SPECULATIVE SCIENCE



Why does tobacco contain nicotine? Does being chemically addictive confer some evolutionary advantage on the tobacco plant? Seth, Edinburgh UK The botanical name of the tobacco plant is nicotiana tabacum and the natives of South America discovered that the leaves when dried and burnt had an interesting taste The fact that the oily sap occurring naturally is carcogenic is incidental at least to the plant. But not of course to the idiots who inhale its fumes. Jack Hill, St Albans England UK Many plants synthesize alkaloids for defense against insects. Nicotine and derivatives are among the earliest known and most potent insecticides. Richard Thompson, Allerod Denmark Nicotine is a highly toxic chemical. However, cigarettes contain obviously much less than is a fatal dose for humans who ultimately tolerate much higher doses of the chemical on continuous use. Smaller animals and insects on the other hand do not tolerate nicotine and it is this fact that confers the evolutionary advantage on the tobacco plant as the leaves tend not to be eaten by animals and insects. In a similar manner, apple seeds contain cyanide in quantities too miniscule to affect humans by their consumption but can be fatal for birds. Thus, birds dont tend to eat apple seeds and there are more seeds for more apple trees. Michelle Groarke, Munich Germany The fact that tobacco contains an addictive substance has ensured that it is a hugely successful species; Humans have chosen to cultivate the plant because of the nicotine, and indeed make sure that weeds and pests may not interfere with its growth. Without the nicotine, tobacco would probably be considered to be just a weed and would not be nearly as successful. The original 'purpose' of the nicotine was probably to poison its natural enemies, which unfortunately it also does to its human cultivists. Chris Wright, Twickenham UK Its addictiveness has led to widespread cultivation by man. So yes, I would suggest that's a evolutionary advantage (although the cocoa plant might disagree every time the american government tries to burn a field or drop caterpillars on it). Craig, London UK If a plant is wounded by a herbivore, a chemical defence mechanism can become activated. This kind of induced plant defence occurs in Nicotiana tabacum (tobacco plant), where the concentration of nicotine already present in the plant becomes increased. Nicotine acts as a toxin by blocking the nicotinic acetylcholine receptors at the neuromuscular junction by competitively inhibiting the binding of the neurotransmitter acetylcholine, threreby preventing the activation of the channel and blocking muscle contraction. Production of nicotine (a poisonous chemical) thus provides protection against being eaten, which is useful since plants cannot run away and don?t have an immune system. As mentioned previously, the addictive properties are incidental to the plant. Michael Calais, London UK Another classic Jack Hill "response" which addresses neither of the questions asked in the most patronising way possible. It is a common misconception that every feature of an organism must have some evolutionary advantage. All that is required is that a particular feature (e.g. the fact that a metabolite is, coincidentally, chemically addictive to some other organisms) is not too great a disadvantage. The human trachea crosses the oesophagus. Definitely not an advantage since it means you can choke, but that's a small enough problem that it wasn't selected out. Simon Blake, Shrewsbury England I have some vague recollection that nicotine apart from being addictive acts as a pesticide (I think an insecticide) with obvious selective advantages. It may be that the fact that it is also addictive is a coincidence. However you might say that since Homo sapiens started have greater environmental influence the addictiveness of nicotine has been of selective advantage by encouraging the forementioned animal species to propagate, cultivate and increase the plant's range of habitats. Roger Humphry, Inverness Scotland Answer the question, Jack, and break the habit of a lifetime. Nicotine is extremely poisonous when ingested, and before the wonderful effects of smoking were discovered, it protected the plant from munchers. Nowadays, of course, it protects the plant even better - the world's enlightened smokers will never let it die. David J Wilson, Albuquerque USA Why is the US government so down on cocoa? I know chocolate is regarded as addictive in some quarters, but this is ridiculous. Mark Power, Dublin If tobacco contains nicotine as an insecticide... To me the real question is why does the tobacco plant contain nicotine and not some other more effective chemical like pyrithinins. Could it be that the nictine content originally was incidental and man has selected out the plants with the best 'kick'. After all its been a few thousand years since its first use! M.Ford, Sussex UK It's intriguing that nicotine is chemically similar to Vitamin B3 or nicotinic acid/nicotinamide, which is undoubtably beneficial to human and animal health. When smokers crave nicotine, is that molecule misperceived by the body as as a healthy substance? Claudia, Muscat, Oman



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