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Animals live in an ever-changing world, but environmental perturbations are occurring at an alarming rate - threatening biodiversity and population persistence. Developmental plasticity may be an effective solution for animals to cope with environmental variation. However, it is unclear how developmental environments affect consistent phenotypic variability and shape individual responses to environmental variation later in life. Understanding these impacts of developmental environments will be important for populations living in fluctuating environments. I employed experimental and comparative approaches to investigate the impacts of incubation temperatures on phenotypic development in an Australian lizard (Lampropholis delicata). Using ‘pace-of-life’ theory as a framework, I investigated how variation in metabolic rate can result in concordant changes in life history. I used a variety of statistical tools to quantify consistent phenotypic variation of energy metabolism and growth. While development temperatures did not affect metabolic rate and its thermal plasticity, lizards reared in hot temperatures exhibited less consistent individual differences in their metabolic rate. This may be problematic in the context for global warming. However, individuals also consistently varied in their acute thermal plasticity and these consistent individual differences were robust to changes in developmental temperatures. This suggests that populations may harbour the ability to evolve suitable responses to a warming climate. Despite there being no developmental changes in metabolism, we found differences in hatching mass that persisted through to the onset of sexual maturity. Growth, and its heritability, were not affected by developmental environments. Instead, maternal effects may play an important role governing variation in growth. While metabolic rate has been purported to be a causal mechanism for variation in life history strategies, I did not find strong support for this hypothesis. Across 500 species of terrestrial ectotherms, I demonstrated that environmental factors that dictate how animals acquire and allocate resources to reproduction are major drivers to life history variation. The environment is comprised of many facets that interact to give rise to the myriad of variation we observe in nature. My thesis highlights the need to shift away from unifying theories and focus on untangling the complexities of the environment in which animals inhabit. that interact to give rise to the myriad of variation we observe in nature. My thesis highlights the need to shift away from unifying theories and focus on untangling the complexities of the environment in which animals inhabit.