Illustration: Rocco Fazzari. We've been too successful for our own good. When humans lived in small groups on the African savannah we were hardwired to be preoccupied with the pursuit of resources, which were scarce. Since our ancestors often couldn't obtain all the food they needed, they were programmed to grab all they could find. Much technological advance is aimed at overcoming this problem of scarcity. And economics, with its emphasis on the efficient allocation of resources, is aimed at assisting the community to overcome scarcity. We have unending wants but only limited means of fulfilling those wants, so need to stretch our resources as far as possible. The trouble is, at least in the developed world, we've been so hugely successful in overcoming scarcity we've acquired the opposite set of problems: abundance. Why is abundance a problem? Because all our evolved instincts tell us to keep pushing for more and more, even though we've already got more than is good for us.

Take food. Technological advances in growing, transport, storage, preservation and cooking food have greatly increased its availability and reduced its cost. As humans have become more time-poor, we've seen an explosion in inexpensive fast food, all of it cunningly laced with those three ingredients our brains have been evolved to crave: fat, sugar and salt. On the other side of the equation, we've see technological advance strip the physical labour first out of work and then out of leisure. Is it any wonder we have a growing problem - so to speak - with overweight and obesity? Our natural urges are badly out of sync with the world we've created. And the purveyors of food use all the wiles of advertising and marketing to persuade us to eat more. Marketers, it turns out, have a much better understanding of how humans tick than economists do. Whereas economists happily assume we're rational in all we do, marketers are under no such delusion. They get under our guard by directing their advertising to our subconscious, instinctive, emotional selves, using pretty women to sell cars or happy families to sell margarine. There's no logical link between pretty women and cars, but there doesn't have to be.

This is the great conundrum of modern life. Evolution has given us brains capable of great feats of reasoning - the most complex mathematics, intricate engineering, brain surgery - while also leaving us with brains that react instantly and instinctively to the most primitive urges. While we lived in a world of scarcity, the duality of our brains - our ability to build a world we weren't smart enough to cope with - didn't matter all that much. But now we've gained mastery over the natural world and transformed scarcity to abundance, the contradictions inside our heads are causing us big problems. A great many of the problems of daily life are problems of self-control, which represents a battle between the two levels of our brain. Eating is the obvious example. Those of us who are overweight know full well we shouldn't eat as much as we do and should exercise more than we do. And yet we have enormous trouble making ourselves stick to a diet or exercise plan. When we see something that looks and smells good our primitive urges take over and we gobble it up. If you're perpetually skinny, don't feel superior. Problems of self-control are ubiquitous. We face temptations to smoke, drink too much, watch too much television, gamble too much, shop too much, study too little, save too little and put too much on our credit cards. The good news is, we're so brainy it can't be beyond our wit to develop ways of gaining mastery over our instincts. If there were items on that list of self-control problems that don't cause you problems, the likelihood is it's because you've successfully developed ''pre-commitment devices'' to keep you out of trouble.

For instance, a friend told me she never uses her credit card on shopping sprees, but limits its use to paying regular unavoidable bills for utilities and the like. But our struggle for self-control would be more successful if the people running our world had a clearer understanding of the nature of the problem. Our politicians have flashes of insight in particular areas, but don't see the systemic problem. That's probably because they take so much of their advice from economists, who are still committed to a 19th century model of the world that sees the central problem as scarcity and assumes we're always rational. If the examples of self-control problems arising from abundance I've quoted seem minor, don't be misled.

The greatest consequence of our transition from scarcity to abundance is that human economic activity, which at first was puny relative to the huge natural environment, is now so big - so many humans in the world enjoying such high material living standards - it's doing great damage to the ecosystem that provides us life. Loading Climate change is the most pressing instance of that damage, but our politicians seem blissfully ignorant of the threat. Ross Gittins is the Herald's economics editor.