Prompt Title: Mating Mares and Jacks

The attraction between female horses (mares) and male donkeys (jacks) to produce mules isn't necessarily a specific romantic or sexual attraction unique to this pairing. Rather, it's the result of human intervention and the deliberate breeding of these two species for specific purposes. Here are some things to consider:

1. Human Intervention: Humans have a long history of selectively breeding animals to produce offspring that have desirable traits. In the case of mules, humans discovered that the hybrid offspring of a mare and a jack had a combination of traits from both species that were beneficial for certain types of work. Mules, for instance, can be hardier, more disease-resistant, and have better stamina than horses. They can also be more patient and sure-footed than horses, which makes them excellent for certain terrains and tasks, such as packing goods in mountainous areas.

2. Fertility and Instinct: In a natural setting without human intervention, it's less common for horses and donkeys to mate simply because they have distinct social behaviors and occupy slightly different niches. However, given the opportunity (such as when they're kept in close proximity with limited access to their own species), their basic reproductive instincts can lead to mating.

3. Resultant Sterility: It's worth noting that mules (the offspring of a mare and a jack) are typically sterile. This means they cannot reproduce. This sterility is due to the different chromosome numbers in horses and donkeys. Horses have 64 chromosomes, and donkeys have 62. The mule, as a hybrid, has 63. This uneven number prevents the chromosomes from pairing up correctly during meiosis, rendering most mules infertile.

In summary, while there isn't a specific unique attraction between mares and jacks, given the right circumstances (mostly human-created), they can and do mate. The primary reason mules exist in significant numbers is due to human intervention and the usefulness of the mule's combined traits.