Using new technology to investigate how multicellular animals developed, their findings revealed a surprising truth that contradicts years of tradition.
“We have discovered,” explains Bernie Degnan, “that the first multicellular animals were probably not like the cells of the current sponges, but rather as a collection of cells that varied constantly. The great-great grandmother of all the cells in the animal kingdom, so to speak, was probably very similar to a stem cell. This is logical because, compared to plants and fungi, animals have many more types of cells, which are used in very different ways, from neurons to muscles, and cellular flexibility has been critical to evolution from the beginning. “
The results, published in Nature, refute a long-standing idea: that multicellular animals evolved from a single-celled ancestor that resembled a modern sponge and was known as co-ocyte. The team led by Degnan made a map of the individual cells, sequencing all the expressed genes, which allows researchers to compare similar types of cells over time. This allowed them to unravel the evolutionary history of individual cell types by looking for the “signatures” of each of them.
“This technology has been used only in recent years,” adds Sandie Degnan, “but it finally helped us to address an old question, discovering something completely contrary to what was believed so far. Someone had proposed. For decades, biologists believed that the existing theory was obvious, since the coanocytes closely resemble organisms considered to be the closest living relatives of animals. But their transcriptome signatures simply do not match, which means that these are not the fundamental pillars of the animal life that we originally thought they were. We are taking a central theory of evolutionary biology and changing it completely. Now we have the opportunity to re-imagine the steps that gave rise to the first animals.”
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