Allow me, DessertWalker and BigBoss, to joint the talk!
Today, most if not all serious animation is done via motion capture technologies.
The poor animator, without a MoCap system,goes for previously captured motions, contained in diverse file formats, being the best know the VBH and BIP formats.
Top-of-the-line motion capture devices allow capturing subtle facial expressions as well as the most complex body motions, at very high frame rates indeed!
Luckily, several new approaches to motion capture are appearing with substantially lower tag values.
Working with prerecorded motion files is a viable alternative, as motions can be mixed, trimmed, accelerated or slowed down.
Last resource... You handy mouse techniques and a lot of work at the character key framed animation.
I don't think any "natural moving" animation can be produced by "scripting" unless is a matter mechanical device animation.
I hope this helps!
Mike

Mike Aparicio-Reallusion Certified Innovative Content Developer