Quote Originally Posted by Archonic Energy View Post
Thu, you know why they are all contemporary and human. they represent us in the whoverse. they get things explained to them so we can understand what's happening, because it's primaraily targeted towards the younger demographics who won't necessarily understand the complexities of life.
Non-contemporary and/or non-human companions would still need things explained to them.

Quote Originally Posted by Sunken Valley View Post
Yes to this. 3 other reasons.

1. It's very difficult to effectively mimic someone from an earlier or later timeline. Sooner or later you'll let some mistake slip and the history buffs will be all over you.
2. An Alien Companion would be accused of being too "humanised". It's not the 80s anymore (the last alien companions were Peter Davidson's Nyssa, Adric and Turlough). You can't get away with giving the alien the same values and personality as a human.
3. Reference Jokes. The Doctor can't make them up unless he has someone who'll get it listening.

Why the companion is often a female and its never been an all boy ensemble on the TARDIS:
1. Doctor Who prides itself on being a gender equal show, not a boy show or a girl show. That way you need a mix of genders. How better to do than make the deuragonist female.
2. If it was all men, the public would scream for gender equality.
3. The companions get themselves into trouble every other episode. The Doctor has to save them. The Doctor looks more heroic doing so if he's rescuing some helpless female. Terrence ***** (writer for Doctors 3 and 4) even said the role of the companion was to be tied up and screaming for the Doctor's aid.
4. Sex Appeal.
Someone from a later timeline can certainly be mimicked, because no-one knows better to contradict the show. As for history buffs getting annoyed at past companions... I imagine history buffs already get annoyed at things on Doctor Who...
So, give the alien companion different values?
Make different jokes? Save the references for when someone's around who will get them?

And then, well, since you're making the gender equality argument it behooves me to point out that the idea that rescuing a helpless female is more heroic than rescuing a helpless male is sexist, and I don't see why you couldn't have a mixture of the two.
Also, if sex appeal is a concern, why should it be put in only for the portion of the audience who are attracted to women?

Finally, all these arguments hinge on the premise of the Doctor only having one companion at a time, which is equally rubbish and something that shouldn't be as almost-constant as it has been.