Final answer:
Most multicellular organisms reproduce sexually because it enhances genetic diversity and adaptability through unique gene combinations, outweighing the potential cost compared to asexual reproduction.
Step-by-step explanation:
The fact that the majority of multicellular organisms reproduce sexually suggests that sex must confer benefits that allow it to persist, despite its potential costs.
Sexual reproduction produces offspring with unique gene combinations, enhancing genetic diversity and potential adaptation to changing environments. Since mutations are the only source of variability in asexual reproduction, sexual reproduction's ability to reshuffle these mutations via meiosis (crossovers during prophase I and random assortment at metaphase I) can be advantageous.
Genetic diversity is likely the key evolutionary advantage of sexual reproduction over asexual reproduction. It increases the likelihood that some offspring will survive in fluctuating environmental conditions because they may carry traits that confer survival or reproductive advantages. Therefore, on average, a sexually reproducing population will leave more descendants than an otherwise similar asexually reproducing population.