Maybe we should use the word "use unknown" instead of "useless" when dealing with things we don't fully understand.
History has humbled us countless times. I recall a recent Veritasium video wherein famous mathematicians of centuries past labelled the concept of negative numbers "useless" (because they didn't understand how they could be useful). My high school bio teacher confidently claimed that the appendix was a "useless organ".
> The appendix has been identified as an important component of mammalian mucosal immune function, particularly B cell-mediated immune responses and extrathymically derived T cells.
This is a widely held misconception. Mammalian genomes contain about 50% of their DNA as repeated sequences, and although there are people who can imagine uses for those sequences, there is no evidence that they are required or even evolutionarily advantageous.
The idea that modern higher organisms have been "optimized" so that every part is essential is not well supported by evidence, and there are many examples of features that simply are historical artifacts or "not-sufficiently harmful". Many evolutionary biologists are comfortable with neutral theories consistent with the idea that large portions of the genome are not under strong (or perhaps even moderate) selection.
> This is a widely held misconception. Mammalian genomes contain about 50% of their DNA as repeated sequences, and although there are people who can imagine uses for those sequences, there is no evidence that they are required or even evolutionarily advantageous.
If you remove noncoding "junk DNA", you alter the higher level spatial configuration of DNA. Histone winding changes which promoter regions are accessible, gene dosing is altered, binding affinity and kinetics change, etc. These are dynamical equations you're dramatically altering.
Non-coding DNA also likely shields against several classes of random point mutations, base substitutions, transposition, etc. preventing cancer and cell physiological disease states.
It's also important for maintaining alignment during crossover.
If it truly served no purpose, it would be gone.
> The idea that modern higher organisms have been "optimized" so that every part is essential
Essential is the wrong word here. Relying on every part for survival would put us at risk. We have plenty of built in redundancies to support degradation, failure, and loss of multiple systems and functions.
I get your argument, but I still disagree. At the species / population level, we have been optimized as wholesale organisms as best as development and body plans will allow. Everything not subject to pressure will get washed away.
Despite our vestigial tails, the coccyx supports our weight while we are seated. As I postulated before, the appendix probably has a net positive function in supporting gut microflora and our "junk DNA" plays a role at the molecular level.
The statement that at some level species have been optimized is a religious belief, not a scientific one. Species are at the end of an evolutionary history that ended in the present. There is no reason to believe that that endpoint is optimal in any sense. It is certainly not globally optimal, and absent very strong selection, it may not even be locally optimal. Evolution explores an infinitesimal fraction of the possible states/pathways available. Without more thorough exploration and strong selection, there is no reason to believe things are optimal.
I think I’m not going out on a limb to say that no modern evolutionary biologist believes organisms are optimal. They simply survived.
Only vaguely. If the DNA was to be compared with our programming languages, it would be like INTERCAL, but a million times worse.
Sections of the genome interact not only with the code right around them, but also with code far away, as a result of the chromosomal folding. So a section of 100 nucleotides might not do anything if you splice it out and throw various enzymes and other chemicals at it, and it might not even matter that much which nucleotides they are, but if you remove them and change the shape of the chromosome, it might not work the same way.
A lot of our knowledge of genetic is limited to the things that are easy to test.
Except our machines are designed around the idea of isolating components and minimizing unintended side effects, while biology has no such compulsion.
Imagine if an extra semicolon in one of your unused files shifted electrical distribution on storage media and that had all kinds of downstream effects on unrelated systems and those effects were critical for multiple other functions.
Only increase complexity enough so the whole contraption is NOT brittle.
You’re talking about messiness in the genotype, but selection pressure happens to the phenotype. The latter I think controls more of what ends up in the former.
Which is what we see all the time in programming: software wins because of its effect, not usually the lines of code needed (or not) to get there.
I'm not sure I understand your argument, but if large portions of the genome have no effect on phenotype, then perhaps we can both agree that those regions would not be under selection. Pressure on the phenotype cannot directly alter the genotype (no Lamarkism), but it could select for or against the fraction of the population with a particular genotype. But only if the genotype produces a phenotype.
Wouldn't assuming a one-copy rule end state is natural cause immense issues with recessive genetic disorders (which could in turn select against it), and also make chromosomal-crossover produce sterilized but viable young at a much higher rate?
Natural selection only pushes towards the removal of things that harm reproduction, not things that harm survival at all ages. If appendicitis mostly happens after the average age of reproduction, then there's not really a big evolutionary pressure to remove the appendix. Sure the person will die of appendicitis, but if at that point they've already had all the kids they're likely to have during their life, then the appendicitis doesn't have an effect on the process of natural selection.
Oh sure, it was reductio ad absurdum, just pointing out that the possibility of appendicitis wasn't by itself an argument against its continued existence - I don't know anyone personally who has ever been diagnosed with it...
