For 440 years, the sudden deaths of Grand Duke Francesco I de’ Medici and his wife, Bianca Cappello, in October 1587 fed one of history’s most persistent murder rumors: that Cardinal Ferdinando de’ Medici, Francesco’s younger brother and political rival, had slipped arsenic into their food to seize the grand duchy. A Yale University and University of Pisa team has now ended that debate with hard molecular evidence — and in doing so, uncovered a previously unknown strain of the world’s deadliest malaria parasite, one whose genetic mutations sit squarely within an ongoing scientific controversy about how Plasmodium falciparum evolves to outpace modern drugs.
The study, published in the journal iScience in July 2026, marks the first time any scientist has genetically confirmed the cause of death for either Medici brother. Its primary finding answers the cold case: malaria, not arsenic, killed Francesco. Its secondary finding — a previously uncharacterized P. falciparum haplotype recovered from the bones of Francesco’s younger brother, Cardinal Giovanni de’ Medici — may matter even more to living people.
Mosquitoes, Not Poison
The Medicis were arguably the most powerful family in Renaissance Europe — bankers to popes, patrons of Botticelli and Michelangelo, and rulers of Tuscany for three centuries. Wealth and influence, however, offered no protection against the Anopheles mosquitoes that bred in the marshlands surrounding their estates.
Giovanni’s malaria death in 1562 had long been accepted without serious dispute. The 19-year-old cardinal fell ill during a trip to the Tuscan coast with his mother, Eleonora of Toledo, and his younger brother Garzia. All three developed recurring fevers in the malaria-thick marshes and died within a month.
Francesco’s death was different — or seemed to be. In October 1587, the Grand Duke and his wife visited the Medici family’s villa in Poggio, surrounded by swampy rice fields. Both fell ill with intermittent fevers and died on consecutive days. Their speed of death immediately aroused suspicion. Cardinal Ferdinando had visited the couple just before they fell ill, he stood to inherit the grand duchy, and he was reportedly at risk of being displaced by Francesco’s illegitimate son, Antonio. A 2006 toxicological investigation even concluded, based on different methods, that the couple had been poisoned with arsenic.
That conclusion has now been overturned. “Now we can say with scientific certainty that malaria, not poisoning, killed Grand Duke Francesco de’ Medici,” said Valentina Giuffra, full professor of history of medicine at the University of Pisa and a co-author of the study.
How Scientists Read 400-Year-Old Bones
The Yale-Pisa team extracted DNA from four rib samples — three from Francesco’s remains and one from Giovanni’s. The brothers are entombed in the Medici Chapels within the Basilica di San Lorenzo in Florence.
What followed was not a straightforward laboratory process. Ancient DNA is chemically degraded, fragmented into tiny pieces, and heavily outnumbered by contaminating DNA from environmental microbes and modern researchers who have handled the samples. The team used targeted enrichment sequencing for mitochondrial genomes — a technique that works by deploying synthetic “bait” molecules designed to selectively capture Plasmodium DNA sequences from a library of tens of millions of fragmented molecules, then sequencing only those captured targets.
Critically, the team authenticated the recovered sequences by analyzing characteristic damage patterns — chemical modifications called cytosine-to-uracil deaminations that accumulate in DNA at fragment endpoints over centuries, serving as a molecular timestamp that distinguishes genuine ancient sequences from modern contamination.
The recovered fragments were small: 185 base pairs (bp) of P. falciparum and 43 bp of P. malariae from Francesco’s bones. Giovanni’s bones yielded far more — 1,865 bp of P. falciparum, enough to characterize the parasite’s haplotype in detail. (A base pair is one rung of the DNA ladder; 1,865 of them represent a modest but workable fragment of a mitochondrial genome that runs about 6,000 base pairs total.)
The team screened for six different Plasmodium species. The results were unambiguous: Francesco carried both P. falciparum — the deadliest form — and P. malariae, consistent with the “co-infection” pattern the researchers had seen in roughly contemporaneous samples from Belgium, though the team notes that further sequencing is needed before co-infection can be definitively confirmed for 16th-century Central Italy.
