Aye aye.

I'm wondering, would the timeline allow the hagerman horse to go extinct or not? Assuming that the lakes change the climate, perhaps it may be possible for their survival and the eventual domestication by Indians?

Would the rockies cause the great lakes on the west coast to be ineffective?

The big lake in Tibet would be partly frozen over. Whilst Australia would be 100% desert out side of the coastline, the big lake inside Australia would have created a fertile shore line for a few miles inland.

Having such a huge timeline will greatly affect evolution (especially humans). I highly doubt any familiar life will exist. But since it's a quite interesting scenario, I ask this. May I join?

Sat, I hadn't thought of that, interesting suggestion, I'll look into it.

Nlen, the deserts in the Rockies are rain-shadow deserts, so the mountains stop more humid air from the east reaching them, making it dry. Having large lakes in the basins between the ranges should offset a lot of that effect, and potentially create a reverse of what we see today, creating a drier Great Plains.

Christina, Tibet lake will not be frozen over, the average daytime temperatures on the Tibetan plateu are around 12 degrees celcius in summer and just above freezing in winter, so no freezing.

And Candies, we understand that, but to create an alt-history with this concept that stays within the bounds of alt-history, then allowances must be made. And sure you may join, it'll be a few days before we allow anyone to start making proposals, but I'll post here and on the main page when you can begin. For now, keep suggesting ideas etc. here. 

I think there'll be a more "active" Central Asia, as larger tracts of arable land (caused by more bodies of water) will probably cause a larger population due to an increased food surplus. There'll be certainly some kind of major effects as a result of this, maybe more Chinese focus on Central Asia?

Potentially, as well as Chinese expansion into Siberia as well

Hit the nail right on the head Can. Chinese definitety - but we will also see a larger influx of local tribes found in the region today as well as Slavs. That region might end up something like the Caucasus.