Related [0], large animals seldom get cancer, at least at rates much lower than humans, which is surprising considering how many more cells they have (each of which has a certain probability of becoming cancerous). The assumption is that, as these animals grew larger, evolutionary pressure selected genetic traits that help counter cancer.
Human vision goes years before our cancer rates spike. We are essentially living past our primitive life expectancy until something fails which is very recent and evolution has had little time to catch up to this.
At a nuts and bolts level cell volume is less indicative of cancer as interfaces like skin, lungs, and intestines are vastly more likely to get cancer than most other tissues. Early cancers are often the result of mutations during growth from a single cell which is closer to log(volume) vs simple volume in terms of risks.
> . We are essentially living past our primitive life expectancy until something fails which is very recent and evolution has had little time to catch up to this.
To my naive understanding of evolution, it has little incentive to fix anything that breaks after reproduction age. So I would not expect evolution to catch on cancer ever.
>> he elderly help the community and this is obviously beneficial for survival and reproduction.
To a point. There is an inflection where the grandparent benefit becomes a burden on reproduction and survival. From a purely evolutionary perspective, this would probably occur where the presence of elderly people starts to impact the number of children born. We are seeing that today as many younger people are burdened with taking care of elderly relatives rather than raise children.
There are parts of the United States where the average age of a woman when she has her first child is 30. All things being equal, that would make a first-time grandparent 60 years old at the birth of her grandchild and over 80 at his college graduation.
Especially given how insanely long our child rearing process is compared to other species, and how as we get more sophisticated it seems to get longer...
"needs" is a strange term, as is "get rid of". In nature, an organism generally doesn't need to "get ride of" anything that isn't actively feeding off it -- The state of nature is for weak organisms to die on their own.
But people never select for "good" elderly so to speak.
Neither do most primates or lions. The elders just happen to be there. So we can't really even say if it's just more elders in the animal kingdom making themselves useful. Which, again, is happening after reproduction typically.
For something to have an effect on reproduction, I would think it would need to be part of the decision beforehand.
These sorts of selections are likely to happen on a group level to the best of my knowledge, and you can easily imagine how selection for good elderly could work if you imagine children's life expectancy being dependent on their parents and grandparents. If (hyper simplified) a mutation that allows people to maintain eyesight for an extra 10 years helps them be extra spotters for the family on the hunt, and in a food scare environment, making one kill is life or death for the children's ability to eat, then that lineage with better eyesight could be selected for
Direct fitness is not the only way natural selection favours individuals. Genes that make individuals past their reproductive age turn into good caretakers (including genes that improve their health) are more likely to increase their frequency in subsequent generations (through the descendants they care for). This is called kin selection.
Kin selection. The elderly can help their grandchildren survive, so genetic predispositions towards living longer and helping your grandchildren can propagate depending on the cost-benefit of that strategy.
Likely a very new concept on an evolutionary timescale, and competing against the survival chance cost of more mouths to feed during an acute resource shortage.
It seems absolutely not a coincidence that the much faster, by orders of magnitude, process of human history got set in motion at a time when grandpatenting, as an evolutionary concept, wasn't quite finished yet.
The elderly would have to specifically help their own grandchildren, not just the community, for evolution to have an effect (otherwise you’re talking group selection nonsense).
I’d imagine it’s debatable whether elderly grandparents past reproductive years are helping their grandchildren be more reproductively successful. Possible, but not a forgone conclusion by any means.
Actually this has been studied, establishing for instance the grandmother effect in pre-industrial Canada [0] ("women with mothers nearby had more and healthier children"). See [1] for more resources.
Anecdotally, I can personally attest that having grandparents too far to help makes it a lot harder to raise our two young children - there will certainly not be a third one.
Just to clarify, this would be a kin selection effect, not a group selection effect. It doesn’t have anything to do with elderly helping the “community” as the parent mentioned.
It’s an interesting hypothesis being studied, but not in any way cut or dry.
