Adaptation In Animals (1963)

e the differences between animals result from countless small changes that have occurred by chance from time to time since life began they are occurring now at this moment they will continue as long as life exists each change makes an animal better able or less well able to get along in its slowly changing surroundings adaptation is the sum of those changes that increase the animals chances for survival in nature survival is a struggle in this fight for a mate the stronger stag will win his offspring are likely to inherit his strength and are more likely to survive because of it in this way strength is preserved and weakness disappears life is a constant process of selection of the strong over the weak in this environment only the hardiest plants can survive the others Die For example here only the toughest plants have a chance to avoid being washed away in this experiment we will see a population become adapted by selection in the dish on the left bacteria are growing on a culture medium we transfer some to the dish on the right in which the culture medium contains stromy a drug that kills bacteria they are too small to see but each time the instrument touches the medium thousands of bacteria are deposited we have planted many colonies of bacteria in this dish containing strepto two days later we see the same dish on the left some of the bacteria colonies were able to survive on the streptomycin they appear as red dots the rest are dead this is a simple example of selection we transfer some of the surviving bacteria onto a normal culture medium then onto a new strepto medium a few days later we see that the bacteria are growing equally well on the two dishes in fact the strepto dish is actually redder indicating that there are more bacteria in it all the bacteria had become adapted to living on the strepto this is a reptile a snake it looks very unlike the chicken but they are alike in one extremely important way both birds and reptiles lay eggs on land like this snake eggs laid in water like these Frog's eggs are soft and unprotected and are often eaten before hatching millions of years ago Birds evolved from early reptiles which laid their eggs on land eggs with a shell to prevent them from dry out and protect the young inside the yolk is food and is used up as the chick grows the chick can develop more fully before leaving the protection of the shell the egg with a shell was a successful adaptation but if that is so why are puppies not born in eggs puppies develop inside the mother for about 50 days before birth to store food enough for such a period an egg would have to be much too big to lay the difficulty was overcome by an organ called the placenta where material is exchanged between the mother and The Unborn rat seeded through this tube nourishment and oxygen from the mother reaches the fetus and wastes return to the mother the placenta allowed the fetus to develop longer before birth the brain became more complex and the cereal cortex larger on the left is the brain of a bird we outline the cortex which is not very highly developed in the brain of a rat it occupies a larger part in man's brain which developed over 9 months a much longer period than the others the cortex takes up most of the total volume another part of the brain is the cerebellum the center for adjusting position for instance during flight the bird arum is a large prominent structure in the rat it is much smaller on land there are fewer problems of balance and for the same reason the man cerebellum is also small in the rat the center for smells the Ola Factory area is well developed in man it is less welldeveloped the most complex brain function is reasoning the areas of the brain involved in reasoning require a long time to develop time made available by the placenta animals without the power to reason have other ways of protecting themselves wolves are strong and cunning deer are fast and often hard to see color is often a protection many animals change color with the season the upper bird has changed from its winter white to the speckled plumage that conceals it best when there is no snow animals whose color matches the coloring of their environment are better able to hide from their enemies and survive why some can change color quickly on the brown log this chameleon is brown how about on the Lea he has a better chance to survive because of his unusual ability to match the color of his surroundings almost immediately environment determines protective coloration it determines many other things as well this is the distant ancestor of all living cats his descendants developed in different ways according to the conditions of their environment some have been pets for thousands of years others lived very differently Winters were very cold where bobcats once lived their coats became thick often their long tails froze and they died in time only short-tailed Bobcats remained another cat the Jaguar became the powerful Silent Hunter stalking his prey in the South American jungle on the plains of Africa this cat the cheetah found little cover for stalking he had to be fast to outrun his prey long legs helped and made survival more likely the cheetah became the fastest animal on earth he can run as fast as 70 M an hour the tree climbing leopard almost invisible in the fork of this tree waits for his prey to pass below there will be a slight difference between this Lion and the Cub she is carrying from generation to generation species change in different environments they develop in different ways that is how different species in time emerge an environment as nearly uniform as the sea often results in widely different species evolving to look alike this is a reptile now long extinct whose ancestors lived on land for reasons we do not know they returned to the Sea where they gradually became fishlike for a number of reasons we believe that the whale's ancestors also lived on land the bones in this front flipper provide one clue the bones are shown in the center drawing compare them with the bones in the left hand drawing of a man's arm the sizes are different but they are all there fingers hand forearm upper arm on the right the bones of a fish's fin are very different the whale is a mammal it has lungs and breathes through this hole unlike a fish its tail fins are horizontal a help in surfacing quickly to breathe the tail even contains the remains of the original land legs the reptile the whale and this shark came from very different ancestors but all three living similar lives in the sea came to look very similar in the world there is room only for the strongest the most successful some bacteria are able to adapt toptoy a most important adaptation was the egg which increased the chances of survival among reptiles and birds the placenta was an improvement and made possible greater complexity animals can continue to exist only by endless change by adaptation