Humans are fickle creatures. Yet, as David Hume, the Scottish philosopher, figured out over 250 years ago, we are driven by our passions far more than reason. It can take an unearthly level of persuasion to alter a passionately held view even if there is irrefutable evidence. And many a time the view prevails.

This story about conservation in the face of scientific evidence makes the same point…

It is often said that the end cannot justify the means. This adage comes for the logic that an immoral act is an immoral act irrespective of when it occurs or for what reason.

The other day I witnessed an argument that left me thinking how this is adage is rarely applied.

The discussion began over a conservation problem that is becoming widespread in the eucalyptus forests of eastern Australia. Mature canopy trees are dying from infestations of sap sucking insects that proliferate to reach huge numbers sufficient to defoliate the tree. This explosion of insects and damage to leaves happens where a bird species, the bell miner, is abundant.

Rather than eat the insects, bell miners eat the sugary lurps that the scale insects use to protect themselves – it is a little like harvesting, for the insects regrow the lurp that covers them and the birds come round again.

Bell miners are aggressive birds and chase away other species. This lowers the predation rate on the insects that, over time, means more insects. The insects feed on the leaves that eventually succumb. When the trees lose too many leaves they die back. The process has been given an acronym BMAD; bell miner associated dieback.

Bell miners do well in disturbed forests because they like the dense undergrowth that comes when a forest is altered by fire, logging or other human interference.

Once established the best way to slow the spread of BMAD is active management involving the removal of shrubs. This means suppression through mechanical means, sometimes fire or, more usually, the application of herbicides.

These are drastic interventions of the kind that the conservation movement opposes with religious fervor. Only BMAD is far worse. So even among the ardent conservationists it has been accepted that intervention to remove shrubs is necessary. It is acceptable to manage with interventions of herbicide a habitat that was disturbed.

All good so far. The argument came of over the next issue.

Someone made the comment that ecologically endangered communities could be managed for improvement.

‘No, no, no you cannot do that’ was the indignant cry. ‘You cannot mess with an EEC, you just can’t.’

It was seen as a morally abhorrent suggestion. If something is designated as endangered it is suddenly untouchable.

But why not actively manage? Is it not exactly the same as the intervention proposed to tackle BMAD. In that thorny issue the end justified the means. But the same means cannot be applied to an EEC.

So in the real everyday world we have selective morality.

Let’s just rephrase this outcome.

A Threatened Ecological Community is determined as such by a Scientific Committee that sits in a room in a city and decides a given vegetation type is rare enough and its integrity and longevity threatened enough to meet a set of listing criteria. The committee members review evidence and decide if there is sufficient threat to place the vegetation on a list of habitat types at risk of extinction.

This appraisal confers some protection where the habitat type exists in the landscape. More critically it confers that protected status in the mind of the conservation manager who could contemplate active management for lurp control but not in a habitat that the evidence said was threatened with extinction. That had to be left to be as it is, even if the habitat was degrading and on it’s way out.

No amount of evidence could shift this view. Ironic given the process of listing is supposed to be science based and objective.

Selective morality is not exclusive to environmentalists but they are very good at it. In a way they have to be because there are few options in a world built and driven by profit. They are forced into leaving alone habitat that will degrade in the absence of active management because management is associated with negative outcomes.

Their passion for protection drives them far harder than any amount of reason.

David Hume’s ghost cannot resist a chuckle