The colonial theory, which made it possible to understand the evolution of multicellular animals, seems not to be as valid as previously thought. The results obtained by a team of scientists from the University of Queensland (Australia) refute the idea that multicellular organisms evolved from a colony of choanoflagellates, unicellular beings similar to the choanocytes of modern sponges.
“We discovered that the first multicellular animals were probably not like today’s sponge cells, but rather like a collection of convertible cells ,” says Professor Bernie Degnan of the research team.
The great-great-grandmother of every cell in the animal kingdom, so to speak, was probably very similar to a stem cell. “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 fundamental to animal evolution from the beginning,” he explains. Degnan– Scattered throughout the history of evolution are major transitions, including the leap from a world of microscopic single cells to a world of multicellular animals. “
“With multicellularity came incredible complexity, creating the kingdoms of animals, plants, fungi and algae that we see today,” says Degnan, whose team mapped individual cells by sequencing all the expressed genes, allowing the researchers to compare similar types of cells over time.
Associate Professor Sandie Degnan, lead author of the study, clarifies that this means that they could uncover the evolutionary history of individual cell types by looking for the ‘signatures’ of each type. “For decades, biologists believed that the existing theory was obvious, since sponge choanocytes closely resemble single-celled choanoflagellates, the organism considered to be the closest living relative of animals – explains the scientist -. But their signatures transcriptome numbers just don’t match, which means these aren’t the building blocks of animal life that we originally thought they were. “
“This technology has been used only for the last few years, but it has finally helped us to address an age-old question and discover something completely contrary to what someone had proposed, ” he adds. The colonial theory about the origin of animals considers them as a product of evolution from colonies of flagellated eukaryotes, and places the point of evolution around 800 million years ago, during the Cryogenic period, through the appearance of cell adhesion molecules and immune complex systems.
“We are taking a central theory of evolutionary biology and changing it from the roots,” explains Professor Degnan, who hopes that the new finding will help us understand our own condition and expand our knowledge about our stem cells and about cancer. “Now we have the opportunity to reimagine the steps that gave rise to the first animals, the underlying rules that turned individual cells into multicellular animal life,” he concludes.
