The Illustrated Book of Animal Life [antikvár]

The Evolution of AnimalsHow, when and why was life created on Earth? How, when and why were plants and animals created? What caused their variety of form? What were their ancestors like? Men have wanted to know answers to these questions for ages past. Even today, only some can be answered. Scientists have only theories regarding the remotest past and the nearer they get to the present the more likely they are to find reasonable explanations to some of the questions.Nobody has yet succeeded in discovering and producing evidence about the beginning of life on Earth, just as nobody has yet found the real cause of its creation. Man's knowledge is poor in this respect, for it is based on few facts. Palaeontologists, who can sometimes back their knowledge by findings of fossil remains, mainly of the hard parts of animals and plants, are in a somewhat easier situation. But such evidence is rarely abundant and the farther we go into the past the rarer it becomes. Through the collaboration of researchers from different fields of science it has been possible to identify some major events in the historical development (phylogenesis) of animals and, on this basis, to derive some of their inter-relationships. It is interesting to consider and speculate about the process which results in the evolution of the most advanced forms even though our knowledge is sometimes patchy.It is always important to bear in mind that the evolution of living things has proceeded in accord with the environment and that it was subject to the following laws. Animals have different characteristics and abilities; in nature we cannot find twoidentical specimens of the same species. Therefore when they face the same kind of stresses, or when they compete for the same resources, they do not respond in the same way. Though each individual tries, according to its ability, to find the best food, to secure the most favourable site, to protect itself and its young against enemies, and to shelter itself against cold, water, heat, or competition, only some can succeed. This effort to survive is the struggle for existence. Those which are able to cope with the external conditions, and adapt themselves, survive. Other individuals, though, are so disturbed by the environmental factors that they are unable to adapt themselves and perish. In other words members of the same species are differently viable, hence they react in varying degrees to pressures of the environment. This force known as natural selection is the sieve through which the fittest pass while the less able are held back. The biological differences between members of the same species is the basic prerequisite for the working of natural selection. Natural selection materializes through the struggle for existence and is the driving force of evolution.On the basis of the latest scientific research, it is currently assumed that life on Earth appeared 2,500 million to 3,000 million years ago. The age of the Earth is estimated at 4,000 million to 5,000 million years. However, our answers on the creation of life are based only on theories. It is assumed that the formation of simple organic compounds was essential for the beginning of life. From these compounds and with the aid of various physical factors, more and more complex substances formed