At https://archaeologynewsnetwork.blogspot.com/2019/05/ancient-dna-tells-st… … ancient dna tells the story of the first herders in East Africa. A collorative study published in the journal Science (by archaeologists, geneticists and museum curators) has discovered DNA that shows herders (food producers rather than simply hunters and gatherers) moved south from NE Africa at the same time the Sahara desert was drying out. The Great Rift Valley of Kenya and Tanzania was a ley route of transition – a specific area that is still diverse genetically, linguistically and culturally. Herders first popped up in northern Kenya and were associated with elaborate monumental cemeteries. Then, spreading south when pastoral Neolithic cultures developed. The DNA evidence reveals they arrived in northern Kenya around 5000 years ago and the secondary migration southwards took place between 4500 and 3500 years ago. In other words the aftermath of the 2300BC event of Moe Mandelkehr (and see his article on worldwide migrations of people at this time). The date of 5000 years ago is also associated with rapid climate change and general folk movements elsewhere in the world so it seems we have a global response to something – climate or whatever induced the change in climate.
After 3500 years ago (1500BC) herders and foragers became genetically isolated in East Africa even though they continued to live side by side.
Another major genetic shift occurred in the African Iron Age (around 1200 years ago). This is in the aftermath of the 6th and 7th century AD climatic downturn but may also coincide with climate blips in the 9th century AD (contemporary with the Viking raids). One would suspect the severe climate downturn in the second half of the 6th century AD played a role especially as some of these people have an origin in West Africa (Bantu speakers) as well as NE Africa (again). They introduced farming and iron working (which group introduced which is left unsaid but presumably as Bantu speakers were farmers the iron working originated in the NE.