New Insights Into Sex Drive and Fertility
The interplay of physical, hormonal, social, and psychological influences effects male and female fertility—and sex drive—in various different ways. New research offers us a glimpse into how.
Physical differences between the sexes begin to emerge at about six weeks after conception, when boys develop testes, and girls develop ovaries. Beginning then, and all the way through puberty and menopause, there are key hormonal and physical differences that influence an individual’s sex drive and fertility levels. While much has been researched, there is still much to learn.
Humans are sexual beings from the beginning. Infant boys have the ability to have erections, and baby girls are capable of vaginal lubrication. By age three, gender identity, or a sense of being a boy or a girl, is typically formed. Puberty brings on a surge of physical changes and hormones ushering in a more defined sexuality.
Boys typically enter puberty between the ages of 13 and 16. Sexually, boys experience maximum arousability and response during their teen years, in large part due to the increase in testosterone and other hormones at this time. Adult men need normal levels of testosterone to maintain interest in sex. As testosterone starts to decline in their 50s, men may see a decreased interest in sex.
In contrast, girls typically enter puberty earlier than boys: between the ages of 9 and 16. Despite their earlier puberty, girls typically don’t exhibit the same sexual interest and response during puberty as boys. Some exhibit strong sexual desire, while others do not. Also interesting, women have been found to be least sexually interested during menstruation and most interested around ovulation—when they are most fertile. Menopausal women may experience a decline in sexual interest, and yet it is uncertain if this is due to waning estrogen levels, or other aspects of growing older.
Men, assumed to be fertile long after women, may be surprised to learn of new research that sheds some doubt on this assumption. Dr. Sergey Moskovtsev, a researcher at Mount Sinai Hospital in Toronto, Canada, examined the DNA of different aged sperm. Dr. Moskovtsev and colleagues examined the sperm of 2134 men who were being evaluated for fertility. Using a fluorescent dye that attaches to DNA, damage was calculated for each man using a 20,000 sperm count sample. The researchers found that DNA damage was significantly higher in men aged 45 years and older compared to all younger age groups. Even more startling was that the damage doubled in men 45 and older when compared to men less than 30 years old. The reason all of Dr. Moskovtsev’s patients had sperm evaluations done was because they were unable to father children. Researchers do not yet know how common DNA damage is in successful older fathers, or whether the degree of DNA damage increases with age in men who do not have a history of fertility impairment.
Female Fertility and Sex Drive
It is well known that a woman’s fertility declines with age. The rate of miscarriages and birth defects also rises as a woman gets older. An estimated two-thirds of women are unable to conceive by the age of 40, while one-third of women over 35 have fertility problems.
One subject of recent study has been how hormonal shifts during a woman’s menstrual cycle affect her “mating” preferences. Researchers Steven Gangestad, et al. examined 237 normally ovulating women to assess their preferences for male behavior during their menstrual cycles. Women in the study were asked to view approximately 40 videotaped men who were competing for a lunch date, and rate them as a long-term or short-term mate. The researchers found that on high-fertility days (i.e. during ovulation) the women displayed an increased preference for men with prominent social presence and sexual competitiveness. Even so, the preference was categorized as short-term. This study (and others) seems to suggest that women’s sexual preferences can vary according to their menstrual cycle.
Timing of Puberty
The variability in human sex drive is wide and not fully understood. Researchers Jennifer M. Ostovich, MA, and John Sabini, PhD, shed some light on the subject. They studied 129 men and 148 women in their early twenties to test sex researcher Alfred Kinsey’s claim that early maturers have a stronger sex drive and more frequent sexual behaviors than late maturers. Participants completed questionnaires on timing of puberty, sexual experience and timing, sex drive, and sexual attitudes and behavior. The researcher’s findings support Kinsey’s claim. Specifically, for both men and women, the earlier the onset of puberty, the earlier the first sexual arousal. In terms of sex drive, the earlier the men’s puberty, the stronger the sex drive. Both sexes showed a correlation between first sexual arousal and current sex drive, the earlier the arousal the stronger the sex drive.
While we may not understand the exact connection between human sex drive and fertility, it would appear from current research that there is one. A woman’s stronger sex drive around ovulation, a man’s healthier sperm at younger ages, and the connection between onset of puberty and sex drive, all point to an interconnection too strong to ignore.
The Medical Institute for Sexual Health
Sexuality Information and Education Council of the United States
American Society for Reproductive Medicine. Patient’s Fact Sheet. Prediction of Fertility Potential in Older Female Patients. Available at: http://www.asrm.org/Patients/Fact Sheets/Older_Female-Fact.pdf. Accessed July 2, 2005.
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European Society of Human Reproduction & Embryology. Damage to sperm DNA affects older men’s chances of fathering children. Available at: http://www.eshre.com/emc.asp?pageId=650.Accessed July 2, 2005.
Gangestad SW, Simpson JA, Cousins AJ, Garver-Apgar CE, and Niels Christensen P. Women’s Preferences for Male Behavioral Displays Change Across the Menstrual Cycle. Pyschological Science. 2004;15:203-207.
Medline Plus Medical Encyclopedia. Puberty and adolescence. Available at: http://www.nlm.nih.gov/medlineplus/print/ency/article/001950.htm . Accessed July 2, 2005.
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Ostovich JM and Sabini J. Timing of Puberty and Sexuality in Men and Women. Archives of Sexual Behavior. 2005;34:197-206.
Last reviewed July 2005 by ]]>Lawrence Frisch, MD, MPH]]>
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