The first mention of Pekin ducks took place in the U.S.A. by an Chinese student in 1870 at some congress-thingy. A person in the U.S.A. and a person in the U.K. imported some.
Here it split.
U.S.A. crossed it to aylesburry to make it a better meat-breed. And so started the American pekin; a heavyweight.
The Dutch (close to U.K.) traveled to Asian places and found the Japanese pinguin duck; which was more upright. On old drawings the Japanese pinguin ducks is absolutely not as straight as an runner; there is no proof that there is any runner ever mixed in; it just looks like the original pekin. the ones "again" found in Japan might have been the same ducks; like they were before being crossed with aylesburry's. They were fat, taller, and in all languages both races described pinguin/pekin sounds the same. The U.K. pekin was crossed with the Japanese pinguin duck. The interest in breeding with this duck declined; except in Germany. There it was kept alive. And "perfected". The orignal pekin crossed with accidentally orginal pekin; had an more upright stand than the orginal peking + aylesburry duck in the U.S.; and the Germans kept breeding it taller and fatter for, I guess; that's what they thought at that time was pretty/handy. It was a time where it was either; the less you can walk the more fatter you get; or the more eggs you want the more you don't wat a duck/chicken/cow to gain any fat. Perfect a breed with short legs and can't run it off; will get fatter. And with short legs; they LOOK fatter then they actually are; which was important in times when "breeding the fattest/best egg-layer" could mean a true income. Due to Germans perfecting this race for so long; it's called German pekin.