I thought the combine and the metrocops were the same thing :)

[Odysseus]

The first time I played the game I didn' t notice combine soldiers and metrocops were separate entities, I thought they were all the same: combine soldiers! I need to be more cafeful the next time

 

[Moejoe]

listen for the beeps after the cops die...that's how i found out

 

[SupaFly138]

wait... so are the metro cops human?

 

[mzhang23]

Civil Protection are made up of unaltered humans, I think.

In nova prospekt you see the trans-human combine forces on the monitor.

 

[Asknoone]

Civil Protection arnt augmented with combine tech...if you listen some citizens say they are willing to join Civil protection jsut to get a decent meal

 

[Merrr]

I think some of them are converted humans and others are the combine/human race.

 

[resien]

There are also combine prison guards which have different uniform to the combine soldiers . As far as i can work out, the metro cops are all civilians/normal humans who are employed to work for the combine, and the combine soldiers are altered humans which have combine technology in them

 

[Cpl_Facehugger]

Metrocops appear to be human, given that Barney was able to pass himself off as one without having any extraneous mechanical implants.

Combine Soldiers seem to be mechanically augmented (See the evoloution poster.)

The Combine Elites (White guys with only one cyclopean eye) are likely the transhuman forces that Breen speaks of, meaning that they're probably been enhanced mechanically and genetically/biologically.

^The above is almost 100% speculation.

 

[mzhang23]

The Elite's one giant red eye is most likely just something to make them look cool. I highly doubt the combine would go as far as converting humans to a one-eyed species, given the evolutionary advantage of two eyes and the difficulty in performing such an operation. It's most likely just an advanced form of helmet visor or something.