Richie, I don't want to get into an argument over this - after all, another thread got shut down... But that 'heart' at 18 days is a one-chamber heart that more resembles a frog embryo. And that "brain activity"? Miniscule would be putting it kindly.

Properly cared for and nourished, yes, that fetus will grow into a person. Any anatomy book can show when certain physiological changes occur. But saying "there's a heart" at 18 days *really* oversimplifies things.