Favourable variations are ones that increase chances for survival and procreation.
In casual encounters with the material universe, we rarely feel any difficulty here, since we usually deal with things that are clearly alive, such as a dog or a rattlesnake; or with things that are clearly nonalive, such as a brick or a typewriter. Nevertheless, the task of defining "life" is both difficult and subtle; something that at once becomes evident if we stop to think.
Consider a caterpillar crawling over a rock.
The caterpillar is alive, but the rock is not; as you guess at once, since the caterpillar is moving and the rock is not.
Yet what if the caterpillar were crawling over the trunk of a tree? The trunk isn't moving, yet it is as alive as the caterpillar. Or what if a drop of water were trickling down the trunk of the tree?
The water in motion would not be alive, but the motionless tree trunk would be.
It would be expecting much of anyone to guess that an oyster were alive if he came across one for the first time with a closed shell. Could a glance at a clump of trees in midwinter, when all are standing leafless, easily distinguish those which are alive and will bear leaves in the spring from those which are dead and will not?
Is it easy to tell a live seed from a dead seed, or either from a grain of sand? For that matter, is it always easy to tell whether a man is merely unconscious or quite dead? Modern medical advances are making it a matter of importance to decide the moment of actual death, and that is not always easy.
Nevertheless, what we call "life" is sufficiently important to warrant an attempt at a definition. We can begin by listing some of the things that living things can do, and nonliving things cannot do, and see if we end up with a satisfactory distinction for this particular twofold division of the Universe.
A living thing shows the capacity for independent motion against a force. A drop of water trickles downward, but only because gravity is pulling at it; it isn't moving "of its own accord. Living things that seem to be motionless overall, nevertheless move in part.
An oyster may lie attached to its rock all its adult life, but it can open and close its shell. Furthermore, it sucks water into its organs and strains out food, so that there are parts of itself that move constantly.
Plants, too, can move, turning their leaves to the sun, for instance; and there are continuous movements in the substance making it up. A living thing can sense and it can respond adaptively. That is, it can become aware, somehow, of some alteration in its environment, and will then produce an alteration in itself that will allow it to continue to live as comfortably as possible.
To give a simple example, you may see a rock coming toward you and will quickly duck to avoid a collision of the rock with your head. Analogously, plants can sense the presence of light and water and can respond by extending roots toward the water and stems toward the light.
Even very primitive life forms, too small to see with the unaided eye, can sense the presence of food or of danger; and can respond in such a way as to increase their chances of meeting the first and of avoiding the second. The response may not be a successful one; you may not duck quickly enough to avoid the rock—but it is the attempt that counts.
A living thing metabolizes. By this we mean that it can eventually convert material from its environment into its own substance. The material may not be fit for use to begin with, so it must be broken apart, moistened, or otherwise treated. It may have to be subjected to chemical change so that large and complex chemical units molecules are converted into smaller, simpler ones.
Anything which is left over, or not usable, is then eliminated. The different phases of this process are sometimes given separate names: A living thing grows.Evidence of common descent of living organisms has been discovered by scientists researching in a variety of disciplines over many decades, demonstrating that all life on Earth comes from a single pfmlures.com forms an important part of the evidence on which evolutionary theory rests, demonstrates that evolution does occur, and illustrates the processes that created Earth's biodiversity.
Evolution - The science of evolution: The central argument of Darwin’s theory of evolution starts with the existence of hereditary variation. Experience with animal and plant breeding had demonstrated to Darwin that variations can be developed that are “useful to man.” So, he reasoned, variations must occur in nature that are favourable or useful in some way to the organism itself in the.
is and in to a was not you i of it the be he his but for are this that by on at they with which she or from had we will have an what been one if would who has her. Port Manteaux churns out silly new words when you feed it an idea or two.
Enter a word (or two) above and you'll get back a bunch of portmanteaux created by jamming together words that are conceptually related to your inputs.. For example, enter "giraffe" and you'll get . Port Manteaux churns out silly new words when you feed it an idea or two. Enter a word (or two) above and you'll get back a bunch of portmanteaux created by jamming together words that are conceptually related to your inputs..
For example, enter "giraffe" and you'll get back words like "gazellephant" and "gorilldebeest". Devil In The Dark () The Horta was an example of Silicon life.; Now we are really sailing off into terra incognito. "Here be dragons" and all that. But if you have starships, you almost have to have aliens (Isaac Asimov's Foundation trilogy being the most notable exception).The "science" is called Astrobiology, the famous "science in search of a subject".