Maverick Mini-Bytes · Oct 18, 2026
Forests and coral reefs aren’t the only ecosystems losing species. Physician-microbiologist Martin Blaser argues that a quieter collapse is under way inside our own bodies, and that it may help explain why asthma, allergies and obesity have surged since the mid-20th century.
Based on: The hidden mass extinction happening inside your body — Martin Blaser | Curiosity Lab (Big Think, October 2026) [1]
The byte
Humans co-evolved with a community of gut, skin and mouth microbes over millions of years. In just a few generations, antibiotics, C-sections, formula feeding and low-fiber diets have thinned that community out. Blaser, author of Missing Microbes [3] and co-author of the 2025 review The Invisible Extinction [2], believes the loss is real, measurable, passed from mother to child, and a likely contributor to many fastest-growing chronic diseases.
A zoo with emptier cages
Blaser’s favourite analogy is a zoo. Every one of us still carries microbes, but over time some cages have emptied: fewer lion species, fewer monkey species, fewer birds. The zoo is still open; it’s just less diverse.
The clearest evidence came from his wife and collaborator, Maria Gloria Dominguez-Bello. Her team sampled a Yanomami village in the Venezuelan Amazon that had no recorded contact with outsiders. Their gut and skin microbiomes were the most diverse ever measured in any human group, roughly double that of people in the United States [5]. Blaser reads that as a sign that we may have lost around half of our ancestral microbial diversity.
Breast milk: food made for microbes
One of nature’s strongest hints that these microbes matter is in breast milk. It contains a whole family of sugars (human milk oligosaccharides) that babies can’t digest at all. Their job is to feed beneficial gut bacteria in the infant [12]. Every mammal does something similar. Evolution doesn’t waste calories on guests it doesn’t need.
The farm-animal clue
Blaser’s “eureka” moment came about 25 years ago, when he remembered that farmers feed low-dose antibiotics to livestock to fatten them for market. Three farm observations stood out:
- Only antibacterial work. Antivirals and antifungals don’t promote growth.
- It works on almost every animal tried, even insects.
- Earlier is stronger. The younger the animal when dosing starts, the bigger the effect.
His lab tested the idea in mice. Farm-level antibiotic doses increased body fat [6]. A short course of low-dose penicillin in early life was enough to cause lasting metabolic changes, even after the microbiome itself recovered.
Transferring the altered microbes into germ-free mice reproduced the effect, showing the microbes rather than the drug were doing the work [7]. Combined with a high-fat diet, the effect wasn’t additive but amplified: in Blaser’s words, “2 plus 2 equaled 9.”
Disrupting growth-hormones. Bacterial fermentation in the colon supplies roughly 5–10% of our calories. Antibiotics act as a selective force, favouring a more energy-efficient microbial community. Nudge that balance during a critical growth window and you may shift a child’s metabolic trajectory. Newer unpublished work from his lab points to disruption of growth hormones such as IGF-1.
From mice to millions of children
In about 14,500 children from Olmsted County, Minnesota, antibiotic exposure before age two was associated with higher odds of all ten chronic conditions studied, including asthma, eczema, food allergy, obesity, ADHD and learning disabilities. Eight associations were statistically significant, and risk rose with the number of courses [8]. Blaser says follow-up analyses in roughly half a million Danish children and over a million children in England pointed the same way, particularly for asthma and allergy.
Born with less, and passing on less
A baby is born essentially microbe-free and gets its founding microbes from its mother during vaginal birth. Delivery mode is the main factor shaping a newborn’s first microbial community [9]. C-sections, formula feeding and early antibiotics all disrupt this hand-off, at precisely the moment a child is calibrating its metabolism, immune system and brain.
The ratchet effect. In 2009, Blaser and Stanley Falkow proposed that if a mother loses microbes before giving birth, she can’t pass them on, and her daughter starts life with fewer [4]. Repeat over generations and diversity steps down each time. Stanford researchers later showed exactly this in mice: on a low-fiber diet, gut diversity fell further with each of four generations, and restoring fiber alone couldn’t bring the lost species back. Only reintroducing the missing microbes plus fiber did [11]. Blaser estimates the US is about seven generations into the modern era; rapidly industrializing countries are catching up fast.
The takeaway: heredity isn’t only about the genes we get from our mothers, but also about the microbes (and their genes) we inherit.
