Installment Three, Genetics in the 24th century: The Trouble with the Trouble with Tribbles

Hang on to your hats, Trekkies, because I’m going to go after “The Trouble with Tribbles”. The Trouble with Tribbles was the 44th episode in the original Star Trek series and was written by Science Fiction legend David Gerrold, who also wrote the Martian Child, which was turned into a great movie. Gerrold wrote two of my favorite novels, When HARLIE Was One and The Man Who Folded Himself.

The Trouble with Tribbles has been hailed as one of the best episodes the franchise has ever put out and I can’t disagree. I love David Gerrold. I am a huge fan. (Do not worry. This post does not involve physics of any kind. No need to break out your Calc III notes or bone up on abstract algebra or quantum mechanics or quantum computing. Check your manifolds at the door. It’s all easy peasy science. Oh and check your inner critic and your studly fan powers at the door. This is about the science not the story. The story is beautiful, the science less so. If you have not read the other two installments: click here for installment one and click here for installment two before reading this post.)

The problem with the Trouble with Tribbles is that when a tribble is born, it’s already pregnant1. Thus, the trouble with ‘Tribbles’ is that the inbreeding coefficient would be 0.5, meaning that the parent self-fertalized. Half the child’s chromosomes would have their “partner” chromosomes replaced by a copy of themselves. That means that every tribble born would have a maximum chance of genetic damage. The child would be like a clone of the parent except with massive genetic damage. In other words, there is a very good chance the tribble would not survive birth.

But let’s say that when the male “partner” first impregnates a female tribble that it also gives genetic material for the creation of the fetus that develops inside the tribble being born. That would put the inbreeding coefficient at 0.25 because the egg for the fetus came from the child and the egg for the child came from the mother thus both the sperm and the egg are duplicated. If the father is inbred, and with tribbles you already know that they are, then the coefficient will be higher, almost approaching 0.5. So, even in this scenario, expect genetic damage.

Finally, the more inbred a population, the more likely the coefficient will approach 1. It may even be 1 but it will not exceed 1. (If you believe me about the tribble inbreeding and don’t care about the math, click here.) “The mathematical reason for this is that although the basic formulae for R and F are Σ(1/2)n and Σ(1/2)n+1 respectively, as inbreeding within a line progresses, the correction terms applied to R for inbreeding (see here) gradually become more important and start to reduce the value of R below Σ(1/2)n.” Taken from “THE COEFFICIENT OF INBREEDING (F) AND ITS APPLICATIONS.”

The method of calculating the F coefficient of an individual is similar to that for the coefficient of relationship (R) between two collateral relatives, and involves the tracing of paths between the two parents via a common ancestor. R denotes the proportion of genes that are held in common by two individuals as a result of direct or collateral relationship. Collateral relationship are individuals who are only related through common ancestors, e.g. cousins.

Calculating the coefficient of an individual.

Equation 1 method of calculating the F coefficient of an individual (F measures the probability that two genes are identical by descent from the common ancestor(s) of the two parents).

Directly and Collaterally Related Parents

To sum up, genetically, Tribbles and their offspring would not be genetically viable even with super alien DNA.

Why is this? How do I even know that they have human-like DNA or any type of DNA at all? First of all, the episode The Chase, a story in five acts. The punchline to this story is that 19 races or more in our galaxy have one single progenitor. Thus explaining why every alien in the Star Trek world looks more or less human. Not only morphologically and phenotypically, but also genetically. Don’t forget, they all can interbreed as seen in various episodes starting with Spock in the original Star Trek series. Spock is half human and half vulcan.

Sure there are a few rock creatures. And sure there are a few energy creatures. But on the humanoid worlds, or on most of them, the animals, plants and people are all Earth-like. As Pulaski points out, humans may not like klingon food, but what will kill a human will also kill a klingon. They have the same biochemistry more or less. (Click here for a list of alien foods.) And since we know that Tribbles can eat human grown grain, see The Trouble with Tribbles, we can assume that Tribbles have a similar biochemistry as humans. We also know that the galaxy was seeded with life by one progenitor, it’s a good bet Tribbles have DNA, whether a double helix or a triple helix or just a helix, and that it will obey the laws of genetics.

However, let’s say that the tribbles are original galaxy stock. They evolved separately before the seeding began and adapted to the biochemistry of the progenitors. Well, any organism that reproduces sexually must pass on their genetic traits somehow. If they don’t have human-type DNA they must have an analog to DNA and RNA, for that matter. The math might be slightly different for the tribble DNA-analog but in the end the inbreeding coefficient will produce genetic defects. R and F will eventually get you.

So my conclusion stands, Star Trek is science fantasy at best and fantasy in science fiction drag at worst. But I still love the show. See my two previous posts: Installment One of Physics in the 24th Century and Installment Two of Physics in the 24th Century: the transporter, science fiction or fantasy?

1. This means we can rule out cloning and budding. Pregnant implies two partners. But even if we assume that tribbles bud, then why are there so many phenotypes? It seems unlikely that they reproduce asexually.


  • Alex Silberman says:

    Hang on Mark,

    Why can’t tribbles operate as bacteria or bananas, which are clones of each other? Why must a tribble remain inbred in this manner? Can’t random mutations create ‘mutated’ tribbles, which over time enhance the species?

    Great read as always!


    • Mark LaPolla says:

      Thanks. I’m glad you liked the post. To answer your questions, Alex, they cannot clone or bud, as I said in my post, because they become pregnant. So, budding is out and cloning is out. One of my FB friends suggested that they may pool genes. That might work but even then I think they would become inbred. (I leave the math to the reader as an exercise.) As to your mutation suggestion, that won’t work in the long term because all the mutations you would get would all be harmful. Mind you, most mutations are harmful. This would mean that your tribble population would slowly, over time, become less viable. Sure, in the short run, they might survive to breed. (Actually, that’s guaranteed since all tribbles are born pregnant but those immature tribbles would probably not survive to give birth.) But with the inbreeding coefficient so high, they just wouldn’t survive past the 4th or 5th generation.

  • Steve T says:

    it looks fine but i question your assumptions – sexual reproduction with two parents. what if, as kurt vonnegut maintained in one of his novels, that the actions of 7 individuals were necessary for a pregnancy to occur? with all these tribbles in intimate contact, what if they all pooled their genes?

    • Mark LaPolla says:

      In Vonnegut’s novels, there were still only two physical parents. The rest were more spiritual and only had to exist. In other words, genetics is about the physical parents, not how many are needed to bring a soul into existence. However, your idea of pooling their genes is a good one. But, I think, that eventually, you’ll have more inbreeding. However, this would mean that one tribble would have to have sex with multiple other tribbles and each “father” would contribute part of the genetic code. Which parent decides on how much and what part each would contribute? That is probably too much work to be a good evolutionary choice. But then again, perhaps not. But I still wonder how long it would take for their to be inbreeding? After all, just like in a normal sexual relationship, eventually you read an F of 1. This might take a little longer but I think eventually, given the makeup of tribbles and their reproduction, that you’d also reach 1. (I leave the math to the reader as an exercise.)

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