Using "new, improved" methods, researchers from the Natural History Museum of Denmark sequenced low-coverage genomes from 101 ancient humans from across Bronze Age Eurasia.
As detailed in their study, Population genomics of Bronze Age Eurasia, the results suggest lactose tolerance - as lactase persistence is also known - was "at a low frequency" in the the Bronze Age - a period that ran from around 3,000 BC to 1,000 BC.
It is generally assumed, on the back of earlier research, that humans in the region developed lactase persistence around 5,500 BC.
Given this, the researchers branded their discovery "surprising."
"Although tolerance is high in present-day northern Europeans, we find it at most at low frequency in the Bronze Age (10% in Bronze Age Europeans), indicating a more recent onset of positive selection than previously estimated," the study concluded.
Further examination confirmed "a low frequency" of rs4988235 - a single nucleotide polymorphism (SNP) associated with lactase persistence - in Bronze Age Europeans, it said.
Among Bronze Age Europeans, the "highest tolerance frequency" was found in the Colded Ware and the "closely-related" Scandinavian Bronze Age cultures.
"Interestingly," it added, "the Bronze Age steppe cultures showed the highest derived allele frequency among ancient groups, in particular the Yamnaya."
This, the study said, indicates "a possible steppe origin of lactose tolerance" - meaning the genetic ability to digest lactose may have originated among people in what is now known as Southern Russia.
Source: Nature doi:10.1038/nature14507
Title: Population genomics of Bronze Age Eurasia
Authors: Morten E Allentoft, Martin Sikora et al.