The downfall of Greece,[6] like that of Rome, has been ascribed by Schultz to the crossing of the Greeks with the barbaric races which flocked into Hellas from every side. These resident aliens, or metics, steadily increased in number as the free Greeks disappeared. Selected slaves or helots were then made free in order to furnish fighting men, and again as these fell their places were taken by immigrants. [6] Certain recent writers who find in environment the causes of the rise and fall of nations, ascribe the failure of Greece to the introduction in Athens and Sparta of the malaria-bearing mosquito. As to the facts in question, we have little evidence. But while the prevalence of malaria may have affected the general activity of the people, it could in no way have obliterated the mental leadership which made the strength of classic Hellas, nor could it have injected its poison into the stream of Greek heredity. It is doubtless true at this day that "no race inhabits Greece," and the main difference between Greeks and other Balkan peoples is that, inhabiting the mountains and valleys of Hellas, they speak in dialects of the ancient tongue. Environment, except through selection and segregation, can not alter race inheritance and the modern "Greeks" have not been changed by it. Schultz observes: 'We are told that the Hellenes owed their greatness largely to the country it was their fortune to dwell in. To that same country, with the same wonderful coast line and harbors, mountains and brooks, and the same sun of Homer, the modern Greeks owe their nothingness.' In other words, it is quite true that the Greece of Pericles owed its strength to Greek blood, not to Hellenic scenery. When all the good Greek blood was spent in suicidal wars, only slaves and foreign-born were left. " 'Tis Greece, but living Greece no more."[7] [7] In contrasting a new race with the old--as the modern Greeks with the incomparable Hellenes--we must not be unjust to the men of to-day whose limitations are evident, contrasted with a race we know mainly by its finest examples. In spite of poverty, touchiness and vanity characteristic of the modern Greek, there is good stuff in him. He is frank, hopeful, enthusiastic. The mountain Greek, at least, knows the value of freedom, and has more than once put up a brave fight for it. The valleys breed subserviency, and the Greeks of Thessaly are said to be less independent than the mountain-born. Furthermore, we do not know that even the first Hellenes of Mycenae were an unmixed race, or that any unmixed races ever rose to such prominence as to command the world's attention. We do know that when war depletes a nation slaves and foreigners come in to fill the vacuum, and that the decline of a great race in history has always been accompanied by a debasing of its blood.