Here's why:

* Genetic diversity: Sexual reproduction involves the combination of genetic material from two parents, creating offspring with unique combinations of genes. This leads to greater genetic diversity within a population, which can increase its adaptability and resilience to changing environments.

* Elimination of harmful mutations: Sexual reproduction allows for the mixing and shuffling of genes, which can help to eliminate harmful mutations from a population.

* Evolutionary advantage: The increased genetic diversity and ability to eliminate harmful mutations give sexually reproducing organisms a significant evolutionary advantage over those that reproduce asexually.

While many eukaryotic organisms reproduce sexually, it's important to remember that some can also reproduce asexually, either as a primary or secondary mode of reproduction. Examples include:

* Plants: Many plants can reproduce both sexually (through flowers and seeds) and asexually (through runners, bulbs, or cuttings).

* Fungi: Fungi often reproduce asexually through spores.

* Animals: Some animals, like sea anemones and starfish, can reproduce asexually through fragmentation.

Overall, sexual reproduction is the dominant mode of reproduction for eukaryotic organisms because it provides a significant advantage in terms of genetic diversity, adaptation, and survival.