variation of sex ratio at birth is due to sex selection between conception and birth. James cautions that available scientific evidence stands against the above assumptions and conclusions. He reports that there is an excess of males at birth in almost all human populations, and the natural sex ratio at birth is usually between 102 and 108. However the ratio may deviate significantly from this range for natural reasons such as early marriage and fertility, teenage mothers, average maternal age at birth, paternal age, age gap between father and mother, late births, ethnicity, social and economic stress, warfare, environmental and hormonal effects. This school of scholars support their alternate hypothesis with historical data when modern sex-selection technologies were unavailable, as well as birth sex ratio in sub-regions, and various ethnic groups of developed economies. They suggest that direct abortion data should be collected and studied, instead of drawing conclusions indirectly from sex ratio as Sen and others have done. James's hypothesis is supported by historical birth sex ratio data before technologies for ultrasonographic sex-screening were discovered and commercialized in the 1960s and 1970s, as well by reversed sex ratios currently observed in Africa. Michel Garenne reports that many African nations have, over decades, witnessed birth sex ratios below 100, that is more girls are born than boys. Angola, Botswana and Namibia have reported birth sex ratios between 94 and 99, which is quite different than the presumed 104 to 106 as natural human birth sex ratio. John Graunt noted that in London over a 35-year period in the 17th century (1628–1662), the birth sex ratio was 1.07; while Korea's historical records suggest a birth sex ratio of 1.13, based on 5 million births, in 1920s over a 10-year period. Female abduction and sale Evidence has shown that number of missing women may be due to other reasons than sex selective abortions or female migrant work. Specifically, female babies, girls and women have been preyed upon by human traffickers. Kidnapping and enslavement of women by the ISIS, especially of Yazidi women and other female prisoners also constitute human trafficking. In mainland China families are less willing to sell male babies even though they carry a higher price in the trade. Females born exceeding the one-child policy can be sold to wealthier families while the parents claim selling their female baby is better than other alternatives. Overseas adoption services for Chinese children