Yeah, that’s a good question and I don’t have a good answer. Obviously symmetry is important almost all animals have it. My guess is that’s because it’s “Easier” — take a good idea (like, say, hands) and just copy it to the other side of the body. In simpler animals, when they just need 1 of something (like a throat, or a stomach) — they were still symmetrical because these organs were simple and right down the middle of the animal. As these organs got more complex (i.e. going from a 1 to 2 to 4 chambered heart) it became necessary to break the symmetry and move them around a bit. That’s just my best guess, though
Very good question yet I don’t know the right answer to that. I agree with Matthew that when organs get more complex, they tend to be asymmetric. Like our brain and heart. If the two parts are identical, it would lose the sophistication we appreciate : )
The body is symmetrical in lots of ways but I think the answer is evolution. If changes happened like Matt said with a heart getting 4 chambers and that animal survives longer than animals with 1 chamber then they have babies and that trait gets passed on. So we have started getting more complex and evolving into our asymmetrical bodies over millions of years!