Which is the best source of information about how an organism has evolved over time?

The best source of information about how an organism has evolved over time is variations in a population over time.

Explanation:

Evolution may be defined as the variations that occur over time within a population. Evolution theory is dependent on the natural selection. Those species that are best suited to survive in an atmosphere, and transfer their features on to their offspring, as per natural selection.

Those individuals are able to cope through the passage of time and are better suited to live in the changes that take place in an setting. For an instance, the three basic periods in human life ranges from ancient then medieval and modern, a giant change can be observed in the population during such time duration.