SKETCH OF FRANCIS GAL TON. n 7 



each case the number of turbot in the sea next year would be double 

 what it is this ; the year after that there would be four times as 

 many ; the next year eight times again ; and so on in a regular arith- 

 metical progression. In a very few decades the whole sea would be- 

 come one living mass of solid turbot. As a matter of fact, since the 

 number of individuals in any given species remains on the average 

 exactly constant, we may lay it down as a general rule that only two 

 young usually survive to maturity out of all those born or laid by a 

 single pair of parents. All the rest are simply produced in order to 

 provide for the necessary loss in infant mortality. The turbot lays 

 fourteen million eggs, well knowing that thirteen million nine hun- 

 dred and ninety-nine thousand nine hundred and ninety-nine will be 

 eaten up in the state of spawn or devoured by enemies in helpless in- 

 fancy, or drifted out to sea and hopelessly lost, or otherwise somehow 

 unaccounted for. The fewer the casualties to which a race is exposed 

 the smaller the number of eggs or young which it needs to produce in 

 order to cover the necessary losses. 



In fish generally it takes at least a hundred thousand eggs each 

 year to keep up the average of the species. In frogs and other am- 

 phibians, a few hundred are amply sufficient. Reptiles often lay only 

 a much smaller number. In birds, which hatch their own eggs and 

 feed their young, from ten to two eggs per annum are quite sufficient 

 to replenish the earth. Among mammals, three or four at a birth is 

 a rare number, and many of the larger sorts produce one calf or foal 

 at a time only. In the human race at large, a total of five or six 

 children for each married couple during a whole lifetime makes up 

 sufficiently for infant mortality and all other sources of loss, though 

 among utter savages a far higher rate is usually necessary. In Eng- 

 land, an average of four and a half children to each family suffices to 

 keep the population stationary ; above that number it begins to in- 

 crease, and has to find an outlet in emigration. If every family had 

 four children, and every child grew up to maturity and married, the 

 population would exactly double in every generation. Even making 

 allowances for necessary deaths and celibacy, however, I believe that 

 as sanitation improves and needless infant mortality is done away 

 with, the human race will finally come to a state of equilibrium with 

 an average of three children to each household. But this is getting 

 very far away indeed from the habits of flat-fishes. Cornhill Maga- 

 zine. 



-+++- 



SKETCH OF FRANCIS GALTOK 



A SKETCH of Francis Galton may appear with manifest fitness 

 in the same number of the " Monthly " in which is published an 

 abstract review of M. de Candolle's researches into heredity and the 

 other conditions favorable to the production of men of science. Mr. 



