Hermit Crabs and Humanity – The Ultimate Evolutionary Convergence

This post is very speculative (a true scientist’s way of saying “it is fun to think about these things”).

Disclaimer: Please keep in mind that with respect to evolutionary theory, I am an interested layperson. You should consult your evolutionary scientist if in doubt about any of the things that you are about to read… (:-)

One of the best-known examples of evolutionary processes is the concept of convergent evolution. Briefly, convergent evolution can be summarized as “similar solutions to a common problem”. In other (more scientific) words, convergent evolution occurs when lineages of organisms not closely related develop similar traits in response to similar environmental challenges. It is important to keep in mind though, that how closely related any two species of organisms may be is subjective. After all, the best available evidence indicates that all living things on earth share a common ancestry; the farther back in time we look, the more closely related all forms of life are.

One of the classic examples of convergent evolution is the very close morphological similarities between three general classes of organisms: mammals, represented by dolphins, fish, represented by sharks and an extinct class of aquatic reptiles, the ichthyosaurs. The fact that convergent evolution happened is immediately apparent in these cases. All three classes of organisms have the same general shape, a muscular cylinder-like shape with an assortment of flippers and a tail. Taken together, these characteristics make all of them excellent, fast swimmers, which is a very good thing if you live in the ocean. This example of convergent evolution is rarely challenged by scientific types. However, in many other cases, convergent evolution is not that self-evident. In order to ellaborate, I need to take a very brief detour to explain a couple of concepts.

One of the main components of evolutionary change is genetics; the second one is the environment and a third one is the differential survival of organisms in a population due to the interaction of the products of their genetic material with environmental conditions (breathe Baldscientist, breathe!).

The genetic endowment of any living being is its genotype, which is DNA in this planet of ours (Dear virologists, please do not send me an email; yes, many types of viruses use RNA as their genetic material, but I am not counting viruses as “alive”).

When information coded in the genotype is expressed, we call it the phenotype. We usually associate phenotypes with physical appearance as in the example we saw before with dolphins, sharks and ichthyosaurs. Other phenotypic traits include big vs small, tall vs short, blue eyes vs brown eyes, etc., for example. Even then, it is not that simple because virtually every phenotype can display intermediate stages. For example, people are not only 5, 6 or 7 feet tall, there’s everything in between.

There are some additional considerations that we must keep in mind when we think about phenotypes. Very rarely a given phenotype is controlled by a single gene; in most cases there are multiple genes involved. Also, let’s suppose, getting into the spirit of the Olympic games, that a child is born with genes that will help her to excel in a given sport, say, the 100-meter dash. If the child gets sick during a critical period of her development or she grows under nutritional deprivation the genes may be there, but the environment will not “cooperate”, in a manner of speaking.

Another aspect of phenotypes is that they are not limited to physical appearance. The biochemistry, physiology and even the behavior of an organism are phenotypes as well. In this latter case, an especially interesting example of convergent evolution is the social behavior of many species of ants and termites and the social behavior of the naked mole rat. It is remarkable how these very different kinds of organisms (insects and mammals respectively) evolved such similar surviving strategies.

Enter the hermit crab.

Hermit crabs are really cute critters. In contrasts to most crabs, they are not protected by a hard shell, therefore they have developed a very interesting behavior. They find their own hard protection, usually in the form of empty snail shells. Hermit crabs are no thieves or bullies though, as they only occupy (yes, even hermit crabs occupy) empty shells. As they grow, they look for bigger shells, and they keep living their lives like this; they take their home with them wherever they go.

So far, so good.

According to the best astrophysical theories, our sun will go through a stage in which it will slowly turn into a red giant star. The sun will grow in size while at the same time turning colder, but still, it will eventually burn through the first three or four planets in our solar system. Please remember that we live on the third planet…

Don’t start packing just yet. This will not happen until about 5 billion years from now. That said, I can’t help but hope that we humans are still around then and that we will keep developing our culture and cherish everything that made us who we are, even if we may have physically evolved by then. If science and technology keep advancing at the rate they have been for the last 100 years, it is entirely possible that by then, we will have the means to escape the fate of the earth. By the way, I do not think our bodies will evolve into something much different than present general form for a variety of reasons, but we’ll talk about this at another time.

Since I am speculating and speculation is free, I want to go even further. If we ever leave the planet, we would be leaving behind the place where our history happened until then; where all happiness and sorrows occurred. Every smile, every tear, every example of the best and the worst that we have to offer as a species happened right here. I am fully aware that there is a sentimental motivation for this, but who’s to say that when the time comes, we will not have developed the technology to take the earth itself in tow? We may be able, to move the whole planet farther from the sun to a new habitable zone for example. Moreover, if we learn to master gravity we can literally make the famous “Spaceship Earth” concept a reality.

Now, this may take years, centuries even; but if we, as a society, return to the frame of mind of commiting to build something bigger than ourselves, something beyond our life span as individuals, it may just happen. Just think about how we built the pyramids and some of the most majestic cathedrals for example.

In time, when our sun finally withers out maybe we’ll know by then how to build a small artificial sun that will orbit the earth (take that, Copernicus!) or maybe even move the whole earth to another solar system.

If and when that happens, we, just like hermit crabs, will take our home with us. In my humble opinion, this will be one of the most extreme examples of convergent evolution in the rich story of life on earth.

N.B., Incidentally, I think this would make a really nice premise or setting for a science fiction story (hint, hint, PC… (:-)…).



  1. Well, Peter, write like the wind!!!! (:-)

    Debra, “The inner light” is one of my two favorite episodes of ST:TNG. the other one is “Tapestry”… (:-)

    Thanks for the comments!


  2. This could almost be the plot line of another novel but it reminds me of two Star Trek episodes. The first is called, “All Our Yesterdays” and is from TOS while the other, Inner Light, is from TNG. As the sun is expanding into a red giant, it is sending enough uv radiation to render most of humanity sterile and the remaining population is numbered in the thousands. These remaining few are sent back in time to live out their days in history. Of course, the people want their culture remembered and they therefore encrypt their important mythology and stories into viral RNA and send that through various wormholes.

    Eventually, this viral RNA is incorporated into the genome of humans who happen to be folks like Tolken and Lucas etc. making all the really good archetypical stories based upon these long extinct cultures.


  3. Hmmm… that certainly gets me thinking… I like the idea of the mini-sun, as that could be used to make rogue planets habitable. Rogue planets are planets that have been flung free from their parent star and now whiz around the galaxy on their own far-flung, independent orbits.

    It is estimated that there may be twice as many rogue planets as there are stars in our galaxy, or possibly up to a phenomenal 100,000x as many rogue planets as there are stars (see http://en.wikipedia.org/wiki/Rogue_planet ). Give an Earth-size rogue planet an artificial mini-sun and you could take billions of people with you as you explore the galaxy 🙂


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