Why is there uniformity in nature?

Question

ie most (all?) mammalian creatures have two eyes, two ears, one mouth, one nose

Answer 1

because thats when the trait evolved(after the two eyed/eared, one mouth/nose, body plan  became prevalent), keep in mind that evolution doesn't have a set in stone path its simply genetics and survival advantages. when you get a system that has underlying rules, no matter how random the original conditions seem there will eventually be order.

Answer 2

This really isn't a physics question, but I'm going to field a physics quote:

"The most incomprehensible thing about the world is that it is comprehensible."

-Einstein

If you're talking about something like physical laws, we don't really know at this point, and there's no particular reason to expect we ever will in a scientific way.

You give a biology example of uniformity in mammals, however, that is easy to explain, at least superficially. Mammals have a similar body plan because they share common ancestors. All of those features were probably present in the common ancestor, and probably continue to provide a valuable competitive advantage to the modern species.

I'm not an evolutionary biologist so I don't know if two eyes was first selected for because it provided depth perception, or because it provided an increased field of view (as seen in whales and most birds who have their eyes on opposite sides of the head). It turns out two eyes are pretty good for both purposes, so it's not hard to imagine that they were selected for strongly.

If you are interested in biology and/or evolution, the best book I can recommend is "The Blind Watchmaker" by Richard Dawkins. If you read it and pay attention it would be difficult to walk away without a firm understanding of what evolution is and isn't. It's the best presentation of the material that I've encountered, including college-level biology textbooks.

Answer 3

If John N is right, that means extraterrestrials may have evolved two eyes and two ears as a result, since two eyes are used for depth perception (needed everywhere) and two ears are used for the triangulation of sounds. One of the complaints that skeptics have made is that aliens "look too much like us". Yet, if these features confer definite evolutionary advantages, aliens that look similiar to us have a great likelihood of existing.

It is well known that the brain functions best when it is not overtaxed with conflicting stimuli, it is hard for people to concentrate effectively on more than one thing at a time. Therefore,having more than two ears would be cumbersome. Two is the optimal number, providing differences while not making the task of hearing or seeing too much of a muli-task.

Actually, although there is one nose, there are two holes in it. This is most probably to help with coordination involving inhalation, a type of "depth perception" as applied to air flow. It allows greater freedom to breathe coordinated breaths.

Answer 4

This more due to evolution. We evolved these traits since they provided specific advantages.

Two eyes provide depth perception.

Two ears provide triangulation of sound.

We have no need for to mouth or two noses - or at leat so far they don't seem to provide with any advantages. I'm not sure if that answers your question of uniformity in nature.

Hope that helps.