Stop digging, start filling in
Blaser’s prescription has two parts.
Stop digging. Use antibiotics more carefully. He notes that Sweden uses a fraction of US antibiotic volumes without worse outcomes, and that prescribing rates vary widely even across US regions, a sign of medical culture rather than medical need. Patients can help by not demanding antibiotics for illnesses that don’t need them.
Start filling in. Dominguez-Bello’s “vaginal seeding” technique, swabbing C-section babies with maternal vaginal fluid, partially restores their early microbiome [10]. In the longer term, science will need to identify which microbes each person is missing and how to return them, which is part of why the pair helped launch an international microbe vault to preserve ancestral strains [2].
On your plate: fiber, fiber and more fiber, plus as varied a diet as possible, because different plant foods feed different microbes. Blaser also flags open questions about antibacterial food preservatives and chlorinated water. Both bring real benefits, but their effects on the microbiome are largely unstudied.
The Maverick take
The disappearing-microbiota hypothesis has moved from fringe to mainstream in 25 years, backed by mouse experiments, multi-generation studies and large population cohorts. But caution is warranted. Much of the human evidence is observational, and Blaser himself says microbial loss is one important factor in these epidemics, not the whole story. Antibiotics remain lifesaving drugs; the lesson is to use them wisely, not to refuse them. And be skeptical of the booming market in microbiome tests and supplements: Blaser warns that very few products have solid evidence behind them.
Mini-Bytes takeaways
- Industrialized people appear to carry far less microbial diversity than isolated traditional communities.
- Early life (birth to around age two) is the critical window for both the microbiome and the child’s metabolism, immunity and brain. Avoid antibiotics!
- Early-life antibiotics are linked to obesity, asthma, allergies and neurodevelopmental conditions in large cohorts, and cause lasting metabolic change in mice.
- Losses can compound across generations, and diet alone may not reverse them.
- What you can do: use antibiotics only when truly needed, support breastfeeding where possible, and eat a fibre-rich, diverse diet.
References
- Big Think. The hidden mass extinction happening inside your body — Martin Blaser | Curiosity Lab. October 2026. https://www.youtube.com/watch?v=k2yIwHYNnmI · Transcript: https://bigthink.com/series/conversations/martin-blaser-microbes/
- Blaser MJ, Dominguez-Bello MG. The Invisible Extinction. Annu Rev Microbiol. 2025;79:311–334. doi:10.1146/annurev-micro-051024-092416
- Blaser MJ. Missing Microbes: How the Overuse of Antibiotics Is Fueling Our Modern Plagues. Henry Holt; 2014.
- Blaser MJ, Falkow S. What are the consequences of the disappearing human microbiota? Nat Rev Microbiol. 2009;7(12):887–894. doi:10.1038/nrmicro2245
- Clemente JC, et al. The microbiome of uncontacted Amerindians. Sci Adv. 2015;1(3):e1500183. doi:10.1126/sciadv.1500183
- Cho I, et al. Antibiotics in early life alter the murine colonic microbiome and adiposity. Nature. 2012;488:621–626. doi:10.1038/nature11400
- Cox LM, et al. Altering the intestinal microbiota during a critical developmental window has lasting metabolic consequences. Cell. 2014;158(4):705–721. doi:10.1016/j.cell.2014.05.052
- Aversa Z, et al. Association of infant antibiotic exposure with childhood health outcomes. Mayo Clin Proc. 2021;96(1):66–77. doi:10.1016/j.mayocp.2020.07.019
- Dominguez-Bello MG, et al. Delivery mode shapes the acquisition and structure of the initial microbiota across multiple body habitats in newborns. PNAS. 2010;107(26):11971–11975. doi:10.1073/pnas.1002601107
- Dominguez-Bello MG, et al. Partial restoration of the microbiota of cesarean-born infants via vaginal microbial transfer. Nat Med. 2016;22(3):250–253. doi:10.1038/nm.4039
- Sonnenburg ED, et al. Diet-induced extinctions in the gut microbiota compound over generations. Nature. 2016;529(7585):212–215. doi:10.1038/nature16504
- Bode L. Human milk oligosaccharides: every baby needs a sugar mama. Glycobiology. 2012;22(9):1147–1162. doi:10.1093/glycob/cws074
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