Haplogroup M423 to L161

Most of modern Haplogroup M423 descendants are in the Balkans. Another 10% is spread out over eastern Europe. These groups are shown as the yellow tracks in the diagram. The tiny remainder are the Disles and L161 Isles haplogroups in Britain, shown as the green line.

18,200 y.a. __ Haplogroup M423 emerged from P37 in the Ukraine Refugium
Migration of M423 and L-161

The founding was in the midst of the extremely severe Oldest Dryas ice age, so it must have happened in a refugium. There is some disagreement as to whether it was the Balkan refugium or the Ukraine refugium. It could have been either one, but the complexities of getting the P37 up the Danube to found M26 in western France and then get M423 back down the Danube (leaving no trace) to found the Dinaric and L161 in the Ukraine refugium is a very complicated scenario. The simple scenario is that P37 was spread out over both the upper Danube and the Ukraine refugium at the same time.

14,670 y.a. __End of the Oldest Dryas ice age; the Bølling-Allerød interstadial, begins.
The Bølling-Allerød warm, moist period only lasted 1,750 years with a very brief interruption by the Older Dryas cool period. Of the two warm periods, Bølling and Allerød, the Bølling is the warmer and came on more suddenly. The duration was quite short, but the impact was immense: sea level rose about 35 m (100 ft.!) due to glacial melt. Ice uncovered large parts of northern Europe and temperate forests covered Europe from 29 deg. to 41 deg. north latitude. During this time, late Pleistocene animals quickly spread northward from refugia: reindeer, horse, saiga, antelope, bison, woolly mammoth, wooly rhinoceros, red deer, and smaller animals, such as fox, wolf, hare and squirrel. They were immediately followed by hunting groups that, over the next thousand years, developed the 'Hamburg' reindeer hunting culture.
13,700 y.a. __The relatively mild Older Dryas cold period lasted about 200 years.

13,500 y.a. __Hamburg culture was established in the north German plains.
The 'Hamburg' (a nomadic reindeer hunting culture) evolved into the similar
Ahrensburg culture. The earliest archaeological finds of bow and arrow artifacts are from the Ahrensburg.
13,400 y.a. __SNP Y3104 emerged from M423, perhaps as a separate branch.
The location was probably somewhere northwest of Lake Pontus (the Black Sea in a freshwater phase). The founding during the Allerod warm climate phase allows for many geographic possibilities from Ukraine to northern Germany.
10,600 y.a. __Haplogroup L-161 branched off from M423 (or Y3104) during the northern migration.
The founding location is very uncertain. It could have been anywhere from the Ukraine refugium to Doggerland, but northern Germany seems most probable.