What is evolution?

Evolution is the name given to the gradual adaptation of living things to take advantage of the environment they live in.

This process, which takes place over millions of years, can mean that both animals and plants can change their appearance, size and habits, and eventually become new species.

We can see how evolution has changed living things by examining fossils. Fossils preserve the body parts of living creatures from long ago so that we can see how they have changed over millions of years. Sometimes the changes are very gradual, while others seem to have taken place quite rapidly. It is often possible to find a series of fossils, with each one showing a gradual change. This can tell us how a creature has altered due to the process of evolution. For example, scientists have traced the evolution of the horse from a tiny ancestor with normal toes to the large-hoofed animal we see today.

Can fish make electricity?

Electric ells are well known, and they can stun their prey with a powerful shock. Other fish can also produce electricity to kill their prey or to defend themselves. They include electric rays, which are common in many warm seas and also electric catfish living in African rivers. fish called mormyrids, which live in very muddy waters in Africa, use electrical fields as a form of radar. This allows them to move about safely and to find food. They can also communicate by means of these electrical signals.

Sharks do not produce electricity, but they possess organs in their skin that can detect tiny electrical currents produced by the muscular movements of other fish. In this way they can hunt without being able to see their prey.

Which is the most successful mammal on Earth?

We like to think that humans are the most successful animals, but it could be argued that rats are even more successful. Rats are found wherever people live, and they can adopt to live in most environment. The two common types are the brown rat and the black rat. rats produce up to seven litters per year, each one containing between six and 22 young.

Rats are a source of disease, and their droppings frequently contaminate stored food. Black rats were responsible for the spread of the Black Death in the Middle Ages, which killed millions of people in Europe. Rats are very difficult to control because they quickly adapt to the effect of poisons and learn to avoid traps.

Rats are also highly intelegent and are able to exploit new food sources. They climb walls to enter food stores, or tunnel beneath walls, and can even bite through palstic or water pipes in order to drink. They are omnivorous, which means that they can live on almost any edible substance.

Which is the largest invertebrate?

The giant squid is by far the largest invertebrate known. This monstrous creature lives in the ocean depths, and is only occasionally washed ashore. The specimens found so far have been 20 meters in length and their eyes are 40 cm across (these are the largest eyes known).

Squids have tentacles like an octopus that surround a powerful beak. Two of these tentacles are enormously long, with gripping suckers at the end. The giant squid's suckers have a ring of sharp teeth around them to help grip their prey. These suckers leave scars on the sperm whales that feed on them, and some of these scars are from suckers nearly three times bigger than those on the largest squid found so far. So there are much larger giant squids still to be discovered.

Why is deforestation damaging the world's ecology?

The world's tropical rainforests are being lost at an alarming rate, and already the effects of the loss can be seen. Rainforest trees are cut down to provide timber as well as land for grazing and raising crops. The remaining scrub and branches are usually burned, providing a rich source of fertilizer for one or two years. Then the land becomes barren. Rainfall washes away the topsoil, leaving bare rock in which very little grows.

The results of deforestation are seen in countries such as Bangladesh, where heavy rains are no longer soaked up by forests in the foothills of the Himalayas. Instead the rainwater sweeps down the valleys, causing enormous flooding and loss of life.

Which are the most poisonous snakes?

Every year about one milliom people are bitten by piosonous snakes, mostly in tropical regions of the world. Between 30,000 and 40,000 of these people die.

There are several groups of poisonous snakes, and their venom can attack the body in many different ways. venom can attack the blood, the nervous system or in the case of the rattlesnake, most of the body organs. The danger depends on how much venom is injected into the body through the snake's hollow fangs when it bites.

Rattlesnakes and copperheads are common hazards in North America, while vipers and their relatives, together with cobras and mambas, are common dangers in Africa and Asia. The spitting cobra is most unusual because it sprays venom into the eyes of its victim to blind it, rather than biting. Snake bites on humans sre nearly always acts of defence. This is because the snake thinks that it is being attacked.

Darwin's Islands

The Galapagos Islands have a unique range of animal life, due to their isolation from the South American mainland. Few new animals have been able to colonize the islands, and the original inhabitants have evolved in isolation. In addition to Darwins' finches, the Galapagos Islands now have a population of penquins ang fur seals that live together with tropical animals. The marine iguanas (large lizards that swim underwater to graze on seaweed) are unique. A different type of the famous giant tortoises has evolved to live on each island inthe group (some are recently extinct). The only natural inhabitant that is not unique to the Galapagos, apart from some bird species, is a small lizard.

How can fish breathe underwater?

Fish are able to breathe underwater because they have special organs called gills. Gills are bars of tissue at the side of the fish's head. They carry masses of finger-like projections that contain tiny blood vessels. Water enters the fish's mouth and flows over the gills. The gill filaments take in dissolved oxygen from the water and pass it into the fish's blood. In this way the gills have the same function as the lungs of air-breathing animals.

Many fish that live in the water containing little oxygen are ble to breathe air. They usually have to do this in foul water, when bacterial decay reduces oxygen levels. Some fish have a special breathing organ called a labyrinth, and they rise to the surface every few minutes to breathe air into this organ. Many catfish breathe air in similar way -- they swallow it and it passes into their gut where oxygen is absorbed through the thin lining of the gut wall.