An animal is born with a shorter tail this makes no difference to its ability to survive or reproduce but as a result of pure luck the no survives reproduces and passes its shorter tail down to it’s offspring overtime the species develops a shorter tail
through natural selection. This process, known as genetic drift, is a random evolutionary mechanism that can result in changes in a population's genetic makeup over time. In this case, the shorter tail becomes more common in the population due to chance rather than any specific advantage it provides.
Over generations, if the shorter tail confers some kind of advantage, such as improved agility or reduced risk of injury, it may become more prevalent in the population through natural selection. However, if it has no impact on survival or reproduction, it may simply persist due to random chance.
In either case, the shorter tail would become a characteristic of the species as a whole, even though its initial appearance was the result of luck rather than adaptation. This example highlights the role of both natural selection and genetic drift in shaping the evolution of species.