Moreover, any problem or misunderstanding would be multiplied within a threesome. Suppose you have two lovers and have a fallout with one of them (A). Can you run to the other (B) for comfort? Can you tell B everything that transpired with A? But you're not talking to a friend, you're talking to a lover! Would A like your shared personal experience revealed in that context? Is B in a position to give you advice? Are you in a position to take it? The existence of a second lover makes matters worse when it comes to communication and evaluation of your feelings.
So in general, polyamory is not practical. It's far more stressful than both monogamy and complete lack of relationships, so it may not provide a stable enough environment to raise children in.
Accepted. My argument was never that polyamory was as *practical* as monoamory, or anywhere near as statistically successful. Quite the opposite, from my limited anecdotal experience, polyamory quite often goes horribly, cataclysmically wrong. I simply argued that it was possible to engage in it and still be emotionally sincere. The outcome is irrelevant to that.
The wolves example I can accept, but lions can do really nasty things to ensure fatherhood (like, kill cubs fathered by another male). So for them, polyamory comes with a heavy price.
Accepted, but one could argue that the cub-killing and such are a separate phenomenon from the polygamy.
What about humans? We are jealous and possessive creatures, so I think our nature steers us toward one-to-one relationships.
Accepted.....somewhat. It's questionable how much of that is nature, and how much nurture. It's extremely difficult to separate biological/instinctual hard-wiring from cultural programming. In any case, however, the wonderful thing about sapience and intelligence is that we are capable of overcoming our own nature within certain parameters, and even capable of overcoming our cultural programming if we set our minds to it.
OK, now we're delving into psychiatry, but here's how I think about it: You fall in love because you have certain emotional and biological needs. If your needs are already satisfied in a relationship, why would your brain push you to venture into another relationship, which could possibly destabilize the original one?
For the same reason that, upon making a friend, you don't necessarily start turning away other people who are interesting and friendly, just because you already have a friend.
If you thought your first friend might be jealous, you might curtail such behaviour, but that wouldn't be your inability to care about making more friends, so much as a conscious decision for the emotional wellbeing of your friend.
Replace "Friend" with "lover" above, and you pretty much have the situation.