I am, by no means, an athlete or even a sports fan, but even I watched Usain Bolt sprint across the finish line during the summer Olympics of 2012. The animal equivalent of Usain Bolt is the cheetah, able to clock in a running speed of 90 kilometres an hour and to pursue its prey [...]

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The Sundaytimes Sri Lanka

Come on baby, do the locomotion

By Dr. Sriyanie Miththapala
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I am, by no means, an athlete or even a sports fan, but even I watched Usain Bolt sprint across the finish line during the summer Olympics of 2012.

The animal equivalent of Usain Bolt is the cheetah, able to clock in a running speed of 90 kilometres an hour and to pursue its prey over 300 metres. A lithe body, a spine with the elasticity of a coiled spring, a small, light head, long legs and a tail which acts like a rudder, combine to make the cheetah of Africa the fastest living land mammal.

A Water Monitor showing undulatory movement © RiazCader

In contrast, the slowest animals are probably the garden snail, crawling at 0.048 kilometres per hour, and the sloths of South America, who move only when they have to, at two metres per minute. (In fact, both words snails and sloths are synonymous with laziness.)

One of the fundamental differences between animals and plants is that most animals, unlike plants, move from one place to another — in search of food, suitable habitat, to escape predators and to find refuge or to look for a mate. This self-propelled movement is called locomotion. Animal locomotion may be in water, on land or in the air. In all these media, an animal has to overcome several natural forces: friction or drag, gravity and inertia. The animal has to counteract different forces in different media. For example, there is more friction in water than there is in air, but gravity is a greater force on land than in water.

An animal has to push something — air, water — backwards in order to move forwards. (This is Newton’s third law of motion.) In the natural world, animals slither, walk, run, jump, climb, swing, glide,swim, fly and burrow. And each time they do so, they are defying natural forces and teetering on misbalancing. Yet, move they do, and in style.

Early animals that evolved lived and moved — swam — in water. Swimming animals have to counteract many forces: gravity versus lift that either sank or buoyed an animal; drag versus thrust that either allowed an animal to move forwards or prevented it from doing so; pitch, roll and yaw that can rotate the animal.

Water usually provided natural buoyancy so gravity was not a problem for animals moving in water, but drag was. A streamlined body was necessary to minimise drag and the best for this is a torpedo-shape. Most fish and marine mammals are adapted to this shape. The thrust to move forward is provided by the tail fluke — which moves side to side in fish and up and down in marine mammals. Other fins — on top, at the bottom and on the sides in front and back, prevented animals from nose diving or rotating.

Sailfish (Istiophorus) are the champion swimmers of the animal kingdom, clocking 112.6 kilometres per hour. If sailfish are the quickest swimmers, then European Eels(Anguilla Anguilla) are the animal world’s marathon swimming champions — known to swim nearly 6,000 kilometres when they migrate to breed.
During the course of evolution, some 375 million years ago, animals moved onto land, and gravity became a huge problem. The weight of an animal dragged it down.

The internal vertebral column that had supported fish quite adequately in water became useless on land. The four-limbed creature (tetrapod) that initially crawled onto land had the same problem as bridge designers had: its vertebral column sagged. The entire skeleton had to change: the vertebral column developed inter-locking mechanisms that allowed for movement while retaining rigidity; fore limbs supported by pectoral girdles and hind limbs supported by pelvic girdles transmitted the animal’s weight to the ground. The pectoral and pelvic girdles anchored the limbs but allowed swinging movement that propelled the animal forward.

Snakes — without any limbs — slither by using the scales on their bellies to hold the ground and redistribute their weight, in a wave-like movement to slither. Other reptiles — such as lizards and skinks — also move with this undulatory movement.

Locomotion changed again with the evolution of mammals 190 million years ago. The limb posture changed from sprawling to semi-erect, with the limbs facing downwards from the vertebral column, not sideways as seen in modern reptiles.

Comparison of changes in the skeleton in a gorilla and human

Mammals generally move using the same limb movements as a crawling baby: first the right forelimb is raised and moved, then the left hind leg, next the left forelimb, and finally the right hind leg. At any given time, the animal is supported by three limbs and can stop without falling. The centre of gravity always falls within the triangle formed by the three limbs on the ground.

An exception to this rule is the camel. Camels move with a swinging stride in which the front and hind legs on each side of their body move in unison. This results in a rolling gait where the weight of the camel moves first to one side and then the next. It is thought that this peculiar gait — called pacing — is an adaptation to conserve energy.

If the cheetah evolved for speed, then hoofed mammals evolved for endurance. These herbivores needed to outrun predators, so outlasting them was the key. Firstly, their limbs lengthened to increase their stride. (Longer legs mean the animal could cover the ground faster.) Hoofed mammals run on the very tips of their toes and many of their foot bones are lengthened too.

