Nature is symmetrical: why?

[doctor-bond]

Hullo Biologists -

 

I've been trying, in vain, to think of a natural (ie living) thing that is not symmetrical, but it seems like symmetry rules.

 

Obviously, living things develop under the influence of outside forces (e.g. trees bent by prevailing winds, three-legged cats); but without such forces, aren't all living things symmetrical? At root (ha!), trees have the same dendritic symmetry; even lichens seem to spread with an alarming regularity.

 

So, has anyone got any examples of living things that aren't symmetrical?

 

And, also, why is symmetry so prevalent: what are the mechanisms that cause it?

 

 

cheers

[EdEarl]

Cells divide into two cells, and this process begins the symmetry. But, that is not really an answer, it is merely an observation of the mechanics that make things symmetrical. No one knows why cells divide into two to replicate, why don't they randomly divide into many? I suppose you could say, DNA is split to cause cell replication, but why is that method chosen rather than another that allows random multiple divisions?

[pears]

There are some interesting responses in another thread on symmetry here http://www.scienceforums.net/topic/78635-why-are-human-beings-symmetric-along-our-length/#entry766627

[Strange]

If you think trees are symmetrical, then I have a feeling you are using a very loose definition of symmetry under which anything can appear symmetrical...

 

What about the fact that organic molecules are frequently chiral? And many organisms exhibit handedness (fiddler crab?).

[studiot]

 

I've been trying, in vain, to think of a natural (ie living) thing that is not symmetrical, but it seems like symmetry rules.

 

 

 

 

There is only one being I can think of that has symmetrical hearts and he was on television over Christmas.

 

you are using a very loose definition of symmetry

 

 

Agreed.

 

Pairing, rather than real symmetry, is more frequent in the externis of living things than the internal structure.

For example you have a left hand and a right hand, they are not symmetrical.

They are, however a reflective pair.

For true symmetry you have to be able to overlay one part on its symmetric partner part exactly by rotation.

 

But there are plenty of examples of monism (Rhino horns, fish fins, etc), and even a few of trilateration eg the now extinct tricertops.

[Endy0816]

Some sponges and adult flatfish are asymmetric.

 

Code size is less. Probably stability is the big issue.

[AndresKiani]

I don't believe its very symmetrical, at least not perfectly. Cellular membrane is never perfectly spherical, DNA is not perfectly lined up and down, there are mutations, there are '3 ends that never get replicated by replication enzymes, so they stick out at the ends. Most organisms are not perfectly symmetrical, I cannot think of one that is.

 

I don't see a perfect symmetry in life, maybe though, the "relatively symmetrical" world we see is symmetrical, because in nature biological creatures that are more symmetrical (Well balanced - homeostasis) tend to be stronger than those a that are less symmetrical (Not well balanced - homeostasis)

 

For us humans this would be the same reason why more symmetrical individuals are more attractive to us...