15.5 ADAPTATION IN ANIMALS

Every organism has to be well adapted to its habitat. For example, water is the habitat of fish and trees are the habitat of monkeys. A fish cannot live in trees and monkeys cannot live under the water! Fish are adaptedto living in water in many ways.They have special organs called gills instead of lungs. The gillsextract oxygen from air that has dissolved in the water,and pass it on to theblood for respiration. Fish also have a streamlined shape so they can slip through the water easily. Their tail fins and backbones, which can flex from side to side, adapt themfor swimming through the water, and their other fins are adaptedfor control and steering.In similar ways, monkeys are adapted to living in trees. They have strong and flexible hands and feet that can grip the branches, and their prehensile tails are adapted to curl around and grip branches too. Like humans, but unlike most other mammals, monkeys’ eyes are at the front of their heads instead of the sides. This gives them binocular vision (Module 7.12)which helps them to judge distances. Binocular vision adapts them for moving around fast in three dimensions,and especially forjumping from branch to branch.

Birds provide many good examples of adaptation. They are adapted for flying in several ways. They have hollow bones and they are covered with feathers.Both these things help to make them very light for their size.They have wings instead of front legs, and their feathers give the wings a big surface area. This gives them more lift when they fly.Unlike fish, birds have a very inflexible backbone. This provides a rigidframework to support an enlarged breastbone to whichenlarged pectoral muscles are attached.The pectoral muscles are the strong musclesthat flap the wings. They are also the breast meat that we enjoy when we eat a bird like a chicken.

In Module 2.9 we saw how the beaks of different birds are adapted for eating different kinds of food. Look at the photos of the duck and the falcon below. The broad, flat beak of the duck is adapted for pulling up weeds from the bottom of a pond or river, but the sharp, hooked beak of the falcon is adapted for killing its prey and tearing off strips of flesh. The feet of these two birds are also adapted for different ways of life. The duck has flat, webbed feet that are adapted for walking on soft mud and that act like paddles under the water to push the duck along when it swims. The feet of the falcon are very different. They have long, strong clawsadapted for gripping prey or perching on rocks.

Charles Darwin was an English biologist. In his famous book,On the Origin of Species (1859), he developed the idea of ‘natural selection’.One of hismany observations concerned the beaks of some small birds called finches which he saw in the Galapagos Islands. He noticed that finches from different islands were very similar and he thought that they must have been a single population to start with. On one island, the finches lived in trees and ate small insects. They had small, grasping beaks. On another island,there were fewer insects and the finches had to dig under the bark of trees to find them. They had longer and thinner beaks that were well adapted for this task. And on another island, the finches lived on the ground and ate seeds. They had bigger, stronger beaks that were well adapted for cracking open seeds. From these and many other studies, Charles Darwin developed the idea of adaptation by natural selection.

  • 1. List and explain as many adaptations as you can for one plant and one animal not mentioned in the last two modules.

15 - 5