Evolution and Heredity

More than a hundred years ago people believed that plants and animals have always been as they are now. They thought that all the different sorts of living things, including men, had been put here by some mysterious (таинственный) power.

It was Charles Darwin, born at Shrewsbury in February, 1809, who showed that this was just a legend. As a boy Darwin loved to walk about the countryside collecting insects, flowers and minerals. He enjoyed helping his elder brother at chemical experiments in a shed (сарай) at the far end of their garden.

These hobbies interested him much more than Greek and Latin, which were his main lessons at school. His father, Dr. Robert Darwin, sent Charles to Edinburgh University to study medicine. But Charles disliked the medical career. He spent a lot of time with a zoologist friend watching birds and other animals in their natural state and collecting insects in the surrounding countryside.

Then his father sent him to Cambridge to become a clergyman¹. But Darwin did not care for lectures. He did not want to be a clergyman. At 22 he graduated from Cambridge University and soon was offered an unpaid post as naturalist on the ship "The Beagle".

The young naturalist asked himself whether all forms of life always existed just as they are now. This was what everyone believed and what he had been taught, but he doubted it very much. Three and a half years travelling around the world on the British ship "The Beagle" convinced Darwin that his doubts were justified. He returned from his travels convinced that man and all the living creatures on earth today are related. All have grown from earlier types, and those from earlier ones in an unbroken line back to a primitive one-cell creature.

More than a thousand million years ago, a small blob of jelly¹ floated on the shallow seas of the young earth. It and others like it were the only life on earth. In half a milliard years that blob of jelly had become different kinds of sea worms (червь) and sea scorpions, sea weeds (морские водоросли) and other simple sea plants.

During the next half milliard years some of this life crawled (ползти) onto the barren (бесплодный) land. The first land animals were "amphibians", equally at home on land and in the water, like present-day frogs. There were also primitive scorpions, the descendants of which became insects or spiders (паук). From the seaweeds that took root on shore came ferns (папоротник) and mosses (мох). The amphibian became reptiles. For one hundred million years they ruled the earth. Out of them came birds and mammals. Gradually the mammals changed into all the different kinds we have today, including man. Each of these changes was very gradual and took thousands of years.

What makes you and your brothers and sisters look somewhat alike? What makes all of you look like your father and mother, and yet also a little different? The answer is to be found in the laws of heredity.

Gregor Mendel, son of an Austrian farmer, wanted to be a scientist but couldn't afford the university. He became an Augustinian monk3 and, in the years between 1843 and 1865, he became a great scientist. In the garden of the monastery he raised garden peas – pure tails, pure dwarf (карликовый) and so on. Then, when he was sure he had pure strains, he began crossing them. He did the same with green and yellow peas. In all he raised and studied more than 10,000 specimens.

From the way these peas transmitted and inherited various traits such as height or colour, Mendel worked out the laws of heredity. They have been found to be true for all types of plants and animals, including man, and have been widely used in the improvement of flowers and agricultural crops and the breeding of dogs and livestock.

Notes

1. clergyman – священник

2. blob of jelly – студенистая капля (комочек)

3. Augustinian monk – монах-августинец

Animal Behaviour

Wherever people have a chance to watch animals – at a zoo, park, pet store, or circus – it is evident that animal behaviour is a source of fascination¹ for most humans. As they watch animals at play and at rest, feeding or protecting themselves, and tending to their young, frequently marvel (восхищаться) at the similarities between animal and human behaviour. These similarities are, in fact, one important reason for study­ing the activities of animals: that is, their implications for the better understanding of human behaviour.

The question of why animals behave the way they do has attracted the interest of scientists from many fields – psychologists, zoologists, ecologists, geneticists, endocrinologists – to name a few.

What is Behaviour? Simply defined, behaviour is activity in response to an internal or external stimulus. All animals make adjustments to information or stimuli, from their external and internal environments. These adjustments may be voluntary or involuntary, and may range from a simple, single act to a complex and elaborate sequence of activities.

Taxis, Kinesis, Reflex. A very important behavioural response in the lives of many invertebrates and some vertebrates is the taxis. This is a directional movement in response to a specific type of environmental stimulus. The taxis response is inborn, and need not be learned; but it is fixed, and cannot be altered to suit unusual conditions.

For example, a moth navigates in a straight line by keeping at a constant angle to the parallel rays of the sun (or more often the moon, since most moths are nocturnal). This taxis works well under natural conditions. However, it can cause trouble² when the light source is so

near that it produces diffused instead of parallel rays, as in the case of a candle (свеча) or a light bulb³. In this case, instead of a straight path, the constant angle may lead the moth into a spiral, so that it circles

ever inward toward the light source and is eventually burned to death.

Another involuntary behaviour pattern, best known in simple organisms, is kinesis. This is an increase or decrease in the movement of an animal in proportion to the intensity of a stimulus. Such movements are not directional like the taxis. Instead, they consist of increases in the rate of turning from side to side, or in other body movements. Planarians, for instance, when placed in the light, do not swim directly back to the darker areas where they normally stay. Instead, they continue weaving from side to side, but they turn more strongly toward the side where they encounter less intense light. This turning eventually bring them back to the dark area.

A third behaviour pattern involving relatively simple, innate responses to stimuli is reflex. A reflex is the involuntary movement of some part of the animal's body in response to a stimulus. A familiar example is the kicking motion you make when the tendons below your kneecap are struck by a doctor's hammer. Unlike the taxis and kinesis, the reflex does not involve a complete body movement.

Notes

1. a source of fascination – источник восхищения

2. trouble – неприятность, беда

3. a light bulb – электрическая лампочка