How did Evolution produce Symmetry?

It's not true that animals are perfectly symmetrical. Only the external organs are (approximately anyway). This makes good functional sense, a fish with one side more developed than the other would swim best in circles, a spider with six legs on one side and two on the other wouldn't walk so well, a fish with two eyes on one side and none on the other would be vulnerable to attack from the side with no eyes, and unable to forage effectively on that side.You'll note that external symmetry is broadly true of man-made vehicles too, look at a car, a bike and a plane for example. Incidently, this is a strawman - evolution is not a random process, although it does have random elements.

How so? Pentadactyl limbs are believed to be an evolutionary 'accident'. As to why we have two hands, see below: We evolved from four legged animals, four legs is the minimum number for easy walking (since you can maintain a stable tripod at all times - which is what the earliest known land animals seem to have done). Symmetry is the best for easy movement. Two is the minimum number required for stereoscopic sensing. If you've got a body plan based on two of things, where is the logical place for something you only need one of? That's right, in the middle. Otherwise you'd de-balance the body plan, with the resultant constructive and mechanical difficulties. Symmetry is almost universally attractive among animal species (including humans). Butterfly decrorative patterns are generally either display, or eye-mimic patterns. Display patterns will want to be symmetrical for the above mentioned reason, eye-mimic patterns need to match the eyes of those they mimic.There is a good reason for the attractiveness of symetrry, perfect symmetry (as opposed to near-perfect symmetry) is very difficult to build, it otherwords it's energetically expensive, while being functionally minimally advantagous. Thus successful mate material will be able to spare the energy required for symmetry while less fit organisms will not.

That was an unnecessarily rude response, Darwinsterrier.

Darwin's Terrier:It was unnecessarily rude for the following reasons:

• While Defender may have been slightly patronising in his post, he was doing so to demonstrate his point rather than insult.
• The information in your post was valid, but by being so rude and adversarial you add nothing to the debate.
• When one is right, one can afford to be gracious.
• An overly aggressive stance such as yours actually weakens your position, and by association, our position.

How about you keep your assumptions to yourself, hey?

You are, of course, correct. There are several (many?) exceptions to the general rule of animal symmetry; I'd considered discussing this in my original post, but felt it would over-complicate matters. What is interesting is that asymmetry always occurs for functional reasons as well.