The latest studies in contemporary human procreation research are indicating that there is a distinct possibility of human beings being susceptible to extinction in the future due to declining sperm counts. Researchers examined the findings of approximately 200 studies in a comprehensive executive summary study that says sperm counts in men from New Zealand, Australia, Europe and North America appear to have decreased by about 50 percent in the last four decades alone.

The executive summary is referred to as the Human Reproduction Update, and it warns that humans could reach extinction if men's sperm counts proceed to drop as precipitately as they currently are. Dr. Hagai Levine, an epidemiologist was the lead researcher on the Human Reproduction Update, and he claimed to be "very worried" about what the future holds for human beings; he says the current trend certainly has the potential to push humans toward extinction. The study marks one of the largest assessments ever conducted, and it collects results from 185 studies published in the span between 1973 and 2011.

"If we will not change the ways that we are living and the environment and the chemicals that we are exposed to, I am very worried about what will happen in the future," Levine explained. "Eventually we may have a problem, and with reproduction in general, and it may be the extinction of the human species." Scientists unassociated with the study have extolled the Human Reproduction Update as being wrought of high-quality research, but they also claim that the conclusions found therein could be a bit premature.

Levine, hailing from the Hebrew University of Jerusalem, concluded that there exists a 59.3 percent decline in total sperm count and a 52.4 percent decline in sperm concentration among men in Europe, North America, New Zealand and Australia. Additionally, the study points to the rate of decline in these countries to be steady with the potential to accelerate.

Despite these alarming findings, though, the study found no evidence of decline in the entire continents of Asia, South America or Africa, which collectively represent the vast bulk of the human population by far; however, researchers highlight the fact that these continents have seen dramatically less studies conducted on the subject in the first place.

It is possible that the lack of evidence for declining sperm counts on these continents is merely attributable to a dearth of data. Levine remains concerned, though, that it may only be a matter of time before evidence is gathered to support sperm count declines being found on every continent in light of the purported causes of these declines being globally ubiquitous.

Some regions bear studies that have looked at only a small number of men or have, perhaps, only included those who attend fertility clinics and are just more liable to report low sperm counts regardless. Some pundits have criticized that scientific journals are simply more likely to be publish the studies in question than studies that negate these findings. Yet another problem in assessing the issue is that the true count of sperm was historically inflated by inferior counting methods when sperm counting first became a research method. Those early overestimations could, therefore, suggest that the decline is less severe than it appears.

All of these factors taken into collective consideration contribute to the pervasive counterargument thus far that this view of falling sperm counts may be erroneous. Even so, the research team responsible for the executive summary have claimed that they took many of these criticisms into account already during their study, which is why certain other experts like Sheffield University's Allan Pacey aren't so incredulous. Pacey remarks, "I've never been particularly convinced by the many studies published so far claiming that human sperm counts have declined in the recent past.

"However, the study today by Dr. Levine and his colleagues deals head-on with many of the deficiencies of previous studies," Pacey explains, elucidating what it is about this comprehensive assessment that distinguishes its veracity from that of the 200 studies it analyzes. Pacey also intimates that, in lieu of this new study reducing the likelihood of error for which previous studies have been criticized, that likelihood is not obviated entirely. As such, Pacey says its results still need to be taken with a grain of salt rather than hysteria.

"The debate has not yet been resolved and there is clearly much work still to be done," Pacey explains. "However, the paper does represent a step forward in the clarity of the data which might ultimately allow us to define better studies to examine this issue."

There still remains a paucity of concrete evidence to support any definitive cause for the observed declines in sperm counts, though many reasons have been postulated over the years and addressed in this very study. The declines have been suggested to hold a causal relationship to the chemicals used in plastics and pesticides, but they have also been correlated with smoking, obesity, diet, stress and even an over-exposure to television in some cases.

Levine points out that there is, at the very least, an urgent need to explain these observations of declining sperm counts in light of the fact that his study debunks so many of the counterarguments that preceded it. "We must take action—for example, better regulation of man-made chemicals—and we must continue our efforts on tackling smoking and obesity."