All humans share a common ancestor if you go back far enough in time. Specifically, mitochondrial DNA evidence suggests all humans share a common maternal ancestor that lived around 200,000 years ago. Additionally, studies of the Y chromosome suggest all humans share a common paternal ancestor that lived around 300,000 years ago. So in that sense, all humans are distant cousins.
However, the term “cousin” typically refers to a closer familial relationship. First cousins share grandparents, second cousins share great-grandparents, third cousins share great-great grandparents, and so on. Most humans share a common ancestor within the last 5,000 years or so. But beyond 5th or 6th cousins, the blood relationship becomes quite diluted.
Some key questions answered in this article include:
When did humans first evolve?
Anatomically modern humans, Homo sapiens, evolved around 300,000 years ago in Africa. Early humans began migrating out of Africa around 100,000 years ago.
How closely are all humans related?
All humans share common ancestors from around 200,000-300,000 years ago. But most Europeans and Asians shared a more recent common ancestor around 5,000 years ago. So distant cousins would be a fair characterization.
Can cousin relationships be traced back throughout history?
Genealogical records allow cousin relationships to be traced back hundreds of years in some cases. But beyond 5th or 6th cousins, ancestry becomes very diluted and hard to trace accurately.
How far back can DNA evidence trace human ancestry?
Mitochondrial DNA and Y chromosome evidence allows common ancestry to be traced back hundreds of thousands of years. But autosomal DNA becomes too fragmented after about 5,000 years to accurately trace relationships.
When Did Humans First Evolve?
Anatomically modern humans, Homo sapiens, first evolved in Africa around 300,000 years ago. Early humans originated in East Africa, with the oldest known fossils found in Ethiopia. Throughout the Pleistocene epoch, early humans migrated and spread throughout Africa. By around 130,000-100,000 years ago, some early humans began migrating out of Africa into Eurasia. This “Out of Africa” migration is supported by genetic evidence showing all humans descending from a common ancestral population in Africa.
Some key milestones in early human evolution include:
6 million years ago
The chimpanzee and human lineages diverge. Early apes begin evolving in Africa.
4 million years ago
Australopiths, an early ancestor to humans, evolve in Africa. They walk upright but still live in trees.
2.5 million years ago
Early species in the Homo genus evolve, such as Homo habilis, using simple stone tools.
200,000 years ago
Anatomically modern Homo sapiens evolve in Africa. They have larger brains and more advanced tools than earlier species.
125,000 years ago
Evidence of early Homo sapiens culture and technology in Africa, such as ostrich egg shell beads.
100,000 years ago
Small groups of Homo sapiens begin migrating out of Africa into the Middle East and Asia.
So in summary, anatomically modern humans evolved around 200,000 years ago in Africa. But Homo sapiens did not migrate out of Africa until around 100,000 years ago at the earliest.
How Closely Are All Humans Related?
All humans share a common ancestor from around 200,000-300,000 years ago. But that is an extremely distant ancestor. Within the last 100,000 years or so, humans have continued diverging into populations that became geographically isolated.
Different human populations have intermixed over time. But some level of genetic divergence built up, allowing geneticists to trace ancestry.
According to autosomal DNA studies, most Europeans and Asians share a relatively recent common ancestor from around 5,000 years ago. So in that sense, nearly all living Europeans and Asians would be no more distant than 5th or 6th cousins.
Some key facts about how closely modern humans are related:
200,000-300,000 years ago
The most recent common matrilineal and patrilineal ancestors of all modern humans lived around this time, based on mitochondrial and Y chromosome DNA evidence.
100,000-125,000 years ago
Early Homo sapiens populations diverge and become somewhat isolated as they spread out of Africa. Populations in Asia/Europe begin accumulating genetic differences from African populations.
50,000 years ago
Modern humans arrive in Australia and become isolated from other populations for millennia, allowing Aboriginal Australians to diverge genetically.
30,000 years ago
Modern humans arrive in Europe, where they can become isolated by ice sheets during the last glacial maximum. European genetic ancestry diverges.
14,000 years ago
As ice sheets retreat, more interaction occurs between Asian and European populations, with peoples like the Proto-Indo-Europeans spreading westward.
5,000 years ago
Most recent common ancestor shared by most Europeans and Asians dates to around this time. So they represent distant cousins no more than 5th or 6th cousins apart.
So in summary, all humans are cousins descended from African common ancestors hundreds of thousands of years ago. But most non-Africans cluster into an Asian/European group sharing more recent common ancestors around 5,000 years ago.
Can Cousin Relationships Be Traced Back Throughout History?
Genealogical records allow cousin relationships to be traced back hundreds of years in some cases. But beyond 5th or 6th cousins, ancestry becomes very diluted and accurate relationship tracing becomes impossible.
Some key facts about tracing cousin relationships through history:
Genealogists can often trace family histories accurately back about 10-16 generations (300-500 years) before records become too sparse. This allows for accurate cousin tracing at the 1st to 6th cousin level.
After about 17-25 generations (500-800 years), written records become too sparse for accurate genealogy. But genetic genealogy can sometimes infer relationships.
Extensive written genealogical records became common for nobility in Europe, North Africa, and Asia after about 1000 AD. These can trace accurate relationships over the past 1,000 years.
Mitochondrial DNA and Y chromosome evidence can trace all human ancestry back to “genetic Adam and Eve” living around this time in Africa. But this represents extremely distant relationships.
|Generations Back||Years Back (25 years/generation)||Degree of Cousin Relationship|
|10||250||1st – 2nd cousins|
|15||375||3rd – 4th cousins|
|20||500||5th – 6th cousins|
|25||625||7th+ cousins, relation not traceable|
So in summary, genealogical records can trace cousin relationships accurately back 5-6 generations or so. Beyond that point, ancestry dilutes too much to reliably trace cousin relationships.
How Far Back Can DNA Evidence Trace Human Ancestry?
Different types of DNA testing have different time depths for tracing ancestry, ranging from a few generations to hundreds of thousands of years:
This DNA recombines between generations, so matching segments become too small to analyze accurately after about 5 generations/125 years. Useful for finding 4th-6th cousins.
Passed down identical from father to son. Mutations allow relationship tracing to 300,000 years ago. Can identify shared patrilineal ancestry.
Passed down intact from mother to child. Mutations allow relationship tracing to 200,000 years ago. Identifies shared matrilineal ancestry.
Recombines less than autosomal DNA, allowing matches to about 8 generations/200 years. Helps find more distant cousins.
So in summary, Y chromosome and mitochondrial DNA can trace ancestry hundreds of thousands of years to our common origins. But autosomal DNA is only useful for finding 4th-8th cousins with shared genealogical ancestors within the past 200 years or so.
While all humans trace back to common African ancestors from 200,000-300,000 years ago, that represents an extremely distant relationship. Within the past 10,000 years or so, most human populations descend from common ancestors within the last 5,000 years due to migration and intermixing. So from a genealogical perspective, the “cousin” relationship describing living humans is quite distant at 5th-8th cousins or so for nearly all pairs of individuals. While we all have an ancient African ancestry, cousin relationships cannot be reliably traced more than about 400-500 years into the past with any genealogical significance. So modern humans represent one large, extended family originating in Africa tens of thousands of years ago.