There seems to have been rather a lot of internet chatter about the cancellation of Doctor Who over the last few days. Pure speculation of course, and ironically turning up in the middle of probably the best two-parter of the series so far.
Spoilers follow, so if you don't want to know the score, come back on Wednesday.
At the opening of Human Nature, The Doctor is, unusually, on the run. On the run from some petty intergalactic crooks, after the life-force of a Time Lord in order gain eternal life and wreak havoc on a far larger scale. As they are, the Family of Blood have a limited time remaining, so the Doctor hides in England, in 1913, by becoming human.
And therein lies the genius of the piece. We get to see a different side to the Doctor (and David Tennant being more Hugh Grant than Tom Baker), and to Martha, who, as a young woman who is 'not exactly white', is forced to act as a servant, while actually being the one in control.
Oh yes, there are scary monsters (and one very disturbing public schoolboy), ray guns and explosions, but there is also the equally scary fact that 1914 looms just the other side of Christmas.
But against all this, and despite the fact that Martha and everyone around him need the Doctor back, having given up his life as a Time Lord, he likes being plain old John Smith and is unwilling to lay down that life. But if he settles for being an ordinary man, living a normal human lifespan, and living it happily married with a family around him, millions will ultimately die at the hands of his enemies. I imagine that is the sort of dilemma Jesus may have faced, just before stepping out of his ordinary existence and beginning his real work.
Ultimately, John Smith, like Jesus, sees what is right, and becomes more than human. And, in becoming the Doctor, he also takes responsibility for punishing his foes. The Family get the eternal life they craved - to spend alone, and suffering.