Diversity and unity of life

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vie biodiversité especes similitudes et differences

All cellsóplant or animal, bacterial or fungalófunction according to identical mechanisms, deriving as they do from the same early life forms that appeared 3.8 billion years ago. Having conquered every habitat, from the iciest, deepest waters of the ocean to the hottest desert wastes, they populate both earth and air, forming organisms that can be anything from a few micrometers to several dozen meters long. The diversity of the living world is immense and biologists today estimate the existence of something between 5 and 100 million species-still only a tiny fraction of the total number of species that have succeeded one another in the life of the planet.

Every year, advances in science uncover a little more information regarding the profound relationships between the species. Humans and chimpanzees share 99% of their genetic inheritance, but the common fruit fly shares 40% of its genes with us and the sea urchin, a marine creature with no head or limbs, 70%! This genetic proximity is mirrored in a compositional proximity-all living organisms being formed of the same basic molecules. This explains how one species can feed off another: in the process of digesting, the first re-uses the elements of the second, rearranging them in its own fashion.

The similarities go even further and explain the effects of numerous molecules used by mankind. Thus, morphine, produced by the poppy, a plant with large, brightly colored flowers, alleviates pain in the human body, causes digestive disorders, and procures intense feelings of pleasure. This action is possible because certain human cells themselves synthesize a form of morphine similar to that of the poppy, and because other human cells recognize and respond to it.

In the same way, the majority of medicines used today are taken from nature. To quote just two examples, aspirin is derived from the willow, and vinblastine used in the treatment of cancer-comes from the Madagascar periwinkle. Today, almost 80% of the world’s population makes direct use of plants for medicinal or cosmetic purposes.

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