This is an interesting one in terms of evolutionary psychology. I'm not sure what I would do in either situation, but I can tell you what I think most people would do in the first one, regardless of what they <i>say</i> they would do (and that includes me).
<i>The scenario is that you and your child/loved one are shipwrecked and are the only survivors. The only hope for survival is a single lifebelt that will only support one of you.</i>
Every creature has a strong survival instinct. If that was the only factor at work, most people would choose themselves over their child. However, there is also the biological urge to pass on your genes and ensure that they survive to the next generation. That complicates things here. Who has the best chance of passing on your genes? You share half your genes with your child, but your child is also younger than yourself. Who is most likely to survive, all things considered? It is difficult to weigh up these factors, and in fact they may be too complex to properly evaluate in the time available. Most like, social factors will dominate in the decision making process. Possible repercussions of the decision will be considered. Most likely, all other things being equal, I think most people would decide to save themselves. After all, the adult is a proven reproducer, having had at least one child already, and presumably the potential to have more. Then there is the strong instinct for self-preservation. Add the social factors and the social pressure to love and care for children might well dominate, as might general altruism of the individual.
Add religion to the mix and belief in the afterlife and the balance tips, I think, heavily towards letting the child live and sacrificing oneself. After all, you'll go to heaven anyway, won't you? (Though presumably, so would the child...)
<i>Another scenario: Your well-loved family pet has fallen into a rough sea and is in danger of imminently being drowned. A man, a complete stranger to you has also fallen into the sea and is also about to drown (assume a non-swimmer). Who do you choose to save and why?</i>
There is no genetic equation at work here, so this situation is purely based on social values and warm fuzzy feelings. Most people still believe that humans are "special" compared to animals, and so would save the human. Some others are animal lovers to the exclusion of humans and so would save the pet. All sorts of extraneous factors may also be important here. Do we have any more knowledge of the stranger?
I really don't think anybody could really answer this until confronted by the particular situation.
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Cris:
<i>The primary purpose of your existence is the survival of the species.</i>
No it isn't. The primary purpose of your existence, as far as your genes are concerned, is to propagate your genes. Individuals care little for "the species".
<i>So I see basic human drives as -
1. Find a mate or multiple mates.
2. Impregnate as many as possible, and as often as possible.
3. Protect your mates and offspring until you are incapable.
4. Self survival.</i>
This is a very male perspective, Cris. It seems your genes are doing a good job of getting their way with you.
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wet1,
A bit of a sidetrack, but how can I make life preservers from my ordinary clothes, should the need ever arise?