The Promised Neverland- Demon Evolution

The Promised Neverland– Demon Evolution

The Promised Neverland

SPOILER WARNING for the latest chapters of the Manga

In chapter 120 of TPN we are finally given some insight into the origins of the demons and their need to eat humans to survive. There were a couple of different ways that the manga could have gone with this and I was intrigued that they used a more scientific approach discussing evolution via vertical and horizontal gene transfer.

horizontal gene transfer

Vertical Gene Transfer

Evolution, as I have covered before, is how an organism slowly changes over time as it acquires traits that help it better survive in its environment. The new traits arise from random mutations and any new trait that helps the organism survive and reproduce is going to become more frequent in the population as organisms with that trait have more offspring that also have the trait. For example, when a new mutation grants an insect resistance to a pesticide, the insects that have resistance increase in number while the ones that don’t die off. This continues until almost all of the insects are resistant to that particular pesticide, as was the case with flies and DDT. Now what I just described is actually vertical gene transfer or the passing of genetic traits from parent to offspring.


FYI- vertical gene transfer is not usually used to refer to this process as it is normally referred to as evolution or natural selection.

Horizontal Gene Transfer

Horizontal gene transfer, on the other hand, works a bit differently and instead of passing genetic material from parent to offspring, the genetic material is passed to another individual in the same generation. Additionally, the information is being passed between organisms that are different species. It most common in bacteria and happens via the transfer of plasmids, which I discussed in my post on the quirks of My Hero Academia. To recap, plasmids are extra chromosomal segments of DNA that can be transferred between bacteria and some single celled organisms like yeast.


The plasmids are not necessary for the bacteria to survive, but they often grant additional traits like antibiotic resistance. The plasmids can be transferred from one organism to another via a process called conjugation. In conjugation the plasmid reproduces and is then transferred to another bacteria via an extension of the cell called a pilus.


Now by this point you are probably thinking this is all nice and good but the demons of The Promised Neverland evolved by eating other animals and absorbing their genes and not by reproducing or sharing plasmids with them. As it turns out, bacteria can absorb plasmids and genetic material from the environment around them, as was discovered by the transformation experiments of Fredrick Griffith that showed that you could turn a harmless bacterium into a pathogenic one via the remains of dead pathogenic bacteria.


Oswald Avery expanded on Griffith’s research on transformation proving that it was DNA passing between the dead and live bacteria that was causing the transformation. This of course fits with the demon’s evolving through absorbing the DNA of other organisms. However, by this point I think we can also assume that demons are eukaryotic organisms, given that they for all intents and purposes appear to be large complex multicellular organisms. So how does gene transfer work in eukaryotic organisms?

horizontal gene transfer

Endosymbiotic Theory

If we go by what Norman says in the manga that the demons might have started as bacteria, the first step in their evolution via horizontal gene transfer would be by absorbing plasmids of other bacteria. But bacteria are small single celled organisms that do not form large complex organisms like the current demons we see in the manga. So how did they become the demons we see in the manga?

As it turns out, horizontal gene transfer played a role in the evolution of eukaryotic cells in the real world. If you know anything about eukaryotic cells, you know that the DNA is contained inside the nucleus and the cell contains structures called organelles. Organelles can be thought of as miniature organs that perform a particular function for a cell like our own organs do for our bodies. There are a number of organelles, but there are only 2 that concern us today and they are the mitochondria and the chloroplast. This is because they both contain their own DNA and replicate separately from the rest of the cell. These two organelles are proof of something called endosymbiotic theory.

In a simplified form endosymbiotic theory is the theory that eukaryotic cells arose when a large bacterium ate another smaller bacterium, and instead of digesting it let it live inside of itself. The smaller cell now lived on inside of the larger one granting it new traits like the ability to perform photosynthesis (chloroplast) or more efficiently breakdown sugar (mitochondria).

endosymbiotic theory

It also fits nicely with Norman’s explanation of demon evolution via eating other organisms. However, their evolution didn’t stop there, as horizontal gene transfer allowed them to continue to evolve.

