The first member of mtDNA Subclade L3d arose approximately 30,250 years ago in Africa.  Today, descendents of L3d are found mainly in West Africa and African Americans (Salas 2002).  Individuals who belong to Subclade L3d are of African ancestry.  L3d is not native to any other continent. 

L3d is characterized by a mutation at location 8618 in the coding region of the mtDNA (the 8618 mutation is included in the mtDNA haplogroup backbone panel) and a mutation at location 16124 in the mtDNA HVR1 region.  

Today, within the continent of Africa, L3d is rarely found in Northern, Central and Eastern Africa.  The highest frequency of L3d is in West Africa (Allard 2005, Carvalho 2008, Rosa 2004, Salas 2002, Salas 2004, Silva 2006), ranging from 7% in Sernegalese to 12% in Niger/Nigeria, with an overall average of approximately 9% (Rosa 2004, Silva 2006). 

Within Western Africa, 10 to 11% of Temne, Mandinka and Fulbe people belong to L3d (Jackson 2005).  Mandinka and Fulbe are large ethnic groups (over 10 million people each) that are distributed throughout different West African countries, whereas the Temne people represent a smaller ethnic group consisting of ~ 2 million people that make up 30% of Sierra Leone’s total population.  Although L3d is very frequently found in West Africa, it is not the most common mtDNA haplogroup/subclade in West Africa.  Subclades L1b, L2a, L2c, L3b, and L3e, are also found in more than 10% of West Africans.  These subclades, together wtih L3d, represent approximately 70% of the Subclades of all West Africans.  

There are 3 known subgroups of L3d:  L3d1, L3d2 and L3d3.  L3d1 is found at a high frequency in a specific Fulbe lineage (Salas 2002).  Although L3d is occasionally found in Southern and Southeastern Africa at low frequencies, the subgroup L3d3 is present in the Khoisan-speaking people (in particular Khwe and Kung) at a considerably high frequency.  The spread of L3d to Southern and Southeastern Africa is likely associated with the Bantu expansion (Salas 2002).

Outside of Africa, L3d is mainly found in African Americans.  Approximately 6% of all African Americans are descendents of the L3d family line (Allard 2005).  When compared to other Haplogroup L subclades, including L2a, L1c, L1b, L3e2 and L3b, that are also present at high frequencies amongst African Americans (18.8%, 11%, 9.1%, 9.1%, and 8.1% respectively), members of L3d are not the largest contributors to the mtDNA lineages of African Americans (Allard 2005).

During the Atlantic Slave trade (15th to 19th century), ~ 8 million of people were forced to move from West Africa to the New World (~13 million including other regions of Africa), with Brazil being the major importer, receiving the largest number of African slaves.  This human movement is reflected by the similar pattern of haplogroup distribution/frequency in North/Central America and West Africa (Salas 2004).