早在1878年，德國解剖學者格根鮑爾（Karl Gegenbaur）曾提出人類四肢與魚鰓的關聯性，但被斥為無稽之談。而今，138年過後，研究者發現他的理論有所根據。
劍橋大學（University of Cambridge）科學家發現，人類四肢與鯊魚、鰩魚、魟魚的鰓，可能有演化上的關聯。
這些軟骨魚綱的魚類，擁有如同人類手指般，呈放射狀散開的「鰓條」（branchial rays）。
人體內有種稱作「音蝟因子」（Sonic hedgehog）的基因。這種基因決定手指的生長方向，也使之完整成長。
「音蝟因子」的命名由來，是因為研究者的女兒是卡通「藍色音速小子」（Sonic the blue hedgehog）的粉絲。
該基因亦透過同樣的成長機制，決定鰩魚胚胎中的鰓條（branchial rays）如何成形。
若在早期抑制該基因發展，鰓條會長錯方向。若抑制後期，鰓條就會長到對的一邊，但數量較少。
這項研究是否意味著，人類是從魚類演化而來？雖然兩者有類似生長機制，但目前仍無化石證據，支持這項理論。
也許再過一百多年，格根鮑爾（Karl Gegenbaur）的理論，才能真正被認可吧。
英文原文：
In 1878, anatomist Karl Gegenbaur proposed a link between human limbs and fish gills that was widely dismissed. One hundred and thirty-eight years later, it turns out the guy was on to something.
Scientists from the University of Cambridge have found a possible evolutionary link between our limbs and the gill arches of sharks, skates and rays.
These cartilaginous fish have gill support structures called branchial rays, which fan out in the same way fingers do.
In humans, a gene dubbed ‘Sonic hedgehog’ determines which fingers go where, and keeps them growing to full size.
The gene was named after the video game character by a researcher whose daughter was a fan of Sonic the blue hedgehog.
This gene is also responsible for the formation of branchial rays in skate embryos, using the same underlying mechanism for growth.
When inhibited early in development, the gene causes the branchial rays to grow on the wrong side. When inhibited later on, branchial rays grow on the correct side, but are fewer in number.
Does this mean we evolved from fish, then? Though the similarities are telling, there is still no fossil evidence to fully back up the theory.
Maybe in another hundred years or so, Gegenbaur will finally get his due.
