Perhaps we have two so that we can save lives. We have the potential at least to do so. --------- From The National Kidney Federation UK It is not clear why there are normally two kidneys. The human body does not need two kidneys, it could manage perfectly well with one kidney. It may just be that it has been useful for us to develop some parts of the body in pairs (arms and legs), so other parts doubled up as well. It is also possible that there is an evolutionary advantage in having a ‘spare’ kidney, and this is certainly important in modern medicine, because people can live live normal lives with one normal kidney. http://www.kidney.org.uk/Medical-Info/kidney-disease/small-singlekid.html

We have two kidneys in order to balance the load placed upon them by the body. In 24 hours the kidneys reclaim about 1,300 g of sodium, 400 g of sodium bicarbonate, and 180 g of glucose. With one kidney only half this amount would be processed. The body can manage with only one kidney but the job is faster and easier with two doing the work. The sooner toxins and waste are removed from the body the better! There is also the issue of body balance and symmetry. If we had only one kidney then one side of the body would be slightly heavier than the other, requiring more balance adjustment to walk and run evenly. It is also good to have two kidneys in case one should become damaged or destroyed. Without kidneys or a dialysis machine cleansing the blood the body dies, overwhelmed by toxins. Furthermore, the kidney did not evolve. A blind, mindless cell could not, under any condition in any amount of time "think" or "will" to come up with such a fabulous design like the kidney. Like all things, the kidney was designed and created by God for a purpose, in this case for waste removal, cleaning the blood, and the production of enzymes and hormones such as Erythropoietin (EPO) and Calcitriol. The human body is a fantastic, wonderfully designed machine with each part working in harmony. You may want to visit the Answersingenesis website for more information about the wonderful things God has made. In response: The body is inded balanced: the liver is balanced by the gall bladder, transverse colon, stomach, and spleen. Both sides are balanced and forms a "rough symmetry" in that area. And it is not nonsense to believe that God created the body. Either you believe that God did it, or you believe the hydrogen and other atoms always existed and formed themselves into molecules in a random swirl over a long period of time.

We are capable of living with one loung, one leg,one arm, part of your brain can be removed as well as other parts of your body that I can not spell, Its best to go back and rethink you question or come up with a better one.

I'll try to approach this a little differently: There are several paired organs in the body. The reasons(s) for some of these are obvious (eyes, ears, arms, legs). Accessory spleens can be scattered throughout the abdomen---perhaps to function if the primary spleen is injured? There are two testicles and two ovaries---to insure reproductive potential for us? It seems to be the obvious answer. And let's not forget the lungs. We can always function better with two lungs, but a single lung can function fairly well. Finally, evolution develops differently than our "logical" minds would dictate sometimes, but the evolutionary answer may not be obvious to us. Remember Jay Gould and the panda's thumb?

So if a zombie comes along, we can rip out one and feed it and it will go away.

We have two of most of our organs. The digestive tract and the circulatory systems are the exceptions. We posess two eyes, ears, nostrils, lungs, testicals or ovaries, brains (yes, if the 'cable' between the right and left hemispheres is severed they each are seperate individual brains - and function as individuals also). This is most likely due to the fact that our digestive tracts and hearts evolved before our remote ancestors (probably Sea Squirt larva) failed to adopt their usual asymetrical sessile adult form and adopted their larval, bilateral mobile form as adults. The existing body of evidence indicates that they eventually evolved into the first vertebrates. It should also be added to this most basic explanation that it has proven to be adaptive to have two of these organs. It most likely provides better reproductive fitness to have two copies, just in case one gets injurred. For Brad Darr: The Theory of Evolution is what the overwhelming body of existing evidence has led reasonable, educated, well informed minds to accept as the most plausible and parsimonious answer. These are the same type of minds that gave you vaccination, the pharmaceutical and medical technologies that exist today, energy systems, etc. I find it striking to consider the similarities between the debate as to our origins in the last century and so far even in the 21st century, and the shape and location of the earth. Think about how Copernicus and Gallieo were treated by the Christian religion as it was practiced then, for thier astronomical studies. Yet the earth is not in the center of the universe, is it? While your creation story is a cute little fable, it really is not nearly as interesting as those of many other cultures. I have no problem with such stories, they do have a great deal of value. However, I really think that the proper setting for such fables is in a Religion, Philosophy, Anthropology, Mythology, etc., class. This was a science question which I answered in a scientific manner. It is ridiculous of you creationists to attack science simply because the overwhelming body of existing evidence supports the idea that we evolved from molecules that spontenously formed in the conditions that existed on earth 3.9 billion years ago. Can't you give your all powerful God enough power to have done it the way that the evidence indicates he did (if he exists at all - another topic altogether)?

Well, if you remove one, it's pretty painful, right? You barely even live if you surgically remove one. That's why we have two, we won't go through as much pain.