This approach is categorically more powerful than the methods used in prior Medici malaria research, which relied on antibody-based immunological detection of parasite proteins in tissue samples. Immunological methods can confirm the presence of Plasmodium but cannot identify the strain, characterize its genetic diversity, or place it in an evolutionary lineage. Only genetic analysis can do that.
Medici Brothers’ Doctors Were Right All Along
Contemporary court physicians recorded that both brothers suffered from “febbre terzana,” the Italian term then used across Central Italy for malaria’s characteristic intermittent fevers — recurring every two or three days in cycles driven by the parasite’s reproductive cycle in the blood. The historical accounts also describe bloodletting as treatment, a common Renaissance practice that almost certainly hastened the patients’ decline rather than helping them, as the Yale press release notes.
“At the time, both were diagnosed with symptoms, such as intermittent fevers, consistent with malaria,” Giuffra said. “This genetic analysis confirms the historical accounts as well as prior research.”
Alexander Ochoa, an associate research scientist in Yale’s Department of Ecology & Evolutionary Biology and Department of Anthropology, and the study’s first author, was careful not to overclaim. Senior author Serena Tucci, an assistant professor of anthropology at Yale, similarly acknowledged that arsenic cannot be ruled out entirely as a contributing factor — but emphasized that malaria “remains the most likely explanation” and that the poisoning hypothesis “doesn’t seem to be well-supported from a scientific perspective — it’s very speculative,” she told Fox News.
Giovanni’s Bones Held a Bigger Surprise
The cold case was the headline. The discovery in Giovanni’s remains was the scientific story.
Giovanni’s P. falciparum sequence represents a previously uncharacterized haplotype — a unique combination of genetic markers not found in any prior database — carrying two novel mutations in two specific locations: an intergenic region and the cytochrome c oxidase subunit 1 (COX1) locus, according to the published paper.
Network analyses comparing Giovanni’s haplotype against nine other ancient Plasmodium falciparum samples spanning from the Iron Age through the 1940s — drawn from remains in Europe, Asia, and the Americas — revealed that this previously unknown strain is closely related to six sequences from Europe, Taiwan, and the Caribbean. The researchers concluded it likely arose during a demographic expansion of P. falciparum across Europe.
The COX1 locus is not an arbitrary location. It encodes a mitochondrial protein involved in cellular respiration, and the P. falciparum electron transport chain — the biological system that includes COX1 — is a target of research into antimalarial compounds. Mutations in the mitochondrial genome, including at COX1, have been studied in connection with parasite drug susceptibility. Ancient DNA studies that recover COX1 variants from pre-antibiotic populations provide data that researchers can use to distinguish mutations that arose under natural evolutionary pressure from those that appear under pharmaceutical selection pressure — a distinction that is genuinely useful for modeling how resistance might spread.
“The study of ancient DNA offers us an opportunity not only to diagnose malaria in the remains of individuals from the past,” Ochoa said. “It also offers us a window for understanding the evolution of malaria species, Plasmodium falciparum in this case, which can help scientists better understand how the pathogen adapts over time.”
Adalgisa Caccone, a senior research scientist in Yale’s Department of Ecology & Evolutionary Biology and a co-author, put it in plain stakes terms: “The more we know about how fast [malaria] can change, the better our methods and models to control it will be.”
Ancient Pathogen, Modern Death Toll
Malaria was eradicated from Italy during the 20th century following sustained disease-control campaigns. It is not gone from the world.
According to the World Health Organization’s World Malaria Report 2025, an estimated 282 million people contracted malaria in 2024, and approximately 610,000 died — a slight increase from 2023. About 95% of those deaths occurred in sub-Saharan Africa, and roughly 75% of the deaths in that region were among children under 5. Plasmodium falciparum, the same species found in the Medici brothers’ bones, is responsible for the overwhelming majority of malaria deaths globally.
The parasite’s continued evolution is also a growing clinical concern. As of 2026, artemisinin partial resistance — P. falciparum’s ability to survive the frontline antimalarial drug longer than it should — has been confirmed or suspected in eight countries, including in East Africa, where it had not been seen before. A 2026 systematic review of P. falciparum drug resistance markers found that the parasite continues to evolve in response to both past and current antimalarial interventions, with alternatives to artemisinin not yet established as first-line treatments at global scale.
