For more than four centuries, one of the great conspiracy theories of the Renaissance held that Grand Duke Francesco I de’ Medici was poisoned by his own brother, Cardinal Ferdinando. New ancient DNA evidence published in iScience (Cell Press) puts that theory to rest: Francesco died of malaria.
A team led by Yale University researchers Alexander Ochoa and Serena Tucci, in collaboration with the University of Pisa’s Division of Paleopathology, extracted DNA from three rib fragments of Francesco de’ Medici (1541–1587). Using in-solution hybridization capture with 80-mer probes targeting mitochondrial DNA of six Plasmodium species, they recovered 185 base pairs of Plasmodium falciparum mitochondrial DNA and 43 base pairs of Plasmodium malariae mitochondrial DNA, confirming a co-infection with both species.
A 400-year-old whodunit
Francesco, the second Grand Duke of Tuscany, and his wife Bianca Cappello died suddenly within days of each other in October 1587 at the Medici villa in Poggio a Caiano. The proximity of the deaths, and Francesco’s tense relationship with his brother Ferdinando, who succeeded him as Grand Duke, fueled centuries of suspicion that Ferdinando arranged arsenic poisoning.
But the genetic evidence tells a different story. Francesco’s symptoms, described by contemporary court physicians as “febbre terzana” (tertian fever), are consistent with malarial infection. And the villa’s location near mosquito-breeding rice fields would have placed Francesco in an area of high transmission risk.
A previously unknown Plasmodium strain
The researchers also analyzed the remains of Cardinal Giovanni de’ Medici, Francesco’s younger brother who died in 1562 at age 19. Giovanni showed a much heavier P. falciparum burden, 1,865 base pairs recovered, covering 31.3% of the mitochondrial genome, representing a previously uncharacterized haplotype with two unique mutations: an intergenic G>T substitution at position 1,917 and a cytochrome c oxidase subunit 1 C>T mutation at position 2,708 (causing p.Thr255Ile).
This strain is closely related to sequences from Italy, Austria, France, Spain, Taiwan, and the Caribbean, likely originating from a demographic expansion of P. falciparum in Europe.
Giovanni died in a cluster alongside his mother Eleonora and brother Garzia, all dead within a month after contracting malaria in the Tuscan coastal marshes.
Broader implications
The study demonstrates the power of ancient DNA to resolve long-standing historical debates, but also provides a genomic snapshot of P. falciparum diversity in 16th-century Europe, an era before modern interventions reshaped parasite populations. The findings suggest that Renaissance-era P. falciparum strains were more genetically diverse than previously appreciated, with implications for understanding the parasite’s historical biogeography.
The authors state definitively: “Malaria, and not poisoning, caused the death of Grand Duke Francesco de’ Medici.”
Sources:
1. Ochoa A, Miller SL, Reilly PF, Fornaciari G, Fornaciari A, Riccomi G, Giuffra V, Caccone A, Tucci S. “Ancient DNA analyses of remains of the Medici family (16th century) provide insights into the genetic variation of Plasmodium falciparum.” iScience. 2026;29(7):116371. DOI: 10.1016/j.isci.2026.116371
2. Reported in Science AAAS. https://www.science.org/content/article/ancient-dna-solves-medici-murder-mystery