This is not really a question about evolution or creation. The answer really has nothing to do with that. In my opinion, it is due to the fact that our bodies are not in a constant state of equilibrium, we do not always have the same demands and stresses, and there are different variables affecting the resources. For example...you could test 100 people and find the output of their kidneys and the capacity for each kidney...but typically in a study people with disease or disorder are eliminated to give an accurate "average", making it not really an average of the population in general, but an average for "healthy" people. That said, what demands are placed on the kidneys of someone who smokes, eats lots of organ meats, has excessive salts and minerals in their diet and drinks alcohol and coffe excessively and doesn't drink enough water? Is it the same as someone who has a healthy diet and lifestyle? No. The kidneys must eliminate a lot more waste products. Then you also have chronic disease and illness that might put extra strain on the filtering mechanisms, and I think that if someone were working hard and creating a lot of lactic acid and waste products as a result of physical exertion there might also be more demand for disposing of or eliminating this waste. A similar thing is found with blood. We each have 8 pints, but we could live with two (if the level was gradually reduced). Why this excess? Because we are not constantly at a state of rest. We might be sitting around using x number of O2 ler hour, then jump up and sprint for a couple hundred meters. If we just maintained the bare minimum we would n't be able to do that. We would get exhausted before we got two steps, and if we got a minor injury the level could only drop a tiny amount before it was fatal. So too with the kidneys, liver, heart and lungs. They must be ready to deal with higher demands, or risk fatal consequences.

Simple. God made us that way. If we had not needed the dual action of two kidneys, we would not have been created or should I say designed that way by the master designer. Even though we can live without one kidney as we all know. I'm sure when a person has to live with one kidney, your body does have to adjust to a different level of funtioning without the other one. Check with a kidney specialist or look it up on line about the dual purpose of two kidneys as opposed to one kidney. Kidneys has to filter all the waste from out body, and the quicker the better, so two is better than one to get the job done. Now who could have thought up such a unique design except the master?

Because we need a spare! Just like we can live with one eye, but we have two! Isn't that fascinating?!

Very early in the development of the foetus, it makes a transformation which gives it a bilateral symmetry: a hoolow ball of cells creases in on itself and the two sides join up, leaving a channel which becomes the digestive tract and a line which later develops into the spine and the core of the nervous system. This means that organs are of two types: a small number of which ther is only one, such as the spine and the digestive tract. and a much larger number which develop one on each side. Basically, the body has a choice, wnen it "decides" to develop a new organ, of developing it out of the "centre line" part of the body, or out of the "paired" part of the body, In the line that led to us, the line that developed the kidneys out of the paired side, giving us two kidneys, beat alternatives which might have developed the kidney as a single, centre-line organ. It may be, as other responders have suggested, that the redundancy of a spare kidney is worth its cost. But it is the bilateral symmetry of the human body that makes this option "cheap".

i truely agree with skull face....we only need one healthy kidney to survive..i was also born with one kidney and just recently discovered it..and i know many people who lived in their 80"s and 90"s with one kidney by birth without any hassles.its just that u dont have a spare one.....!and most of the kidney diseases effect both the kidneys together..... i do play sports ..drink..and into bodybuilding.... just scared to have excess protein... and bi d way mel gibson was born with one kidney(horseshoe)

My brother has just been told that he needs to have his kidney removed, as he has a tumour, so I am here, seeing what changes it will make to his life. I guess the answer lays in it being beneficial to have two, and maybe those who have one have to be more careful. I remember when my other brother had his appendix out, I wondered why we even had appendix. Apparently, you can live without appendix altogether, but are more prone to some infections or diseases. It is still very unlikely, just more likely than if you have them. Maybe it is the same with kidneys. Both kidneys serve a purpose, but you can live with one. However, living with one may increase slightly your chances of problems down the track (it is definately preferential having two). Also, on evolution vs creation. I will not debate that here, only to say that I need to pray and believe that God will look after my brother. No matter what your beliefs, if praying for someone comforts them, then it is a good thing.

It's a vestigial trait. Just like the fact that at one point, we had gill slits... And the same reason we have goosebumps (it's supposed to make your hair stand up like a...cat when it's freaked out) And the same reason we have tonsils...

It's your backup, baby!

we have two of just about everything....a question of equilibrium, symmetry.....but as they say in Fench: un c'est bien, mais deux c'est mieux! (one is good, but two is better)

In case you screw one up, you can still live.

I am glad I had two, because I lost one. "Healthy humans have two kidneys, a redundancy that enables living donors (inter vivos) to give a kidney to someone who needs it. The most common transplants are to close relatives, but people have given kidneys to other friends. The rarest type of donation is the undirected donation whereby a donor gives a kidney to a stranger. Less than a few hundred of such kidney donations have been performed." Source and further information: http://en.wikipedia.org/wiki/Organ_donation "Generally, humans can live normally with just one kidney, as one has more functioning renal tissue than is needed to survive. Only when the amount of functioning kidney tissue is greatly diminished will chronic kidney disease develop. Renal replacement therapy, in the form of dialysis or kidney transplantation, is indicated when the glomerular filtration rate has fallen very low or if the renal dysfunction leads to severe symptoms." Source and further information: http://en.wikipedia.org/wiki/Kidney Further information: http://en.wikipedia.org/wiki/Renal_failure