Mars was habitable
By evry indacation from our probes mars had liquid water at one time so it is very pobable that at one point in time life was possable there. As far as Venus goes I don't know but I think a different more reflective atmosphere could make a difference.
Life forms
Mars has human like intelagent creatures with B.C tecnology they are about 4feet tall .
Venus has only animal life mostly deep jungle continuos cloud cover
What if mars and Venus were always habitable?
This would not have ben determined untill the mid sixties when the mariner probes were sent.
How would that knowledge have effected the space race and Russia US relations?
Would the Vietnam war have happened, would we be at peace with the commies...