Biology is the study of living things. Traditionally, all living organisms were classified in the plant or animal kingdom. This distinction has been replaced by a system of five groups or kingdoms. Either way, the phenomena are similar in all five groups, making it possible to establish common principles for all the living world.
Living things have certain powers that distinguish them from inanimate matter. The characteristic property of life is reproduction. Under normal circumstances, all life can give rise to other individuals like himself. In the simplest form this is done by dividing the individual originating two new bodies, in the most complex involving specialized cells, sperm and ova, which combine to form the egg cell or zygote that give rise to new body . The higher degree of complexity is reached with the differentiation of the species into two sexes: When sperm and egg are carried by two different individuals.
Reproductive capacity is related to two typical characteristics of living things: growth and inheritance. The first is the natural increase in size and the second is the continuation of specific characteristics of parents in the new individuals.
Another property is the sensitivity, which makes it possible to respond to external mechanisms produce changes that can adapt to environmental requirements.
While it is an ancient science (men began to study for many centuries in an effort to explain the mysteries of life) is in another sense, a young science, as their most important and revolutionary discoveries date from recent times.
The scientific method
To understand a biological fact is necessary to carry out three basic operations: observation, interpretation and experimentation. Adequate observation raises the possibility of reflecting on the observed facts and hypotheses which are reasonable interpretations, and through the experiment tests the hypothesis formulated. One hypothesis, or set of them duly noted, is a theory: for example, the theory of evolution.
The emergence of life
Over millions of years there were no conditions for life on our planet.
In the early atmosphere had no free oxygen, but was combined with other gases. There was water vapor, methane, carbon dioxide and carbon monoxide, nitrogen, hydrogen sulfide and ammonia.
On cooling the Earth's crust, water vapor condensed into rain, accumulated water covered the surface of the globe and led to the oceans. In the primeval waters were the first signs of life. This arose from inanimate substances as a result of favorable factors combined so as to give rise to the first organisms. At one point, the crust became cool enough to be already available compounds with carbon and other elements suitable for generating organic matter.
Over time, millions of years, certain life forms spread to dry land, free of standing water and there began another long process of adaptation.