Fred Hoyle was right. There is life everywhere in the universe.
It is self-organizing. Given sufficient time, a multicelled organism will need complex limbs to manipulate it's environment. The simplest design is generic, with limbs able to fashion what is needed from surrounding elements without dedicated functionality. The simplest complex limb is a pad with an opposable thumb.
Complex limbs need to be distinct from locomotion in order to do both at the same time. This means walking erect and keeping some limbs free of the stresses of impact with the ground.
Now sexual dichotomy permits males to pursue food while females nurture young. Colder climates require greater intelligence, child nurture and group altruism than warmer climates.
Of course, what follows is most critical of all to improving the quality from here on in : What sexual selection method is best? Rape or female partnering? Obviously, female initiated choice will be superior to simply allowing the biggest males to rape at random.
Once they are bipeds with sexual dichotomy, you can go the Neanderthal route and end up with better people or go the Sapiens route which is a genetic dead end.
We are a freakish anomaly in-between. A race of genetic losers coupled with genetic winners. So we have traits of both. The Sapiens is outbreeding the Neanderthal, as always. So brain size has been shrinking for 20,000 years without any sign of a bottom. What was gained by splicing in the Neanderthal is being lost through Sapiens just being sapiens.
The biggest handicap of Homo Sapiens is that his tribe sizes are so large socially they actually permit the existence of specialized internal predators and parasites. Neanderthals had no psychopaths and sociopaths. Homo Sapiens is incapable of reaching a stable social configuration for this reason. The same social faculties that make such large tribes possible practically guarantee failure at the hands of internal predators.