Sperm counts across the globe are lowering according to newly released research.
Researchers, assessing nearly 200 studies, say sperm counts among men from three continents seem to have halved in less than 40 years.
Experts looked at men from North America, Europe, Australia and New Zealand, with chief researcher Dr Hagai Levine stating he was 'very worried' about what might happen in the future.
Dr Levine, an epidemiologist, told the BBC: "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.
"Eventually we may have a problem, and with reproduction in general, and it may be the extinction of the human species."
Credit: PA
Many scientists have praised the study, yet still think it is too early to reach such a dramatic conclusion.
From the four areas studied, a 52.4 percent decline in sperm concentration and a 59.3 percent decline in total sperm count were found.
Interestingly, there was no such significant decline found in South America, Asia and Africa - but this might be due to the lack of previous studies conducted in these continents.
Issues with previous studies however mean that these figures could have been exaggerated. Such problems include: declines are more likely to reported than other findings, and methods of counting sperm may have overestimated the true count.
Credit: PA
However, Professor Allan Pacey of Sheffield University said of the study: "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."
As to what causes the decrease, there is no concrete evidence, but an exposure to chemicals in pesticides and plastics has been blamed, as have obesity, smoking, stress, diet and even watching too much TV.
Dr Levine added: "We must take action - for example, better regulation of man-made chemicals - and we must continue our efforts on tackling smoking and obesity."
Featured Image Credit: NHS