Category Animal World

          How many kinds of animals do you know? If you start writing down the names of the animals that you know, the list would be very long. There are innumerable animals in the world. However, we have found ways to classify them too.

          There are a million different kinds of animals, belonging to different species. Scientists have divided them into two main groups – those that have a backbone or vertebrates, and those that do not have a backbone or invertebrates. Some vertebrates are cats, dogs, horses and humans. Jellyfish, sponges, octopuses and squids are some examples of invertebrates.

          Within the vertebrate group, there are five different classifications. These classifications are mammals, fishes, amphibians, birds and reptiles.

          Of the millions of species of animals on Earth, 97 percent are invertebrates. Common invertebrates are insects, spiders and worms. Some of the major invertebrate groups are Porifera, Cnidaria, Platyhelminthes, Nematoda, Mollusca, Annelida, Echinodermata and Anthropoda.

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Science was never satisfied with the creation myths of various religions that explained the origin and development of life on Earth. Charles Darwin, an English naturalist, provided a solution in the form of a theory called the Evolution Theory in 1859.

            According to Darwin, the living things we see today have evolved gradually over millions of years. This theory also says that different species may show some similarities because they have evolved from a common ancestor. Charles Darwin explained that different species evolve by a process known as natural selection.

            The characteristics of each individual are determined by extremely small pieces of genetic material called genes. Genes are present in the nuclei of the body’s cells. Sometimes, certain changes, known as mutations take place in the genes. These mutations cause the formation of new characteristics in individuals. Some mutations are harmful, and make it difficult for the babies to survive. Animals that possess these harmful mutations may not be able to compete with other animals for food and space to live. Therefore, they will gradually die. Other mutations make animals more fit and able to survive in new conditions. These animals will gradually increase in number. In this way, Nature selects those animals and individuals who are best suited to survive in a changing environment. This is called natural selection.

            The giraffe is an excellent example of natural selection. Animals that had longer necks than others were able to reach up higher and get more food. They survived, while those with shorter necks could not compete with them and, therefore, died.

 

 

 

 

 

 

 

 

 

 

 

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          While the oceans provided the most conducive atmosphere for the occurrence of life, the dry lands offered further opportunities for growth and development. In the process of evolution, the movement of animals from the oceans to land was an important milestone.

          In the earliest stages of life on earth, organisms lived only in the sea. Single-celled organisms gradually developed into multi-celled organisms. The first forms of plant life were algae, lichens and mosses. These plants provided food for the early forms of animal life in the sea.

          In the course of time, in fact, millions of years, new forms of plant life developed. These new plants were more complex. They had some new features such as roots, stems and leaves, which made it possible for them to survive on land as well. Giant horse-tail plants and tree ferns started growing on land, mostly in wet, swampy areas on land.

         When there was food available on land as well, animal life gradually began to evolve in order to survive on land. The availability of food was an important factor in the movement of animals to land. The first animals to move to land were probably worms and other soft-bodied invertebrates. They were followed by certain fishes that developed limbs to crawl and lungs for breathing. Reptiles that could live on both land and water came next. Such animals, as you know, are called amphibians.

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            We cannot travel to the past to see how life began on Earth. All we can do is to speculate and hypothesize. Some scientists tried to recreate the prehistoric past when life was non-existent and the earth had just started cooling down. Stanley Miller, an American chemist, conducted many experiments in this regard and tried to prove how life came into existence.

             Miller conducted an experiment in 1953, which shed light on the sprouting of life on Earth. He filled a laboratory flask with a mixture of gases.

            These gases were similar to those that made up the atmosphere of the earth billions of years ago. He then fired electrical sparks through the gases for a week. The electrical sparks had the same effect on the gases in the flask that bolts of lightning had on the earth’s atmosphere before the appearance of life.

            The results were revelatory. Miller discovered that a variety of substances had formed in the flask, including amino acids and sugars, which are necessary for life to occur. From Miller’s experiment, scientists concluded that the fierce flashes of lightning  that were common during the early days of the earth reacted with the gases in the atmosphere to produce the substances necessary for introducing life on Earth.

 

 

 

 

 

 

 

 

 

 

 

 

              Have you tried to stay underwater holding your breath? We cannot live in a sea or river like a fish, because our body cannot take oxygen from water. However, there are innumerable organisms in oceans. In fact, life began in water.

              Two-thirds of the surface of the earth is covered with water. Oceans and seas were formed very long ago, long before there were any plants, animals or people on Earth. The earth was made up of red-hot rocks then. When they cooled, they gave off steam. This steam became rain, which fell and filled up the hollows and deep holes in the earth’s surface to become oceans.

              The first life was not as complex and developed as it is found now. It probably was one-celled organisms. The first plants that appeared on this planet were microscopic, single-celled organisms floating in the world’s oceans, billions of years ago. That is why we say that life began in water, and not on land.

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