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Comment by VeejayRampay | Hacker News Reader

The way the title is phrased is strange. To the young/uneducated reader (not so many around here, but still), it reads like humans evolve to develop a particular trait, when we know that people who developed that trait got an evolutionary advantage and ended up spreading their DNA more than others on average.

Not as catchy a title, sure, but at least, it doesn't misrepresent the evolutionary process.

NOTE: I am not an evolutionary biologist, so there is most likely an even better way to rephrase my rephrasing. I'd be glad for anyone to do so, the more accurate, the better.

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> humans evolve to develop a particular trait

> people who developed that trait got an evolutionary advantage and ended up spreading their DNA more than others on average.

The first is shorthand for the second.

Ah OK, my bad then.

It's sloppy shorthand though because it can be (deliberately) misconstrued to suggest agency and directional purpose.

> it reads like humans evolve to develop a particular trait, when we know that people who developed that trait got an

people who developed that trait had to evolve to do so, no? Not as an entire population, but maybe over the live span of individuals.

Maybe the smoke itself caused that, as exposure often does, "evolving" in some individuals who then pass immunity markers down over generations through blood in the womb rather than genetically. Or maybe the smoke is cancerous and caused beneficial mutations. I should read the paper (edit: it says genetic). All I'm trying to say is, either development is subsumed under evolution.

> people who developed that trait had to evolve to do so, no?

The word "evolve" in English means a gradual change, so no.

Random genetic mutation isn't a response to the smoke, and there isn't anybody born unadapted who then adapts by exposure. The species evolves, individuals don't.

>"The species evolves, individuals don't."

You are made of cells that are many generations separated from the fertilized egg. I don't see why you accept evolution at the species level but not cell level.

This sounds like a kind of reverse creationism, where macro-evolution is ok but micro-evolution is not.

Um, honestly not sure what you're getting at there. The individual cells in your body are genetically the same as what you started with, with occasional random mutations. The body defends itself against those mutations and most will be eliminated. Some will become cancers. They don't affect the DNA you pass on to your offspring and so aren't a part of the evolution of your species. None of them are going to give you superpowers unless you happen to be living in a comic book.

Say a person is exposed to smoke often since being a young child. At some point, a lung cell is dividing and randomly gains a mutation that increases expression of some smoke-protective protein. This lung cell is then more fit (to the smokey environment) than the surrounding lung cells. As a result, its daughter cells will divide more often than the others and populate the tissue.

Are you denying this can happen? Or is it that you do not consider that process to be evolution?

That absolutely can happen - but remember that the traits of the 'evolved' lung cell will not be passed to offspring, as the genetic makeup of gametes (sperm) is a random (50%) subset of the main genetic code.

Sure, but the population of cells we call an individual human being does "evolve" over the course of its life.

The vast majority of random mutations are harmful.

The number of random mutations necessary to produce one lung cell that is better adapted to smoke inhalation is large enough that the entire remainder of the lung already has carcinogenic mutations.

Sexual reproduction is a mechanism to eliminate harmful mutations without discarding the occasional beneficial mutation.

It is not necessary for that purpose, but it is sufficient. Humans are now technically capable of identifying a potentially beneficial genetic mutation, and inserting it into an unrelated person's genome. It is, however, more likely that the protein result of the mutation will be used to research and develop a pharmaceutical drug or medical procedure that replicates the beneficial effects of the mutation.

In short, the probability of you spontaneously developing an adaptive mutation in a non-germline cell is absolutely infinitesimal in comparison to the probability that someone in the last 10000 generations of your ancestors developed such a mutation when producing a sperm or egg cell and passed it along to you.

Many interesting points here that I wish were backed up by refs.

> "The vast majority of random mutations are harmful."

- You sure they aren't "neutral"?

> "The number of random mutations necessary to produce one lung cell that is better adapted to smoke inhalation is large enough that the entire remainder of the lung already has carcinogenic mutations."

- No, in principle it can be a single point mutation to a promoter that increases affinity for a transcription factor.

> "Sexual reproduction is a mechanism to eliminate harmful mutations without discarding the occasional beneficial mutation."

- So are apotosis and immune surveillance.

