IN THE evolution of organs, skin came first. The discovery that even sponges have a proto-skin shows that the separation of insides from outsides in multicellular animals was key to their evolution.
It has been known since the 1960s that , or epithelium. But because sponges lack the genes involved in expelling molecules, it was assumed that this was not a functional organ. and her team at the University of Alberta in Edmonton, Canada, have now shown otherwise. When they grew flat sponges on thin membranes, with liquid above and below, they found that the epithelium kept some molecules out, sometimes only allowing 0.8 per cent through in 3 hours ().
Sponges were the first multicellular animals to evolve, so the finding means all complex life has a skin. Leys thinks the organ was vital as it isolated animals’ insides from their surroundings. As a result, cells could send chemical signals to each other without interference, setting the stage for complex organs to evolve.
Rather than loose clusters of cells, sponges are self-contained animals, meaning they are much more like other animals than we thought, says of the University of California, Berkeley.
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This is an updated version that corrects a misquotation of Scott Nichols’ comments
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