George Parker Bidder (21 May 1863 – 31 December 1953) was a British marine biologist who primarily studied sponges.

[1] In 1932, Bidder made a major contribution to the field of biogerontology by proposing that senescence was the effect of a "regulator" responsible for ending growth.

[4][5] This theory, known as "Bidder's hypothesis" has been refuted in numerous experiments, starting with Alex Comfort's 1963 study on guppy, a species that ages while growing.

Finders were requested, in English, Dutch and German, to send a postcard enclosed in the bottle to the United Kingdom's Marine Biological Association in Plymouth, for a shilling reward.

[7] The majority were recovered just a few months later, but one was found on the German island of Amrum, as late as April 2015, and its postcard was duly returned to the MBA.