What is the basic idea with original sin?
To ask what is the basic idea with original sin it is helpful to ask what is the basic idea with sin. Sin is – in its essence – sub-optimal behaviour.
(Theologically, this can be understood as action leading to separation from God, where God = the Good. Also see here. From a secular viewpoint, however, this is to confuse the issue, as it brings God in first, where the idea of God is in question. In more secular language, we can say sin is behaviour leading to separation from the Good. In Christianity, this idea is refined and developed, and often related to other theological concepts. That sub-optimal behaviour is the essence can be seen by considering things like the 7 deadly sins, which are typical sub-optimal behaviours such as over-eating, laziness, and so on.)
Original sin, then, is the idea that there is something heritable in human nature that can lead to sub-optimal behaviour. Often, people can get pulled off the track by details in the story of the Garden of Eden – was there really a garden, were there really just two primordial humans, was there really a serpent, and so on.
In more secular terminology, we might say there is something related to the brain that can often lead to sub-optimal behaviour in humans, especially in a non-natural environment. This latter point can use some expansion.
Adam and Eve leave the ‘garden’ – my guess is that this comes from a cultural memory of entering agricultural society, including, among other things, more difficult child birth (Genesis 3:16), something that tends to be easier in hunter-gatherer societies for some reason (including increased pelvic depth, perhaps due to nutritional differences), and ’toiling the land’ (Genesis 3:17), a seemingly direct reference to some kind of shift to agriculture as opposed to hunting-gathering or primarily pastoralist society.
So, the basic idea is we now have a mismatch, where part of how our brains often work (captured by the change in human cognitive nature told in the story of the garden) tends to lead to certain kinds of sub-optimal behaviour, at least in a society like we have now (having left ’the garden’).
So understood, the idea of ‘original sin’ seems relatively obvious. Many people engage in sub-optimal behaviour, like gambling, over-eating, and so on, and this probably has something to do with our evolved cognitive structures, and perhaps in specific with a mismatch between our agricultural (industrial, and so on) society and the one we evolved for a longer period of time in.
It seems part of getting this point for many people is probably switching from an articulation of what is going on in traditional theological terms to a conceptual vocabulary that connects more easily with other contemporary ideas.