their sexually experienced classmates on all questions regarding suicide.3

In all likelihood, none of these young people were aware that depression and suicidal thoughts might be caused in part by their sexual behavior. Consider the following questions:

  • Why are those who were not virgins when they married more likely to divorce than those who remained abstinent until marriage?4
  • Why are sexually active adolescents more likely to be depressed than their abstaining peers?10
  • Why do married couples report higher levels of sexual satisfaction than unmarried individuals with multiple sexual partners?5

The answers, of course, lie in the fact that human beings are creatures who are much more than physical bodies. We possess the ability for cognitive thought, which includes judgment, abstract thinking, planning for the future, moral intelligence, and other processes that govern our lives. Our decision-making ability, coming from the highest centers of the brain, can guide an individual to the most rewarding sexual behavior—unless bad programming from premature and unwise sexual behavior during the adolescent years has occurred, adversely affecting the brain’s ability to make healthy decisions.6

This is a risk about which most young people and most parents are totally unaware.

Fortunately, modern neuroscience of the past few years has opened a door of understanding that provides incredibly helpful guidance away from trouble. Many of the answers to the questions above, and others, may be found in modern neuroscientific research, the study of the human brain and nervous system, which has revealed startling new information about how sex affects the brain.

In the past, efforts to accurately assess the connection between sex, love, sexual desire, sexual risk-taking, and so on with brain activity were limited. But with the aid of modern research techniques and technologies, scientists are confirming that sex is more than a momentary physical act. It produces powerful, even lifelong, changes in our brains that direct and influence our future to a surprising degree.7 This new neuroscience information, which has greatly expanded over the past three decades, has transformed the scientific discussion about sex. Perspectives from medical, public health, and social science literature will also be utilized in this book to enhance our understanding of sexual behavior in adolescents and young adults in the larger cultural context.

The uniqueness of becoming an intimate part of another person’s mind and body—emotional and physical bonding, both experienced in a healthy way, and the vital role this plays in one’s health, happiness, and hope for the future—are  the central issues we will be explaining in this book. It is probably the most important outcome of healthy, positive sex.


  1. Harden, K. Paige. "Genetic influences on adolescent sexual behavior: Why genes matter for environmentally oriented researchers." Psychological Bulletin 140.2 (2014): 434.
  2. Pringle, Jan, et al. "The physiology of adolescent sexual behaviour: A systematic review." Cogent social sciences 3.1 (2017): 1368858.
  3. Kann L, McManus T, Harris WA, et al, “Youth Risk Behavior Surveillance – United States, 2017,” MMWR Surveillance Summaries/ Vol. 67/No. 8
  4. Wisnieski, Deborah, Renee E. Sieving, and Ann W. Garwick. "Influence of peers on young adolescent females' romantic decisions." American Journal of Health Education 44.1 (2013): 32-40.
  5. Wilcox WB and Wolfinger NH, “Men and Marriage: Dubunking the Ball and Chain Myth”, Institute for Family Studies, accessed June 2018
  6. American College of Pediatricians, “The Teenage Brain: Under Construction,” May 2016
  7. Jensen, Frances E (2015) The Teenage Brain, New York, NY Harper Collins