Some bible objectors argue that the existence of asexuality in nature proves that sex/gender is fluid and the bible is wrong about sex/gender being binary. Does what animals do, have anything to do with what humans do? The Bible says that humans are designed explicitly as male and female (Gen 1:28, Gen 2:24). There are intersex people but those are outliers caused by mutations. If every person in the next generation was intersex and potentially sterile because of it, we would be facing potential extinction as a species. Therefore humans are made to reproduce sexually by design.
As for animals, the land and flying animals that get on the Ark do so in pairs of male and female (Gen 7:15-16). However, there is no scripture giving exclusivity of sex to any species other than humans. There are a few land animals like various kinds of Snails, Slugs, as well as earthworms that are NATURALLY hermaphrodites. More specifically they are Simultaneous hermaphrodites, which means they have both genitals and can reproduce asexually. Fish sex is never mentioned in the bible, and hermaphroditism and alternative sex mechanisms are most common amongst sea creatures. Sheephead fish are Protogynous, which means they start off as female and certain ones become male at sexual maturity based on dominance. The opposite happens, like in the case of clownfish, who start as males and later become females based on dominance, they are Protandrous. In addition, sea horses have opposite gender roles (the males get pregnant).
Every creature that’s not asexual requires the two complementary sexes to reproduce. In the case of seahorses, they’re still classified as male and female respectively based on gametes produced. What makes them unique is the role reversal in the process of procreation, because the female lays eggs in the male’s “womb”. Hermaphrodite creatures are born with the ability to either self-reproduce or transition their sex naturally. They don’t need external hormone manipulation and surgery to do so. If a creature can do it naturally then it’s by design. Humans can’t do these things naturally so they’re not this way by design. Humans like most other creatures, reproduce sexually and are not hermaphroditic, meaning they have permanent male and female bodies. Most land creatures reproduce sexually with complementary sexes, the rare exceptions are mainly some mollusk and amphibians. Creatures that have these abilities are a unique exception to the rule.
From a biblical perspective, the existence of alternative sex mechanics like hermaphroditism and asexual reproduction in animals doesn’t apply to humans. The naturalism ideology goes after the credibility of the Genesis account by connecting humans with animals so that the culture can apply new non-binary sex ideas to humans. However, the bible doesn’t support this because it says humans are a special creation made in God’s image (Gen 1:26-27). Jesus died for humans, not animals, therefore only humans are made in God’s image. Only humans have a language system that can be spoken, written, and transmitted through space and time with special technology that only humans can create. It’s the likeness and image of God that makes us unique. We are not mere animals nor is our design based on them.
More on the uniqueness of human language here.
More on Evolution in the Bible here.
Gender Bending fish