“For in and out about above below
It’s nothing but a magic shadow show
Played in a box whose candle is the sun Round which we phantom figures come and go”– Omar Khayyam, in The Rubaiyat
One of the strangest phenomena discovered by scientists in recent times is the ability of some animals to find their bearings—north/south, up/down—by their response to the Earth’s magnetic field. This can also be called the faculty of ‘magnetic sensitivity’. Human beings take their ability to tell up from down for granted mainly from their experience of gravitation. It, therefore, naturally comes as a surprise to them to find that several species ( of the animal world) use a different force to get the same information.
It would appear that certain kinds of bacteria, birds and bees are indeed magnetically sensitive. The common Pacific dolphin has been found to have a magnetic substance, an oxide of iron called magnetite, the fabled lodestone, in its head. Our peculiar human chauvinism is perhaps responsible for tempting us to think that such sensitivity is used only for north-south orientation. We are conveniently forgetting the fact that we spend most of our lives moving in two dimensions only, whereas most of these creatures are ideally equipped and thus adapted to live in three. If we learn to understand this phenomenon better, we may find this adaptation useful as we move into gravity-free space and lose our traditional up-and-down benchmark.
How exactly do bacteria know up from down—and why should they bother? Because for certain water-dwelling varieties, down is where the bottom sediments on which they feed are. They find their way there with the help of the Earth’s magnetic field.
It is well known that lines of force of the geomagnetic fields are parallel to the Earth’s surface at the magnetic equator and vertical to it at the magnetic poles. A freely mounted compass needle would be horizontal at the geomagnetic equator; as it is moved its point would dip until, at the pole, it would be pointing straight down. If you plotted the path of the point it would form a downward sloping curve (if we disregard a few zigzags caused by local iron deposits). There is a similar curve in the southern hemisphere.
Magnetostatic bacteria are a group of polyphyletic group of bacteria that orient themselves along the magnetic field lines of Earth’s magnetic field. The biological phenomenon of microorganisms tending to move in response to the environment’s magnetic characteristics is known as magnetotaxis. When they are gathered together in a drop of water they bunch up near the northern end of the drop in the northern hemisphere. The opposite is true on the other side of the equator, and near the geomagnetic equator itself the bacteria seem confused about which way they should go.
In the northern hemisphere, if the bacteria move north, the downward curve points to the direction of the bottom; they know where the crucial food supply is. Indeed, if the same bacteria were moved into the southern hemisphere they would be in danger of starving to death. As they TOOK the customary northern route they would be following the rising curve from the southern magnetic pole to the equator—up and farther and farther away from the food supply. Therefore, such a drift would prove disastrous.
The geomagnetic field has been reversing itself once in about every 2,00,000 years in recent geological time, and seven species of marine protozoans called Radiolaria became extinct during one such reversal. Could they have been heading north and up in search of nourishment when they should have been heading south and down? Since the northern magnetic pole is, as observed from the western hemisphere, at present slightly to the west of the geographical North Pole and the southern magnetic pole is to the east of its partner (the situation would of course be reversed for an observer, say in Japan), there is a small angle between lines drawn, through the two sets of poles. Accordingly magnetic-sensitive animals live with a slightly different equator—one that skews north of Africa, but below the geographical line in South America.
European robins and homing pigeons have a built-in compass that takes into account the magnetic field lines in all three dimensions and uses the directions in which the lines go down to the Earth to make an estimate of the direction of north.
Researchers have noticed that honey bees appear to use a more intricate mechanism. Electron microscope photographs reveal iron particles in some of their cells. This finding promises to be exciting because, in bacteria, iron particles are associated with magnetic field orientation. Hence, it is quite possible that the iron in the cells of the honey bee may be used for sensing the Earth’s magnetic field.
Magnetic sensitivity in animals has attracted the attention of scientists seriously only since the 1970s. Most magnetically sensitive creatures live in environments that are alien to us and our criteria from telling up from down are peculiar to them. Instead, they respond to the Earth s magnetism and scientists are quite justified in suggesting that they probably deal with it as naturally as other species deal with gravity.
Indeed, the ways of some animals do seem strange and mysterious. For example, scientists in Texas have found that certain animals have internal clocks. For instance, the internal clock of a chicken which runs for about 24 hours each cycle is called a ‘circadian clock’.The word circadian is derived from the Latin expression circa diem meaning ‘about a day’. While it has been suspected by scientists that such clocks do exist, what they had not known earlier was that it would be possible to take the clocks out of the animals, put them in test tubes and they will continue to tick over.
In a chicken, the internal circulation clock is located inside a very important gland in the head called the pineal gland (there is speculation that humans also have a pineal gland beneath the forehead).The scientists at Texas tried to experiment on the pineal glands of chickens by taking them out of the heads of the chickens and keeping them‘ alive’. The glands were put into incubators inside culture flasks. They were soaked in nutrients which ‘fed’ them and were tilted every 30 seconds so that they could be ‘gassed’ by exposure to a mixture of 95 per cent oxygen and 5 per cent carbon dioxide. These fed and gassed glands survived quite happily for some days. Since all their bodily needs were taken care of, the glands did not die but instead carried on with their work. This meant they continued to operate as 24-hour clocks and to produce various hormones and so on at regular and precise intervals.
Experiments conducted on the first batch of glands found that they were still at their task after two days. So another batch of glands was prepared to see how long they would continue and they were found to be happily ticking away, leading to the obvious inference that the 24-hour clock phenomenon noticed in chickens could have a parallel in humans also and if so could be exploited to look after the hormonal requirements of the human body when necessitated in certain situations.