> The grandmother hypothesis is a hypothesis to explain the existence of menopause in human life history by identifying the adaptive value of extended kin networking. It builds on the previously postulated "mother hypothesis" which states that as mothers age, the costs of reproducing become greater, and energy devoted to those activities would be better spent helping her offspring in their reproductive efforts. It suggests that by redirecting their energy onto those of their offspring, grandmothers can better ensure the survival of their genes through younger generations.
If the grandmother hypothesis is true, then you’re still talking kin selection effect via grandparents, which is very different than group selection. I concede that kin selection is very possible, but again, as this is an unproven hypothesis at the moment, still a matter of scientific debate, hence not really clear or obvious.
Again, reproduction is happening prior to any potential partner even knowing of a grandmother in many places in the animal kingdom. Even for humans actually.
So you're subscribing to the more adaptationalist line of reasoning for the existence of menopause. Which is fine. But you should concede that fact. Many others might subscribe to any of the other hypotheses for reproductive senescence. I subscribe to the artifactualist line of reasoning. ie - people just started living too long, and our bodies adapted for a 20-40 year life span. But there are numerous other hypotheses out there, many of them every bit as plausible as my artifactualist hypothesis. I only subscribe to the artifactualist hypothesis because it is the hypothesis most in line with the theory of evolution.
How long is too long? A woman is fertile through age 40 (and useful to care for offspring for another 10-20 years), a man is fertile through age 80 (and a genetically fit male would have valuable sperm long after his fitness showed in his phenotype). Why would our bodies adapt for a 20-40 year life span?
I don't think you were downvoted for providing scientific valid information in regard to conjecture. My best guess is that you were downvoted for calling something nonsense without anything to back it up. Maybe using gentler language would have helped here.
Given how high the birth death rate is (for the mother), and presumably older bodies are weaker, there should be some evolutionary pressure for the menopause - simply said, as the P(death at childbirth) rises above some threshold, it's more beneficial for the mother to not be able get pregnant (and potentially die) again but instead continue nursing her existing children.
No such pressure exists for men because men have no cost of having extra offspring.
> To my naive understanding of evolution, it has little incentive to fix anything that breaks after reproduction age. So I would not expect evolution to catch on cancer ever.
To my naive understanding of evolution, it has little incentive to fix anything that breaks after reproduction age. So I would not expect evolution to catch on cancer ever.
What if there were artificial evolutionary pressure? What if researchers start identifying specific mutations which are associated with cancer, then start editing them out of the DNA of unborn children?
It is only ability to focus that goes down so for a person without myopia only near vision is affected. This is still bad as it affects the gatherer part of hunter-gazerer society, but it does not imply that evolution has not tried to optimize vision for people over 40 years old. They still can spot a lion far away.
That does not imply that evolution has not tried. Human ancestors had much shorter life span and even millions of years can be not enough to fully adapt the vision for a longer lifespan especially when things works good enough.
Witness flatfish. We have good records for species to see that it took tenths of millions years for eyes to move 90 degrees on the head after fish ancestors decided to lay flat on the side on ocean floor.
It was good enough for the fish to see with single eye most of the time and evolution had little room for improvements since any wrong move with change in vision implied no vision and death.
Evolution has clearly been doing quite a bit. But, so much about our environment has been changing so quickly it’s more like a first pass than the deep optimization you see with say sharks. If the Bronze Age had lasted 10+ million years many things would have changed.
>We are essentially living past our primitive life expectancy until something fails
I will chime in and say "not really". If a human makes it past say 10 years old (even really makes it past 2 years old), odds are they make it to 55-80 without modern medicine, civilization, etc.
The only reason life expediencies appear lower than 50 (all the way down to the 30s) in places and in eras is due to insane infant mortality driving the numbers down. The life expectancy of those who make it to 2 years old is dramatically higher than that general life expectancy number.
>The only reason life expediencies appear lower than 50 (all the way down to the 30s) in places and in eras is due to insane infant mortality driving the numbers down.
