• Mammals vs. birds: Of the 1,176 species analyzed, female mammals lived an average of 13 percent longer than males. In contrast, among birds, males lived about five percent longer than females.
• Mating strategies matter: In species where competition for mates is intense -- as is true for most mammals -- males tend to die younger. In species that form monogamous pairs, such as many birds, males often outlive females.
• Zoo comparisons: The gap between male and female lifespans is greater in wild populations than in zoo environments. This pattern indicates that both genetics and external conditions influence how long each sex lives.

Across nearly every country and historical era, women tend to live longer than men. While medical advances and improved living standards have reduced this gap in some places, new findings suggest the difference is deeply rooted in evolution and unlikely to vanish. Similar patterns appear across many animal species, hinting that the roots of longevity go far beyond modern life.

A team of scientists led by the Max Planck Institute for Evolutionary Anthropology in Leipzig, working with 15 collaborators around the world, carried out the largest and most detailed analysis ever of lifespan differences between male and female mammals and birds. Their results offer fresh insight into one of biology's most enduring questions: why do the sexes age at different rates?

Longevity: A question of chromosomes?

In most mammal species, females live longer -- for example, female baboons and gorillas often surpass males in age. But this pattern reverses in other groups. In many birds, reptiles, and insects, it is the males that have longer lifespans. One possible explanation, known as the heterogametic sex hypothesis, links these differences to sex chromosomes. Mammalian females possess two X chromosomes, while males have one X and one Y (making them the heterogametic sex). Having a pair of X chromosomes may shield females from harmful mutations and extend their lifespan. In birds, the system is reversed: females are the heterogametic sex.

Using data from more than 1,176 mammal and bird species in zoos around the world, researchers observed a striking contrast that supported this hypothesis. In most mammals (72 percent), females lived longer, by an average of twelve percent. In most bird species (68 percent), males were the longer-lived sex, averaging five percent longer lifespans. Yet the pattern was far from universal. "Some species showed the opposite of the expected pattern," explained lead author Johanna Stärk. "For example, in many birds of prey, females are both larger and longer-lived than males. So sex chromosomes can only be part of the story."

How mating and parenting shape longevity

In addition to genetics, reproductive strategies also play a role. Through sexual selection, males in particular develop conspicuous characteristics such as colorful plumage, weapons, or large body size, which increase reproductive success but can shorten lifespan. The new study supports this assumption: In polygamous mammals with strong competition, males generally die earlier than females. Many birds, on the other hand, are monogamous, which means that competitive pressure is lower and males often live longer. Overall, the differences were smallest in monogamous species, while polygamy and pronounced size differences were associated with a more pronounced advantage for females.

Parental care also plays a role. The researchers found evidence that the sex that invests more in raising offspring -- in mammals, this is often the females -- tends to live longer. In long-lived species such as primates, this is likely to be a selective advantage: females survive until their offspring are independent or sexually mature.

Zoo life reduces -- but does not erase -- lifespan gaps

A long-held idea suggests that environmental pressures, such as predators, disease, and harsh weather, drive differences in male and female lifespan. To test this, the scientists turned to zoo populations, where such risks are minimal. Even in these safe conditions, lifespan gaps persisted. Comparing zoo and wild data showed that while the differences were smaller in captivity, they rarely disappeared altogether. This pattern mirrors the human experience: better healthcare and living conditions may shrink the gap between men and women, but do not erase it.

Taken together, the findings indicate that lifespan differences between males and females are deeply embedded in evolution. They are shaped by sexual selection, parental care, and genetic factors linked to sex determination. The environment influences how large these gaps become but cannot remove them entirely. These contrasts between the sexes are not simply a product of circumstance -- they are woven into our evolutionary past and are likely to persist far into the future.

At the same time, an increasing number of researchers are making their sequencing results publicly accessible. This has led to an explosion of data, stored in major databases such as the American SRA (Sequence Read Archive) and the European ENA (European Nucleotide Archive). Together, these archives now hold about 100 petabytes of information -- roughly equivalent to the total amount of text found across the entire internet, with a single petabyte equaling one million gigabytes.

Until now, biomedical scientists needed enormous computing resources to search through these vast genetic repositories and compare them with their own data, making comprehensive searches nearly impossible. Researchers at ETH Zurich have now developed a way to overcome that limitation.

Full-text search instead of downloading entire data sets

The team created a tool called MetaGraph, which dramatically streamlines and accelerates the process. Instead of downloading entire datasets, MetaGraph enables direct searches within the raw DNA or RNA data -- much like using an internet search engine. Scientists simply enter a genetic sequence of interest into a search field and, within seconds or minutes depending on the query, can see where that sequence appears in global databases.

"It's a kind of Google for DNA," explains Professor Gunnar Rätsch, a data scientist in ETH Zurich's Department of Computer Science. Previously, researchers could only search for descriptive metadata and then had to download the full datasets to access raw sequences. That approach was slow, incomplete, and expensive.

According to the study authors, MetaGraph is also remarkably cost-efficient. Representing all publicly available biological sequences would require only a few computer hard drives, and large queries would cost no more than about 0.74 dollars per megabase.

Because the new DNA search engine is both fast and accurate, it could significantly accelerate research -- particularly in identifying emerging pathogens or analyzing genetic factors linked to antibiotic resistance. The system may even help locate beneficial viruses that destroy harmful bacteria (bacteriophages) hidden within these massive databases.

Compression by a factor of 300

In their study published on October 8 in Nature, the ETH team demonstrated how MetaGraph works. The tool organizes and compresses genetic data using advanced mathematical graphs that structure information more efficiently, similar to how spreadsheet software arranges values. "Mathematically speaking, it is a huge matrix with millions of columns and trillions of rows," Rätsch explains.

Creating indexes to make large datasets searchable is a familiar concept in computer science, but the ETH approach stands out for how it connects raw data with metadata while achieving an extraordinary compression rate of about 300 times. This reduction works much like summarizing a book -- it removes redundancies while preserving the essential narrative and relationships, retaining all relevant information in a much smaller form.

"We are pushing the limits of what is possible in order to keep the data sets as compact as possible without losing necessary information," says Dr. André Kahles, who, like Rätsch, is a member of the Biomedical Informatics Group at ETH Zurich. By contrast with other DNA search masks currently being researched, the ETH researchers' approach is scalable. This means that the larger the amount of data queried, the less additional computing power the tool requires.

Half of the data is already available now

First introduced in 2020, MetaGraph has been steadily refined. The tool is now publicly accessible for searches (https://metagraph.ethz.ch/search^[1]) and already indexes millions of DNA, RNA, and protein sequences from viruses, bacteria, fungi, plants, animals, and humans. Currently, nearly half of all available global sequence datasets are included, with the remainder expected to follow by the end of the year. Since MetaGraph is open source, it could also attract interest from pharmaceutical companies managing large volumes of internal research data.

Kahles even believes it is possible that the DNA search engine will one day be used by private individuals: "In the early days, even Google didn't know exactly what a search engine was good for. If the rapid development in DNA sequencing continues, it may become commonplace to identify your balcony plants more precisely."