Monday, January 21, 2013

‘Taint’alizing studies: The connection between male taint length and fertility

Are you a man who spits on homeless people for fun? Do you regularly cut off pregnant women for the last seat on the bus? Are you really good at dodging child support payments?

If you answered “yes” to any of these questions, there may still be hope. Fortunately for you, the real measure of a man may have less to do with the measure of his character and more to do, from a biological perspective, with the measure of his taint. 

Though not commonly thought of in this sense, from an evolutionary biological perspective, a good man is one who amply fulfills his role as a provider of DNA by passing his genes to many offspring. In order to do this, having good quality ejaculate is a must. But how good is your semen really?

To find out, you could sleep around and count the number of children you have, but that could be costly for a lot of reasons. A less expensive (and more reasonable) method could involve going to a doctor or a fertility clinic to have your semen analyzed. However, you would probably do this only after some fertility issues are noticed. This may be a time when there aren't many corrective actions to take. If you could assess your fertility much earlier, possibly even during puberty with an assessment that is as simple as a breast exam, you might intercept the issue and increase the chances of passing down your genes. 

So why not measure your taint? 

Finding an easy to assess indicator of male fertility and genital health were two of the many motivations behind research suggesting a link between smaller male taint lengths and decreased fertility. But how exactly did they find this out?

Well, if you were a male participant in one of the studies(ref 1), the researcher would have started by asking personal questions like “When was the last time you ejaculated?” (Note: He’s not interested in how you spend your Friday nights; times between ejaculations are thought to affect semen quality(ref 8*)). Sometime afterwards, you would be asked to ejaculate into a container. Then finally, you would be told to take off your underwear, lay down exposed on an examining table, and take the lithotomy position (an example of which can be seen in Figure 1). You would then have your taint (also known as anogenital distance and shown beautifully in Figure 2) measured twice with a stainless steel digital caliper. Feeling uncomfortable yet? Luckily, 124 young men already did this for science, so you don’t have to.

Figure for Blog 

After many a seed was sown, counted and analyzed, the researchers from this study, as well as similar study conducted at fertility clinic comparing fertile and infertile men (ref 2), reported that smaller measurements from the center of a man’s anus to the most posterior portion of his testicles were associated with decreased fertility. Shorter taint lengths/anogenital distances were correlated with ejaculates that contained smaller volumes of semen, along with sperm that had poor directed movements and a smaller size and shape. (In case you’re curious, the mean anogenital distance in the infertility study(ref 2) for fertile men vs. infertile/childless men was 44.6 mm vs. 31.8 mm, do what you will with these numbers….).

At first glance, this seems like a popular science study just using bizarre research findings to grab attention. However, there is actually an important underlying connection. 

The relationship between anogenital distance and fertility is thought to begin before the male is even born. While the fetus is still developing, there comes a time when male sex hormones (also known as androgens), like testosterone, become critical for making the switch from the female reproductive system (the genetic default) to a male reproductive system. This period of time is known as the male programming window. During this window, testosterone becomes a signal for the extension of the taint and for the maturation of cells in the testes that maintain and house premature sperm (known as Sertoli Cells). Testosterone is so crucial at this point that suppression of it’s levels at this time can lead to misplaced urethra openings (hypospadias) and testis that have difficulty dropping (cryptorchidism)(ref 3). So if you’re a male who appreciates his taint, the potential to have kids or peeing straight into the toilet, this was a very important time for you.

The ideas on how this process works wasn’t dreamt up by some scientists obsessed with taints. They were also based on studies and experiments that suggested there were time sensitive effects of testosterone on male genitalia. 

Researchers found that when babies are birthed by mothers with higher than average levels of phthalates (chemicals found in plastics that are thought to suppress male sex hormones), their offspring tend to have smaller taints(ref 4). Though one would hope that growth spurts during puberty might offer some compensation, there are studies suggesting that adult males with lower testosterone levels generally have smaller taints, and even lower quality sperm(ref 5). However, these are just correlations; because the participants from the study live their lives outside of the laboratory, there are many other influential factors that could have led to these results, so researchers could not conclude for certain that the low testosterone levels (or some other action of phthalates) contributed to the development of smaller taints.

Fortunately for us, when it comes to genital development, humans ‘taint’ all that special. Rats go through a similar development process. Researchers took advantage of these similarities to more conclusively assess the effects of low androgen exposure on taint size and fertility. Pregnant female rats were injected with phthalates to see how their sons’ genitals would develop. They found that not only did the mother’s small tainted male babies become small tainted adults, but that these offspring were also less fertile(ref 6).

