Bangladeshi boys who grow up in the United Kingdom reach puberty earlier, have higher testosterone levels as adults and end up taller than those living in Bangladesh, suggests a study published online this week in Nature Ecology & Evolution. These differences are probably a result of similar environmental factors experienced during childhood, such as exposure to infectious disease.
Male reproductive investment, which is considered energetically costly, is reflected in testosterone level, timing of puberty and height, and correlates with local environments. However, it is unclear whether male reproductive investment is determined during childhood development, mediated through adulthood, or varies by ethnicity.
Kesson Magid and colleagues studied Bangladeshi men who had moved to the UK as children. The authors found that these migrants were at least as tall as and had higher salivary testosterone levels than British European men of similar socioeconomic status who had spent their whole lives in the UK. They also found that the greatest differences between migrant men and those who remained in Bangladesh occurred in men who had migrated before the age of eight.
The authors propose that investment in reproductive development is ‘traded off’ against other energy-costing processes during childhood, such as fighting infection. The results are similar to previous studies into the onset of puberty and reproductive hormone levels in migrant women. These insights may help us understand changes in the timing of puberty and hormone-related diseases with increasing affluence and nutritional status in populations around the world.