Overstates scientific confidence: The claim is phrased in a way that suggests there is a causal relationship between genetic mutations, enlarged spleen, and enhanced diving ability. However, more data is required to establish this causality.
FULL CLAIM: “A unique genetic mutation in the Bajau people of South-East Asia” allows them “to dive underwater for hours each day.” ; The adaptation “includes the development of larger spleens”.
REVIEW
An Instagram post from June 2024 claimed that the Bajau people, a Southeast Asian ethnic group, evolved to become remarkable breath-hold divers thanks to a “unique genetic mutation”. The mutation associated with an enlarged spleen, which allows them to breath-hold dive for several hours per day. The post received more than 22,000 likes by the time of this review’s writing.
This claim is mostly accurate and is based on results published in 2018 by Ilardo et al.[1].
That said, the post’s labeling of this information as news is unusual, given that reports of the study first appeared about six years ago in National Geographic and The Atlantic. The account that made the post identifies itself as a “News/media company” named Intels, but we were unable to find any information about who runs the account or the website associated with the account (https://intelsmedia.com). The website also provides no information about its writers or its editorial policy. We found a few instances in which the website had copied content from other news outlets; for example, it copied this CNBC article without proper attribution.
In brief, while the particular post by Intels contains mostly accurate information, the account itself exhibits several red flags that users should be aware of when evaluating its credibility.
Study found gene mutations linked to larger spleen sizes and improved oxygen availability in the Bajau people
The study was led by Melissa Ilardo, a scientist currently working at the University of Utah studying genetic adaptations in indigenous populations.
In an interview with the BBC, Ilardo described the Bajau people as a semi-nomadic group from Southeast Asia who live in boathouses and “visit land only occasionally”, so their lifestyle is mostly centered around the sea. As such, Bajau divers could spend up to 60% of their work day—about five hours—fishing underwater. According to National Geographic, some Bajau divers can spend several minutes without breathing, when most people would be able to do so for around one minute.
To understand how the Bajau people were capable of such a feat, Ilardo and colleagues measured spleen size in 43 Bajau individuals. The authors focused on the spleen because previous research associated this organ with breath-hold diving ability in mammals. For example, one comparative study reported a correlation between the spleen size and length of dive duration in seal species[2].
The spleen stores red blood cells and many mammals have the ability to release those cells into the blood circulation by contracting the spleen, which increases the body’s ability to transport oxygen[3].
Although spleen contraction is not as developed in humans as in other mammals, one study observed spleen contraction and an increase in circulating red blood cells in Korean breath-hold divers after they went underwater[4]. To illustrate this, Ilardo described the spleen as a kind of “scuba tank” of oxygenated blood that activates during breath-hold diving.
Ilardo and colleagues observed that the spleen in the Bajau people was bigger (175 cubic centimeters of volume on average) than the spleen in the Saluan people (100 cubic centimeters of volume on average). The Saluan people are close geographic neighbors of the Bajau, living on the shores of the same peninsula, but only minimally interact with the marine environment.
The authors also found that spleen size was comparable between diving and non-diving Bajau people. This is important as it suggests that the enlarged spleen of Bajau people isn’t the result of intense training from breath-hold diving, but rather a genetic trait shared by a large part of the population.
Finally, the authors identified mutations in a gene called PDE10A in the genome of the Bajau people. This gene is associated with enlarged spleen size. Follow-up research published in 2021 showed that mice with lower levels of PDE10A protein had an enlarged spleen, similar to what was observed among the Bajau people[5].
From all these observations, the authors suggested that genetic mutations occurring in the Bajau people over thousands of years allowed them to develop remarkable diving abilities and to be particularly adapted to a sea-centered lifestyle.
Other researchers praised the importance of the study on the Bajau people, but pointed out that more data would be required to establish a causal association between the natural selection of PDE10A mutations, an enlarged spleen, and enhanced diving abilities.
There are also other forms of evolution occurring in humans to adapt to low oxygen levels. Research has shown that Tibetans adapted to low-oxygen altitudes in part from the natural selection of a specific variant of the gene EPAS1, which regulates the body’s production of hemoglobin, responsible for carrying oxygen in the blood[6,7].
Archeologist Mark Aldenderfer told Science Magazine that the cases of Tibetans and the Bajau people illustrate that “natural selection continues to work on human populations”.
REFERENCES
- 1 – Ilardo et al. (2018) Physiological and Genetic Adaptations to Diving in Sea Nomads. Cell.
- 2 – Mottishaw et al. (1999) The Diving Response Mechanism and its Surprising Evolutionary Path in Seals andSea Lions. American Zoologist.
- 3 – Stewart & McKenzie (2002) The human spleen during physiological stress. Sports Medicine.
- 4 – Hurford et al. (1985) Splenic contraction during breath-hold diving in the Korean ama. Journal of Applied Physiology.
- 5 – Ilardo et al. (2022) An Erythropoietin-Independent Mechanism of Erythrocytic Precursor Proliferation Underlies Hypoxia Tolerance in Sea Nomads. Frontiers in Physiology.
- 6 – Huerta-Sánchez et al. (2014) Altitude adaptation in Tibetans caused by introgression of Denisovan-like DNA. Nature.
- 7 – Beall et al. (2010) Natural selection on EPAS1 (HIF2alpha) associated with low hemoglobin concentration in Tibetan highlanders. PNAS.
