Scientists at The University of Queensland have upended biologist's century-old understanding of the evolutionary history of animals. When the team used new technology to investigate how multi-celled animals developed, their discoveries showed a surprising truth.
According to Professor Bernie Degnan, the results of their research contradicted years of tradition. Explaining further, Professor Degnan noted that they have discovered that the first multicellular animals probably weren't like the modern-day sponge-cells, but were more like a collection of convertible cells.
In all essence, the great-great-grandmother of all cells in the animal kingdom was probably quite similar to a stem cell. Somewhat intuitive as this could be, compared to plants and fungi, animals have many more cells types, used in quite different ways, from neurons to muscle, and cell-flexibility has been critical to animal evolution from the start.
The results of the study disprove a long-standing idea: that multi-celled animals evolved from a single-celled ancestor resembling a new sponge cell known as a choanocyte. Professor said that scattered throughout the history of evolution are significant transitions, including the leap from a world of microscopic single-cells to a world of multi-celled animals.
There was incredible complexity with the advent of multicellularity, and it creates the animal, plant, fungi, and algae kingdoms that we see today. There is diversity in these large organisms from the other more-than-99-percent of biodiversity that can only be seen under a microscope.
The team mapped individual cells, sequencing all of the genes expressed, allowing them to compare similar types of cells over time. In his words, fellow senior author, Professor Sandie Degnan, said that this meant scientists could tease out the evolutionary history of individual cell types by searching for the signatures of each type.
She explained that biologists for decades believed the existing theory was a no-brainer as sponge choanocytes look so much like single-celled choanoflagellates, the organism considered to be the closest living relatives of the animals. However, their transcriptome signatures don't match, which means these are not the core building blocks of animal life that scientists initially thought they were.
They have only been using this technology for the last few years. However, it has helped them finally address an age-old question, discovering something utterly contrary to what anyone had ever proposed. She emphasized that they are taking a core theory of evolutionary biology and turning it on its head.
At present, they have an opportunity to re-imagine the steps that gave rise to the first animals, the underlying rules that turned single-cells into multicellular animal life. Professor Degnan hoped the revelation would help them understand their condition and their understanding of human stem cells and cancer.
