A new genetic study in 2003 thought it was dealing
a blow to claims that humans had reached America at least 30,000
years ago - around the same time that modern humans were first
The subject of when humans first arrived in America
has been hotly contested by academics. On one side of the argument
are researchers who claim America was first populated around 13,000
years ago, toward the end of the last ice age. On the other are
those who propose a much earlier date for colonisation of the
continent - possibly around 30,000-40,000 years ago.
The authors of this particular study rejected the
latter theory, proposing that humans entered America no earlier
than 18,000 years ago. Later evidence would prove them wrong, but
this what how they reached their conclusions.
They looked at mutations on the form of the human
Y chromosome known as haplotype 10. This is one of only two
haplotypes carried by native American men and is thought to have
reached the continent first. Haplotype 10 is also found in Asia,
confirming that the earliest Americans came from there.
The scientists knew that determining when mutations
occurred on haplotype 10 might reveal a date for the first entry of
people into America. Native Americans carry a mutation called M3 on
haplotype 10 which is not found in Asia. This suggests that it
appeared after people settled in America, making it useless for
assigning a date to the first migrations.
But a mutation known as M242 looked more promising.
M242 is found both in Asia and America, suggesting that it appeared
before the first Americans split from their Asian kin.
Already knowing the rate at which DNA on the Y
chromosome mutates - errors occur - and the time taken for a single
male generation, the scientists were able to calculate when M242
originated. They arrived at a maximum date of 18,000 years ago for
This means that the ancestors of modern native
Americans were still living in Asia when M242 appeared and could
only have begun their migration eastwards after this date. Dr
Spencer Wells, a geneticist and author who contributed to the
study, was of the opinion that they entered the Americas within
the last 15,000 years.
In opposition to this, in 1997, a US-Chilean team
uncovered apparent evidence of human occupation in 33,000-year-old
sediment layers at Monte Verde in Chile. They claimed that burned
wood found at the site came from fires at hunting camps and that
fractured pebbles found there were used by humans to butcher meat.
But the interpretation of these remains was questioned by several
experts who opposed the 'early arrivals' theory.
The debate over the biological origins of the first
Americans has wide-ranging political and racial implications. In the
US, the 'Native American Graves Protection and Repatriation Act'
(Nagpra) has resulted in the handover of many scientific collections
Some archaeologists have argued that the remains of
early Americans are sufficiently different from their descendents to
be exempt from Nagpra. For example, a 9,300 year-old skull from
Washington State which is known as Kennewick Man has been interpreted
as having a European appearance due to its long, narrow (dolichocephalic)
skull shape. More recent American populations tend to have short, broad
The native Americans who met Europeans from the fifteenth
century AD onwards all displayed the typical Asiatic skull
type, having long since subsumed any potential European types