## Did you know that...

...a mutation in the ACTN3 gene appeared more than 50,000 years ago when modern humans migrated from Africa to the colder climate of central and northern Europe. Indeed, natural selection favoured the XX genotype of this gene in a colder environment. People lacking α-actinin 3 were found to maintain body temperature better during immersion in cold water due to a change in skeletal muscle thermogenesis. Better body resistance to cold in individuals with the XX genotype was not accompanied by increased energy expenditure, but by an energetically efficient increase in the tone of type I slow-twitch muscle fibres that generate heat.