I'm leery of "lower" and "higher" comparisons of animals.
Perhaps it is more useful to think in terms of different strategies. Some creatures rely on producing mass quantities of young and provide no postnatal care whatsoever; some creatures produce single or few young at a time and invest tremendous amounts in their survival. Pretty much every strategic approach between these two extremes is utilized. I suspect the differences can be accounted for by the ecological contexts--past and present--in which each organism evolved.
As to the emotional state: perhaps the question is upside down. What is it about the physiological response which produces the emotion that is useful to the defending parent? Consider our own adrenaline rush and its conferral of hyperalertness, sharper response times, inurement to pain, heightened strength: the emotional element is our experience of that state.
As to more complex emotional experiences, I think the Rev is right on about their roots in our social existence.
"Dost thou think because thou art virtuous there shall be no more cakes and ale?"
-Sir Toby Belch,
Twelfth Night
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