When population of a particular country rises in the manner of 2, 4, 8, 16, 32, 64, etc. This is explained by Thomas Robert Malthus as :

Geometric progression Demographic progression Arithmetic progression Population progression

Geometric progression

As per Malthus, population rises in geometric progression (i.e., like 2, 4, 8, 16, 32 etc.), agricultural production can only grow in arithmetic progression (i.e., like 2,4, 6, 8, 10 etc.).