Credit: Maely Gauther
We only just survived being told we have the same basic gene set as a roundworm – 20,000 genes give or take a few. But a recent report goes too far: the sponge!
It’s just a blob with no eyes, no nervous system, no muscle, no gut, no circulatory system, no tissues of any sort really – just cells embedded in a jelly matrix. They’re not even considered true animals.
Yet, according to the Nature report by researchers at the University of Queensland and the Department of Energy’s Joint Genome Institute in California, the sponge genome also sports much of the basic tool kit of all animal life.
“There’s been a lot of surprises,” admits Bernie Degnan, the leader of the University of Queensland team that collected the decoded sponge, Amphimedon queenslandica, from the Great Barrier Reef. “We time travelled 600 million years back to reconstruct the ancestor of all living animals. Now we’re rewriting the way we perceive evolution.”
In recent years, biologists have had a treasure trove of creatures’ genomes to peer into. At first, it was their favourite lab models such as the fly and the worm.
But increasingly the choices have become more strategic: those creatures that occupy key branches on the tree of life. Ever since 19th century taxonomists took a close look at the sponge, they realised it occupied a landmark position.
It was considered an ‘ur-animal’. Like the first attempt at civilisation in the ancient city of Ur in Babylon, the sponge was seen as a first attempt at multicellular life. It was not quite there, but possessed the hallmark features of an animal, instead of a plant or fungus.
For instance, they have soft membranes around their cells, unlike the rigid wall of plants or fungi. And like all animals, they rely on outside sources to get their food – they filter water to capture bacteria and organic matter. They also had the key hallmark of being animal – they were a society of different cell types that had learnt to live together.
The reading of this animal’s genome promised to reveal crucial things about what it took to become an animal. More importantly, we would learn valuable things from what it didn’t have. The ‘missing’ genes would provide clues to how to make things that belonged to real animals, such as brain cells or muscles.
Researchers were staggered to find that in fact the sponge was not missing much at all. The gene number, though yet to be finalised, seems to be in the range of 20,000. Most of the components of the animal gene kit are there.
For instance, though the sponge does not have anything like a brain cell, it has most of the genes needed to make one. “Some of the molecular machinery for making animals predates animals – it’s quite a surprise,” says David Miller, who is hard at work reading the coral genome at James Cook University in Townsville.
It’s an eerie finding - the sponge all tooled up as if anticipating the future of evolution. Imagine archaeologists excavating a Palaeolithic cave and pulling out silicon chips and wires.
It’s enough to conjure up scenes of the monolith urging humanoids to evolve in 2001 or the whispering phantom urging Kevin Costner to “build it, he will come” in Field of Dreams.
