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Our evolution from jelly!

By Dave Armstrong - 20 Feb 2015 9:40:0 GMT
Our evolution from jelly!

The impressive but small ctenophores like Pleurobrachia represent a non-stinging branch of early metazoans, cruising here past a coral reef. They also provide great evidence of how and why our nervous systems developed !Ctenophore image; Credit: © Shutterstock

Without self-regulation and communication, multicellular animals have little they can use to influence their environment. The Metazoa now seem to have had neurons as a nerve net from the beginning, with the neuron-less sponges and others simply a regression or backward evolution. We aren’t supposed to say that, but it infers the obvious - they cannot evolve far beyond simple spongedom.

Successful animals and even some plants have advanced by evolving reaction to a point at which they can gain from their behaviour. Many different sensory inputs are capable of reproducing responses that often involve rapid intercellular communication. The comparison with the evolution of computers is fairly obvious. Both, for example, can be dominated by the basic size of their CPU, but brains aren’t everything.

In his essay for the Journal of Experimental Biology, Professor Peter AV Anderson (University of Florida, US) has surmised a lot about the relevance of the genomes of ctenophores such as Pleurobrachia bachei. Why are their genomes so relevant to all our evolutions? As 70% of a genome is involved in these precious neurons, neurobiologists can probably take heart, if not brain, from the research that will now take place in their field. Peter sets the problem as why specifically did nerve nets and neural systems appear.

The first neuron-like cells must have been able to transmit impulses, but epithelial and sensory cells also do that. Even the long protrusions (axons and dendrites) aren’t unique but we have to start somewhere with a cell dedicated to this kind of distant electrical communication. The ctenophore neurons are basic to discussion simply because they possibly evolved independently of all advanced metazoans, but they are quite close to the more-familiar stinging Cnidaria (jellyfish group.)

The full significance of this is that ctenophores are likely to be ancestral to almost all the animals we know. In this case, what did they use their neurons for? The selective advantage was almost certainly the advanced capabilities bestowed by controlling opposing muscles - movement could be precise for the first time. The movement and feeding of these first metazoans would have been greatly improved with cells such as these. The best predators and the most elusive prey could have sprung evolution into the fantastical (and often unknown and lost) biodiversity we can all appreciate!