Essay warning! I've given in to the urge. Sorry, everyone!
My current 'bible' (an ill-chosen word on this board, really) is Paul Gilbert's The Compassionate Mind. I have been 'working' it for nearly two years.
Eight years ago, I joined a 12-step programme (long story). I drink now, but continue to 'work' my steps as I consider them a very sound foundation for a morally and emotionally healthy life. A lot of people have issues with the program, some of which are reasonable, but it should be noted that the Higher Power wording in British versions is "God as we understood Him." Very few of the London groups I attended used the word god at all. They said "higher power" which can be anything you like. It's intended as a psychological device to lift damaging cycles of self-blame.
Compassion theory also uses this concept: Gilbert borrows from buddhism, while making it clear the reader may choose any 'compassionate focus' they like and change it as often as they wish.
I don't want to get too massively into the psychology of it all; I want to stress that Gilbert's work is solidly grounded in neuropsychology. It goes roughly like this:-
The human brain comprises every brain our species had throughout our evolution, in layers starting from fish. The 'fish brain' (brain stem, medulla) does the autosomal functions like breathing, heartbeat, etc. The 'reptile brain' (amygdala) controls the basic instincts: feed; fuck; fight; flee; family. After that we build through various cognitive and reasoning functions until you get to apes, which have been adding large amounts of forebrain. Humans have increasingly well-developed frontal lobes (we're still evolving). This area handles reasoning, forward thinking, social behaviours, evaluation, motivation - the qualities we're used to saying make us human.
Ever since we were apes, we've been evolving groups and communities, with 'morals' to help us work in teams and keep our numbers up. We're pretty crap at running, are not very strong and have extremely blunt senses compared to our would-be predators. However, we have opposable thumbs and the ability to think. As long as we maintain strength in numbers, we can work together with our hands and minds. This makes us powerful.
Of course, the different areas of the brain don't operate in isolation. Although our forebrain is the biggest area, the tiny 'fish brain' keeps us alive by responding to information fed back to it by other areas and sending out instructions. Interestingly, the next most powerful part is the 'reptile' amygdala. We were reptiles for far longer than we've been mammals. The amygdala has direct lines to all other parts of the brain, and some directly to the body. It controls what we call our animal instincts. Not only is it constantly communicating with the newer parts of our brain, it can override them.
Reptiles haven't been observed to show any signs of what we'd call compassion, though they have basic 'morals' of the type displayed by Phil Mitchell in East Enders (!) They protect their young, for example. Once you start looking at mammals, they do exhibit morals and compassion. The more sophisticated their group structures, the more compassionate behaviours are observed. You also see morality-based emotions, like shame and pity. There are some fantastic films of wolf packs displaying both. This goes to show that morality is hard-coded in our brains as part of our survival strategy.
The invention of the PET scanner has revealed some remarkable things. One is that the brain is extremely changeable. Every new experience (or thought) you have creates a new synapse. Old ones can be smoothed over. You can do this consciously by means of rehearsed thinking. You can grow more brain, and alter the distributions of your brain areas, by doing and thinking. Emotions - which are 'thoughts' as far as your brain's concerned - have tremendous impact on your brain configuration and function. A happy, enthusiastic brain is more efficient than a miserable, bored one. These effects are lasting. Emotions experienced by a pregnant woman also affect the brain of her foetus, and so do emotions experienced by babies too young to 'think' about what they're feeling.
Compassion theory is about encouraging the newer parts of the brain to maximise the efficiency of the whole. This is done by, basically, bringing the community-based imperatives to the fore: consciously developing one's sense of care, concern, reason and belonging; working deliberately to improve two-way communication between the frontal lobe and amygdala to enhance smooth functioning.
The 'higher power' element of all this hasn't been scientifically explained as far as I know, though it has been proved to assist healthy development. It's likely that all daylight creatures experience the sun, for example, as a higher power as it's essential to our survival - this part of our thought/feeling base might actually be sited in the amygdala, as reptiles cannot generate warmth internally and die without sunshine. Where the compassion work is concerned, a 'higher power' is used to dissipate shame-based feelings such as self-loathing and fear. 12-step programmes do the same. Shame-based feelings stunt the brain and inhibit its functioning. I don't pray as a christian does, but I do have imaginary chats with a made-up "compassionate focus", and/or with myself, when I need to sort out my head :)
So. According to this very long post, morality is hard-coded in our brains; we thrive only to the extent that our community/society thrives. Sophisticated morality is also hard-coded and is fairly new in evolutionary terms. Because it's new, it's prone to under-performing - which allows the 'old brain' to trample over it - and to turning on itself. It's very open to change and development. It can be trained to train the older parts, too: the parts all work together. Quite dramatically, compassion is the key to higher functioning. I've now read reams of research around this and am quite convinced.