Tehran black rain, nicotine genetics, Neanderthals interbreeding and vitiligo therapy explored by Naked Scientists

This Naked Scientists episode covers four interconnected science stories: how black rain from Tehran’s oil facility strikes may affect health, genetic variants linked to nicotine addiction, evidence of interbreeding between Homo sapiens and Neanderthals—especially on the X chromosome, and a new vitiligo therapy using a JAK inhibitor cream called Opzelura. Experts discuss mechanisms, data gaps, and potential public health implications, offering a window into how genetics, environment, and medicine intersect in human health and evolution.

Overview

The Naked Scientists episode guided by host Chris Smith surveys four major science threads spanning environment, genetics, anthropology and dermatology. The program opens with a discussion on air quality and health in conflict zones, then moves to a genetics-driven exploration of nicotine addiction, followed by an ancient DNA study on Neanderthal and modern human interbreeding, and ends with a medical advance in treating vitiligo. Throughout, experts weigh both the science and the practicalities of measuring health impacts in settings of political instability, complex gene-environment interactions, and long timescales for public health effects.

"the boundary layer, which is kind of like the bottom of the atmosphere during nighttime in particular, pushes air down into the city" - Doug Weir, Director, Conflict and Environmental Observatory

Environmental Health in Conflict: Tehran's Black Rain

The discussion centers on residents in Tehran reporting black rain following strikes on oil facilities. Environmental scientists explain how fires emit a plume of pollutants that mix with moisture in the atmosphere and eventually return to Earth as rain. The boundary layer at night can trap pollutants near ground level, concentrating exposure for a densely populated city of about 9 million people. The pollutants mentioned include carbon monoxide, sulfur dioxide, nitrogen oxides, volatile organic compounds, soot and trace metals. The debaters highlight that such incidents are under-documented, yet the health risks—acute and long-term—are significant. They also discuss how fires and munitions contribute to a broader mix of urban air pollution that can affect respiratory health, especially among vulnerable groups. Long-term risk factors include carcinogenic compounds such as polycyclic aromatic hydrocarbons, furans and dioxins. Monitoring in conflict settings is challenging, and the potential for soil and groundwater contamination remains a pressing concern, particularly if pollution dries and is re-entrained as dust during different seasons.

Genetics and Nicotine Addiction: Variants That Reduce Smoking

The episode then shifts to a genetics-centric study described by Gonzalo Abecasis and colleagues from the Regeneron Genetics Center. The researchers catalogued protein-coding variations across genomes, analyzing about 150,000 individuals from Mexico City, including roughly 40,000 current smokers, to link gene variations with the amount smoked. A key finding was a variant in a subunit of brain nicotine receptors that strongly reduces smoking. Individuals with one copy smoked a little over five cigarettes per day on average, dropping to about four per day with one copy, and to roughly one cigarette per day with two copies, an overall reduction of about 80%. The team discusses possible mechanisms—whether the variant dampens the reward signal or shortens the duration of nicotine's effect—and considers how these insights could guide drug development aimed at mimicking the effect to help people cut back on smoking. The researchers emphasize that this line of work could ultimately support strategies to reduce smoking prevalence, given that a substantial fraction of smokers express a desire to quit.

"our general approach is we try to read every protein coding letter. So the genome, as you said, is about 3 billion letters" - Gonzalo Abecasis, Regeneron Genetics Center

Interbreeding Between Humans and Neanderthals: X Chromosome Enrichment

The program then covers Neanderthal ancestry analyses, using three high-quality Neanderthal genomes to compare with modern human genomes. The research team differentiates regions that flowed from Neanderthals into modern humans from those that flowed the other way. They date some modern human ancestry in Neanderthals to around 250,000 years ago, implying a much earlier admixture than the later Neanderthal-to-human exchanges that left present-day Neanderthal ancestry in non-African populations. A striking finding is the enrichment of modern human ancestry on the Neanderthal X chromosome, approximately 62% more than elsewhere in the Neanderthal genome, which led the researchers to propose a scenario in which Neanderthal mating with anatomically modern human females was more common than the reverse. The discussion is grounded in the availability of multiple Neanderthal genomes and diverse modern human data, notably from sub-Saharan Africa, to root the directionality analysis.

"there is a lot more modern human ancestry on the X chromosome than everywhere else in their genome. It's about 62% more modern human ancestry" - Daniel Harris, University of Pennsylvania

Vitiligo Therapy: Opzelura and Ruxolitinib

The final scientific thread examines vitiligo, an autoimmune condition that causes depigmented patches on the skin. The NHS-approved repigmentation therapy Opzelura uses the JAK inhibitor ruxolitinib as a topical cream. When applied to patches for several months to over a year, the treatment can promote repigmentation by dampening inflammatory signals, allowing pigment-producing melanocytes to repopulate the skin from surrounding areas. In some cases the pigment returns to around 90% of the original color, although complete repigmentation is not always achieved. The discussion underscores that vitiligo can carry psychosocial burdens, given its visible nature and the association with autoimmune comorbidity. The expert, Victoria Elithiriadou, explains the mechanism and potential cosmetic outcomes of treatment with Opzelura.

"the active ingredient in it is ruxolitinib, which is what we call a JAK inhibitor. When you apply it on the white patch, it can bring the color back in this patch" - Victoria Elithiriadou, Dermatologist and spokesman for the British Association of Dermatologists

Wrap-Up and Context

The episode closes with reflections on environmental remediation after conflict, the high cost and long timelines for cleaning up polluted sites, and the importance of cross-disciplinary collaboration between the health and environmental communities to monitor long-term health outcomes. The hosts acknowledge data gaps in conflict zones, displaced populations, and the need for sustained investments in health surveillance, environmental monitoring, and evidence-based policy responses. They also invite listener support for the Naked Scientists program and highlight avenues for feedback and donations.

Final Thoughts

Across these stories, the program emphasizes how genetics, environment and medical advances intersect to influence health, behavior, and the trajectory of human evolution. The discussions illustrate how modern technology—genomic cataloguing, ancient DNA analysis, and targeted pharmacology—can illuminate complex biological and societal questions while reminding us of the practical challenges of data collection, ethics and public health implementation in real-world contexts.