Why is variation important for the survival of a species, especially in changing environmental conditions? Illustrate with an example.

Variation is crucial for the survival of a species because it provides the raw material for natural selection to act upon, allowing populations to adapt to changing environmental conditions.

If all individuals in a population were genetically identical, a sudden change in the environment (e.g., a new disease, climate change, or a new predator) could potentially wipe out the entire species if no individual possessed a trait that allowed them to survive the change. With variation, some individuals might possess traits that make them better suited to the new conditions. 

These individuals are more likely to survive, reproduce, and pass on their advantageous traits to their offspring. Over time, the frequency of these beneficial traits increases in the population, leading to adaptation and the continued survival of the species. 

Example: Consider a population of insects living on a plant species. If a new pesticide is introduced that kills most of the insects, a few individuals might have a naturally occurring genetic variation that makes them resistant to the pesticide. These resistant insects will survive while others perish. 

They will then reproduce, and their offspring will inherit the resistance. Over several generations, the population will evolve to become largely resistant to the pesticide, ensuring the survival of the species despite the environmental challenge.