[H] Asus m/b search?

[DSinc]

I notice that all of the "Z77" series Asus m/b's come with varying 
numbers of
PCIE v3.0 slots. Darn!

Is a PCIE v3.0 slot BACKWARD compatible to v2.0 and v1.0??????
I sense some trouble. Wondering.
Thank you,
Duncan