Two of everything - (Dec/19/2005 )
Why do many organs/structures come in twos? And where in the course of evolution did 'twoness' appear?
Still Many things we have in ones. Viz nose, head, tongue,*****, brain etc 
Absolutely right answer Molonco 
yeah, exept for lungs, eyes, ears and well arms and legs most of the stuff is stand alone... but its a thought....cos we can survive with just one of the "twos" one kidney, one ear, one eye - we wld still be alive... not so sure abt the lung one...
*shrug*
Bilateral symmetry. It is extremely adaptive and allows for survival long enough to pass on the genes.
yes but i'm still facing people who don't have one brain....
two neurons at least...
that is too true fred!
actually most of the things come in two, the brain has 2 hemispheres, the nose has 2 tonsils, the teeth are in pairs, the tongue has a symetrical anatomy, 2 testicles/ovaries. etc. Only the digestive system seems to have only one of each...
go figure.....
two neurons at least...
I think I don't have a brain for science, but have a brain for joke.
As someone's said above we can survive with another one if one of the two's is disabled.Bu then why not radial symetry.I think radial symetry has lower advantage/energy expenditure ration. Bilateral keeps our sense and motors active in considerably large volume still having lower energy expenditure.
But other organs that come singly still are bilaterally symmetrical.So it think symmetry is important.
Pisces and tetrapods seem to have generalized bilateral symmetry.
hrushikesh