(The term 'Cro-Magnon' is no longer used for people living after the end of Aurignacian.)
The Gravettian was the culture developed from the Aurignacian. People during the Gravettian period used nets to hunt small game and small pointed blades for big-game hunting (bison, horse, reindeer and mammoth). They are noted for their many carvings of 'Venus figurines'.
The Gravettian was spread from Ukraine to Spain probably by Haplogroup I . The area was so large that the culture developed a western version in France and an eastern version for Central Europe and Russia.
28,000 y,a. ___End of the Denekamp warm period. The ice returns with a vengeance.
All northern European populations were driven south where they survived living in "refugia". There were three main refuge areas: Ukraine, Balkan and Iberian.
Life in the refugia may have been very difficult. All of the Rev. Malthus dire predictions may have prevailed in these over-populated areas that also had severe, but not lethal climates. One would expect disease, starvation, and war, resulting in a Malthusian catastrophe. The catastrophe would return population to a lower, more "sustainable", level. One outcome would be 'Founder Effects', which we see in the diversification of haplogroups and in the spread of pale skin. 20,000 y.a. __End of the LGM. The Meiendorf Interstadial warm period begins.
The populations cooped up in the refugia expanded in a 'demic diffusion' into new territory made habitable by the retreat of the glaciers and the alleviation of the 'polar desert' environment as the climate improved during the Meiendorf.
Our ancestors followed the animals north into new territory and, unwittingly, into a climate trap. The short warm period was quickly followed by the 'Oldest Dryas', a lethal return of the ice, killing most and forcing the few survivors back into the refugia.