Here's why:

* Limited Sexual Reproduction: Unlike eukaryotes, prokaryotes rarely undergo sexual reproduction. They primarily reproduce asexually through binary fission, which creates clones of the parent cell. This limits the generation of new genetic combinations.

* Horizontal Gene Transfer: HGT is the transfer of genetic material between organisms that are not related through direct descent. Prokaryotes have three main mechanisms for HGT:

* Transformation: The uptake of naked DNA from the environment.

* Transduction: The transfer of DNA by bacteriophages (viruses that infect bacteria).

* Conjugation: The transfer of DNA through direct contact between bacteria, often via a pilus.

Why HGT is Important:

* Rapid Evolution: HGT allows prokaryotes to acquire new genes quickly, facilitating adaptation to changing environments and promoting rapid evolution.

* Increased Diversity: The exchange of genes between different species leads to increased genetic diversity within prokaryotic populations.

* Antibiotic Resistance: HGT plays a significant role in the spread of antibiotic resistance genes, making it a major challenge in public health.

While mutations still occur in prokaryotes, they are typically less frequent and less impactful in generating variability compared to the significant contributions of HGT.