“Our findings suggest the house and Bactrianus sparrows probably split from each other about 11,000 years ago, around the time that humans were developing agriculture in the Middle East,” said Dr. Ravinet. “We also found evidence that the number of house sparrows greatly increased around 6000 years ago.”

This population increase ties in well with previous suggestions that the spread of house sparrows was closely associated with the spread of early agriculture.

What do these sparrows’ genes tell us about human evolution?

How did agriculture affect the house sparrow genome?

“We found several genes which seem to have been under strong recent natural selection in the house sparrow, but not in its wild close relative,” Dr. Ravinet said.

Dr. Ravinet and his collaborators discovered two of these genes located next to each other on chromosome number 8. One gene, COL11A, is involved in skull development whilst the other, AMY2A, plays a role in digestion of starches. Abnormal expression of a similar skull development gene in humans is associated with Marshall’s Syndrome, a genetic disorder characterized by increased skull thickness and abnormal facial structure. This is consistent with what we see in house sparrows, which have a more robust skull and craniofacial structure along with a longer beak than Bactrianus sparrows (

ref). The shift in skull and beak morphology between these sparrow lineages is widely attributed to their dietary shift from natural seeds to agricultural food waste during the development of commensalism. (Similarly, introduction of human food resources appears to have altered beak morphology and — weirdly — weakened bite force in Darwin’s finches [

ref].)

“The skull gene is interesting because we know that house and Bactrianus sparrow skulls differ in shape,” Dr. Ravinet elaborated. “But we were really excited to see the digestion gene there too.”

The other gene that experienced strong selection in Passer sparrows is AMY2A. AMY2A is part of a gene family linked to the transition to starch-based diets in both humans and dogs during the first agricultural revolution, which began during the Neolithic period, around 10,200 years BP (ref & ref): previous research found both dogs and humans increased copy numbers of their versions of this gene as their diets changed to include more agriculture-based grains.

Dr. Ravinet and his collaborators’ study neatly adds more detail to the emerging picture of how the Neolithic agricultural revolution presented a common selective pressure that resulted in similar adaptations in similar genes for three very different animals: humans, dogs and sparrows.

“We still have some way to go to investigate this further,” Dr. Ravinet said. “But it is exciting to think that the evolution of a species so familiar to us is tightly linked to a major event in the development of modern human civilization.”

Source:

Mark Ravinet, Tore Oldeide Elgvin, Cassandra Trier, Mansour Aliabadian, Andrey Gavrilov and Glenn-Peter Sætre (2018). Signatures of human-commensalism in the house sparrow genome, Proceedings of the Royal Society of London B: Biological Sciences, published online on 8 August 2018 before print | doi:10.1098/rspb.2018.1246

Also Cited:

Tore O. Elgvin, Cassandra N. Trier, Ole K. Tørresen, Ingerid J. Hagen, Sigbjørn Lien, Alexander J. Nederbragt, Mark Ravinet, Henrik Jensen and Glenn-Peter Sætre (2017). The genomic mosaicism of hybrid speciation, Science Advances, 3(6):e1602996 | doi:10.1126/sciadv.1602996

Lorna M. Shaw, Dan Chamberlain, and Matthew Evans (2008). The house sparrow, Passer domesticus in urban areas: reviewing a possible link between post-decline distribution and human socioeconomic status, Journal of Ornithology, 149(3):293–299 | doi:10.1007/s10336–008–0285-y

H. Jensen, B.E. Sæther, T. H. Ringsby, J. Tufto, S. C. Griffith, and H. Ellegren (2003). Sexual variation in heritability and genetic correlations of morphological traits in house sparrow (Passer domesticus), Journal of Evolutionary Biology, 16:1296–1307 | doi:10.1046/j.1420–9101.2003.00614.x

Shachar Ben Cohen and Roi Dor (2018). Phenotypic divergence despite low genetic differentiation in house sparrow populations, Scientific Reports, 8:394 | doi:10.1038/s41598–017–18718–8

Sepand Riyahi, Øyvind Hammer, Tayebeh Arbabi, Antonio Sánchez, Cees S Roselaar, Mansour Aliabadian and Glenn-Peter Sætre (2013). Beak and skull shapes of human commensal and non-commensal house sparrows Passer domesticus, BMC Evolutionary Biology, 13:200 | doi:10.1186/1471–2148–13–200