Where I live, it is possible to vary between 100f (or more) to -50f (38c to -45c) summer to winter. Let us consider that 9000 to 6000 years ago the North hemisphere was closer to the sun in the winter then it is now. This would have made the temperature more moderate in both winter and summer. While the mathematics might be a little more complex than every 26000 years we can point out that the most recent interglacial occurred about 20,000 years ago. Before that there was another one about 40,000 which possibly killed out the majority of the neanderthals. Before that was the Toba Catastrophe roughly 75,000 years ago. While it was caused by the a volcano which caused a volcanic winter, that might have been a symptom of precession.