So we’ve seen that there is some connection between male babies and adults with small taints also having low levels of androgens (male sex hormones). We’ve also noted that when manipulated in rodents, low androgen levels in utero are followed by the development of males that are less fertile and have smaller taints. However, if one were to perform the critical experiment to show this also applies to humans, it might involve making similar manipulations before birth which is unethical, to say the least.

However, one experimental study may have skirted the ethical line to bridge this gap in knowledge. Investigators in England injected testes from aborted human fetuses into the bodies of mice to examine the effects of human testes testosterone production on taint length and fertility. By administering phthalates at different times during fetal development, the researchers were able to note when androgens such as testosterone, may influence taint size and fertility. The results from the study showed that if the mice with human testes had testosterone suppressed at a time right before birth (slightly outside of the expected male programming window) they developed smaller taints and less Sertoli cells (which harbor premature sperm and would likely affect fertility)(ref 7). 

While the seminal results from these studies provide a strong basis for understanding the taint length-fertility relationship, it is worth mentioning that no study is perfect. For example, in the first study mentioned(ref 1), the participants were generally 18-22 year old young white males. This lack of diversity in age and race limits how much of the much findings can be related to other kinds of men. Fortunately due to the support of the many other studies and experiments listed, there’s a strong indication that the measure of a man’s taint may generally be a sign of his fertility. However, it still couldn’t hurt to have more guys participate in studies like this to strengthen confidence in the results. So the next time a stranger in a lab coat asks you to pull down your paints, ejaculate into a container and lay down on his table for a taint check, please, just do it. It’s for science (hopefully….).


TL;DR: Studies involving guys dropping trou, rat hormone suppression, and mice grafted with aborted human testes suggest that fetal testosterone exposure may be the reason why human males with small taints are generally less fertile.



1. Mendiola, Jaime, et al. "Shorter anogenital distance predicts poorer semen quality in young men in Rochester, New York." Environmental health perspectives 119.7 (2011): 958. DOI: 10.1289/ehp.1103421

2. Eisenberg, M. L., Hsieh, M. H., Walters, R. C., Krasnow, R., & Lipshultz, L. I. (2011). The relationship between anogenital distance, fatherhood, and fertility in adult men. PLoS One, 6(5), e18973. DOI: 10.1371/journal.pone.0018973

3. Sharpe, R. M. (2008). “Additional” Effects of Phthalate Mixtures on Fetal Testosterone Production. Toxicological sciences, 105(1), 1-4. DOI: 10.1093/toxsci/kfn123

4. Swan SH. (2008). Environmental phthalate exposure in relation to reproductive outcomes and other health endpoints in humans. Environ Res 108:177–184. DOI: 10.1016/j.envres.2008.08.007

5. Eisenberg, M. L., Jensen, T. K., Walters, R. C., Skakkebaek, N. E., & Lipshultz, L. I. (2012). The relationship between anogenital distance and reproductive hormone levels in adult men. The Journal of urology. DOI:

6. Scott, H. M., Hutchison, G. R., Jobling, M. S., McKinnell, C., Drake, A. J., & Sharpe, R. M. (2008). Relationship between androgen action in the “male programming window,” fetal Sertoli cell number, and adult testis size in the rat. Endocrinology, 149(10), 5280-5287.DOI: 10.1210/en.2008-0413

7. Mitchell, R. T., Childs, A. J., Anderson, R. A., van den Driesche, S., Saunders, P. T. K., McKinnell, C., ... & Sharpe, R. M. (2012). Do phthalates affect steroidogenesis by the human fetal testis? Exposure of human fetal testis xenografts to di-n-butyl phthalate. Journal of Clinical Endocrinology & Metabolism, 97(3), E341-E348 DOI: 10.1210/jc.2011-2411

8. Moshe Matilsky, Shlomo Battino, Moshe Ben-Ami, Yoel Geslevich,V. Eyali and Eliezer Shalev (1993). The effect of ejaculatory frequency on semen characteristics of normozoospermic and oligozoospermic men from an infertile population. Hum. Reprod. (1993) 8 (1): 71-73.

Editor’s Note: *The reason for asking participants when they last ejaculated was presumably based on the idea that shorter times between ejaculations lower sperm volume and other attributes. However, there are many studies about abstinence and semen quality in human males and many of them report contradicting results. Comments and some references to these results are noted in the introduction of this publication, Jonge et al, 2005 doi:10.1016/j.fertnstert.2004 03.014


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