Horizontal Gene Transfer in Multicellular Organisms

Now this is were we get to some very new and interesting aspects of biology. Studies have shown that horizontal gene transfer has happened between various organisms such as:

Bacteria to fungi, plants, and animals

Insects to fungus and round worms

Human to protozoan

Scientists know that these transfers have occurred but the how and why has yet to be determined; it is suspected that DNA transposons are involved. Transposons are segments of DNA that do not like to stay where they are in an organism’s genome and have a tendency to jump around. Think of it like a page in a book that keeps jumping around the book. Lastly, all of this transferring is thought to play a role in the evolution of numerous species, but it is only just now being investigated. In fact, up to 3% of the human genome could be made of transposons. So modern science does still match up with Norman’s explanation of horizontal gene transfer playing a role in the evolution of demons.

Development of Language and Culture

horizontal gene transfer

Now this is where Norman’s explanation starts to go off the rails a bit, as I read that last part stating the demons developed language and culture as a direct result of eating humans and not as a result of their improved mental capacities via gene transfer. It is as if they gained the knowledge as a direct result of eating humans. FYI- while we are on the subject, what about the other intelligent animal species like gorillas or dolphins, as they too would have influenced the demon’s intelligence and development?

By this point you are all probably saying well, duh, you can’t absorb another organism’s knowledge by eating it……

Well, this is where it gets interesting. In the 1950’s and 60’s a scientist by the name of Dr. James V. McConnell was investigating memory using flatworms.

flat worm

His experiment was rather simple, in that he would train a flatworm to go through a maze and then cut up the worm into tiny pieces feeding it to other non-trained flatworms. The non-trained flatworms would then be able to go through the maze like a trained worm. Does this mean the demons of The Promised Neverland are really just mutated flatworms?

No, because scientists could never reproduce the study, and the original study was shown to have a number of flaws. FYI- Some more recent studies have shown that flatworms do have some interesting quirks when it comes to memory. First off, let me inform you that flatworms have an amazing ability to regenerate and that includes having their head cut off. In this case trained flatworms had their heads removed and yet still remembered the training even after the brain was completely regrown. Whether this means that their body has some other way of retaining memory outside the brain or that the study was flawed in some way is still open to debate.

That’s not how it works

horizontal gene transfer

Honestly, I don’t know what else to say to this part other than that’s not how biology and genetics works. You can’t lose a genetic trait once you have it, even if it is a plasmid. According to Norman the demons will lose their human intelligence, becoming wild, after not eating humans for 6 months.

horizontal gene transfer

Oh, and an organism whose genetic code can change that much would have a lot of problems with cancer and other cell growth disorders. FYI- yes, I know that some viruses can mutate very quickly, but viruses are not considered to be living things, as they lack cells, among other things.

Plot Point

Now if you were like me when you read chapter 120 you were thinking, wait a minute, something doesn’t add up. Well it looks like Emma and Ray thought the same thing too as of chapter 123.

They also come up with several explanations as to why Sung-joo and Musica are able to retain human form and intelligence without eating humans. We will have to wait until their talk with Norman to find out the answer to that question.


The Promised Neverland has been one of my favorites for a while now, with its mix of action, adventure, and mystery. The latest chapters have been no different and it’s refreshing to see a manga use new discoveries in science as part of the plot. I do realize that it does get some things wrong, but I’d like to think I wasn’t the only one who went to go look up more about the topic. As much as I liked the use of biology in chapter 120 of The Promised Neverland, I am going to have to call it busted.


For now, anyway, because it looks like there is still more to be revealed about the biology of demons. This is because of the way they seemed to gain knowledge and intelligence. The manga also downplays standard evolution a bit too much for my liking. Then there is the matter of the fact that the demons will revert to wild animals after not eating humans for 6 months, which I do realize is questionable right now, so I will revisit the topic in the future as the manga reveals more information.

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