Any Italian will tell you that the north and south are poles apart, and it appears those differences may have begun as many as 20,000 years ago.
New research suggests that genetic adaptions to environmental changes, such as those that occurred soon after the Last Glacial Maximum, could explain some of the genetic differences between northern and southern Italian populations today.
A team from the University of Bologna sequenced the genomes of 38 unrelated participants from different regions in Italy, each the third generation of their family native to each region.
The genomes were selected as representative of known genetic differences across the Italian population and over 17 million distinct genetic variants were found between individuals.
Marco Sazzini and colleagues then compared these variations with existing genetic data from 35 populations across Europe and the Mediterranean and with variants previously observed in 559 ancient human remains, dating from the Upper Palaeolithic (around 40,000 years ago) to the Bronze Age (4000 years ago).
“When comparing sequences between modern and ancient genome samples, we found early genetic divergence between the ancestors of northern and southern Italian groups dating back to the Late Glacial, around 19,000-12,000 years ago,” Sazzini says.
“Migrations during the Neolithic and Bronze Age periods, thousands of years later, then further differentiated their gene pools.
“Divergence between these ancestral populations may have occurred as a result of temperature rises and subsequent shrinking of glaciers across northern Italy during this time, allowing ancestors who survived the glaciation period to move north, separating from groups who remained in the south.”
The researchers note, however, that they are unable to prove causation or to rule out the possibility that more recent gene flow from populations exposed to diverse environmental conditions outside of Italy may have also contributed to the different genetic signatures.
Writing in the journal BMC Biology, they say their analyses reveal signatures ascribable to specific biological adaptations in northern and southern Italian genomes suggestive of habitation in differing climates.
The genetic history of northern Italians shows changes in the genes responsible for regulating insulin, body-heat production and fat metabolism, while southern Italians showed adaptations in genes regulating the production of melanin and responses to pathogens.
“Our findings suggest that the ancestors of northern Italians adapted to lower environmental temperatures and the related high-calorie diets by optimising their energy metabolism,” Sazzini says.
“This adaptation may play a role in the lower prevalence of Type 2 Diabetes recorded in northern Italy today. Conversely, southern Italian ancestors adapted to a warmer climate with higher UV levels by increasing melanin production, which may explain the lower incidence rates of skin cancers recorded across southern regions.”
The genomes of southern Italians also showed changes in the genes encoding mucins, which play a role in protection against pathogens, and genetic variants linked to a longer lifespan.