Final answer:
Sexual reproduction's main disadvantage compared to asexual reproduction is a reduced population growth rate due to the need for two parent organisms and only half the population being capable of reproduction.
Step-by-step explanation:
The disadvantage of sexual reproduction over asexual forms of reproduction is the reduced population growth rate. This occurs because sexual reproduction requires two parent organisms to contribute genetic material, leading to time and energy expenditure on finding a mate. Moreover, in sexual populations, typically only half of the population (females) can produce offspring, while all individuals in an asexual population, which are usually female, can potentially contribute to population growth. As a result, an asexual population could theoretically grow at twice the rate of a sexual population.
In contrast to asexual reproduction, which can rapidly produce offspring that are all genetically identical to the parent, sexual reproduction introduces genetic diversity through mechanisms like the random assortment of chromosomes. This is advantageous in changing environments, providing a better chance for offspring to adapt. However, this process is slower and involves more steps than asexual reproduction, limiting the speed of population growth.