Human Organ Duplication

[Dekan]

The human body has some internal organs which are single. But others, we've got two of.

 

For example, we've got two kidneys, and two lungs - but only a single liver. Yet the liver is an essential organ. If it fails, we die. Shouldn't it have a back-up, like a kidney has - if a kidney fails on one side, there's another on the other side, to take over. A person can survive with one kidney. And it's the same in the case of the lungs. A person can have a lung surgically removed, and still get by on the other "back-up" one.

 

This "back-up" principle seems very sensible and prudent, from a survival viewpoint. And survival is what Natural Selection is supposed to be all about. So I wonder why Natural Selection hasn't resulted in duplication of all our essential organs.

 

Surely it would advantageous to have a duplicate liver - is there a good reason we haven't got it?

[Ringer]

There are tons of things you could point out and say, our bodies would be better if . . . Natural selection doesn't work that way, though. Natural selection hasn't favored a 2 liver system in us because there wasn't a time in our evolutionary history where 2 livers was necessary, perhaps even substantially, better for survival.

[Dekan]

There are tons of things you could point out and say, our bodies would be better if . . . Natural selection doesn't work that way, though. Natural selection hasn't favored a 2 liver system in us because there wasn't a time in our evolutionary history where 2 livers was necessary, perhaps even substantially, better for survival.

 

Thanks Ringer. But the 2 kidneys though. They must be somehow better for survival, than the logical single central kidney. But it's not easy to see why.

[Zedition]

Actually we only have one of most organs. Duplication of organs is the exception, not the rule.

 

Evolutionarily, it does not make sense to duplicate organs. In nature, injuries serious enough to prevent any one organ from functioning are almost always fatal. It's not like lions eat one kidney and then run away. Biologically duplicating an organ is really a massive waste of energy, why do we need two kidney's is a better question? The answer is sometimes there's an evolutionary advantage to have split-process systems. With kidney's, maybe smaller organs instead of one larger one is more efficient. Or possibly kidney's have a high rate of blockage and that means swift death to septic shock. By having two, one can keeps functioning while the second repairs itself. Liver's on the other hand are not prone to blockage in the slim, healthy people homo sapians were for 6,000 of the last 6,003 generations.

 

So the answer is that we don't have two of most things because having two is not an advantage. We're not the Borg, we can't have backups and spare parts. We're a single unified system that sometimes has a little bit of duplication, but only rarely. Skeletal radial symmetry in vertebrates gives an illusion that we have two of many things, but our outward physical form is not what keeps us alive.

[Dekan]

Actually we only have one of most organs. Duplication of organs is the exception, not the rule.

 

Evolutionarily, it does not make sense to duplicate organs. In nature, injuries serious enough to prevent any one organ from functioning are almost always fatal. It's not like lions eat one kidney and then run away. Biologically duplicating an organ is really a massive waste of energy, why do we need two kidney's is a better question? The answer is sometimes there's an evolutionary advantage to have split-process systems. With kidney's, maybe smaller organs instead of one larger one is more efficient. Or possibly kidney's have a high rate of blockage and that means swift death to septic shock. By having two, one can keeps functioning while the second repairs itself. Liver's on the other hand are not prone to blockage in the slim, healthy people homo sapians were for 6,000 of the last 6,003 generations.

 

So the answer is that we don't have two of most things because having two is not an advantage. We're not the Borg, we can't have backups and spare parts. We're a single unified system that sometimes has a little bit of duplication, but only rarely. Skeletal radial symmetry in vertebrates gives an illusion that we have two of many things, but our outward physical form is not what keeps us alive.

 

Thanks Zedition, excellent and insightful post.

[CharonY]

There is also reason in the evolutionary history of development. For developmental reason certain elements may be replicated with others it is not possible.

[Ahsan Iqbal]

As Ringer said, there are thousands of things in your body which according to you should have been the other way, but we are what we are.

And by the way, the fact that you have two kidneys doesn't mean that one is for backup. A person who donates one kidney, or whose one kidney is damages, has to reduce his physical activities to a great extent. Other wise the single kidney becomes overloaded. So for normal activities, both kidneys has to perform and there is nothing like backup.