This is what happens when self-declared popular media "journalists" report in a frenzy about a scientific paper they think their readers will find titillating, and then the internet multiples this by 1000x.
The penis-lengthening-trend study in question was published on Valentine's day, and the Stanford press release on the same day includes a picture of a tape measure worthy of Cosmopolitan Magazine. This has led me to wonder if the study is a hoax, or at least tongue-in-cheek, in the style of an April Fool's article (see my conclusion at the end). But even if real, the data contains an interesting inconsistency. Understand that the authors made no measurements, but simply reviewed results published by 75 others from 1942 to 2021, that is, over the last 81 years. However, they do not report the data trend over this whole 81 years period in the sensational headline, but compare a point in the middle, 29 years ago, with current data. Look at some of the points they didn't mention in the headline:
- Kinsey Study (data taken 1948 but not published until later), 75 years ago: Average length 6.21 inches
- Claimed average length 29 years ago, Stanford paper: 4.8 inches
- Ansel/Lifestyles Condom study (2001) 22 years ago: average length 5.9 inches
- Claimed average length today, Stanford paper: 6 inches
So, one could argue the penis has shrunken 3% over the last 75 years, from 6.21 to 6.0. Or did men shrink 23% between 1948 and 1994, and then grow most of it back? Or, has there been just a 1.7% growth over the past 22 years (5.9 to 6.0)? Was there a sudden groth spurt from 4.8 to 5.9 inches (+23%) in just 7 years? Or has it always been around 6 inches, and 4.8 is in error? Etc...
Kinsey's data has often been criticized because it was self-measured, and, well, men do find ways to exaggerate. But at least Kinsey had his subjects hard for the measurement, and requested them to do it on top-- many modern studies estimate probable erect length from a stretched-flaccid measurement. And many recent studies also rely on self-measurement. But even clinical measurement is fraught with variables...measure on top or on the side? Fat pad? Curvature? Etc.? There is also the question of who got measured. For example, some studies were done on soldiers, who may have less fat pad than the average joe. Since the studies were voluntary, there is the question of "Volunteer Bias," that is, men who believe they are hung may be more likely to sign up to whip it out and be measured that someone who feels insecure about a small penis. The
Ansel/LifeStyles study was done with 400 young men on spring break at a club in Cancun, measured by nurses, and with actual erections. Fully 25% of them had to be excluded because they couldn't get it up, not surprising given spring break alcohol consumption. But were the other 75% at full mast? Would they have measured an average of 6.0 or 6.2 under more sober circumstances? So, subtle differences in how a particular study is conducted can skew the results, particularly when the studies are performed decades apart.
The reported data over the years is full of hills and valleys. If you pick two points of your choosing, you can claim almost anything, as I did above. Because the various studies were conducted in different ways, it is hard to determine how to aggregate and average them. But for decades, there has been an argument back and forth: one group seems to cluster around 5 inches, and the other around 6. The authors of the Ansel/LifeStyles study linked above point this out in their conclusions, and attribute the difference to self-measurement (6ish) to clinical measurement (5ish), but put the exaggeration as more like half an inch, not a full inch. But curiously, Ansel's own clinical measuments come out at 5.877, nearly the 6 inches they attribute to self-measurement.
There is a lot of current research that points to alarming drops in male fertility in the industrialized world, based on sperm counts, motility, and other sperm quality measures. Some of these researchers actually mention a shrinking trend in penis size, contrary to the Stanford paper. On the other hand, one could argue that given declining sperm quality, a long penis would be favored, as it can make the most of such sperm as it has, by delivering it closer to where it counts. But as 29 years is barely one human generation, such a section process, if possible, has not had enough time to develop.
Early in my career, when I worked in analytical chemistry, prestigious journals occasionally published papers that were terrible science (and the editors knew it), but were amusing because they dealt with sex, and provided some levity in an otherwise dry field. Given the Valentine's Day publication date, I'll assume the Stanford paper was another of these.
