Homo Erectus was already building small grass huts big enough to house between four and eight people , years ago. The sculptor must have been familiar with the concept of procreation. Rudolf Feustel, a historian specializing in the prehistoric age, concluded that the artists' goal was to stimulate "raw animal lust. The fur-clad hunters of the Stone Ages spent their days traveling through the countryside in groups of 15 to 30 people -- for mothers, each baby represented an extra load to carry on their backs. There is "no reason to think that we do more now than in the past, although we are certainly more frank about it ," Buss told LiveScience. The only exceptions to tightly controlled sexual behavior happened during territorial disputes with neighboring clans. This kind of evidence is practically tailor-made for the socio-biologists, who say that these sculptures prove just how uninhibited life around the campfire used to be. To the men of that period, the fact that the female body would periodically swell up until a screaming baby would emerge from the woman's lap was nothing less than astonishing. Bits of fabric, perhaps parts of priestly robes, were found. While 53 percent of Norwegians wanted more sex than they were having a respectable 98 times per year, on average , 81 percent of the Portuguese were quite happy with their national quota of times per year.