The notion of evolvability has been put forward to describe the "core mechanism" of natural and artificial evolution. Recently, studies have revealed the influence of the environment upon a system's evolvability. In this contribution, we study the evolvability of a system in various environmental situations. We consider neutrality and variability as two sides of evolvability. The former makes a system tolerant to mutations and provides a hidden staging ground for future phenotypic changes. The latter produces explorative variations yielding phenotypic improvements. Which of the two dominates is influenced by the environment. We adopt two tools for this study of evolvability: 1) the rate of adaptive evolution, which captures the observable adaptive variations driven by evolvability; and 2) the variability of individuals, which measures the potential of an individual to vary functionally. We apply these tools to a Linear Genetic Programming system and observe that evolvability is able to exploit its two sides in different environmental situations.