What do you think, do you suppose the Doctor, or most Timelords, have some kind of preset appearances built into there molecular make up that are randomly selected on regeneration and this image above was what one incarnation of the Doctor was always meant to look like?
While the New Adventures played with the idea that the Doctor's personalities, both past and future, lived in his mind, no one's really taken the stance that the Doctor's incarnations are genetically pre-determined.
Big Finish's
Unbound audios make the argument that they're not. Likewise, Lance Parkin hints that they're not in
Ahistory and
The Gallifrey Chronicles.
For instance, in
Sympathy for the Devil and
Exile we have two very different versions of the third Doctor, and neither of them resemble Jon Pertwee. Especially not the one with breasts.
And in
The Gallifrey Chronicles, the Castellan Marnal sees that the eighth Doctor has three different ninth incarnations running around time and space. (One is Eccleston, one is Richard E. Grant, and one is Rowan Atkinson.
Ahistory explains the first two, but there's no explanation of where the point-of-departure to get from McGann to Atkinson is in the Doctor's personal timeline.)
If you can accept the premise that Troughton's regeneration (or forced change of appearance) can produce Pertwee, Warner, and Arabella Weir, then it's unlikely that any incarnation is genetically pre-encoded.
Unless you accept the premise that the Doctor is somehow linked to the Other, in which case there
is some genetic pre-encoding if the seventh Doctor can resemble the Other.
Correction: Lawrence Miles'
Interference presupposes that the Doctor's incarnations are genetically pre-encoded, unless the third Doctor's premature regeneration on Dust caused more damage to the timeline than anyone suspected.
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