We can explain the existence of humans just fine. And we dont need a moral basis for equality of rights, we have a practical basis. Equal rights maximizes your societys output, because you have more people in a position to contribute to the full extent of their ability. The more of your society that gets deliberately held back the less of your society that is producing and inventing and just generally supporting it. There was a great article about a decade ago talking about how Islamic treatment of women holds their society back, by telling over half their society no when it comes to pretty much everything theyve turned half their society into deadweight, they have specifically outlawed Madame Curie and Lady Ada. Equal rights is just plain good business. What if it becomes "bad business," ie, like Malthus, you think we have too many people, which is therefore a detriment to what you call "society"?