Brainstorming the evolutionary purpose of some plant orders and families

I’m just trying too insert some provoking thoughts into a lecture on evolutionary biology. It’s enough to start with solanes and euphorbia.
Why is euphorbia there? As far as I’ve checked, it has produced no food for humans, and some for very few insects. Why did it develop such strange reproductive system?
Why has Solanaceae develop such nightmarish pyschedelic poisons?
These two families seem to be from outer space :-)

Potato and tomato nightmares. They say it was difficult to convince people to eat them at first. But. That’s POISON!

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In terms of evolution, it’s herbivores that evolve to take advantage of plants, not plants that evolve to provide anything for humans or other species. Part of the reason for the success of Euphorbiaceae and Solanaceae is that they have chemical defenses that make them less vulnerable to herbivory and thus more likely to survive and produce offspring.

Also, while we might not eat Euphorbia species, we have taken advantage of at least one species in the family Euphorbiaceae. Cassava is one of the world’s most important staple crops. It needs to be soaked and cooked to make it edible for humans.


The organisms most able to pass on their genes are the ones that evolve. There is no purpose to any of it.


In addition to cassava, globally a massively important crop, the mongongo nut or manketti tree (Schinziophyton rautanenii) is a staple food for !Kung San in Botswana. Other euphorbs are used for medicines and a few are edible as well.

Several key things to keep in mind about evolution: it’s not trying to make things “useful” for other species, it has no goal other than for the individual species to reproduce (or perhaps more appropriately, for genes and alleles to be passed on to offspring), and it works with that it has available, so evolution tends to wander down odd pathways determined and limited by the paths it has taken in the past.

Many species that have potent toxins or complex reproductive systems evolved to protect themselves against a wide range of species, except for a select few that they co-evolved with, resulting in very specific and unique relationships.

When there is a discussion of evolution there should never be any portion that implies that species “have a use” or a “purpose”, as that gives a very misguided view of evolution, the process behind it, and it encourages exploitative “this is useful, this is not useful” thinking about the natural world.


If you wouldn´t have said it, I would have. It´s the wrong question to ask in in terms of evlution. I mean… why are humans there? Or any other organism. They just happen to be succesful in spreading their genes…


There are many species of Euphorbias. Some of these plants look like cactus. Cacti are mentioned as almost exclusively from the new world, while Euphorbias are from the old world. In africa, madagascar ? They occupy places on earth which very few plants can survive. Some forest trees are in the Euphorbiaceae family. These trees do not look like euphorbias, maybe the seed pod have some similarities. The trees provide food for small birds and insects. Plants do not always evolve with humans, as human’s existence on earth is not very long. Plants evolve with various creatures. Humans may select various nice garden varieties of euphorbias and those species evolve with humans. The reproduction is quite typical of flowering plants. There are seeds. There are birds and insects pollinating the flowers. Some euphorbias are used as medicine, but the milky sap is known to be toxic in the raw form. Often seen macaques and wild boars feeding on rubber tree seeds. Rubber tree originally from South america.
Solanum plants, I guess from South america. There are some poisonous plants and food crops. A few species may be native to europe and asia. I guess spread by birds or by other means before christopher columbus travelled to the new world. There are some semi-wild and cultivated eggplant species in africa and asia. Articles said deadly nighshade, and Datura metel are very poisonous.


These are very odd questions to be asking–especially for someone preparing to teach evolutionary biology. Before asking those questions, you need to ask this question: Are there mechanisms of evolution that guide evolution to produce traits other than those that improve reproductive success? These are the known mechanisms of evolution:

  1. mutation (a random process, does not occur to meet some desired end goal)
  2. gene flow (the movement of alleles/traits geographically)
  3. genetic drift (this increases frequency of certain traits randomly, not to meet some desired end goal)
  4. non-random mating (this just puts alleles together in certain combinations and doesn’t really increase or decrease frequency of traits over time)
  5. selection (this increases the frequency of traits that confer a reproductive advantage of the organisms as they function within their particular environment at the moment, not to meet some desired end goal)

There are no other evolutionary mechanisms that we know of, and none of these will create organisms with traits that serve some grander purpose. None are goal oriented. Organisms alive today have the traits that they do for no other reason than this: that those were the particular traits, of the many alternative traits produced by mutation, that happened to improve [or did not considerably hinder] the reproductive success of their ancestors within the context of their ancestor’s environment.

