Thursday, November 17, 2005

On pluricellular organisms.

Why would one species evolve from one cell into a multicellular being?

This question can only be answered if we consider that in multicellular organisms only a small group of cells is allowed to duplicate endelessly (the germ line cells as well as the stem cells). All other cells in an organism are there just to perform a task and when they are no longer healthy they are replaced by newly specialized stem cells that promptly loose their high reproductible capability.

Two things are necessary for a cell to be useful to the organism: it must not be able to reproduce independently and it shall be specialized in a way that a specific trait (or group of traits) will be pushed to the maximum so this cell will perofrm tasks for the sake of the organism and not of itself.

Imagine for instance a single-cellular organism that creates a copy of itself but this copy due to some sort of mutation cannot reproduce. This copy will tend to grow and accumulate energy but since it cannot reproduce this process should proceed until it either dies or the nutrients flow out of its cytoplasm and be ingested by the normal reproducing cells. This is an example of "cooperation" between a germ line cell and a somatic cell. The term cooperation is quoted because in fact the copy is being enslaved by the other cell that is using it to acquire more energy and reproduce. If this cell manages to keep the capability of creating both normal daughters and "slave" copies it will have an advantage against the other cells that only create normal copies of itself.

The lack of reproducibility being the first specialization necessary for the somatic cell, let's pass to the next step: imagine that the slave cell now suffered some sort of mutation that causes it to produce an enormous amount of nutrients ( aminoacids, ATP, or any other metabolite necessary for survival) and after overproducing this payload it dies, suffers necrosis and the "master" cell captures all this energetic package. Once again we have an advantage for the master cell. This kind of specialization can be extended from energy metabolism to oxygen transport, mechanic protection, termal protection or any other kind of use; It's life using life to survive.

This makes us wonder who's really in control of our lives: our brain or our gonads?


Anonymous Anonymous said...

hi, new to the site, thanks.

12:29 AM  

Post a Comment

<< Home