Why do most living creatures look symmetrical on the outside?

Answer 1

The basic answer is that symmetry is efficient from the point of view of growth of a multicellular creature. The same DNA plan to construct the left side can also construct the right side.

The bigger question is why are we symmetrical from left to right, but *asymmetrical* from front to back? (Dawkins covers this.)

The answer goes all the way back to an early stage in evolution where, basically, worms were the dominant body plan.

There are advantages to creating a separate opening for eating and excreting ... namely, it reduces the chance that the worm will reingest something it has just excreted. So one end becomes the "front" end, for eating, and the other end the "rear" end for excreting. As sense organs are far more useful for eating, they would tend to develop near the front end. This in turn would cause nervous-system organs for processing sense information to be near the senses (the brain also goes to the front). And all appendages that develop for locomotion, would develop to propel the organism forwards (towards the "front"), which is why tails (originally used for swimming) develop in the "rear" end, fins and legs are structured to push backwards. And so on.

However, while there is an advantage for front-rear asymmetry, there is no significant advantage to left-right asymmetry. We don't find food more often on the right than on the left. Predators don't attack more often from the right than from the left. So it is advantageous to have sense organs arranged to look both left and right (two eyes two ears), and limbs arranged to move us both left and right (left limbs, right limbs). So left-right symmetry has stayed.

So basically, we are bilaterally symmetrical, because almost all animals (except for things like starfish), had a common ancestor with a 'wormlike' body plan.
.

Answer 2

For the answer to that, I recommend reading "The Ancestor's Tale" by Richard Dawkins. I can't explain it completely myself, but the basic reason is that there's no reason why an animal/plant shouldn't be symmetrical.

Answer 3

one million) "All evolutionary concept can merely be approximately risk or improbability, with the aid of fact the approach - in the majestic variety stepped forward by making use of Darwin - has not been, and could't be spoke of, and for this reason can not be examined against the thought, or used to foretell activities." the approach has been spoke of and is persevering with to be spoke of. Human lifespan keeps increasing and human beings are on popular greater and smarter. we are additionally gazing species dieing out with the aid of fact of environmental differences, in time different species will take their place. 2) "that's incredible what number supporters of the thought of evolution by making use of organic determination can not see the version between the micro-evolution of version or alteration interior species, and the much extra formidable advancements of macro-evolution, in my view qualitatively distinctive, which Darwinists have self assurance in." Given some mass extinction worn out the dinosaurs, smaller creatures took over and grew in length and persevered to evolve to their atmosphere. large mammal fossiles are actually not got here across on the comparable time of dinosaurs. 3) "The fossil checklist is crammed with gaps and distinctly ambiguous. Species look and disappear unexpectedly, which I could have concept could disenchanted the Darwinist place particularly badly, yet by some potential does not." certainly it helps the Darwinist place - the fossil information instruct how species recognized replaced and died out, then different species grew to take their place. at last, guy will maximum possibly be wiped off of this planet, and something else will take his place. The identification place is merely that each and every thing became into created at as quickly as and not something new has arisen over the years. they decline to describe the upward thrust of the dissimilar species.

Answer 4

through evolution. the survival of the fittest.