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Ancient Genes Reveal Our Precambrian Ancestor

The Amphimedon sponge

The Amphimedon sponge (shown here inside a pink soft coral) is the first sponge to have its genome sequenced. Photo: Maely Gauthier

By Claire Larroux

The genome of a sponge found on the Great Barrier Reef is helping scientists to reconstruct the 600 million-year-old ancestor of the entire animal kingdom.

Claire Larroux completed her PhD at the University of Queensland, and is now a Humboldt postdoctoral fellow in the Department of Earth & Environmental Sciences, Palaeontology & Geobiology at the Ludwig-Maximilians-University in Munich.

The full text of this article can be purchased from Informit.

One of the great questions in evolution is how complexity evolves. How does one go from a single-celled organism to a complex animal?

Fossils appear to tell us that most animal forms we know today arose in a short window of time during the Cambrian explosion approximately 540 million years ago. Creationists use this sudden appearance of complex animals to deny that evolution occurs.

But what happened before the Cambrian? The sparse fossil record of sponges and the enigmatic Ediacaran fauna suggest that animals were already experimenting with multicellular life during this Precambrian period. Was there a gradual increase in complexity in the first animals?

A modest sponge from the Great Barrier Reef is helping us to answer these questions. Amphimedon queenslandica, named after the state of Queensland, has the honour of being the first sponge to have its genome sequenced.

Sponges are the most ancient animals on Earth, dating back to well before the Cambrian period. As a representative of our oldest animal cousins, the Amphimedon sponge genome is helping us to piece together our common ancestor with all other animals, which lived more than
600 million years ago.

To put this ancestor into context, the only visible life-forms in the ocean when it evolved were mats of blue-green bacteria and small filamentous green and red algae. Hence...

The full text of this article can be purchased from Informit.