While evolution has stopped being just a theory a long time ago, we’re still missing a lot of key pieces that would better show how exactly we got here. There are simply too many evolutionary steps we went through in order to get where we are today, and without the evolutionary intermediaries we can’t really understand everything about our genetic history.
But of course, as with most things in science, there are workarounds. Since the creatures that first started walking on land are long gone, scientists can’t really analyze them for information. So, they went for the next best thing – genetic information from even older creatures that haven’t changed all that much over the years.
So, according to a study led by biologist Andrew Gillis from the University of Cambridge, genetic evidence suggests human limbs evolved from shark gills. While this has been suspected for quite some time now, the problem was that there was a complete lack of evidence to support it. Not anymore.
Gill arches are what scientists refer to the collection of looped bones that support gills and that serve as the developing point for branchial rays, or gill arch appendages. The theory that hasn’t been confirmed up until now was that these arches gave way to paired fins in early fish, and later to paired limbs in mammals.
Looking into how limbs, gill arches, and fins developed in their embryonic state, researchers came upon a gene referred to as the ‘Sonic the hedgehog’ gene. This pop-culture reference of a gene plays a similar role in governing the formation of all three features, producing a signaling protein that plays an essential role in determining the developmental axis and in controlling the growth of the limb skeleton.
According to Gillis, there are two possible explanations for this. Either two unrelated appendages use the same gene for the same function (highly unlikely) or there is a deep evolutionary relationship between the two. As one explanation would make more sense than the other, the team will choose to consider it as true, but also to take into consideration the other possibility during subsequent experiments.
This scientific discovery could very well prove itself to be a breakthrough for multiple fields of science, including evolutionary biology, anthropology, and even genetics. One way or the other, branchial rays (or gill arches) will play a huge role in the story of the evolutionary origin of vertebrate animal appendages.
It will either finally shed light on the evolutionary precursors to paired fins and limbs, or it will teach us about the genetic mechanisms involved in animals developing new appendages. Either way, the discovery was published in this week’s Development journal, and the findings have been submitted for reviews.
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