A new study has suggested that people who work hard could face more risk of poor health.
According to the study of a cooperative bird in the Kalahari Desert, unequal sharing of workloads in societies could leave the most industrious individuals at increased risk of bad health and prone to accelerated ageing.
Scientists at the University of Exeter studied white-browed sparrow weavers, a social species in which all group members share offspring care duties, but the dominant male and female work hardest.
Dominants are the only birds that breed, with dominant males singing to attract a mate and dominant females producing all of the eggs and providing most of the care for nestlings.
In order to assess how these unequal workloads impact the health of the birds, the researchers measured the level of antioxidant protection in 93 sparrow weavers before and then again after a long breeding season.
Antioxidant defences help animals to protect themselves against the damaging effects of free radicals, but if hard work overwhelmed the protection, it could result in oxidative stress, implicated in a range of diseases and ageing.
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The study found that, while dominants and subordinates had comparable levels of antioxidant protection before the breeding season, once the intensive six-month breeding period had passed, the hardest working dominant females were suffering from weakened antioxidant protection.
The findings are among the first of their kind for social vertebrates and suggest that social dominance in such species may entail hidden physiological costs, with implications for the patterns of health and ageing in societies.
The study is published in the journal Functional Ecology.