Let's grant the truth of the statement that I critiqued in my last post. So, there exists the same basic standards of morality across cultures. Let's call this proposition E.
According to Shenvi, E is likely due to the existence of objective moral values. In other words, E is explained by, or consistent with, the existence of objective moral values.
And I agree -- this is aligns with his theory. But that doesn't mean there's not a better explanation for E.
A better explanation is that humans generally have the same desires, and these desires resulted in E.
Take the desire not to be murdered, for example. Ancient humans who desired not to be murdered were more likely to survive and have children with the same desire, while ancient humans without that desire were less likely to survive and have children because they were murdered more often. Therefore, as this scenario played out over generations, most humans (and any species, for that matter) eventually had the desire not to be murdered.
The reason we find cultures with rules against murder is because cultures without those rules died out.
The same could be said for lots of the basic rules within the "standard morality" found across cultures -- those rules fulfill common human desires. All cultures share the same basic desires. Therefore, all cultures have the same basic rules.
To be fair, Shenvi mentions several moral actions that are more difficult to explain. For example, he mentions throwing oneself onto a live grenade to save ones' platoon. According to Shenvi, this is best explained by objective moral values. However, Shenvi has not shown that this act is universally considered to be morally good. Therefore, by Shenvi's criterion of objective morality being universal, it doesn't not count as evidence toward objective morality. But even if it was universal, is there a better explanation for it?
I think a better explanation is that the desire for survival can be fulfilled in a variety of complex ways.
If there's a live grenade threatening ones' platoon, the most prudent option, given the various ways one can promote survival, might be to jump on the grenade. For example, if the result of jumping on the grenade is that ones' platoon stays strong, wins the war, and ones' community to thrives (which all promote survival), then one might jump on the grenade. Though the one individual would die, the survival and the thriving of ones' family and community would be more likely.