Here's why:

* Gene shuffling: This refers to the process of reshuffling genetic material during meiosis, the cell division that produces gametes (sperm and egg). This shuffling happens through two main mechanisms:

* Crossing over: Homologous chromosomes (pairs of chromosomes from each parent) exchange genetic material, leading to new combinations of alleles.

* Independent assortment: Chromosomes from each pair are randomly distributed into the gametes, creating further diversity in the genetic makeup of each gamete.

* Inheritable differences: These are variations in traits passed down from parents to offspring. These variations are primarily driven by differences in the genetic code, which is what gets shuffled during gamete production.

Other sources of inheritable differences:

While gene shuffling is the primary source of inheritable differences, other factors can contribute:

* Mutations: Changes in the DNA sequence can occur spontaneously or due to environmental factors. These mutations can introduce new variations into the gene pool.

* Horizontal gene transfer (in some organisms): This is the transfer of genetic material between organisms that are not parent and offspring. It is more common in bacteria and some other microorganisms, but it can contribute to diversity in those cases.

Conclusion:

Overall, gene shuffling during gamete production is the main driver of inheritable differences in sexually reproducing organisms. This constant reshuffling of genetic material is the foundation for the vast diversity we see in living things.