Animals embryos evolved before animals, study reveals

Earlier, researchers at the University of Queensland had solved the billion-dollar 'chicken or egg' paradox

A research conducted by a team of scientists at Bristol University has found that animal embryos evolved before animals. Until now, the evolution of animals was studied by analyzing living animals and their relatives.

But now, the research team has found that fossilized embryos that resemble multicellular stages in the life cycle of single-celled relatives of animals, which indicates that animal embryos started evolving first.

Animal embryo evolved first

Primate embryo
Day 17 of a cultured primate embryo; the various colors indicate markers of cellular differentiation (specialization). Weizhi Ji/Kunming University of Science and Technology

During the study, researchers discovered these fossils from 609 million-year-old rocks in the Guizhou Province of South China. Scientists have named these fossils Caveasphaera, and they are just only about half a millimetre in diameter. X-ray analysis done on these fossils revealed that they were preserved all the way down to their component cells.

"X-Ray tomographic microscopy works like a medical CT scanner but allows us to see features that are less than a thousandth of a millimetre in size. We were able to sort the fossils into growth stages, reconstructing the embryology of Caveasphaera," said Kelly Vargas, a researcher at the University of Bristol's School of Earth Sciences in a recent statement.

Did embryo develop into complex organs?

Zongjun Yin, from Nanjing Institute of Geology and Palaeontology in China, who is the co-author of the study suggested that Caveasphaera sorted its cells during embryo development in just the same way as living animals that include human beings. However, he made it clear that there is no evidence that these embryos developed into complex organs.

"Caveasphaera had a life cycle like the close living relatives of animals, which alternate between single-celled and multicellular stages. However, Caveasphaera goes one step further, reorganizing those cells during embryology," said John Cunningham, co-author of the study.

Few months back, a study conducted by a team of experts at the University of Queensland and Neel Institute had solved the billion-dollar 'chicken or egg' paradox. After using various theories of quantum physics, researchers found that both the chicken and egg can come first. However, another study conducted in 2014 argued that chicken came first, as proteins found in the body of chicken are necessary to form an egg.