> "Humans are now technically capable of identifying a potentially beneficial genetic mutation, and inserting it into an unrelated person's genome."

- No, they aren't. They modify and select cells in a dish, not in a person.

> "It is, however, more likely that the protein result of the mutation will be used to research and develop a pharmaceutical drug or medical procedure that replicates the beneficial effects of the mutation."

- Ok, I am just including this for completeness sake.

> "In short, the probability of you spontaneously developing an adaptive mutation in a non-germline cell is absolutely infinitesimal in comparison to the probability that someone in the last 10000 generations of your ancestors developed such a mutation when producing a sperm or egg cell and passed it along to you."

- You are talking of 10^4 fertilized eggs vs 10^13 cells in my body[1]. I'm not sure how many divisions it is from egg to egg, but it has to be less than the 10^16 supposed to happen during the human life span[2].

Actually I am pretty sure I have read somewhere that the human body probably contains at least one cell that has a mutation at any given bp. I will see if there is time to find it later.

[1] https://www.ncbi.nlm.nih.gov/pubmed/23829164

[2] http://bionumbers.hms.harvard.edu/bionumber.aspx?id=100379

You forgot to include the probability that any given mutation occurs in a cell where such mutation can be observed to produce a beneficial effect.

If one cell in your body mutates such that it might protect your lungs against damage from smoke inhalation, it won't do you any good (nor ill, probably) if that cell is in your toenail matrix.

Nor do all cells in the body divide at a uniform rate.

I would guess that the one type of cell most likely to show an effect from non-germline mutation are the hematopoietic stem cells. They produce all types of blood cell, are self-renewing, and blood cells touch every other part of the body. But they are also only 1/10000th of all myeloid cells. There may be only 10^6 HSCs in one body

Your reference [1] only included the abstract: https://www.researchgate.net/publication/248399628_An_estima...

Also, 10000 generations of ancestors is not 10^4 fertilized eggs. Most people have two parents. 0 generations of ancestors is 1 fertilized egg. 1 generation is 3. 2 generations is 7. 3 generations is 15. The upper limit on N generations is 2^(N+1)-1 fertilized eggs. For 10000 generations, that is 4e3010 cells. Though the number of individuals in the species eventually limits that number, as multiple inheritance causes some of your ancestors to be counted more than once. The lower limit would be the degenerate case where all 10000 generations were siblings that had at least one son and one daughter, and that is 2e4. So quite a lot of room for variability in there.

>"Nor do all cells in the body divide at a uniform rate."

Knowing that rate in the various tissues even to within a few orders of magnitude is the holy grail.

And then that person has kids, and obviously they don't get the mutation. Is that part of the process of human evolution? No.

(By the way, you didn't mention the most common way that lung cells mutate in a smoky environment and begin to divide more often.)

Evolution involves random mutations and the filter of natural selection. The process you're describing doesn't participate in the filter, and random mutation alone gets you vastly more downside than upside. The only reason evolution works is because of the filter which lets us keep the upside in the gene pool while the downsides are filtered out.

Evolution occurs via reproduction over the span of many generations. Individual adaptation on a single-lifespan scale occurs via epigenetic methylation tagging of the existing (evolved) genome.

You cannot become better adapted to smoke unless your genome already contains a gene that mitigates the damage, or a gene that can regulate expression of a damage-mitigating gene based on that specific stimulus.

So if you breathe smoke frequently over your lifespan, you may have a gene related to mucus in the lungs expressing its protein at maximum capacity 24-7, while someone who never breathes smoke has that gene "turned off" most of the time.

Transfer of individual adaptations, usually in the form of antibodies that can teach immune cells to respond to a specific hazard, is very limited, and will only last as long as that specific threat is continuously endemic. We have mostly supplanted that natural capacity with artificial vaccinations.

Random mutations are usually harmful. Sexual reproduction and selection is the mechanism to shuffle the most harmful mutations out of the genome while still retaining the rare beneficial mutation. If the mutation rate is too low, the species cannot evolve quickly enough in changing environments. If the mutation rate is too high, sexual reproduction cannot eliminate the bad mutations fast enough.

I think you are saying that there is no teleology in the theory of evolution.

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