Fossils and genes are primarily used to determine how species will change over time and differences between organisms. Fossils provide evidence of past life forms and how they have evolved, while genetic analysis helps in understanding the relationships and variations among different organisms.
In summary, the key uses are:
- How species will change over time: Fossil records help trace the evolutionary history and changes in species.
- Differences between organisms: Genetic comparisons reveal the degree of similarity and difference among species.
If you need to choose the best response from the options provided, it would be how species will change over time.