Since humans are not necessarily the main competition, food source or predator for a lot of life forms, you’d assume a lot of single celled organisms, insects, plants and animals produce poisons and toxins that are deadly to certain life forms, but may be totally harmless to us.
Antibiotics for example, many are created from bacteria to fight other bacteria. They are pretty much harmless to us.
RNA interference, not really applicable to us unless our own RNA is involved (I think this is mostly a defense against viruses so human RNA wouldn’t be affected).
Are there bigger life forms like plants or animals that produce toxins that may be extremely toxic to its natural predator, but totally harmless to humans?
The bacteria which turn milk into yogurt produce lactic acid. Most humans can eat yogurt without ill effects, but the acidity of the yogurt inhibits the growth of other bacteria or molds.
I believe most all spiders produce venom … but only a few are poisonous to humans … unless you live in Australia … where all the animals kill humans … or so I’ve heard …
Most spices and flavorings we use are actually compounds made by plants to defend against insects, other herbivores, or fungi. They are not toxic to us in small doses. Likewise the active compounds in marijuana and other drugs.
By that logic, does oxygen count? It’s certainly toxic to a class of anaerobic organisms that were the dominant form of life before the build up of oxygen in the atmosphere, even though it isn’t toxic to humans (at normal atmospheric concentrations).
Not only are all spiders venomous, but their venom is toxic to humans. It’s just that for most spiders, it’s not potent enough to do more than give a human an irritating itchy welt. Plus, of course, most of them wouldn’t even consider us an appropriate target for a bite.
Which brings up another category, substances which are toxic to humans and insects alike, but which typically occur in doses too small to do significant harm to a creature our size.
From an evolutionary efficiency perspective animals or plants should develop defenses, including toxins, appropriate to their needs and not much farther past that. Certainly there will be exceptions, but they’ll be comparatively rare.
IOW, the venom dose of a small snake is suitable in (toxicity * dosage) to subdue mice, not lions. The venom dose of a larger snake would be enough to take out guinea pigs or young small mammals. But not elephants.
etc. Once in awhile a species stumbles upon some venom that whole classes of animals have no defense against. Essentially it targets a chink in the biochemical armor of, say, all mammals. That’s where you get things like Inland taipan - Wikipedia. Which (of course) hails from Australia.
There aren’t many species that produce toxins that are toxic to its natural predator. Usually, the natural predator is a species that have evolved to be immune to the toxins produced by the prey. For example, glucosinolates are chemicals that give broccoli, brussel sprouts, etc their bitter taste. These plants produce it because it’s toxic to most insects. But some insects have evolved to be resistant to the toxin, and now only eat those plants. Similarly, onions, garlic etc contain sulfer compounds that are toxic to many insects and even some mammals (e.g. dogs), but others (e.g. humans) tolerate and even enjoy those chemicals.
When I was a kid, I was always told that there are only four venomous snakes in the USA: the rattler. the cottonmouth, the copperhead and the coral snake.
Today, we know that isn’t true. MANY snakes, including “harmless” ones that are sold as pets, do in fact have SOME venom. It just so happens that a garter snake doesn’t produce enough venom to people hurt most people.any real harm.
Similarly, MOST frogs and toads have SOME toxins in their skin. Poison dart frogs aren’t unique. It just so happens that most frogs don’t produce toxins potent enough to sicken people, let alone kill them.
Not that you’re wrong, but I think you’re overlooking the obvious - even if snakes have no need to eat lions, they still benefit from a type/amount of venom that is sufficient to make sure lions don’t eat snakes. Especially true if they employ some kind of a warning system to make sure everything stays far away, and you see snakes doing just that with loud hissing, hooded cobras, rattling rattlers and colorful patterns.
Theobromine is actually nearly as poisonous to humans as it is to dogs. The differences are just that, first, most humans have more body mass than most dogs, and second, humans will exercise more restraint in their eating than dogs will.
Wikipedia says dogs metabolize theobromine more slowly than humans, though there are no numbers quoted. I think the implication is that it’s easier for dogs to accumulate a dangerous dose in their system.
I didn’t know this so I looked up the details. The LD[sub]50[/sub] for humans is about three times that for dogs in terms of mg/kg of body weight (1000 vs. 300). So a snack having 2400mg of theobromine would be fatal to a 9kg (20 lbs) dog. That’s about 6 oz. of unsweetened baking chocolate. For a 68kg (150 lbs) human, the lethal amount would be about 10.5 pounds. However, adverse affects can appear before you get anywhere near 10.5 pounds.