We cannot preserve a species that doesn't have a name
In the overlooked world of eight-legged harvestmen, a team at the University of São Paulo has uncovered something rare: a creature whose males evolved to guard their young not once, but many times over, through pathways distinct from those taken by females. By turning to iNaturalist—a global archive of amateur observation—the researchers doubled a century of documented knowledge in a single week, revealing that the evolution of care is neither simple nor singular. The study, published in the Zoological Journal of the Linnean Society, asks us to reconsider both the origins of parental devotion and who gets to participate in the act of scientific discovery.
- A century of fieldwork had documented parental care in 80 harvestmen species—then two days on iNaturalist added 62 more, exposing just how much biology has been hiding in plain sight.
- Harvestmen represent less than one percent of arthropod diversity yet account for more than half of all known independent origins of paternal care, making them an almost improbable key to understanding why males ever bother to protect eggs at all.
- The data revealed a striking asymmetry: maternal care evolved only from the absence of care, while paternal care could emerge from either no care or from maternal care—suggesting males and females have been shaped by entirely different evolutionary pressures.
- Researchers propose that when paternal care replaced maternal care, female preference may have driven the shift—males who guarded eggs were chosen more often, until caregiving became the norm through sexual selection.
- The study exposes a paradox of the big-data era: citizen science can generate knowledge at extraordinary speed, yet identifying species, sexing individuals, and interpreting behavior still demands the irreplaceable judgment of trained taxonomists.
- For scientists in the Global South working with constrained budgets, iNaturalist's open access represents a genuine redistribution of research power—but only if the taxonomic expertise needed to interpret its images continues to be cultivated.
When Glauco Machado and his team at the University of São Paulo asked how parental care evolved in harvestmen—the spindly, eight-legged arachnids most people never pause to notice—they expected a long search. What they did not expect was to find their answer partly in the hands of amateur naturalists around the world.
Traditional scientific literature had spent 89 years accumulating records of parental guarding behavior in 80 harvestmen species. Machado's team found 62 new cases in two days by searching iNaturalist, a global platform where ordinary observers upload photographs of organisms they encounter. Within a week, a century of knowledge had more than doubled.
The findings, published in the Zoological Journal of the Linnean Society, revealed something deeper than sheer numbers. Harvestmen—an order of over 6,900 species—account for more than half of all known independent origins of paternal care in the animal kingdom, a trait so rare it offers an exceptional lens on evolutionary pressure. Mapping care across the group's family tree, the researchers found that maternal care arose only from the complete absence of care, mirroring patterns seen in insects. Paternal care, however, followed a different logic: it could evolve from either no care or from existing maternal care. Machado theorized that when fathers replaced mothers as guardians, female preference likely drove the transition—females choosing males who guarded eggs, gradually making caregiving a male norm through sexual selection.
Beyond the biology, the study carries a quieter argument about who science is for. A researcher in São Paulo, Lagos, or Manila can now access global observations without museum visits or distant fieldwork, a shift that matters most where research budgets are smallest. Yet the researchers are careful to note that data abundance does not replace human expertise. Distinguishing species in a photograph, determining sex, and separating parental care from mere mate guarding all require knowledge no algorithm reliably provides. Taxonomists, Machado observed, have become more essential in the age of big data, not less—because a species without a name cannot be protected.
The study acknowledges its own blind spots: guarding behavior is easier to photograph than its absence, and that visibility shapes what gets recorded. But with more than half its documented cases entirely new to science, the work stands as both a finding and an invitation—to researchers studying insects, amphibians, and any group where the question of why animals care for their young remains, as Machado sees it, far from settled.
A team of researchers led by Glauco Machado at the University of São Paulo set out to answer a deceptively simple question: how did parental care evolve in harvestmen, those eight-legged arachnids that most people walk past without noticing? What they discovered, published in the Zoological Journal of the Linnean Society, rewrites our understanding of how animals come to protect their young—and reveals something unexpected about the power of crowdsourced science.
The breakthrough came from an unlikely source. Rather than spending years in museums or the field, Machado's team turned to iNaturalist, a global database where amateur naturalists upload photographs and observations of organisms they encounter. Between 1936 and 2025, traditional scientific literature had documented parental guarding behavior in 80 species of harvestmen. Using iNaturalist, the researchers found 62 new cases in just two days. In a single week of searching, they had more than doubled a century of accumulated knowledge.
