Transmit me some of what you're smoking (or don't. The Japanese go apeshit over this sort of thing much more so than the USA)

anyway, while it is possible that planets may share similar bacterial roots, the slightest difference in temperature, radiation mix from the sun, rotation of the home planet, etc etc could produce rapidly different life forms. Even if all planets have an end-game of sentient life, it would still look and live radically different time and again

You should watch BBC's Wonders of the Universe, it talks alot about this subject. If you follow the creation of the Universe from a scientific perspective we are all made up of stardust and the same elements that are seen throughout the Universe, so we share the same building blocks of any other life that may exist.

The place were we may see a difference is in life that isn't carbon based as we are, such as Silicon or Nitrogen based lifeforms (if they exist).

Let us think of it as in the terms of dogs.  You know we inbreed a shitload of dogs (I don't think it is right).  Let us say humans died off tomorrow.  What dog would survive?  Would the small piece of shit dogs survive?  No..  Now let us think of what the dog would turn into after humans are taken out of the equation. We already have this evidence from roaming packs of wild dogs.  They pretty much turn into a wolf. 

Now let us use this information for this topic.  Even if life did end up different perhaps space travel would just turn every race of alien into grey, small body, big head aliens.

I think if a species was intelligent enough to travel between planets, then i m sure they would put forth measures to prevent such changes. Things like muscular training could keep your body from shrinking. As for the gray color, I'd say they could also replicate sunlight if they could do space travel.

I heard they are Turtles...

cause:

result:

Conclusion:

TMNT?

Isn't History Channel famous for being pretty crazy and full of what-ifs with little actual scientific or historical backing behind, and with laughable experts?

I'm kinda reminded of this one show on Science Channel that said that if physics is the same throughout the universe, then Aliens would have features that complimented the physics and by extension gravity on their planet. Like on high gravity planets, the 'aliens' would have to be able to support their own weight and therefore have to more durable.