Scientists at The University of Queensland have upended biologists’ century-old understanding of the evolutionary history of animals.

Using new technology to investigate how multi-celled animals developed, their findings, published in Nature, revealed a surprising truth.

Professor Bernie Degnan said the results contradicted years of tradition.

“We’ve found that the first multicellular animals probably weren’t like the modern-day sponge cells, but were more like a collection of convertible cells,” Professor Degnan said.

Adult sponge Amphimedon queenslandica. Photo credit: Karin Taylor. Adult sponge Amphimedon queenslandica. Photo credit: Karin Taylor.

“The great-great-great-grandmother of all cells in the animal kingdom, so to speak, was probably quite similar to a stem cell.

“This is somewhat intuitive as, compared to plants and fungi, animals have many more cell types, used in very different ways – from neurons to muscles – and cell-flexibility has been critical to animal evolution from the start.”

The findings disprove a long-standing idea: that multi-celled animals evolved from a single-celled ancestor resembling a modern sponge cell known as a choanocyte.

“Scattered throughout the history of evolution are major transitions, including the leap from a world of microscopic single-cells to a world of multi-celled animals,” Professor Degnan said.

“With multicellularity came incredible complexity, creating the animal, plant, fungi and algae kingdoms we see today.

“These large organisms differ from the other more-than-99-per-cent of biodiversity that can only be seen under a microscope.”

Scanning electron microscopy image of an Amphimedon queenslandica intact chonanocyte chamber in which many individual choanocytes are visible. Photo credit: Rebecca Fieth. Scanning electron microscopy image of an Amphimedon queenslandica intact chonanocyte chamber in which many individual choanocytes are visible. Photo credit: Rebecca Fieth.

The team mapped individual cells, sequencing all of the genes expressed, allowing the researchers to compare similar types of cells over time.