Spiders were the first creatures on Earth to evolve knees, according to a new study that also explains how this happened.
Knees began as a gene in fruit flies and other insects that duplicated and evolved in spiders, resulting in primary leg joints, reports the study, published in the journal Molecular Biology and Evolution.
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"Species constantly adapt and evolve by inventing new body features," lead author Nikola-Michael Prpic of the Göttingen Center for Molecular Biosciences explained in a press release.
Prpic and his colleagues focused their work on a particular gene called dachshund, or dac for short. The name reflects a bit of nerd humor, because the gene was first discovered in fruit flies, and was named for the missing leg segments and shortened legs that result from dac mutant flies.
What clued the scientists in on this gene in the first place is that arachnids, such as spiders, possess a second dac gene, dac2. It results only in the spider's kneecaps (patellas) during the individual's overall growth and development.
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The researchers used a technique called RNA interference to deactivate dac2. The deactivation caused the kneecaps to fuse to the tibias, resulting in single knee-less leg segments.
Spiders therefore likely experienced ancient gene duplication of the original dac gene. Over time, dac2 led to the evolution of an entirely new function and unique way of walking in spiders.
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Prpic said, "Our work shows how a gene can be duplicated and then used during evolution to invent a new morphological feature."
In humans, scientists continue to investigate how genes affect our knees. Many medical experts have theorized, for example, that fragile knees could be inherited. At least we only have two knees to deal with, as opposed to spiders and their multiple leg joints.