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I found the article confusing, I don't understand the link between the paper and evolution: 1. APOE-Alzheimer-propensity gene is a new gene, emerging in the you

I found the article confusing, I don't understand the link between the paper and evolution: 1. APOE-Alzheimer-propensity gene is a new gene, emerging in the younger population. (Clearly, prevalence of this gene reduces a person's life-expectancy but not until they are done giving birth). 2. Same with CHRNA3-heavy-smoking-propensity gene. 3. These genes are not evolutionary drivers since they don't effect E[number of offspring] or E[survival rate until given birth to final offspring]. 4. From an evolutionary perspective, prevalence of these genes should be found in equal proportion across all ages of the population. 5. Then why are these genes emerging? Isn't it far more likely that there is some new factor in our lifestyle/diet/habitat etc that is causing the gene to appear in the population? Which has nothing to do with evolution. Where in the paper do they talk about evolution?

perlgeek 9y ago
The confusing part is that we are used to thinking about evolution as spanning multiple generations: a gene increases fitness, so its prevalence increases over the generations. Or the flip side: it decreases fitness, so the members that have it reproduce less, its prevalence decreases. But this study takes a snapshot of a population, and looks at gene prevalence as a function of age. So what you see are not effects of reproduction, but rather on survival. It finds the Alzheimer's gene less in 70 year olds, because those with the gene are more likely to have died earlier, and thus not appear in the study. Thus your statement "APOE-Alzheimer-propensity gene is a new gene" is likely not true. It is likely just as prevalent in the current generation as two generations before; just those individuals from two generations before who had it are more likely to be already dead. So the study looks at how genes influence survival rates -- something that is very obviously related to evolution if it occurs before reproduction. If survival rates only depend on some genes in higher age, they have only small, second-order effects on reproduction (like a child being more likely to survive if it has healthy grandparents or parents). (Disclaimer: I'm not a biologist, so take this with a grain of salt).
- Udik 9y ago
  > It finds the Alzheimer's gene less in 70 year olds, because those with the gene are more likely to have died earlier, and thus not appear in the study. So wouldn't the study be: "Those carrying genetic disease have a tendency to die early(er)"? What does evolution have to do with it? BTW, it's perfectly possible for a gene to be wildly successful from the evolutionary point of view, while at the same time killing its owner invariably by the age of 50. How would this study have classified such a gene?
- riazrizvi 9y ago
  I suppose that does explain the drop off in expression of the gene: Alzheimer's risk of death/year 1-3% [1]. That annual mortality rate is in the right ballpark to explain the frequency of gene expression decrease by about 50% between ages 40 and 80 [2]. Agree the study does look at genes influencing survival rates. I still don't see the link to the headline 'humans are evolving!'. Small second-order effects, okay, sure. So how about, 'Massive Genetic Study shows genetics affect mortality rates, plus maybe there's a small secondary effect on reproduction, who knows?'. [1]. 83,000 (i) or 3,349 (ii) Alzheimer's deaths per year out of 2mm deaths (iii) => 1-3% i) http://www.nydailynews.com/life-style/health/alzheimer-kills-previously-thought-study-article-1.1712078 http://www.nydailynews.com/life-style/health/alzheimer-kills... ii) http://www.alz.org/mglc/in_my_community_60862.asp http://www.alz.org/mglc/in_my_community_60862.asp iii) https://www.cdc.gov/nchs/fastats/deaths.htm https://www.cdc.gov/nchs/fastats/deaths.htm [2] See graphs in paper.
  - Retric 9y ago
    People over 40+ still have kids. So, there would be a direct link if people started to die at 41.
  - mirimir 9y ago
    I'm confused. Sure, they identified two alleles with occurrence that decreases with age. And sure, that does suggest that those alleles reduce survival rate. But to demonstrate evolutionary change, they'd need data on occurrence of these alleles as a function of birth date, stratified by age. It'll take some time to get such data. Probably at least a few decades.
azernik 9y ago
With regards to your third point, there is a third optimization target you're not considering: E[(other two factors for relatives) • (probability said relative shares the given gene)] - hence humans not doing immediately after ceasing to be fertile, tending to care more about their kinship groups, and possibly also explaining genetic factors in homosexuality (since they may have handy side effects when it comes to capability to help out relatives).
Iv 9y ago
Evolution wants individuals to die soon after giving birth or in the case of mammals, soon after their offspring are independents. Older individuals take resources and keep around an old gene pool. When considered in a population, mortality is a feature, not a bug. Actually, it seems like aging is an additional feature, not a constraint of our bodies. There are animals that seem to have "accidentally" deactivated it: Galapagos giant turtles, some species of shrimps and, I think, some naked mole rats. These animals seem to have enough causes of mortality to keep evolving, without the need of a timer.
- patrickg_zill 9y ago
  I thought the classical understanding of evolution was that it had no desires...
  - Iv 9y ago
    I consider my interlocutors smart enough to understand that it is an image and that evolution is an emergent behavior.

