I agree that our attitude towards not killing strangers at mortal cost to ourselves is mostly academic today. So that’s why its so easy to speculate either way.
But I don’t agree that a few thousand years puts us that far removed from our eat-or-be-eaten forebears on an evolutionary scale. Forced into the right circumstances, those survival instincts will quickly re-surface. Haven’t you watched McGuyver?
Rigil
I think our survival instincts here in SA is far more honed than somebody from say, Sweden. We’re bombarded with violence on a daily basis and we are all very, very aware that we might find ourselves in such a situation sooner rather than later. Our tempers are short (think roadrage), and the majority of us are concerned when our partners/kids go out on their own and we only settle down once they’re back home.
@Boogie - I tend to agree with you, I’d kill without a second thought or hesitation to save my S/O and children. without hesitation.
Two things: First, truly altruistic behaviours such as self-sacrifice may not be genetically fixed. Rather, they probably exist as propensities that only manifest in certain narrow circumstances. Second, on the assumption that such altruism is indeed genetically mediated, those genes certainly can propagate if the individual who has them procreates before becoming a victim of their own altruism.
ETA: The same principles apply of course also to memetic considerations. What’s more, if a genetic propensity for altruism is somehow coupled to a tendency for wanting more offspring (and it’s not a huge stretch to imagine that this might actually be so in view of the fact that the two may be driven by similar emotions), then the prevalence of the altruism genes can increase over time. One might even argue that this effect is at least partly responsible for humanity’s path from parochial savagery to cosmopolitan civilisation.
'Luthon64
A memorable section from the BBC series Walking with Cavemen has Robert Winston discuss how it came about that we came down from the tees and started walking upright.
Walking upright had no immediately obvious advantage over going on all fours, but after the bio-mathematicians had crunched their numbers - no doubt taking into account that the landscape at the time was moving away from forests towards Savannah plains - it turned out that animals that walked upright saved on average the energy equivalent of one packet of tennis biscuits per year. That’s bugger all in itself … but combine that saving with enough time, and the upright apes were naturally selected for.
Flagrant altruism is more detrimental than a lack of cookies.
Rigil
I thought the theory was that as forest gave way to savannah, it became advantageous to stand up on your hind legs to see hungry toothy things approaching over the top of the grass. The okes who were still crawling about on all fours got pounced upon and eaten, whereas those who were standing up could make a swift and graceful exit.
I very much doubt that’s true of a herd or a society whose food and safety requirements are largely satisfied. Moreover, I doubt even more that much, if any, flagrant altruism would be shown in herds or societies where those needs have not been taken care of. There is a contextual setting that is at least as important as a propensity for particular behavioural patterns for the latter to be actualised.
Like I said: “(Propensities for altruistic behaviours) … only manifest in certain narrow circumstances.”
Yes, a behaviour seen in meerkats and baboons. In fact, they are altruistic because they noisily warn their fellows of approaching danger.
'Luthon64
I will risk my life for 2 siblings or 8 Cousins 
Actually that's the point me and Majin got to in our conversations last night. What if *I* am in the next room with a gun to my head. She can either pull the trigger, or see me get shot. What then?I was adamant that she’d pull the trigger in a heartbeat. She said she wouldn’t, she’d be heartbroken but wouldn’t feel responsible for my death, as my captors would be the ones responsible.
The way she explained it, I almost believed her.
I will kill or hurt someone to defend Boogie Monster or anyone I love if they or I get threatened in anyway accept when it comes to shooting someone for him to live. I would not be able to live with my concious. I do not want that power over another persons life.
The whole point of what I meant was that I would not like to kill in war or follow the governments rules blindly even if I am forced. And that is where I am blessed - I think if I lived in a country where death and violence was common, I would properly not be fazed much. I think everyone in the end can be influenced but the age of the person determines how much can be changed.
In this scenario you DO have that power over another person’s life. The choice is whether its the life of someone you love or a stranger’s. Would you be able to live with your concience if your loved one died and you had the power to save him? Would you REALLY? I’d be able to soothe my own concience far easier if I killed the stranger, after all, I saved my S/O’s life…
Yes I do have the power over their lives. But I choose not to. The power then lies with the people that were forcing me… Don’t get me wrong I love Boogie Monster. But a stranger’s life is important as well. In that situation I wouldn’t be able to pull the trigger. If someone attacked him yes, I will think differently on that persons life.
Well, Boogs, looks like some sort of Kevlar® vest might be in order. ;D 
By choosing not to have power over their lives, you abdicating your own, leaving yourself powerless in the process. Have you though about this and how this might affect who you are in the long run?
This is quite an outrageous scenario, granted, but how do you (in real life) react to the power you hold over other people, would you submit under pressure for little (but important) things or do you fight for what you rightly feel is due to you? How you react when someone attempts to steal your job by falsely accusing you of fraud (after all the stranger’s need in wanting your job is important too) is pretty much how you’ll react in a scenario where you have a gun in your hand and the threat of a loved one being killed.