406 PEOGEESS AND NECESSITY. 



hunting state. The shepherds of the boundless plains, 

 when one pasture is devoured by their flocks, migrate 

 to another pasture where they find grass and water in 

 abundance. But when in a land like Egypt, the inhabi- 

 tants are confined to a certain tract of land they are 

 unable to evade the famine of food produced by the 

 vicissitudes of nature and the law of population ; they 

 are compelled to invent in order to subsist ; new 

 modes of life, new powers, new desires, new sentiments 

 arise ; and the human animal is changed. Then a 

 second period of immobility arrives ; by means of des- 

 potism, caste, slavery, and infanticide, the statu quo 

 is preserved. 



In the primeval sea the conditions of life were con- 

 stantly changing, but its inmates could usually keep 

 them constant by migration. For instance, let us 

 imagine a species accustomed to dwell at the bottom 

 of the sea, feeding on the vegetable matter and oxygen 

 gas which come down by liquid diffusion from the 

 waters of the surface. By elevation of the sea-bed, 

 or by the deposit of sediment from rivers, that part of 

 the sea which this species inhabits, becomes gradually 

 shallow and light. The animal would migrate into 

 deep dark water, and would therefore undergo no 

 change. But let us suppose that it is prevented from 

 migrating by a wall of rocks. It would then be ex- 

 posed to light, and to other novel forces, and it would 

 either change or die. 



Here progress is the result of absolute necessity, 

 and such must always be the case. Animals which 

 inhabit the waters have no innate desire to make ac- 

 quaintance with the land ; but it sometimes so hap- 

 pens that they live in shallow places, where they are 

 left uncovered at low water for a certain time, and so, 



