8 Inferring Human Demographic History from Genetic Data
197
though quantifying the amount or the timing of admixture depends on specific
assumptions about modern human population structure. Taken at face value, these
studies suggest that admixture between modern and archaic humans may have been
a relatively common occurrence, involving Neanderthals, Denisovans, and one or
more archaic human groups (in sub-Saharan Africa) for which no ancient DNA
samples are currently available.
8.8
Other Ancient DNA Studies
The previous section describes what insight has been gained from studies of
admixture between modern and archaic human groups. Ancient DNA studies
involving only modern human samples have also been very informative about
human demographic history. In particular, a comparison between an ancient DNA
sample and modern human sequences can provide information on genetic affinities
between the population that the ancient sample comes from and extant human
groups. For example, Rasmussen et al. (2010) generated a high-coverage wholegenome sequence from a 4000-year-old hair sample from Greenland and found that
the genome sequence obtained was most similar to sequences from extant Siberian
populations. They concluded that the population from which the hair sample came
represented a separate migration than the one that gave rise to modern Native
Americans and Inuit. In another example, Rasmussen et al. (2011) sequenced a
100-year-old hair sample from an aboriginal Australian; their analyses provided
additional support for the early (>50 Kya) colonization of Melanesia and the
Southern route hypothesis. Other studies have also elucidated the recent movements
and population affinities of groups across Eurasia (e.g., Lipson et al. 2018; McColl
et al. 2018; Harney et al. 2019; Narasimhan et al. 2019; Shinde et al. 2019).
Finally, ancient DNA studies have helped to understand the relationship between
Neolithic farmers in Europe and contemporary European Paleolithic huntergatherers roughly 6–10 Kya. Specifically, a long-standing debate has centered
on the extent to which the Neolithic transition was cultural, with populations
adopting farming technologies from their neighbors, versus demic, with farming
populations replacing nonfarmers. So far, most of the early ancient DNA studies
have suggested that demic diffusion was predominant (e.g., Bramanti et al. 2009;
Malmstrom et al. 2009; Haak et al. 2010; Skoglund et al. 2012; but see Sampietro
et al. 2007). Later studies have been able to quantify the relative contributions of
various ancestral European groups, including ones that were previously unknown,
and have highlighted the enormous complexity in European demographic history
over the past ~40,000 years (e.g., Lazaridis et al. 2014; Seguin-Orlando et al. 2014;
Jones et al. 2015; Lipson et al. 2017).
197
though quantifying the amount or the timing of admixture depends on specific
assumptions about modern human population structure. Taken at face value, these
studies suggest that admixture between modern and archaic humans may have been
a relatively common occurrence, involving Neanderthals, Denisovans, and one or
more archaic human groups (in sub-Saharan Africa) for which no ancient DNA
samples are currently available.
8.8
Other Ancient DNA Studies
The previous section describes what insight has been gained from studies of
admixture between modern and archaic human groups. Ancient DNA studies
involving only modern human samples have also been very informative about
human demographic history. In particular, a comparison between an ancient DNA
sample and modern human sequences can provide information on genetic affinities
between the population that the ancient sample comes from and extant human
groups. For example, Rasmussen et al. (2010) generated a high-coverage wholegenome sequence from a 4000-year-old hair sample from Greenland and found that
the genome sequence obtained was most similar to sequences from extant Siberian
populations. They concluded that the population from which the hair sample came
represented a separate migration than the one that gave rise to modern Native
Americans and Inuit. In another example, Rasmussen et al. (2011) sequenced a
100-year-old hair sample from an aboriginal Australian; their analyses provided
additional support for the early (>50 Kya) colonization of Melanesia and the
Southern route hypothesis. Other studies have also elucidated the recent movements
and population affinities of groups across Eurasia (e.g., Lipson et al. 2018; McColl
et al. 2018; Harney et al. 2019; Narasimhan et al. 2019; Shinde et al. 2019).
Finally, ancient DNA studies have helped to understand the relationship between
Neolithic farmers in Europe and contemporary European Paleolithic huntergatherers roughly 6–10 Kya. Specifically, a long-standing debate has centered
on the extent to which the Neolithic transition was cultural, with populations
adopting farming technologies from their neighbors, versus demic, with farming
populations replacing nonfarmers. So far, most of the early ancient DNA studies
have suggested that demic diffusion was predominant (e.g., Bramanti et al. 2009;
Malmstrom et al. 2009; Haak et al. 2010; Skoglund et al. 2012; but see Sampietro
et al. 2007). Later studies have been able to quantify the relative contributions of
various ancestral European groups, including ones that were previously unknown,
and have highlighted the enormous complexity in European demographic history
over the past ~40,000 years (e.g., Lazaridis et al. 2014; Seguin-Orlando et al. 2014;
Jones et al. 2015; Lipson et al. 2017).