Obesity increases, sperm count drops. If it is valid for one male it could be valid for whole population.

what factors/causes are there for this?

Probably plastics and other long-lived chemicals in the environment, many of which can affect hormonal responses when they get inside the body.

https://www.mcrmfertility.com/wp-content/uploads/2021/05/Glo... mentions "No clear etiologic factors have been identified; however, multiple factors have been shown to have correlative associations" then lists some possibilities:

* Increased obesity.

* Changes in diet, to have more fats.

* More people with chronic diseases like diabetes and hypertension.

* Environmental toxins including bisphenol A (BPA), phthalates, triclosan, and air pollutants.

* Tobacco, including "parental tobacco exposure in utero has been reported to affect male fertility in the offspring."

* Increased marijuana use ("though the field is under-researched")

* "Sedentary lifestyle, stress, and lack of sleep"

Too many incels worshipping Musk thinking that you get women by imitating his behaviors.

I'm not sure it's that specifically but that definitely doesn't help.....

Seems to solve a lot of problems at once. 9 billion humans is too many.

Thank you Klaus, very cool!

Important part in towards the end..

While their research did not explore the causes of this drop in sperm counts, the authors say it reflects "a global crisis related to our modern environment and lifestyle," and they point to the disrupting role of chemicals on our hormonal and reproductive systems.