 A fairly comprehensive demographic study was done by historian John Demos for his seminal 1970 work on the Pilgrims A Little Commonwealth . He reports that the colony 's average household grew from 7 @.@ 8 children per family for first @-@ generation families to 8 @.@ 6 children for second @-@ generation families , and to 9 @.@ 3 for third @-@ generation families . Child mortality also decreased over this time , with 7 @.@ 2 children born to first @-@ generation families living until their 21st birthday . That number increased to 7 @.@ 9 children by the third generation . Life expectancy was higher for men than for women . Of the men who survived until the age of 21 , the average life expectancy was 69 @.@ 2 years . Over 55 percent of these men lived past 70 ; less than 15 percent died before the age of 50 . For women , the numbers are much lower , owing to the difficulties inherent in childbearing . The average life expectancy of women at the age of 21 was only 62 @.@ 4 years . Of these women , less than 45 percent lived past 70 , and about 30 percent died before the age of 50 . 