Antonio de Dios Martinez, an archaeologist and ancient DNA expert at the University of Tartu who was not involved in the research, assessed the study in Science/AAAS: “The success of this approach is remarkable.” He noted that it does more than provide genetic evidence of past malarial infections — it simultaneously closes a centuries-old cold case by confirming the brothers died of natural causes.
David Caramelli of the University of Florence, also not involved in the study, told CNN the research “represents an important step forward and demonstrates how paleogenomics can contribute to addressing longstanding historical questions.”
What Ancient DNA Still Cannot Tell Us
The study is not without limitations, and the authors are transparent about them. The fragments recovered from Francesco’s bones were small — the 185 bp of P. falciparum mtDNA is enough to confirm the parasite’s presence but does not provide the coverage needed to characterize his strain’s haplotype in the same detail as Giovanni’s. The researchers noted that additional analysis of the brothers’ bones is needed to determine the precise evolutionary relationship between the two strains they carried.
The comparison with Belgian samples showing co-infection, while suggestive, also requires additional sequencing before researchers can confidently generalize it to 16th-century Central Italy. The team’s framing of it as a data point rather than a confirmed regional pattern is the appropriate scientific register.
What the study does establish, with a level of confidence prior Medici investigations could not reach, is straightforward: both brothers died of what their physicians suspected in real time, and the poison rumors that have shadowed the Medici story for four centuries rest on no genetic foundation. Cardinal Ferdinando, history’s chief suspect, is exonerated.
The DNA that finally cleared him was extracted from rib bones he would have been buried near — in the same church in Florence where the Medici family has lain since the 15th century. “Sometimes,” senior author Tucci has said, “working on ancient DNA truly feels like looking directly through the keyhole of history.”
Frequently Asked QuestionsDid the Medici brothers really die of malaria, or were they poisoned?
Genetic analysis of their 400-year-old rib bones has now confirmed the presence of Plasmodium falciparum — the parasite that causes the deadliest form of malaria — in both brothers. The study, published in iScience in July 2026 by researchers from Yale University and the University of Pisa, marks the first time genetic evidence has been used to confirm the cause of death for either man. The senior author acknowledged that arsenic cannot be completely ruled out as a contributing factor, but the malaria evidence is specific, authenticated, and consistent with everything contemporary physicians recorded at the time.
How do scientists extract usable DNA from 400-year-old bones?
The technique used in this study is called targeted enrichment sequencing. Researchers extracted what little DNA remained from rib bone samples, built molecular libraries from the heavily degraded fragments, then used synthetic “bait” probes designed to capture and concentrate any Plasmodium DNA sequences in the mix. The resulting captured fragments were sequenced and then authenticated by looking for characteristic chemical damage patterns — a specific type of molecular modification called deamination that accumulates in genuine ancient DNA over centuries and distinguishes it from modern contamination.
What makes the novel malaria strain found in Cardinal Giovanni’s bones scientifically significant?
Cardinal Giovanni’s bones contained a P. falciparum strain with two unique mutations not previously recorded in any database — including in the cytochrome c oxidase subunit 1 (COX1) locus, a gene in the parasite’s mitochondrial genome that researchers studying antimalarial drug targets have examined. Ancient DNA datasets that catalog P. falciparum variants from before the era of pharmaceutical drug pressure help researchers calibrate evolutionary models that predict how drug-resistance mutations might spread in modern parasite populations. That is why a 460-year-old skeleton’s pathogen DNA has direct relevance to contemporary malaria control strategy.
How deadly is malaria today, and why does ancient parasite research matter now?
Malaria killed approximately 610,000 people in 2024, according to the World Health Organization’s World Malaria Report 2025, with about 95% of deaths occurring in sub-Saharan Africa and roughly 75% of those in children under the age of 5. Plasmodium falciparum — the same species identified in the Medici bones — is responsible for the majority of those deaths. The parasite is also showing increasing resistance to artemisinin, the world’s frontline antimalarial drug, in parts of Africa and Southeast Asia. Understanding how fast and in which directions the parasite’s genome changes over time, using ancient specimens as data points, is one tool researchers are using to stay ahead of those resistance trends.