The egg is an organic shuttle?

Sometimes it happens that living organisms are in the need to colonize an environment quite different from the original, so different to be prohibitive for survival. Often there are no alternatives to death but some species have been successful in the enterprise, thanks to a simple but ingenious strategy: to create a protection around them, a sort of housing within which preserving or reproducing a portion of the original environment.
This is what vertebrates did passing from the oceans to the mainland; Indeed, their skin became a waterproof casing that prevented a rapid dehydration and that kept inside an environment favorable to life of their cells. Even today the salt concentrations in the blood and other body fluids of mammals, as the sweat and tears, are very similar to the ocean, that is that environment that was our first cradle, which we have abandoned about 400 million years ago, but that we still carry inside us.
The same strategy was used to allow the development of their offspring: eggs of reptiles and birds, and the uterus of mammals, reproduce the wateriness, the hydrostatic drive and salinity of the original water.
This technique is perhaps the oldest of all: it is in fact assumed that inside the cell membrane of bacteria, as inside the nucleus of some more complex cells, an environment similar to that in which life was born is reproduced.
It is a simple, essential and ancient technique but always valid; it is actually the same as we men use when we build submarines and space ships, which are large containers of a portion of Earth environment, with air for breathing and controlled temperature, which can travel in environments for us uninhabitable.

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ANTONI VAN LEEUWENHOEK

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