Heritability of telomere variation: it’s all about the environment!

Individual differences in telomere length have been linked to survival and ageing. Understanding the heritability of telomere length can provide important insight into individual differences and facilitate our understanding of the evolution of telomeres. However to gain accurate and meaningful estimates of telomere heritability it is vital that the impact of the environment, and how thismay vary, is understood and accounted for. The aim of this review is to raise awareness of this important, but much under-appreciated point.We outline the factors known to impact telomere length and discuss the fact that telomere length is a trait that changes with age. We highlight statistical methods that can separate genetic from environmental effects and control for confounding variables. We then reviewhowwell previous studies in natural vertebrate populations have taken these factors into account. We argue that studies to date either use methodological techniques that confound environmental and genetic effects, or use appropriate methods but lack sufficient power to fully separate these components.We discuss potential solutions.We conclude that we need larger studies, which also span longer time periods, to account for changing environmental effects, if we are to determine meaningful estimates of the genetic component of telomere length. This article is part of the theme issue ‘Understanding diversity in telomere dynamics'.