It wouldn’t be entirely accurate to say the Kikuyu are 50% Maasai, but it isn’t completely off either. The Kikuyu, along with closely related Eastern Bantu communities, and the Maasai share roughly 50% of their DNA because both groups were formed in part by the assimilation of Southern Cushitic populations. These groups were referred to by different names over time, with early ethnographers in the 1800s often using the term “Ndorobo.”
While the Kikuyu speak a Bantu language, their genetic makeup is only half Bantu, with the remainder being mostly Cushitic and a small Nilotic component. On the other hand, the Maasai speak a Nilotic language but also have significant Cushitic ancestry, around 50%.
This helps explain why many Kikuyu who take DNA tests through services like AncestryDNA often show about 50% Nilotic, largely because Maasai samples were used in that category. However, more detailed analyses from tests like 23andMe indicate that much of this ancestry is actually Cushitic.
So yes, Maasai and Kikuyu are about 50% genetically similar, primarily because they assimilated the same group of early Kenyan communities.
The heritage of these early groups is still very visible in both, not just genetically but also in many cultural elements, such as initiation practices.
Below is one of the earliest videos of the Ndorobo
Did you that Kikuyus are actually 50% Maasais?