For generations, many Bajau communities across Southeast Asia have maintained a close relationship with the ocean. Often referred to as “Sea Nomads,” some Bajau traditionally depend on fishing, marine gathering and repeated breath-hold diving as important parts of everyday life. Experienced divers can spend substantial periods of their working day repeatedly entering the water without using conventional scuba equipment. Their abilities have attracted scientific interest because working underwater while holding the breath places considerable demands on the human body.
Researchers therefore began investigating whether generations of this maritime lifestyle might be associated with measurable biological differences. A widely discussed 2018 study found evidence suggesting that the answer may involve both spleen size and inherited genetic variation. Researchers led by Melissa Ilardo studied Bajau participants in Indonesia and compared them with members of a nearby population whose traditional lifestyle did not involve the same level of breath-hold diving. The scientists used ultrasound examinations to measure the spleens of participants and collected genetic information for further analysis.
Their results showed that the Bajau participants had significantly larger spleens on average than members of the comparison population. The difference was particularly interesting because it was found among Bajau individuals regardless of whether they personally practiced regular diving. That observation suggested that repeated diving practice by itself might not fully explain the larger average spleen size. Researchers therefore investigated whether inherited characteristics shaped by natural selection might also be involved.
The spleen may seem unrelated to underwater performance, but it has an important role during breath-holding. The organ stores a reserve of red blood cells, which are responsible for carrying oxygen throughout the body. During apnea, or voluntary breath-holding, the spleen can contract and release additional red blood cells into circulation. This can temporarily increase the blood’s capacity to transport oxygen. For someone performing repeated breath-hold dives, even a modest increase in available oxygen could potentially be useful. Researchers therefore proposed that a larger spleen could contribute to the ability of experienced Bajau divers to repeatedly work underwater.
This response is part of a broader physiological process commonly known as the human diving response. It is not exclusive to the Bajau. When humans hold their breath and become submerged, the body can make several adjustments intended to conserve limited oxygen. Heart rate may decrease, blood vessels in the arms and legs can constrict, and circulation becomes more focused on supplying vital organs. The spleen may also contract as part of this process. These mechanisms help explain how humans can temporarily function without breathing, although the length of time varies greatly among individuals depending on training, health, physiology and other factors.
The genetic component of the Bajau study attracted particular attention. Researchers identified several areas of the genome showing patterns consistent with natural selection. One important signal involved a genetic variant near a gene called PDE10A. This gene is associated with biological pathways involving thyroid hormones, and earlier animal research had suggested that thyroid hormones could influence spleen development. The researchers therefore proposed a possible connection between inherited genetic variation and the larger average spleen size observed among Bajau participants. The findings provided evidence of adaptation, although scientists did not claim that one gene alone explains the population’s diving abilities.
This distinction matters because descriptions suggesting that the Bajau developed a completely “new mutant gene” are misleading. The research did not discover a newly created gene that suddenly gave people the ability to dive underwater. Instead, scientists found differences in the frequencies of genetic variants already present within human populations. Over many generations, natural selection can make certain variants more common when they provide an advantage under particular environmental or lifestyle conditions. The Bajau study suggested that this kind of evolutionary process may have occurred in connection with a long tradition of marine living and breath-hold diving.
Traditional Bajau diving can involve repeated underwater trips over the course of a working day. Experienced divers may descend considerable distances while searching for fish, shellfish and other marine resources. Some accounts describe particularly skilled individuals reaching impressive depths and remaining underwater for several minutes. However, these abilities should not be generalized to every Bajau person. The Bajau consist of diverse communities, and individual diving performance varies considerably. Age, training, health, experience and personal physiology all influence how deep or how long someone can safely dive while holding their breath.
Cultural knowledge is another important part of the explanation. Bajau diving traditions have been passed between generations, allowing experienced divers to develop techniques for moving efficiently underwater, managing breath and navigating marine environments. These learned skills cannot be explained by genetics. Someone with favorable physiological characteristics would not automatically become an exceptional diver without practice and experience. Similarly, extensive training can improve breath-hold performance even in people who do not come from traditional diving populations. The remarkable abilities associated with experienced Bajau divers therefore appear to reflect an interaction between biology, culture and individual training.
The larger average spleen size discovered by researchers should also be interpreted carefully. It does not mean that Bajau people possess a fundamentally different type of spleen from other humans. Their spleens perform the same basic biological functions. The difference identified in the study concerned average organ size between the populations examined. A larger spleen could potentially store a larger reserve of red blood cells and release more of them during contraction. That could provide an advantage during repeated breath-holding, but it represents only one component of the body’s overall response to underwater activity.
