Because, through evolution, we have lost the need for a few organds that once did have a specific function. I forgot which one it is, maybe the liver, not sure, that doesn't do anything to help us anymore but it use to filter out poisons for us. Since we have evolved, we have lost the need for that function because we don't digest poisons much anymore.

Could I ask you where you're from? In the United States, the word redundant means unnecessarily duplicative. (In other words, that its function is already covered by something else.) In the the United Kingdom, the word redundant means, basically, not needed. Which one did you mean? (I once took part in a negotiation between the U.S. government and the Canadian government. There was a proposal that the Canadians were expected to make that we didn't like, and when they said they wanted to table the proposal, all the other Americans relaxed. Because in American English, tabling a proposal means dropping it - in British and Canadian English it means to put it forward for consideration. Odd, isn't it -- it's the same language and in the same context the same word means exactly the opposite to some people as it does to others.)

Some organs we no longer need, such as tonsils or an appendix. But there are no organs that serve the exact same function as others unless they have a twin, such as the kidneys.

1) I am not absolutely sure what you are meaning with redundant. We have: - some vestigial organs, which have lost all or most of their original function through evolution. - some few organs that could be donated by a *living* donor, with various disadvantages. It is generally considered that there are not so major disadvantages in donating a kidney. However, it involves, at least, an operation; and in case of a kidney failure, it is better to have two kidneys. Same with blood donation. But some other living donor donations are more controversial. - some organs are present in pairs. However, the suppression of one element of the pair would be an evident disadvantage for the person. For instance: eye, ear, lung... 2) "In the context of human evolution, human vestigiality involves those characters (such as organs or behaviors) occurring in the human species that are considered vestigial - in other words having lost all or most of their original function through evolution. Although structures usually called "vestigial" are largely or entirely functionless, a vestigial structure may retain lesser functions or develop minor new ones. Vestigial characteristics occur throughout nature, one example being the vestigial hind limbs of whales and snakes. Many human characteristics are also vestigial in other primates and related animals." Source and further information: http://en.wikipedia.org/wiki/Human_vestigiality 3) "There are many forms of living donation. This page includes information and links to sites with more details on living donation other than kidney, liver, and bone marrow. Click on the subject of interest below. Living Lung Donation | Living Pancreas Donation | Blood Donation | Living Heart Donation Human Egg and Sperm Donation | Human Milk Donation | Living Nerve Donation Living Skin Donation | Living Intestine Donation" Source and further information: http://www.livingdonorsonline.org/other/other.htm 4) "Riley: Surely there are ramifications for those who would donate a kidney to someone. What are some of the considerations? Would that in some way be entering a market? Lawler: I have been thinking about this . . . The Catholic Church endorses without reservation kidney donation. It is based on this principle: a donation is not an invasion of your bodily integrity if you surrender an organ that is redundant. Almost the only organ you have that is redundant is your “extra” kidney. You are only slightly, slightly, slightly worse off if you have only one kidney. It could be that men are more susceptible to high blood pressure if they have only one kidney, but the jury is still out. Given that, the Catholics are okay with donation, but they stop short of the market. But if we were to enter into a market, we would have to be careful that no other organ, including the liver, would be included. The danger with liver donation is much greater. Part of your liver is not really redundant: you are better off with a whole liver. So a lot of prudent people are starting to think, is there any way we can have a carefully regulated kidney market without creating a devastating precedent? This is a dilemma specific to a certain stage in science. Eventually, science will come up with something better than transplanting kidneys. Some of the scientists say that xenotransplantation (basically using pig kidneys) might end up working. Maybe they will develop an artificial kidney. Maybe they will come up with a cure for chronic kidney disease. But for now, there is nothing. Riley: So must we seriously consider a market for kidneys? Lawler: My own opinion for now is that the precedent that we would set would be so devastating that there would be no going back on it. We would want to put the kidney thing in a box, and not have it affect other areas. I think that wouldn’t work out. What makes this seem fairly benign is the Medicare entitlement, that people would get lots of money for their kidney. Libertarians who are for the kidney market also know that Medicare has no future. So what happens when demographic pressures cause Medicare to collapse? We all know that will happen. Then we will have something much closer to a free market in kidneys. The price will plummet. The kidney market will globalize. Then you will start to have the ugly transfer from healthy young people to sick, rich, and old people. That wouldn’t happen now because of the Medicare entitlement, but that will happen eventually." Source and further information: http://bioethics.com/?m=200807 By the way, notice that the kidney consists in at least *three* organs, only one of which will be used by the receiver of an organ donation, as far as I know: - the kidney itself (which is donated) - the adrenal medulla - the adrenal cortex

I'm not certain what you mean..do you mean why are we partially bilaterally symmetrical ?