After monitoring 10 generations of these fish, the researchers discovered that the females\u2019 preference for unusual males didn\u2019t improve the survival rate of their offspring. However, it did offer an indirect advantage: their sons \u2014 by inheriting these unusual traits \u2014 were more attractive and achieved more matings. This is known as the \u201csexy son\u201d hypothesis. The indirect effect maintains the preference for the unusual and explains, in part, the dazzling diversity of colors and sexual characteristics that we see in nature.<\/p>\n
These results, published in the journal Science in 2023, had a major impact. But what\u2019s rarely mentioned is the work that took place behind the scenes, with teams of young people getting up at 5 a.m. to scour the jungle in search of fish. This is the case of Ignacio Paulin, who \u2014 having recently graduated in biology from the University of Oviedo, in Spain \u2014 was hired as a field assistant for the Guppy Project.<\/p>\n
\u201cI was used to the mountains of Asturias, where you can see for miles around. But I understood that the jungle was a place to focus on the small details, because your world shrinks to a tiny bubble,\u201d Paulin notes. The biologist describes his experience: \u201cEvery [16 feet, there] was a new universe full of things to discover. I went [to Trinidad] for three months, but I immediately thought, \u2018I\u2019m not leaving here so soon.\u2019\u201d <\/p>\n
At 6 a.m., he and his team were already in the car. After an hour\u2019s drive, they began trekking into the jungle. \u201cWe were walking through the middle of nowhere. It\u2019s undoubtedly the most remote place I\u2019ve ever been to,\u201d Paulin recalls. Each of them carried a backpack full of empty bottles. Upon reaching the river, they tried to capture as many adult guppies as possible. They would place them in the bottles and note the exact stretch of the river where they found them. Back at camp, the fish were transferred to small aquariums to be studied.<\/p>\n
![\"Male](\"https:\/\/www.newsbeep.com\/ca\/wp-content\/uploads\/2026\/06\/DYTWSQJ3DBFVPPYLHAPDWZEF5Y.jpg\")
Male guppies in an aquarium in Virginia, February 2012.\u00a0The Washington Post (The Washington Post via Getty Images)<\/p>\n
The next day, in the lab, the fish were anesthetized one by one and examined under a microscope, so that the researchers could read the color code tattooed on their skin, which served as their identification. If they had no code, it meant that it was their first time being captured: subsequently, a new code was tattooed and a DNA sample was taken. If they were already tagged, the database was consulted to record their weight and size, with a new photograph being taken before releasing them back into the river.<\/p>\n
This routine has allowed researchers to track the evolution of guppy populations in Trinidad for years. They know how long each fish lives, how its appearance changes, where it moves, as well as its lineage. \u201cAround 4,000 fish come through the lab every month. Since the project began, 115,000 individuals have been recorded. And, since many are caught multiple times, we now have over half-a-million records,\u201d Paulin explains. <\/p>\n
Although the fieldwork was fascinating, Paulin felt it wasn\u2019t enough. He was drawn to studying animal behavior and wanted to formulate his own hypotheses. After getting to know Trinidad and its guppies firsthand, he decided to combine that experience with mathematics, so as to analyze the guppies\u2019 behavior. He enrolled in a Master\u2019s program in ecology, evolution and animal behavior at the University of Konstanz, in Germany. There, he met Alex Jordan, a researcher at the Laboratory of Evolutionary Behavior.<\/p>\n
\u201cOne day, we were introduced. And he asked me, \u2018Why are you here?\u2019 I told him that I had just arrived from Trinidad and that I wanted to return [to the island, so that I could] apply computation to the study of animal behavior. [And I told him] that I needed a place to learn how to analyze all the data,\u201d Paulin recounts. \u201cIt was amazing: we clicked from the start. He loved my proposal.\u201d <\/p>\n
During his graduate program, he returned to Trinidad, this time determined to study guppy courtship. To attract females, the males perform a ritual known as the sigmoid display: they position themselves in front of the females and perform a \u201cdance,\u201d by arching their bodies in an S-shape. During this display, some of their colors \u2014 regulated by hormones \u2014 intensify. It\u2019s their way of pleading for a chance.<\/p>\n
It\u2019s worth noting, however, that male guppies aren\u2019t always so chivalrous. These fish have another reproductive tactic: catching females off guard, darting past them like shooting stars\u2026 and fertilizing them unexpectedly. This tactic avoids relying on their consent (although the probability of successful fertilization is lower).<\/p>\n
That\u2019s why guppies end up resorting to courtship dances, even though they might be rejected. But the dance also carries a risk, because they become more visible to predators. And this is where Paulin\u2019s research comes in: \u201cI\u2019ve recorded the fish\u2019s courtship dances in different rivers on the island. Some have predators, while others don\u2019t. Right now, we\u2019re training a machine learning model to detect the fish\u2019s posture and movements.\u201d The biologist continues: \u201cWe want to study how the dance has evolved and see if its intensity changes between populations that live with predators and those that don\u2019t.\u201d<\/p>\n
Currently, Paulin is at the Max Planck Institute for Animal Behavior in Germany, analyzing his data. He\u2019s worried he won\u2019t be able to return to Trinidad. For the first time since 2007, the Guppy Project has closed its doors. \u201cThe Trump administration decided to cut funding<\/a>. It\u2019s incomprehensible to let a project of this magnitude \u2014 in which so much has been invested \u2014 [just] die,\u201d he laments. \u201cRight now, there\u2019s no one left at the station in Trinidad.\u201d<\/p>\n \u201cBeyond the science,\u201d he details, \u201cthere\u2019s the human aspect: we lived at the edge of the rainforest, near a small community that welcomed us for 16 years. We felt like part of them. I had a close relationship with the children; we played together and they showed me the rainforest. The thought that all of that could disappear forever makes me very sad,\u201d he laments.<\/p>\n Scientific projects are much more than the articles published in a journal. Thanks to the Guppy Project, Paulin and hundreds of other young people found inspiration in Trinidad to launch their research careers. Today, at 26 years old, Paulin has extensive experience studying fish\u2026 and many questions left to answer. <\/p>\n