Any organism requires a specific environment to survive or thrive. The expression of genes is triggered and associated with specific physical and biochemical stimuli. Temperature can be a trigger for functions that when decoded by genes will activate thermogenesis or heat dispersal. The function of skin pigments such as melanin also depends on how the environment, spanning generations, acted as a master control for genes that needed to adapt and produce more dark skin pigment when living at locations that induced more sun exposure.
Even living most of the day indoors or outdoors, or being part of a great family or living alone can trigger definite functions, such as oxytocin release, which may reduce anxiety and increase trust. Even your natural talents and career choices may influence certain genes to express and others to remain unexpressed.