Amazing stuff! What was first, the egg or the chicken? Or did evolution develop the same thing twice independently?
"Chromosphaera perkinsii is a single-celled species discovered in 2017 in marine sediments around Hawaii. The first signs of its presence on Earth have been dated at over a billion years, well before the appearance of the first animals. ...
this species forms multicellular structures that bear striking similarities to animal embryos. These observations suggest that the genetic programs responsible for embryonic development were already present before the emergence of animal life, or that C. perkinsii evolved independently to develop similar processes. ...
By observing C. perkinsii, the scientists discovered that these cells, once they have reached their maximum size, divide without growing any further, forming multicellular colonies resembling the early stages of animal embryonic development. Unprecedentedly, these colonies persist for around a third of their life cycle and comprise at least two distinct cell types, a surprising phenomenon for this type of organism. ..."
From the abstract:
"All animals develop from a single-celled zygote into a complex multicellular organism through a series of precisely orchestrated processes. Despite the remarkable conservation of early embryogenesis across animals, the evolutionary origins of how and when this process first emerged remain elusive. Here, by combining time-resolved imaging and transcriptomic profiling, we show that single cells of the ichthyosporean Chromosphaera perkinsii—a close relative that diverged from animals about 1 billion years ago—undergo symmetry breaking and develop through cleavage divisions to produce a prolonged multicellular colony with distinct co-existing cell types. Our findings about the autonomous and palintomic developmental program of C. perkinsii hint that such multicellular development either is much older than previously thought or evolved convergently in ichthyosporeans."
The egg or the chicken? An ancient unicellular says egg! "A cell division resembling that of an animal embryo has been observed in a prehistoric unicellular organism, suggesting that embryonic development might have existed prior to the evolution of animals."
A multicellular developmental program in a close animal relative (no public access)
A cell of the ichthyosporean C. perkinsii showing distinct signs of polarity, with clear cortical localization of the nucleus before the first cleavage. Microtubules are shown in magenta, DNA in blue, and the nuclear envelope in yellow.
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