Martha and The Doctor in “The Lazarus Experiment”

I still don't understand where that thing came from. Is it alien?

No, for once it's strictly human in origin.

Human?! How can it be human?!

Probably from dormant genes in Lazarus's DNA. The energy field in this thing must have reactivated them. And it looks like they're becoming dominant.

So it's a throwback.

Some option that evolution rejected for you millions of years ago. But the potential is still there, locked away in your genes, forgotten about until Lazarus unlocked it by mistake.

It's like Pandora's box.

Exactly. Nice shoes, by the way.