To protect their toes, a hard hoof developed. All joints became dead-locking and the limbs moved only forward and backward in a piston-like movement. The vertebral column became stiff to support these changes. Hoofed mammals, such as horses and deer, therefore, cannot climb.

The champion marathon runner in the animal world is the Pronghorn (Antilocapraamericana) which can run for miles at about 44 kilometres per hour. They can spurt at double the speed for shorter distances.
Other animals climb. Small animals — such as squirrels— scamper up and down trees using their claws to grip branches. In others — such as monkeys — the entire skeleton is changed for moving among the trees. The back, arms and legs became long.

The limb connection with the girdles changed to allow rotation (ball and socket joints developed) and the digits of the hands and feet became flexible and critically, one digit could be moved in opposition to the others so that grasping was now possible. Skeletons became flexible so that climbing was enabled. Monkeys and their relatives — apes and other primates — have such flexible skeletons, that they can run, jump, climb and sit upright.

Gibbons of Southeast Asia have perfected the art of swinging from branch to branch using only their arms. The mode of locomotion is called brachiation. A gibbon can brachiate as fast as 55 kilometres per hour and move as far as six metres in one swing!

Jumping is a different form of locomotion where the animal is temporarily airborne. Generally, jumpers have elongated and strong hind limbs that are used to push against the ground to launch the animal upwards and forwards. Also elongated are foot and ankle bones that add length to the stride. Frogs and toads are champion jumpers whose hind legs can be twice their body length.The Striped Rocket Frog (Litorianasuta) of Australia can jump four metres from the ground — which is 100 times its body length. Spittlebugs or Froghoppers — tiny insects found worldwide — can jump 70 centimetres vertically, 100 times their body length, the equivalent of a tall human jumping over a building that is 210 metres tall.
Flying poses an entirely new set of problem in locomotion. But many groups of animals — such as insects, birds and bats — do fly.

The extinct pterosaurs also flew. Animals who fly have wings that function as airfoils. An airfoil is a structure with curved surfaces that gives the best ratio of lift to drag in flight. Several forces are exerted on an airfoil. Weight, forcing the airfoil downwards;lift forcing it upwards; thrust, moving the airfoil forwards and drag, retarding this forward movement. For flight, lift must be maximised and drag minimised.

Feathers attached to wings and finely adjusted by muscles, allow a bird wing to function as a perfect airfoil. Flapping their wings provides the thrust for birds. There are also many weight reducing adaptations: the number of bones in bird skeletons has been reduced drastically and the bones themselves are hollow; there are no teeth, but lightweight beaks; and a large keel-like breastbone allows for attachment of wing muscles.
The fastest flyer in the world is the Peregrine Falcon (Falco peregrinus) that can dive through the air to catch prey at 320 kilometres per hour — the speed of a racing car!

While the great majority of land living vertebrates are quadrapedal — moving with four limbs — some are bipedal, that is, they move on two limbs. Many primates are often bipedal, birds on the ground are bipedal, and kangaroos and some rodents, with a little help from a strong tail that serves to help balance them, are also bipedal.

The only bipedal habitué is a human being. Our human bipedal gait is really a marvel of balance, and each time we take a step, we teeter on the edge of falling over.

There is no consensus about scientists about why bipedalism evolved. One of the main theories propounded is that the landscape changed from closed forest to open savannahs, and early hominids stood up to look for danger and found it easier to move in these open spaces while upright.

Bipedalism in humans involved considerable changes in the skeleton. The skull was now balanced on top of the vertebral column and with it came changes to the first few vertebrae to pivot and rotate the skull. The vertebral column took on an S shaped curvature, one flex at the neck and another near lower back, to accommodate weight bearing. Without the second curve, the vertebral column would always lean forwards, tipping the person forwards. The shape and position of the pelvic girdle changed completely, and was now wider and upright to distribute weight.

The change in the shape of the pelvis brought the vertebral column closer to the hip joint, providing a stable base for support of the body while walking upright. The legs became elongated — particularly the thigh bone, knee joints enlarged to transfer weight and feet changed to form platforms to support the entire body weight. Toes were no longer needed for grasping, so they became short. Each foot contains an arch to distribute weight much like the base of the Eiffel tower supports the rest of it.

Bipedalism in humans is learned — a baby needs to learn how to walk. During this period, a baby lurches like a miniature drunk as it learns to balance. Often babies who are learning to walk grip the floor hard with their toes, and hold their arms up for balance, like gibbons.

There may be many theories about why bipedalism evolved, but no one disputes the fact that bipedalism in humans resulted in increased brain development. Bipedalism required so many skeletal and muscular changes, as well as changes in balancing, that the brain had also to be changed. Freeing the hands from locomotion set off a series of adaptations —such as enhancement of the senses, fine muscular changes — that further developed the brain. Freed hands allowed for tool-making and much later, writing, all leading to a superior cognitive intelligence among humans, unmatched in any other animal.

And all this started with locomotion. . .




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