Harvestmen—an order containing over 6,900 recognized species—occupy a peculiar place in the animal world. They represent less than one percent of arthropod diversity, yet they account for more than half of all independent origins of paternal care, a trait so rare in nature that it offers researchers an exceptional window into evolutionary pressures. By mapping when parental care appeared, vanished, and reappeared across harvestmen's family tree, the team discovered a pattern: maternal care evolved only from the absence of care, mirroring what scientists see in insects. Paternal care, however, told a different story. It could evolve from either no care or from maternal care—suggesting that males and females faced fundamentally different evolutionary incentives.
Machado theorized that when paternal care emerged from maternal care, it likely represented a sexually selected behavior. Females, in other words, may have preferred males who guarded eggs, creating an advantage for caring males that eventually became the norm. This hypothesis, known as enhanced fecundity, explains why the same behavior could arise through different pathways depending on what came before it.
What makes this research significant extends beyond harvestmen themselves. The speed and scale of discovery through iNaturalist highlights a transformation in how science works. Machado emphasized that the platform's true value lies not just in the data it contains, but in its accessibility. A researcher in São Paulo or Lagos or Manila can now access observations from across the globe without the expense and time required to visit museums or conduct fieldwork in distant locations. For scientists in the Global South, where research budgets are often constrained, this democratization of data represents a genuine shift in what becomes possible.
Yet the study also underscores a paradox at the heart of modern biology. While citizen science platforms can accumulate vast amounts of data with remarkable speed, the researchers stress that human expertise remains irreplaceable. Identifying which species is in a photograph, determining the sex of an individual, and distinguishing between parental care and mate guarding all require knowledge that no algorithm can yet reliably provide. Taxonomists—the scientists who name and classify organisms—have become more essential, not less, in an age of big data. "We cannot preserve a species that doesn't have a name," Machado noted. "And names are provided by taxonomists."
The work does carry limitations. Parental care is inherently easier to observe and photograph than its absence, introducing bias into the dataset. A harvestman guarding eggs makes for a compelling image; a harvestman doing nothing does not. Yet the researchers argue that studies like this one are filling critical gaps in understanding where care exists and where it does not. With more than half of the cases documented in this study entirely new to science, Machado sees the work as an invitation to other researchers studying insects, amphibians, and countless other groups where both maternal and paternal care occur. The question of how and why animals evolve to care for their young remains far from answered—but the tools to answer it have suddenly become far more accessible.
Citações Notáveis
It's very rare in nature, paternal care, and this behaviour evolved many times independently. By looking at harvestmen we can explore questions related to the factors that led to the evolution of this behaviour.— Glauco Machado, lead researcher
I think taxonomists' role in modern science is more important than ever. We cannot preserve a species that doesn't have a name. And names are provided by taxonomists.— Glauco Machado
A Conversa do Hearth Outra perspectiva sobre a história
Why does it matter that paternal care evolved multiple times independently in harvestmen? Couldn't that be true of any trait?
It could be, but it's not. Paternal care is genuinely rare in the animal kingdom. Most species either show no parental investment or only maternal care. Finding that harvestmen—less than one percent of arthropods—account for more than half of all independent origins of paternal care means they're a natural laboratory for understanding what conditions allow males to evolve caregiving behavior.
The study found that paternal care can evolve from either no care or from maternal care. Why would those two pathways matter?
Because they suggest different evolutionary pressures. If paternal care only ever evolved from maternal care, you'd have one story. But when it evolves from scratch—from no care at all—that's a different selective pressure at work. The researchers think that when it emerges from maternal care, females are actively choosing caring males. That's sexual selection. It's a mechanism, not just an outcome.
How does iNaturalist actually change what's possible for a researcher like Machado?
It removes the gatekeepers. Traditionally, you'd need funding to travel to museums, time to visit institutions, connections to access collections. iNaturalist is public and global. A researcher in Brazil can search observations from every continent in hours. The data is already georeferenced, already photographed. That's revolutionary for scientists who don't have the resources for expensive fieldwork.
But doesn't citizen science introduce bias? People photograph interesting things, not boring things.
Absolutely. That's the limitation the researchers acknowledge. Harvestmen guarding eggs is photogenic. Harvestmen doing nothing is not. So the dataset skews toward care. But the researchers argue that even with that bias, they're filling gaps that didn't exist before. You can't study what you don't know about.
The study emphasizes that taxonomists are still essential. Why? Isn't that a bit defensive?
No, it's honest. A photograph of a harvestman tells you there's a harvestman. It doesn't tell you which species, which sex, or whether what you're seeing is parental care or something else that looks similar. That requires expertise. Machado is saying that in an age of massive data, the human ability to interpret and classify remains irreplaceable. You can't name a species you can't identify.