Sperm study splits Japanese men in two

By Ryann Connell
October 6, 2004

Japanese sperm counts vary according to the season, according to research done by a pair of scientists written up in Asahi Geino.

As well as changing with the weather, Japanese sperm counts also come, literally, in two different types, so the scholars say.

Studies by Yutaka Nakabori of Tokushima University and St. Marianna University's Akihiro Iwamoto showed that one strain of Japanese sperm dominates from July to December and another from February to July.

Nakabori's team of semen scholars tested seed donated by 764 men whose wives were pregnant at various times from 1999 to 2002. They looked into the role the Y chromosome was playing in the sperm.

What they apparently discovered was that the disparity in the discharges had roots that can be traced back to a primeval past. The first type comes from those who can claim their ancestry from Japanese who lived in the Jomon Period, which went from about 12,000 BC to around 300 BC. The second strain of semen givers are the descendants of inhabitants of the Yayoi Period, which began roughly 3,000 years ago.

Jomon semen counts dominated from July to December, while the Yayoi seed assumed the ascendancy from February to July.

"Jomon descendants have lower sperm counts. This has been public knowledge for some time, but our studies largely confirmed the accuracy of that assumption," Nakabori tells Asahi Geino. "We plan to announce our results in detail and receive even more information."

Modern Japanese are nearly all drawn from those who lived in the Jomon and Yayoi periods, which local scholars claim each had a distinctive appearance.

"Broadly speaking, the Jomon were swarthy, square-faced, had wide noses and double eyelids," archeologist Ryoji Yamagishi says. "The Yayoi, on the other hand, had longer faces, thinner noses and single eyelids."

Jomon and Yayoi women also differed.

"Jomon Period women were short and squat with bodies good for childbearing," Yamagishi tells Asahi Geino. "It is though that the agricultural lifestyle that gave the Yayoi people more stability also gave them a greater sperm count than the hunter-gatherer Jomon people whose lives were unregulated."

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