Time to talk about some of the character dynamics in my current favorite show, Primeval.
Even before they "get together," Abby and Connor always seemed a pair, if not yet a couple. Add Rex (who is essentially Abby's baby) (and later the two other critters) and you essentially have a family unit, with Abby at its head. If Abby is the head, then, it follows that Connor and Rex share certain similarities (correction: it doesn't necessarily follow, but it makes sense).
Consider how many near-death experiences the two have. Connor hitting his head has almost reached the level of a running joke (of course it is his head that has to be most vulnerable--as the "smart person," it's what would be worst, symbolically, for him to lose). Then there was the time he almost froze and the time he was dragged underground by the burrowing creature. For Rex, there was the time Caroline shut him up in the refrigerator, when he was shot, and when he almost suffocated. I'm sensing some direct correlations: both characters almost froze and both had a bad experience in the environment-controlled room.
And of course Abby is always willing to risk herself for these two--she's smart, but when it comes to them, she'll stop at nothing. Just think of all the times we hear Abby's voice shout out, stressed and worried. She's either calling to Connor or Rex. She has to protect them both.
They share other traits, too. Both are in the small handful of characters introduced in the first episode that actually make it all the way to the end. Both are quirky--often comedic, usually smiling. Neither one exactly fits in, though being a refugee from an anomaly to the Permian is (just a bit) more drastic than being the nerd.
I wonder what the actors would think about this comparison . . . Next time, I will compare Helen to Cathy from Wuthering Heights.