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Show 126 CONDI'f!ONS AFFECTING THE the power of production of nutriment, and that thus some check must arise to the further increase of those organic beings. At the end of the ninth year we have seen that each plant would not be able to get its full square foot of ground, and at the end of another year it would have to share that space with fifty others the produce of the seeds which it would give off. \iVhat, then, takes place? Every plant grows up, flourishes, occupies its square foot of ground, and gives ·Off its fifty seeds; but notice this, that out of this number ·only one can come to anything; there is thus, as it were, forty-nine chances to one against its growing up; :it depends upon the most fortuitous circumstances whether any one of these fifty seeds shall grow up and flourish, or whether it shall die and perish. rrhis is what Mr. Darwin has drawn attention to, and called the " STRUGGLE FOR ExisTENCE; " and I have taken this simple case of a plant because some people imagine that the phrase seems to imply a sort of fight. I have taken this plant and shown you that this is the result of the ratio of the increase, the necessary result of the arrival of a time coming for every species when exactly as many members must be destroyed as are born; that is the inevitable ultimate result of the rate of production. Now, what is the result of all this? I have said that there are forty-nine struggling against ,·every one; and it a1nounts to this, that the smallest possible start given to any one seed may give it an advantage which will enable it to get ahead of all the others; anything that will enable any one of these seeds PERPETUATION OJ<' LIVING BEINGS. 127 to germinate six hours before any of the others will, other things being alike, enable it to choke them out altogether. I have shown you that there is no particular in which plants will uot vary from each other; it is quite possible that one of our imaginary plants may vary in such a character as the thickness of the integunient of its seeds. It might happen that one of the plants might produce seeds having a thinner integument, and that would enable the seeds of that plant to germinate a little quicker than those of any of the others, and those seeds would most inevitably extinguish the forty-nine times as many that were struggling with them. I have put it in this way, but you see the practical result of the process is the same as if some person had nurtured the one and destroyed the other seeds. It does not matter how the variation is produced, so long as it is. once allowed to occur. The variation in the plant once fairly started tends to become hereditary and reproduce itself; the seeds would spread themselves in the· same way and take part in the struggle with the fortynine hundred, or forty-nine thousand, with which they might be exposed. Thus, by degrees, this variety, with some slight organic change or modification, must spread itself over the whole surface of the habitable globe, and extirpate or replace the other kinds. That is what is meant by NA'rURAL SELECTION; that is the kind of argu-. ment by which it is perfectly demonstrable that the conditions of existence may play exactly the same part for natural varieties as man does for domesticated varieties. No one doubts at all that particular circumstances may be more favourable for one plant |