Violence (leading to either immediate death, or due to infection) and epidemics (e.g. HIV) are also very significant factors.
Civilization has done quite a bit. Violence, starvation, even predation used to be far more common issues.
Modern medicine and in many ways hygiene has removed many diseases like cholera, typhoid, smallpox, tuberculosis, and malaria from huge swaths of the global population. By one estimate Malaria alone has killed 50 Billion people throughout human history.
Between 1850-1880, life expectancy in England was as long or longer than it is now. This predates antibiotics and nearly all vaccines, let alone what we today think of as advanced medical care.
> Human vision goes years before our cancer rates spike.
But is this due to how we use our eyes? I always wondered how it could be that maybe half of everyone I knew in uni used glasses, when you'd think a 20-year old hunter-gatherer would need to be able to see stuff.
Different mechanisms of action. Age related deterioration of eyesight, presbyopia, is caused by hardening of the lens and weakening of focusing muscles. Myopia is probably caused by lack of exposure to the extremely bright light of the sun during childhood and adolescence. Twenty year old hunter gatherers have great eyesight, sixty year old ones, not so much.
> Myopia is probably caused by lack of exposure to the extremely bright light of the sun during childhood and adolescence
Is there research on this? Just wondering since I ended up having issues with nearsightedness in my early 20s but feel like I spent a lot more time outdoors as a child compared to children these days.
> I always wondered how it could be that maybe half of everyone I knew in uni used glasses
There are many possible factors, including genetics, light exposure, amount of time spent on closeup vs distance, and a shortage of vision therapy / behavioral optometry experts.
That is because they stave to death when their sixth set of teeth wear out. To get cancer at anything similar to human rates elephants need to live longer.
They are also exposed to far less carcinogens. Half of cancers as far as I read on Wikipedia can be attributed to artificial factors like smoking, alcohol, diet triggered obesity, etc.
It's always a combination of genetic predisposition and external effects working together (except, of course, in very rare cases of lethal-dose exposures to carcinogens). Usually external effects just increase the chances of mutations, and then fate and your genetics role the dice.
Not to forget Chemicals like PVCs plasticizers, solvents like benzene in paints, bis-phenol A in plastic bottles, flame retardants in our home that we breathe whenever we sit down in something soft, insecticides(air in cities is super polluted of them) and diesel particles.
Those things are extremely dangerous, but we have not natural sensors to detect and avoid exposure to them.
I bought a geiger detector and it surprised me to find places with thousands of times more radiation than others.
That's not usually true. A large proportion of pet rats die from tumours. Furthermore although e.g. in mice, there's Oncomouse, bred with a susceptibility to cancer, rats have been resistant to similar techniques (https://en.wikipedia.org/wiki/Knockout_rat#Production_challe...)
Agrobacterium grows in the tumorous gall tissues in trees. They use these growths to multiply and trick the host to upregulate the nutrients for tumor and bacterial proliferation. These tissues then rot and bring the tree down with them.
Agrobacterium is frequently used in the lab to induce pluripotency or do gene injection.
While agrobacterium directed growth is a leading cause of plant tumors, the mechanism is one of positive feedback: plant hormones, xylem, etc. are upregulated in tumorous growths, causing them to grow faster. I'm not a botanist, but I'd be surprised if these didn't arise spontaneously due to random events.
While it's true that plants grow much differently than animal tissues, and that the rate of spontaneous cancer development is much greater in animals as a consequence, it is factually incorrect to say that plants don't die from cancers. We must also remember that a large number of human cancers are promoted by infectious agents.
Interesting that this was one of the most popular questions on Reddit's r/askscience subreddit two days ago; I wonder if PBS editors also trawl there for interesting topics.
Oh, wow! I'm totally wrong, then - I wonder if it was coincidence, or if someone saw that headline without having time to read it, and went to Reddit instead.
Technically plants die from cancer, is just that what we call cancer in plants is different that what we call cancer in animals.