Plant toxins typically evolve probably to reduce herbivory. Those that are pyschedelic may just happen to be so just by coincidence. After all, snow can be used to create snowmen, but I doubt that is its purpose. It’s really difficult to know exactly why any particular trait happened to evolve and not another alternative trait. There are often multiple traits that are equally suited to solving a particular problem (for keeping warm for example: hair vs. feathers vs. behaviors that allow organisms to move to locations that are the best temperature all work equally well as we see many birds, mammals, and “cold-blooded” animals doing quite well). It’s just which particular series of mutations occurred along the ancestral lineage of an organism.

Related to this are what we call “just-so” stories. Rather than starting by asking “what is the purpose of this trait?” and then making up a story that sounds good, one always needs to first ask “does this trait have a purpose”?
There are several good articles about “just-so” stories. Here’s one and here’s another.


I think it makes sense to look at plants as their own unique lifeforms, outside of whatever uses people have for them.

It took me some time to appreciate and not be offended about plants like Poison Hemlock (Conium maculatum), Poison Oak (Toxicodensron diversilobum), or Castor Beans (Ricinus communis) growing where I like to hike. Now, I enjoy seeing the cool berries on Poison Oak, even when it means I’ll probably have a rash later…

Evolutionarily, they’re around because they’re able to thrive and reproduce in the environment, not because humans use them or think of them as beautiful. Granted, things like Corn (Zea mays) probably thrive only because of humans and are exactly opposite the topic.


When I taught Parasitology, I told students on the first day of class that the actual name of the class was “Parasite Appreciation” as the goal would be to explore the variety of amazing traits that parasites have evolved.


The idea that organisms or their traits exist to fill a need or reach an evolutionary goal or purpose is a non-normative idea about evolution. Check out this table that summarizes the normative foundations of evolution, compared to some naive beliefs. (Well summarized by @pfau_tarleton)

Screenshot 2022-07-12 155410

Moharreri, K., Ha, M. & Nehm, R.H. EvoGrader: an online formative assessment tool for automatically evaluating written evolutionary explanations. Evo Edu Outreach 7, 15 (2014).


along the lines of what I perceive is your thinking, gorillas or even orangutans should have become the species that would have originated megaprojects and ethics, but we evolved meaningful languages before anyone else :-)

this is some free thinking, I’d say outside the box.

Cassava has less than 2% protein. Maybe together with eggplant it is good for thinking exercise, comparing it to the protein bearing plants.

Or to simply not hinder reproductive success. Not every trait is a result of selection for, sometimes it’s just that the trait wasn’t selected against.


When I teach evolutionary biology, one of the first things I teach my students is to avoid thinking in terms of purpose. Traits don’t have a purpose and taxa don’t have a purpose. Traits and taxa have, under the right circumstances, ecological functions. But the whole idea of purpose is one that needs to be rejected to begin to understand evolution beyond intentional breeding.


I am no educator or a lecturer, and the question has arisen due to having to lead a discussion on investigative ecology, as in invasive species, out of place weeds, and forensic botany.

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I’ve done cursory search on Google scholar. Without compiling a long list of URLs, I would summarize the scan by saying that eggplant and peppers have the classic set of solanaceae alkaloids, albeit at varying, very low levels. Eggplant contains nicotine, especially its notably bitter seeds.
So funny you should mention nightmares, since there are other solanaceae that cause nightmarish hallucinations. Some memory loss. Or urinary problems. So it is for the scaredy cats’ knee-jerk reaction to wake up one day and decide to start a solanaceae-free diet.

mm I mean when they were first exported to countries where edible Solanaceae were not known.

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Here popular story is the opposite, people knew tomatoes and thought potatoes were for fruits too, though it’s likely not a true story, it sounds plausible at least for someone.