Life began on our planet about 3,500 million years ago. The first living things were found in the sea, and over the course of millions of years, from these early life forms, a rich variety of animals has descended. Through the process we call evolution, animals have become adapted to enable them to live in all parts of the world, sometimes in the most hostile environments.
Almost 600 million years ago, the invertebrates appeared i.e. those animals without backbones - insects and other minibeasts. The earliest vertebrates i.e. animals with backbones, were in the form of primitive fish and appeared around 500 million years ago. From these, all other fish descended, as well as amphibians, reptiles, birds and mammals.
The animal kingdom is enormous and we do not know for certain how many species there are in the world. Around 1.6 million species of animal have been named and described by scientists - and over a million of these are insects. It is known that there are about twice as many animals in tropical rainforests than in any other habitat, and it is here that there are likely to be countless numbers of species yet unknown to science. It has been estimated by some scientists that the total number of insect species alone could be around 30 million!
It is just possible, but unlikely, that there are a few large animals remaining to be discovered, but what we can be sure of is that the most numerous large animal on Earth is Homo sapiens - the human! Modern humans appeared about 30,000 years ago and has increasingly come to dominate the planet. The steady increase in population was speeded up by advances in civilization such as the Industrial Revolution and better health and medical care.
This population explosion means that millions of people suffer from hunger and disease, and more and more wild places are taken over, causing animals and plants to suffer too.
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