I think scientists should have their emotions ripped out the moment they hire on as a "scientist".
And I think cars should have their engines ripped out the moment they are made, that would eliminate exhaust fumes.
Emotions are the thing that drives us, according to Antonio Damasio, emotions help us to make rational decisions, and indeed without any, we could not decide at all. This has enormous applicability to science, as there are way too many variables in any given hypothesis, that emotions are needed in order to help eliminate some. Furthurmore, there is no rational way of choosing between competing theorys, according to Kuhn, it's often many un-scientific factors which determin the winning theory. And even still, most scientists are driven by their desires to be held greate, this too encourages checking your peers work for errors (because if they are wrong, you could be right) and thus, allows for scientific progress.
So, in conclusion, emotions are one of the driving factors behind science.
Now to try and address the actual topic...
While I'm not sure how well we can justify our current ethics with science, It does however appear to be a good way of determining ethics (though by no means the only).
For example we ethicaly shouldn't kill large animals in vast numbers, or start campaigns to eliminate smaller ones (ie an intentional extinction of say spiders), or use bioamplifying pesticides like DDT.
We can come to this scientificaly because killing other animals, without controll, would resault in their extinction and thus damage to the ecosystem, which would then resault in damage to us, we can figure this out scientificaly.
Now, as for humans acting stragely when allone, this is natural as we are meant to be sociable, and furthurmore, doesnt matter as laws are built for societys, in which case this wouldnt be a problem.
You mentioned fighting over women as an example, and I would say that, while science may show we would naturaly do this, we are also capable of learning better methodes to deal with problems (and technicaly science shows we can learn, but thats fairly intuitive for everyone)
Thus rather than cream the other guy, one could work it out by talking; most specificaly with the girl, as she is the one who gets to choose.
So I would say that yes we can justify, at least partialy, our ethics in a scientific standpoint.
-Andrew