Plants can stand better mutations than animals because they have a clonal structure and asexual reproduction. There are "bricks" in this structure called "leaves", "roots" or "stems between nodes", repeated again and again in the entire creature. Mutations lead often to stunted growing, thus health clones just overgrow and kill the damaged parts. They have an autoprune system also.
Or make the human the power source? Jobs for everybody! Just have humans pedal a generator for a living. It’d require lots and lots of people and it’d solve our obesity problem.
> Plants, however, develop in a much more flexible and organic way. Because they can’t move, they have no choice but to adapt to the circumstances in which they find themselves. Rather than having a defined structure as an animal does, plants make it up as they go along.
The relevant paragraph is actually this: And while radiation and other types of DNA damage can cause tumours in plants, mutated cells are generally not able to spread from one part of the plant to another as cancers do, thanks to the rigid, interconnecting walls surrounding plant cells.
Plants also lack a closed circuit circulatory system designed to accommodate autologous cells. So not only can the cells not get out of their walls, there wouldn't be much of anywhere to go if they did.
In order for a cancer-like mutation to kill a plant it would probably have to cause mechanical damage. Tumors completely circling the trunk of a tree might have an effect like girdling the tree and kill the tree. A tumor growing in the center of a stem might compress the xylem and phloem enough to choke them off.
This kind of fatality happens with humans, too, even if the cancer doesn't spread beyond the origin site.
Maybe this has some weigth>
"the nuclear accident was far less destructive to the local ecosystem than we were. In driving ourselves away from the area, we have created space for nature to return."
Similarly I always feel little stitches from rhetoric use of the perceived degree of organicity a thing possesses in contrast to another.
It's such a vague metaphor. I guess what usually counts as more organic is:
- stuff that decomposes, is not ignored by destruents and stinks
- stuff that is complex and semi-random, no central, overall plan
So maybe it's the last point. For an animal you need a thorough layout, like for a cathedral (but, well there are also Gaudí's which aimed to be more "organic" - all these metaphors are so messy, maybe natural language is too organic)
The question’s framing precludes the answer. Plants do die from environmentally distributed host subversion that can eventually become a systemic failure. We insist on clear interdisciplinary divisions throughout science, so by necessity, we anneal such siloing with “object with forces” paradigm (appropriated from physicist’s tool chest) which in turn feeds back into “world as a collection of objects” (set theory) outlook.
Is it known why plant cell structure don't ever detach ? even accidentally. They have tube so "technically" something could move, if it breaks from the ~ECM
"Plants don't die from cancer" for the same reason "plants don't scream": These are human created concepts that are rooted in humanocentric mental models and plants fail to conform to our conceptual framework. It's much the way sexism, racism etc work.
Reality: Plants give off a pulse when attacked. Human ears don't "hear" it, so we don't count it as "screaming." They also communicate chemically with nearby plants when they get infested with hostile insects. You could say they put out the word and nearby plants of the same species act to protect themselves.
I don't think this is about anthropocentrism. Death and cancer are reasonably well-defined concepts across a vast range of species. Plants do get cancers, it's just nowhere near as fatal as it is for humans.
Title of the piece: Why plants don’t die from cancer.
If the title were "Why cancer is nowhere near as fatal in plants as in humans," then your rebuttal would hold water. But that's not the title, so it has no bearing on my critique of the actual title.
Forgive me if I'm being ignorant or pedantic. Is your criticism that the title fails to clarify that it's using generalised notions of death and cancer? I personally found that I automatically translated the title to
> Why DNA mutations associated with abnormal division of cells in plants do not correlate with high fatality rates
This was surprising to me because a priori I didn't see why plants should cope with abnormal growth any better than humans. This made the question intriguing. The explanation that plant cells are designed so that dead cells can be quickly replaced and that cells are surrounded by rigid walls was gratifying in a way that "question is too anthropocentric" isn't.
[0] https://www.economist.com/science-and-technology/2019/06/29/...