Science: Ancient gene flow shaped wild boar and pig body size

Enlarge

A new study in Science, co-authored by Dr. Edward Ricemeyer and Prof. Laurent Frantz from our Chair, reveals where Eurasian wild boar originated and how ancient hybridization shaped the diversity of today’s domestic pigs. Prof. Frantz is one of the corresponding authors, and he also helped conceive and supervise the study.

A South Asian origin
The international team analysed 745 genomes from 58 populations across Eurasia, including 256 newly sequenced samples from South Asia and mainland Southeast Asia. South Asian wild boar turned out to be the oldest lineage. They split from all other wild boar roughly 660,000 to 690,000 years ago, and the species then expanded across Eurasia during the Middle Pleistocene.

A gift from an extinct relative
Before this expansion, ancestral South Asian wild boar interbred with an archaic, now extinct lineage of the pig subfamily (Suinae) about 3 to 5 million years ago. This introduced a ~43 Mb haplotype on the X chromosome. It carries variants linked to larger body size and to adaptation to cold climates, in line with Bergmann’s rule: larger animals tend to live in colder regions.

Selected three times independently
The haplotype spread with the wild boar to Europe and northern China. During domestication it was selected at least three times independently (in Europe, northern China and South Asia) and contributed to modern large-bodied breeds. The region also accumulated many structural variants and shows suppressed recombination against the ancestral haplotype. Gene expression data from crosses between large Duroc and miniature Luchuan pigs point to candidate genes behind the effect, including several with known roles in growth and development.

The study shows how ancient introgression can act as a long-lasting reservoir of genetic variation that both natural and human-driven selection can later draw on.

The work was led by Huazhong Agricultural University (Wuhan, China) together with partners including the University of Oxford, the International Livestock Research Institute (ILRI) and the Yazhouwan National Laboratory. Research at LMU was supported by the European Research Council (ERC), and computing resources were provided by the LRZ Munich. Data and code are openly available via NCBI, Zenodo and GitHub.

Publication: Chen, J.-H., Du, X., Zheng, Z., Gorkhali, N. A., … Ricemeyer, E. S., … Frantz, L. A. F., Larson, G., Han, J., Zhao, S. (2026). Ancient introgression drives wild boar expansion and phenotypic diversification of domestic pigs. Science 393 (6818), 1335–1341. DOI: 10.1126/science.adq7553