Final answer:
For variation to meaningfully contribute to evolution, it must be heritable, meaning that it has a genetic basis and can be transmitted from one generation to the next. While mutations introduce randomness, sexual reproduction and natural selection are not entirely random, and together they shape the evolutionary process.
Step-by-step explanation:
For variation to be a meaningful contribution to evolution, it must be heritable. This means that the traits which vary among individuals in a population must have a genetic basis, allowing them to be passed down from one generation to the next. Heritable variation is the raw material upon which natural selection acts. A trait that is not heritable, such as one acquired during an individual's lifetime, generally cannot be acted upon by natural selection and therefore does not contribute to the evolutionary process.
Gene mutations and sexual reproduction introduce genetic variance into a population, which is crucial for evolution. While mutations occur randomly, the combination of genes through sexual reproduction is not entirely random due to mate choice and other factors. Collectively, these mechanisms influence the genetic and phenotypic variance of a population, playing an essential role in the evolutionary process.
It's also worth noting that not all evolution is adaptive or leads to an increase in fitness. Factors such as genetic drift and gene flow can also introduce changes to a population's gene pool that may not necessarily be advantageous.