The past few years have seen a cascade of headlines talking about the "sperm-count crisis", with grim predictions of rampant human fertility problems and even extinction in the not-too-distant future. But are our species’ swimmers really that doomed? Are environmental pollutants sparking a "spermageddon" that will soon send human populations into a dramatic decline? Perhaps not, a new study, published in the journal Human Fertility, argues.

Much of the talk around the “sperm-count crisis” is based on a colossal meta-analysis published in 2017 that found the average total sperm concentration among men from “Western” countries has decreased by almost 60 percent since 1973. If this trend continues, the researchers argue, then large parts of the world could have a median sperm count of zero by 2045. 

Dr Shanna H Swan, a leading environmental and reproductive epidemiologist at the Icahn School of Medicine at Mount Sinai, who was part of the 2017 study, has since written a new book that argues how this decreasing sperm count trend may be linked to the growing use of phthalates, a prolific group of chemicals used in hundreds of everyday items, from kids’ toys and food packaging to hair sprays and paints. 

However, not everyone is convinced by the interpretations that have sprung out of the influential 2017 meta-analysis. In the recent study, an interdisciplinary team of researchers from Harvard University, Columbia University, and the University of Adelaide took a fresh look at the data used in 2017 and came up with a new interpretation.

In short, they argue that sperm counts have a very wide range of natural variability and the “optimal” sperm count is not clear. The study reads: “the data points that make up the 2017 meta-analysis simply demonstrate that sperm count varies across bodies, ecologies, and time periods.” Some people will have a high sperm count, others will have a lower, many will have an average count. This, they argue, is normal and a sperm count isn't an indicator for better health, nor necessarily an indicator of high fertility.

The “normal” sperm count ranges from 15 to 250 million sperm per milliliter of semen, while a low sperm count is considered fewer than 15 million sperm per milliliter. However, there’s no evidence that suggests fertility scales proportionately with sperm count; once sperm count hits a relatively average threshold, fertility levels off and more sperm will not increase the chance of reproductive success. 

Sperm counts are also highly context-sensitive: tight pants, a hot bath, a recent bout of illness, and even the time of the year can cause sperm counts to vary. As such, a one-off measure of sperm count is a pretty unreliable gauge of fertility across a lifespan.

There’s also a chance the sperm counts gathered in the 1970s were simply miscounting the sperm cells. In a 2013 paper, a researcher noted that the methods used for counting had been improved since the 1970s. As the tests became more accurate, declines in sperm count were seen, which the researchers argue is suspicious. In the words of the paper “are sperm counts declining? Or did we just change our spectacles?” 

Furthermore, the new research argues the data is centered around the sperm counts in English-speaking developed nations of the 1970s. This is treated as the "species optimum" with very limited data on individuals' sperm counts elsewhere in the world. For instance, the 2017 meta-analysis simply breaks down the participants as “Western” and “Other.” It also failed to take into consideration the difference between rural and urban populations. 

Not only does this embed all kinds of Western-centric assumptions in the study, it also suggests certain parts of the world (such as Europe, North American, and Canada) were overrepresented. This helped to drive the narrative that it’s mainly “Western” nations that are feeling the sting of this fertility problem. The researchers explain that this caught the attention of white supremacist groups and conspiracy theorists who erroneously used this as evidence that masculinity and “the West" were under threat.

Without a doubt, this latest rebuttal is not the end of the wider debate around fertility and sperm counts in the 21st century. Just as many will critique or refute the idea of the “sperm-count crisis,” many will back it to the hilt. As more evidence is gathered, however, this new study argues that we should be cautious about how this data is collected and how it's interpreted.