[tachyonbeam]

> The evolution of organisms that gene mishmash (aka sexual reproduction) is thought to be the result of an ongoing arms race between gene sequences that "try" to stay unchanged (in higher level species) and gene sequences that "try" to "free ride" (from viruses etc.)

Sexual reproduction means your species has a very large gene pool, and individuals with new combinations of genes can be produced very quickly. That's not just an advantage against viruses. It's also very useful for adapting rapidly and competing against other species when your environment changes. New threats (and new opportunities) show up all the time, be it dwindling or changing availability of food, climate change (e.g. new ice age), new predators or new preys, and also a group of individuals migrating to a new region of the world with a different climate.