Why are some steam organs, but others? And can a person develop the second heart?
In fact, in the human body, absolutely everything is symmetrically. At least at the stage of embryonic development. And the axis of symmetry is the digestive system. The organs are built around it so that each cell is close to the "trough", to give a sufficient amount of nutrients.
In the process of the development of the embryo, some organs merge, while others remain divided. Why? Everyone has its own cause. So, the heart is laid in the form of two adventures that they grow precious because his work should be agreed. Whether in a person two hearts, the second certainly knocked the cycle of the first. At the same time there are organs that are good to have "stock". These include kidneys. It will damn one – the second will remain. Also with ovaries.
Even those organs that seem to be unpaired are actually those are not
Although most pair bodies do not duplicate each other, but work together. Two eyes are necessary for binocular surround. You can see one, but at the same time the perception of the surrounding world is broken. Two ear needed to better determine the direction of sound and the distance to its source. And two nostrils help to more accurately find out the direction of the smell and more efficiently clean the air during the breath. The need for two lungs is no doubt: so their surface is much more.
But even those organs that seem unpaired are in fact such not. More precisely, the left and right side are distinguished in them. Brain, of course, one, but it consists of two hemispheres. Or heart. He has the right and left atrium working together. And the spine consists of vertebrae located on the left and right of the axis.
Sometimes failures are, and in this case, a person is born with extra bodies: kidneys, hands, legs, and so on. Most often, this is due to a violation of the development of the embryo, including under the influence of the environment. For example, if during pregnancy a woman underwent intoxication, the risk is a great risk that the child will be born from the cleft sky. In the people, this disease is called the wolf to the mouth or hare lip. Another example of mutation are Siamese twins – single-time twins, which are not fully divided in the embryonic period of development and have common parts of the body or internal organs.
There are such pathology and animals. But a person in this case is more likely to survive and lead more or less normal life. Animals with unnecessary or, on the contrary, missing bodies, parts of the body may die as a result of natural selection. (A five-fifth calf that "adopted" the American family is actually incredibly lucky.) True, if the mutated version will be more convenient for life, after a while it will fix. But now we now live in stable conditions, and further changes in the symmetry of organs are unlikely. In any case, the environmental conditions will not be changed.