Scientists sometimes use an informal comparison describing the spleen as a type of “biological scuba tank.” The phrase can help communicate the basic idea, but it should not be interpreted literally. A real scuba tank contains compressed gas that a diver can breathe underwater. The spleen does not supply fresh air or allow a person to breathe beneath the surface. Instead, its contraction releases additional red blood cells already stored inside the body. Those cells can increase oxygen-carrying capacity temporarily, helping the body make better use of the oxygen available before a dive begins.
The Bajau findings also provide an interesting example of continuing human evolution. Evolutionary change is sometimes imagined as something that occurred only in the distant past, but natural selection can continue whenever inherited characteristics affect survival or reproduction. Human populations have developed measurable adaptations to different environments, including high-altitude regions where oxygen levels are lower. The Bajau research suggests that a specialized marine lifestyle may represent another example. Generations of repeated exposure to breath-hold diving could have created conditions in which physiological characteristics helpful for managing low oxygen became more common.
Researchers identified additional genetic signals beyond the region associated with PDE10A. Some were connected to biological processes that could potentially be relevant to oxygen management and diving physiology. However, genetic studies require careful interpretation. Finding evidence of natural selection near a particular gene does not automatically prove exactly how that gene affects a complex ability such as diving. Many biological traits involve numerous genes interacting with environmental and developmental factors. Scientists therefore continue studying these mechanisms rather than treating the original findings as a complete explanation.
The research also has potential value beyond understanding the Bajau themselves. Scientists are interested in how the human body responds when oxygen temporarily becomes limited. Similar biological pathways can be relevant when studying medical conditions involving reduced oxygen supply. Researchers such as Rasmus Nielsen have noted that studying populations adapted to unusual environmental pressures can help identify genes and physiological pathways associated with responses to low oxygen. Such discoveries do not automatically produce medical treatments, but they can identify mechanisms that researchers may investigate further.
More recent studies of trained breath-hold divers have continued examining how the human body manages prolonged apnea. Scientists have investigated changes in hemoglobin concentration, circulation, cardiovascular function and the redistribution of blood during breath-holding. These studies reinforce the idea that exceptional underwater performance cannot be reduced to a single physical characteristic. The heart, blood vessels, lungs, spleen, nervous system and learned diving techniques all contribute to how someone responds underwater. The Bajau research adds an evolutionary component by suggesting that inherited differences may operate alongside universal human physiology and training.
The study therefore does not support claims that Bajau people can breathe underwater or remain submerged indefinitely. Like everyone else, Bajau divers must surface to breathe and remain constrained by the amount of oxygen their bodies can store and use. Their impressive diving abilities involve breath-holding rather than underwater breathing. Skilled divers may be able to use available oxygen more effectively through a combination of physiological adaptations and extensive experience. Presenting their abilities accurately makes the scientific findings more interesting rather than less remarkable.
It is equally important to avoid describing the Bajau as biologically uniform. Not every person belonging to a Bajau community is a professional diver, and individual characteristics vary just as they do in every human population. The 2018 study identified statistical differences between groups rather than a feature guaranteed to appear identically in every individual. Population-level genetic research examines patterns and averages, not absolute rules about every member of a community. This distinction prevents scientific findings from being transformed into stereotypes about an entire ethnic or cultural population.
What researchers discovered is remarkable without requiring exaggeration. Bajau participants in the study had larger spleens on average than the neighboring comparison population, and genetic analysis revealed evidence consistent with natural selection. These findings provide a plausible biological contribution to the extraordinary breath-hold diving abilities observed among some experienced Bajau divers. At the same time, cultural traditions, lifelong practice, individual physiology and the normal human diving response remain important parts of the explanation. The scientific picture is therefore more complex than the idea of a single special gene.
The Bajau study offers a compelling example of the relationship between human culture and biology. A way of life centered heavily on marine resources can shape daily behavior and the skills passed between generations. Over longer periods, environmental pressures may also influence which inherited characteristics become more common within a population. Researchers studying the Bajau found evidence suggesting that both processes may have operated together. Their findings provide scientists with another opportunity to understand how adaptable the human body can be when populations live under distinctive environmental conditions for many generations.
This account is based on published scientific research and publicly available institutional information about Bajau physiology and population genetics. It is written entirely from an outside, third-person perspective and does not claim that the publisher belongs to a Bajau community, personally observed traditional divers, or speaks on behalf of communities in Indonesia or elsewhere in Southeast Asia. It also avoids describing genetic variation as a completely “new mutant gene,” because that is not what the research established. The evidence instead supports a more precise conclusion: researchers found larger average spleen size and genetic signatures consistent with natural selection in a population with a long-standing tradition of breath-hold diving.
