Ponder this one in the bath. Chances are you've just scrubbed your back with a choice example of one of evolution's greatest inventions. Or at least, a good plastic copy.
Sponges are a key example of multicellular life, an innovation that transformed living things from solitary cells into fantastically complex bodies. It was such a great move, it evolved at least 16 different times. Animals, land plants, fungi and algae all joined in.
Cells have been joining forces for billions of years. Even bacteria can do it, forming complex colonies with a three-dimensional structure and some division of labour. But hundreds of millions of years ago, eukaryotes - more complex cells that package up their DNA in a nucleus - took things to a new level. They formed permanent colonies in which certain cells dedicated themselves to different tasks, such as nutrition or excretion, and whose behaviour was well coordinated.
Eukaryotes could make this leap because they had already evolved many of the necessary attributes for other purposes. Many single-celled eukaryotes can specialise or "differentiate" into cell types, dedicated to specific tasks such as mating with another cell. They sense their environment with chemical signalling systems, some of which are similar to those multicellular organisms use to coordinate their cells' behaviour. And they may detect and capture their prey with the same kind of sticky surface molecules that hold cells together in animals and other multicellular organisms.
So what started it? One idea is that clumping together helped cells avoid being eaten by making them too much of a mouthful for single-celled predators. Another is that single cells are often constrained in what they can do - for example, most cannot grow flagella to move and also divide at the same time. But a colony can both move and contain dividing cells if each cell in it takes its turn.
Researchers are now trying to reconstruct the biology of the first multicellular creatures by studying the genomes of their nearest living relatives. "We're trying to peer back hundreds of millions of years," says Nicole King, a molecular biologist at the University of California, Berkeley. She and her team are studying single-celled protozoans called choanoflagellates to understand how animals came to evolve from them some 600 million years ago. Choanoflagellates and sponges - the only surviving witnesses to this step - share a common ancestor and King has found that choanoflagellates have a surprising number of equivalents to the signalling and cell-adhesion molecules unique to animals.
Yet bigger and more complex isn't necessarily better. As King points out, unicellular life still vastly outnumbers multicellular life in terms of both biomass and species numbers. "So you could say unicellular life is the most successful, but that multicellular life is the most beautiful and dramatic."
Claire Ainsworth. Back to top
THEY appeared in an evolutionary blink and changed the rules of life forever. Before eyes, life was gentler and tamer, dominated by sluggish soft-bodied worms lolling around in the sea. The invention of the eye ushered in a more brutal and competitive world. Vision made it possible for animals to become active hunters, and sparked an evolutionary arms race that transformed the planet.
The first eyes appeared about 543 million years ago - the very beginning of the Cambrian period - in a group of trilobites called the Redlichia. Their eyes were compound, similar to those of modern insects, and probably evolved from light-sensitive pits. And their appearance in the fossil record is strikingly sudden - trilobite ancestors from 544 million years ago don't have eyes.
So what happened in that magic million years? Surely eyes are just too complex to appear all of a sudden? Not so, according to Dan-Eric Nilsson of Lund University in Sweden. He has calculated that it would take only half a million years for a patch of light-sensitive cells to evolve into a compound eye.
"Eyes sparked an evolutionary arms race that transformed the planet"
That's not to say the difference was trivial. Patches of photosensitive cells were probably common long before the Cambrian, allowing early animals to detect light and sense what direction it was coming from. Such rudimentary sense organs are still used by jellyfish, flatworms and other obscure and primitive groups, and are clearly better than nothing. But they are not eyes. A true eye needs something extra - a lens that can focus light to form an image. "If you suddenly obtain a lens, the effectiveness goes from about 1 per cent to 100 per cent," says Andrew Parker, a zoologist at the University of Oxford.
Trilobites weren't the only animals to stumble across this invention. Biologists believe that eyes could have evolved independently on many occasions, though genetic evidence suggests one ancestor for all eyes. But either way, trilobites were the first.
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More Greatest Inventions
Tue Nov 20 15:28:21 GMT 2007 by Gerard Jagers Op Akkerhuis
1. It seems that the ''invention'' of eukaryocy is lacking. Yet, without that the multicellularity item would not even exist.
2. I would like to ask your attention for the ''invention'' of first-next possible closure. That is: the possibility nature has found to create next complexity level system types by means of the first-next possible closure process. This ivolves the step from chemistry to bacterial cells, from prokaryotic cells to eurkaryotes, from single cells life to multicellulars and from multicellulars to hypercyclic neural networks.
More Greatest Inventions
Sun Aug 16 22:20:42 BST 2009 by T. Mayy
Sure! but consider this;
Trilobites Rock baby! Yeah!
Mon Dec 10 16:42:27 GMT 2007 by Ohuauhuh
Sheep give us wool, meat and are good pets
Sat Feb 02 09:26:00 GMT 2008 by Ilmer Tabares
I am one of the students of South Western University here in Cebu City, Philippines. One of our requirements to pass our Science, Technology and Society (STS) subject is to e-mail researchers like you.
In line of the above, the undersigned would like to have a copy of your research if that is possible.
Thank you and hoping for a favorable response.
Ilmer B. Tabares
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