Kerry made a strong start by ripping off his shirt, pounding on his chest and emiting a roar sound. Bush followed suit in his rebuttal, but it was weak immitation of the Kerry opening gambit. Bush's first offensive attack seemed like a sure thing, when he lept upon Thersea Heinz Kerry, but the way he lept back in pain from her devistating bite really knocked him down a few pegs in stature. Speaking of which, Kerry is quite a bit taller than Bush and was wearing a more powerful tie, at least as long as they were wearing ties. Bush seemed more muscular overall, but his shortness combined with his defeat in hand-to-mouth combat with the candidate for first lady both made him appaear weak. He tried to regain lost ground by jumping on on his podium and howlind at the top of his lungs, however once Kerry climbed on to his own podium, he was, once again, taller. Also, it was brilliant rebuttal on Kerry's part to then rush over and topple Bush's podium.
Bush then tried to retake the offensive by attacking Jim Lehrer, the lowest ranking male on the stage. However, I think most viewers quickly realized that this attack, while it will require Lehrer to get seven stiches, was Bush essentially ceeding the role of alpha male to Kerry.
Thus, after the first debate, Kerry has proven that he has strong alpha capabilities and would make a good potential mate and will act to protect the tribe from attack from hostile bands of other primates.