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The Conditions of Existenceby Thomas H. HuxleyIN the last Lecture I endeavoured to prove to you that, while, as ageneral rule, organic beings tend to reproduce their kind, there is inthem, also, a constantly recurring tendency to varyto vary to agreater or to a less extent. Such a variety, I pointed out to you,might arise from causes which we do not understand; we therefore calledit spontaneous; and it might come into existence as a definite andmarked thing, without any gradations between itself