Can’t an inherited trait be “neutral”? By that I mean it confers neither a benefit nor a detriment? It’s my understanding that the baby toe, for example, isn’t particularly useful anymore. But having or not having the baby toe(s) isn’t likely to help or hinder a person’s ability to reach adulthood and reproduce. There must be a lot of traits like that, right? Like eye color or maybe wisdom teeth. No one (as far as I know) is selecting a sex partner based on whether their wisdom teeth were impacted or not.
That's only if the gene's to express an appendix ever go away.
I always think back to Richard Dawkins explaining how a particular vein in a Giraffe's neck is wrapped around a lower neck bone and has grown 2x to accommodate the long neck instead of regrowing in a more efficient way (not wrapping).
Others have said this using different words, but evolution relies on the preservation of low-cost mutations. It took many mutations to get from photoreceptors to the mammalian eyeball.
If the cost is small enough that other factors dominate your ability to procreate, it will spread to all of your descendants. If other genes in your genome make you reproductively successful, that gene edit will spread and spread.
It’s a good thing these cheap changes are preserved, or viruses and bacteria would have wiped out all multicellular life early on by practicing patience. We all have genes that make us less susceptible to some pathogens than others and if a bad enough variant comes around, suddenly we are over represented in the next generation. If the hits keep coming eventually our family reunion may be the only one being held.
It certainly does apply: why do men have nipples? Likely for reasons similar to why we have an appendix.
Fundamentally, natural selection and evolution are models that help explain general biological processes, to help us comprehend a bigger picture. Around the edges of that picture, it's not fully clear.
The truth is that the universe is governed by laws that are deeply unintuitive: general relativity and the standard model. Each layer of abstraction on these makes the periphery of the image fuzzier, but allows us to make more sense of the part of the image that we're focusing in on.
It looks like the only person who described them as useless is the editor who wrote the headline, and they did it in an incredibly disingenuous (and grammatically incorrect way) by putting quotes around it. That implies that someone in the study used the word useless, which doesn't actually appear to be the case.
Your point of view in evolution is called Adaptionism, but there are those who believe otherwise, and use the term "spandrel" to talk about the "useless" things that evolution carries along.
Of course, something that is currently useless may become useful as the environment changes. Or it may not. Personally, I find a healthy sense of detachment from purpose, and certainly from any sort of teleology, is necessary to become philosophically consistent with the evidence from evolutionary biology.
Thanks for the rabbit hole ( I've never really studied evolution outside of CS applications ).
Your point of view about detachment makes quite a bit of sense to me, and if the spandrel idea proves true I guess we (Homo sapiens) will just have to take it on the chin...
This is quite interesting! Thanks for sharing! So might it be that a species, as a whole, benefits from carrying around a certain amount of “spandrels”? A genetic insurance policy of sorts to protect against/quickly adapt to unforeseen changes? Has there been any research into the prevalence (or absence) of spandrels in species that have gone extinct?
I'm not sure if there's much research in evolution about species that have gone extinct versus extant species, or at least I haven't encountered it.
The human genome carries around a massive amount of spandrels, in the form of what is called "selfish DNA." About 15% of the human genome consists of repeats of a single sequence: the Alu gene, which seems to primarily exist to replicate itself in the genome. This is part of a class of genes called transposable elements:
And when discovered in corn, accounted for 85% of the genome. Barbara McClintock, their discoverer, hypothesized that they serve as a growth bed for evolution. And over the years it has indeed been found that individual transposable elements can serve as the seeds for new control sequences that coordinate when to turn genes on and off. The major forces of evolution in vertebrates are not big changes in proteins, but rather changes in when and how various proteins get activated, and transposable elements serve a big function in allowing that sort of evolutionary change in genomic sequences.
Does most repetitive DNA in the genome seem to be useless, in that its deletion or replacement have little effect on the genome? Probably! But all that fluff also facilitates more easy rearrangement of the genome, because if every part of the genome was essential, randomly moving a chunk of DNA into a new spot would likely kill off some useful stuff. But if there's a bunch of stuff that is useless, randomly copying some stuff into a random spot is less likely to disrupt something. If the genome is a hard drive, there's no "free list" or file system for the genome, so random writes are less likely to be disastrous if there's nothing of importance on most of the drive.
I used to get upset at the term "junk DNA" but I don't really care one way or the other now. One cell's junk is another's treasure.
this cost of "DNA size" is a long and ongoing argument in biology with no clear answer. Here's the strongest straw man argument in favor of "there are large amounts of non-funcitonal DNA which has zero evolutionary cost": https://www.cell.com/current-biology/pdf/S0960-9822(12)01154...
Certainly there are thing that formerly had a use but are less useful now. I'd be careful calling something useless, but if there isn't an advantage to getting rid of a feature, I see no reason it would be gotten rid of.
To their limited knowledge, it was indeed useless. Scientist can make such statements if they feel up to, but they must also have the humility to later eat their own words when they are proven wrong.
History has humbled us countless times. I recall a recent Veritasium video wherein famous mathematicians of centuries past labelled the concept of negative numbers "useless" (because they didn't understand how they could be useful). My high school bio teacher confidently claimed that the appendix was a "useless organ".