Digest of terms
natural and unnatural
'nature' is sometimes appealed to as a moral arbiter. This is based on the observation of the natural world and the detection of ordered routines. That there are such patterns, as for instance amongst animals, is not in contention. Whether they provide a basis for extrapolating to how human beings should behave is, however, very much in dispute. For instance, does the 'survival of the fittest', both between and within species, justify indifference towards the 'weaker' human beings on the part of the strong? There was a time, in the early twentieth century, when eugenicists (and not only Nazi policy-makers) thought that it did, yet today such conclusions are regarded as morally repugnant. Objections to homosexuality once found justification in the claim that this does not happen 'in nature'. In fact, it is now well documented in other species besides humans, but that in itself is no guarantee of its morality or otherwise.
By contrast, self-correcting ecosystems do provide a remarkable model of living harmony, and both birds and animals show a capacity for 'self-sacrifice' in their behaviour, most especially when their offspring are in danger. Irrespective of the prevailing law in a particular society, strong opprobrium is invariably shown across different cultures towards mothers who deliberately or negligently damage their children. More exceptionally, the behaviour of some step-parents towards the offspring of another partner can be wilfully rejecting and cruel. Both these reactions can be attributed to natural inheritance. From a human perspective, 'doing what comes naturally' may in practice be highly moral, morally ambiguous or even morally repugnant. (is/ought distinction; moral foundations theory)
See Concept Scenarios.