Hello,

Yes, humans have evolved smoke resistance because humans carry a genetic mutation in the AhR gene that reduce our sensitivity to cancer causing chemicals found in wood smoke.

The AhR gene codes for aryl hydrocarbon receptor that helps regulate our response to carcinogenic polycyclic aromatic hydrocarbons often found in wood smoke.

The AhR is a ligand-activated transcription factor in eukaryotic cells that alters gene expression in response to a wide range of exogenous and endogenous molecules including the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD).

AhR also regulates the function of proliferative factor E2F. TCDD activates physical interaction between AhR and pRb promoting binding to E2F and stops cell-cycle. Also, TCDD stimulates interaction between AhR and p300 which leads to displacement of p300 from E2F sites.

I hope this is helpful.

Best.

You ask 3 questions. Malcolm Nobre only answered your last question.

A few notes with that answer:

- Cigarette smoke and wood smoke are quite different. Cigarette smoke has many carcinogens regardless of whether the tobacco was exposed to any pesticides.

- Observed resistance at molecular level does not mean removal of 100% of the risk associated with wood smoke. After all evolution due to exposure to wood smoke there is still an association between exposure to wood smoke and cancer. Resistance is at most partially preventing cancer risk.

I think that the answer to your first question (Is the carcinogenic effect of smoking solely due to pesticides?) is therefore: No!

PLEASE don't let anybody put their life at risk due to a sense of reassurance from smoking pesticide free cigarettes.

I don't know of any research (but I am not aware of all research on this topic) that has tried to observe any difference in cancer risk associated with pesticides in cigarettes. I expect that the reason for that is that no researcher believes that there is any practical possibility to discern a risk difference. If pesticides in cigarettes would cause any cancer, a researcher considering investigating that, would still have to conclude that the cancer risk from the rest of the cigarette is so very much higher that it is practically impossible to demonstrate the separate effect of pesticides in cigarettes.

Furthermore, the evidence of a relationship between smoking and lung cancer started to show already to an extent to cause concern in the early 1950s (see e.g. https://www.cancer.org/latest-news/the-study-that-helped-spur-the-us-stop-smoking-movement.html)

An important reason for why it was not so easy to establish the evidence for smoking causing cancer, is the decades between exposure to smoking and the resulting cancer. I would say that those decades of delay provide some evidence that cigarettes without lindane and DDT also cause lung cancer, because lindane and DDT were not used on crops before 1945.

Pesticides are obviously not without harm. However when consider the choice of either stopping smoking or switching to organic only, for your personal health it is overwhelmingly preferable to stop smoking.

Next to that, environmental impacts seem a much more important concern than the health effects on humans of their consumption of pesticides on agricultural products.

Dear Malcolm Nobre , Usman Abid

I have added my response to the "discussion" similar to the above "technical question":

https://www.researchgate.net/post/Is_the_carcinogenic_effect_of_smoking_solely_due_to_pesticides_Is_there_any_evidence_that_ecological_tobacco_causes_cancer_in_humans2

From the discussion similar to this question:

Dear @Robert Boer

I think, there should be a distinction between, what is smoke carcinogens in rodents and what is smoke carcinogens in humans. I think, you missed that point in my question, when you write:

”Cigarette smoke has many carcinogens regardless of whether the tobacco was exposed to any pesticides.”

And I think, you can’t know that cigarette smoke ”regardless ...” has many human-carcinogens, without knowing the effect of humans smoking ecological tobacco.

The carcinogenic effect of smoking tobacco plus pesticides can be either due to tobacco, due to pesticides or due to both tobacco and pesticides. It is at present impossible to conclude which, as @Usman Abdid (partly) writes.

From this I will of course not recommend anyone to start smoking. However, I will strongly recommend smokers, who really want to smoke or can’t stop to smoke, to smoke ecological tobacco. In two of the three possible cases above it would be healthier. I will strongly urge health authorities to make the same recommendation. And I will strongly urge politicians to lower tax on ecological tobacco or only increase tax on non-ecological tobacco. I think, that this could save many lives. - Smokers lives also matter !

I only used DDT and Lindane as examples of pesticides. Here are many more, of which many are more than likely to cause cancer when inhaled (warmed, heated and/or incompletely combusted) by smokers:

”Up until the 1940s inorganic substances, such as sodium chlorate and sulphuric acid, or organic chemicals derived from natural sources were still widely used in pest control. However, some pesticides were by-products of coal gas production or other industrial processes. Thus early organics such as nitrophenols, chlorophenols, creosote, naphthalene and petroleum oils were used for fungal and insect pests, whilst ammonium sulphate and sodium arsenate were used as herbicides. The drawback for many of these products was their high rates of application, lack of selectivity and phytotoxicity9. The growth in synthetic pesticides accelerated in the 1940s with the discovery of the effects of DDT, BHC, aldrin, dieldrin, endrin, chlordane, parathion, captan and 2,4-D”. (1)

”In 1934 farmers in the U.S. used the following insecticides –

• Arsenicals, 80-90 million pounds
• Sulfur, 73 million pounds
• Kerosene, 10 million gallons
• Mineral Oil Emulsion, 40 million pounds
• Naphthalene and paradichlorobenzene, 21 million pounds
• Pyrethrum, 10 million pounds
• Nicotine sulphate, 2 million pounds
• Rotenone, 1.5 million pounds.” (2)

So there were good reasons to concern in the early 1950s.

However:

”DDT, Lindane Can Cause Cancer, WHO Says.” (3)

1) http://agrochemicals.iupac.org/index.php?option=com_sobi2&sobi2Task=sobi2Details&catid=3&sobi2Id=31

2) https://livinghistoryfarm.org/farminginthe30s/pests_03.html

3) https://time.com/3931725/ddt-lindane-cancer-who/

Further links:

Divergent Ah Receptor Ligand Selectivity during Hominin Evolution : https://academic.oup.com/mbe/article/33/10/2648/2925595

Where there's smoke -- and a mutation -- there may be an evolutionary edge for humans : https://www.sciencedaily.com/releases/2016/08/160802192629.htm

https://www.beyondpesticides.org/resources/pesticide-induced-diseases-database/cancer

Pesticides and Their Impairing Effects on Epithelial Barrier Integrity, Dysbiosis, Disruption of the AhR Signaling Pathway and Development of Immune-Mediated Inflammatory Diseases

Article Pesticides and Their Impairing Effects on Epithelial Barrier...