perlgeek 9y ago

The confusing part is that we are used to thinking about evolution as spanning multiple generations: a gene increases fitness, so its prevalence increases over the generations. Or the flip side: it decreases fitness, so the members that have it reproduce less, its prevalence decreases. But this study takes a snapshot of a population, and looks at gene prevalence as a function of age. So what you see are not effects of reproduction, but rather on survival. It finds the Alzheimer's gene less in 70 year olds, because those with the gene are more likely to have died earlier, and thus not appear in the study. Thus your statement "APOE-Alzheimer-propensity gene is a new gene" is likely not true. It is likely just as prevalent in the current generation as two generations before; just those individuals from two generations before who had it are more likely to be already dead. So the study looks at how genes influence survival rates -- something that is very obviously related to evolution if it occurs before reproduction. If survival rates only depend on some genes in higher age, they have only small, second-order effects on reproduction (like a child being more likely to survive if it has healthy grandparents or parents). (Disclaimer: I'm not a biologist, so take this with a grain of salt).

Udik 9y ago
> It finds the Alzheimer's gene less in 70 year olds, because those with the gene are more likely to have died earlier, and thus not appear in the study. So wouldn't the study be: "Those carrying genetic disease have a tendency to die early(er)"? What does evolution have to do with it? BTW, it's perfectly possible for a gene to be wildly successful from the evolutionary point of view, while at the same time killing its owner invariably by the age of 50. How would this study have classified such a gene?
riazrizvi 9y ago
I suppose that does explain the drop off in expression of the gene: Alzheimer's risk of death/year 1-3% [1]. That annual mortality rate is in the right ballpark to explain the frequency of gene expression decrease by about 50% between ages 40 and 80 [2]. Agree the study does look at genes influencing survival rates. I still don't see the link to the headline 'humans are evolving!'. Small second-order effects, okay, sure. So how about, 'Massive Genetic Study shows genetics affect mortality rates, plus maybe there's a small secondary effect on reproduction, who knows?'. [1]. 83,000 (i) or 3,349 (ii) Alzheimer's deaths per year out of 2mm deaths (iii) => 1-3% i) http://www.nydailynews.com/life-style/health/alzheimer-kills-previously-thought-study-article-1.1712078 http://www.nydailynews.com/life-style/health/alzheimer-kills... ii) http://www.alz.org/mglc/in_my_community_60862.asp http://www.alz.org/mglc/in_my_community_60862.asp iii) https://www.cdc.gov/nchs/fastats/deaths.htm https://www.cdc.gov/nchs/fastats/deaths.htm [2] See graphs in paper.
- Retric 9y ago
  People over 40+ still have kids. So, there would be a direct link if people started to die at 41.
- mirimir 9y ago
  I'm confused. Sure, they identified two alleles with occurrence that decreases with age. And sure, that does suggest that those alleles reduce survival rate. But to demonstrate evolutionary change, they'd need data on occurrence of these alleles as a function of birth date, stratified by age. It'll take some time to get such data. Probably at least a few decades.

azernik 9y ago

With regards to your third point, there is a third optimization target you're not considering: E[(other two factors for relatives) • (probability said relative shares the given gene)] - hence humans not doing immediately after ceasing to be fertile, tending to care more about their kinship groups, and possibly also explaining genetic factors in homosexuality (since they may have handy side effects when it comes to capability to help out relatives).

Iv 9y ago

Evolution wants individuals to die soon after giving birth or in the case of mammals, soon after their offspring are independents. Older individuals take resources and keep around an old gene pool. When considered in a population, mortality is a feature, not a bug. Actually, it seems like aging is an additional feature, not a constraint of our bodies. There are animals that seem to have "accidentally" deactivated it: Galapagos giant turtles, some species of shrimps and, I think, some naked mole rats. These animals seem to have enough causes of mortality to keep evolving, without the need of a timer.

patrickg_zill 9y ago
I thought the classical understanding of evolution was that it had no desires...
- Iv 9y ago
  I consider my interlocutors smart enough to understand that it is an image and that evolution is an emergent behavior.