Why do evolution theorists explain a physical trait as being necessary, yet other animals get along fine w/out

Question

this trait, even though they live in the same exact environment?

So a dull, brown bird living side by side with a colorful parrot shouldn't exist, because he's too dull and colorless to find a mate. Or, on the other end of the argument, the colorful parrot shouldn't exist, because his colors betray his location to predators. Yet, dull brown birds to in fact live side by side with parrots...

And of course, it's "obvious" that humans walk on two legs so we could see over the grass. But this doesn't explain why the grass still seems to be taller than many other animals. Did the grass evolve to hide the animals from us? Does seeing over the grass really help that much, when both predators and prey can both hide within the grass?

When a butterfly evolved to metamorphosize, how can this be a trait passed on to future generations? How in the h**l can this trait be passed on? I am d**n certain butterflies didnt get this trick down pat on the

Answer 1

Your assumptions about evolution are incorrect at the most basic levels.  Why not actually do some research into the theory instead of building logically flawed "questions" based upon your flawed and overly simplistic understanding.

Answer 2

Evolution diversity accounts for all the things you're saying.  Every species has it's own form of what worked and what didn't and what still needs to be changed.  So we DON'T have all herbivores looking the same in the same environment, eating the same things, running from the same looking predators.

Genetics, mutations, luck of the draw, all this comes together to shape each species and subspecies.  Nature still experiments--there are cheetahs with stripes (look up "King Cheetah"), there are albino and dark eyed white forms for every species, including humans and octopus.  There are dark phases for many as well (black leopards, dark rabbits, black phase forms on raptors).  Spontaneous mutations in cats still show up -- the American Curl, the Manx, the two types of Rex, the Munchkin, the PixiBob, all started with natural mutations.

Answer 3

This is a good set of questions, but one requires that you improve you understanding of what evolution says. I really like the fact that you are trying to think about these topics analytically. I wish I had you for one of my students.

Natural selection selects for those traits in a species that give a competitive advantage to a member of a species over the other members of THAT species. The traits are not necessary; they are an advantage. In particular, an advantage to reproducing more members of the species with that trait.

Further, natural selection can only work on traits that are present in the species, at least one member of the species. New traits come from random mutations. Good mutations are extremely rare and occur randomly. They often occur in one species and not another. So natural selection can only cause them to propagate in species that are lucky enough to get that mutation.

Next, species live in different ecological niches in the same environment, with different needs and different traits. All these effect whether a new mutation will be a benefit or liability.

Taking your zebra vs antelope example. Antelopes are browsers that live in small heards. They inhabit taller grass and bushes where camoflage works better. Zebra's are grazers that live on the open plain in large heards. They have little opportunity for hiding. The large heards give an opportunity for confusion making zebraflage a competitive advantage.

Next lets take your dull bird, bright bird example. Birds are not just birds. Every bird species is unique and infact every bird is unique. For example, one bird may eat fruit and another may eat seeds. This gives each bird different needs and different traits to which new traits are introduced. The fruit eating bird would be at an advantage if it was attracted to bright colors (ripe fruit).

Once this trait evolves in the species, a male that was brightly colored would tend to attract more females. This would give it an advantage over the other members of ITS species, but would have little effect on the dull colored seed eater species.

Next lets look at upright locomotion. One of the frequent mistakes that teachers make when teaching evolution is giving students the impression that animals have a trait for ONE reason. This is almost never the case. The traits that are selected for, are the ones that confer a reproductive advantage. Traits that give many minor advatages to an organism are just as good if not better than than traits that are good for one reason.

Upright locomotion does indeed confer vision advantages and many quadrapeds will stand on their hind legs to get a better look at the environment, including most primates, some deer, and bears. This is particularly important for an animal like us which has poor hearing and sense of smell but relatively good color and motion vision. Nevertheless, it is naive for us to believe that this is the only reason for being upright. Biophysicist have calulated that it is much more energy efficient to be bipedal. Being bipedal makes you look larger and it able to intimdate some predators (bears rise up in threat situations also). Bipedalism allows you to carry food and offspring better, if you have grasping hands. I am sure there are many more reasons why bipedalism was a good choice for the hominid species.

There is a good explanation for butterflies dramatic metamorphosis, but I am too tired to go through it in detail. Suffice it to say that many insects undergo a much less dramatic series of metamorphoses in which they gradually aquire the winged adult form. These intermediate metamorphoses are just slight modifications of the the process of growth associated with shedding the exoskelaton. Look up nymphs and instars to see examples of these partial metamorphoses. Mutations that collapsed these multistep metamorphoses into one step would be favored since partly formed wings are mostly useless, they add extra weight, and they can be damaged before they are complete.

I really like the fact that you are thinking about these things analytically. You ask better questions than most people who are skeptical about evolution. Questions like yours have been asked and answered sucessfully for the last cenrtury by some of the smartest people who ever lived. Unfortunately this is not the ideal forum exchanging complicated ideas. Feel free to write me directly as you have more questions. I am impressed by your ability to see subtle issues.