# Genes and heritability **URL:** \ **Category:** Factual Questions\ **Created:** [April 27, 2021, 2:16pm UTC](https://boards.straightdope.com/t/genes-and-heritability/940862 "2021-04-27T14:16:18Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [April 27, 2021, 2:16pm UTC](https://boards.straightdope.com/t/genes-and-heritability/940862/1 "2021-04-27T14:16:18Z")
In this video, the narrator talks about the palmaris longus, a forearm muscle that some people have and some people don’t. Fair warning, he points this muscle out on the arm of a cadaver. [![](https://img.youtube.com/vi/yc1VgVw7F9w/maxresdefault.jpg "Are YOU Missing a Muscle??? | Here's a Test to Find Out!!") ](https://www.youtube.com/watch?v=yc1VgVw7F9w) The whole video was interesting, but the subject of this OP is about a specific part of it. At 4:40 he starts talking about evolution and speaks of how organisms, through exposure to certain environmental factors and engagement in certain behaviors, can “activate” certain genes. He goes on to claim that the “activation” of genes somehow makes them more likely to be passed on to offspring. My layperson’s understanding of genetics is that the genes you inherit from each of your parents is completely random, and that evolution was guided only by survival of the fittest. So what’s the deal? is genetic inheritance _not_ entirely random? Is there another mechanism (besides SOTF) by which evolution can shape the next generation? ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [April 27, 2021, 2:59pm UTC](https://boards.straightdope.com/t/genes-and-heritability/940862/2 "2021-04-27T14:59:12Z")
I think he’s just talking about the basics. If the muscle is significant to survival and reproduction in a particular environment, and the gene already exists to produce it with some occasional exceptions, then the exceptions will dwindle away. And conversely the exceptions can increase in frequency based on other factors if the muscle is not a survival factor. It’s not so much about how this muscle evolved in the first place, it’s about what happens to such genetic features when they are no longer important in a a particular environment. ---
**Author:** ![gdave](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gdave/32/3683_2.png) [@gdave](https://boards.straightdope.com/u/gdave)\ **Post date:** [April 27, 2021, 4:02pm UTC](https://boards.straightdope.com/t/genes-and-heritability/940862/3 "2021-04-27T16:02:29Z")
Caveat: I Am Not An Evolutionary Biologist. I was hoping, this being the Dope, someone who was more knowledgeable would respond. Since that hasn’t happened yet, I’ll take a crack. I believe what the presenter is referring to is epigenetics: > **[Epigenetics](https://en.wikipedia.org/wiki/Epigenetics)** > > Pages for logged out editors learn more > > > In biology, epigenetics is the study of stable phenotypic changes (known as marks) that do not involve alterations in the DNA sequence. The Greek prefix epi- (ἐπι- "over, outside of, around") in epigenetics implies features that are "on top of" or "in addition to" the traditional genetic basis for inheritance. Epigenetics most often involves changes that affect the regulation of gene expression, but the term can also be used to describe any heri... Epigenetics is, to my lay understanding, a complex process of nested feedback. There are genes that respond differentially to different environmental cues, and genes that modulate that response, and genes that moderate _that_ interaction. And, like most genes, a gene that’s involved in epigenetic expression may also have different roles in other traits. And for that matter in different epigenetic interactions. It’s also my _very_ lay understanding that “survival of the fittest” is an oversimplification. It’s not wrong, but it’s not really a term actual evolutionary biologists use. “Natural selection”, which isn’t quite the same thing, and genetic drift are two major processes, but not the only ones, that act upon genetic variation, which itself has numerous sources, and results in evolution. ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [April 27, 2021, 4:09pm UTC](https://boards.straightdope.com/t/genes-and-heritability/940862/4 "2021-04-27T16:09:01Z")
To see more on the preceding post, look at [DNA methylation - Wikipedia](https://en.wikipedia.org/wiki/DNA_methylation). The point is that while the gene is passed down in the usual way, so is the methylation. But the methyl group can be added or deleted in response to environmental factors. Perhaps someone more knowledgeable can go into more detail. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [April 27, 2021, 4:39pm UTC](https://boards.straightdope.com/t/genes-and-heritability/940862/5 "2021-04-27T16:39:17Z")
Did he mention anything resembling epigenetics? I think he was stating in a poor manner how genes come and go in species over time. I certainly may be wrong, but is there any similar case where epigenetics would lead to the disappearance of a muscle or tendon? ---
**Author:** ![gdave](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gdave/32/3683_2.png) [@gdave](https://boards.straightdope.com/u/gdave)\ **Post date:** [April 27, 2021, 4:56pm UTC](https://boards.straightdope.com/t/genes-and-heritability/940862/6 "2021-04-27T16:56:10Z")
I’m at work and can’t watch the video (and, again, IANAEB), but this part: > [@Machine\_Elf](#): > > At 4:40 he starts talking about evolution and speaks of how organisms, through exposure to certain environmental factors and engagement in certain behaviors, can “activate” certain genes. He goes on to claim that the “activation” of genes somehow makes them more likely to be passed on to offspring. sure sounds like epigenetics. Even if the presenter isn’t referring to epigenetics, it at least seemed like @Machine_Elf might not be aware of it, and that there’s a _lot_ more to the modern understanding of evolution than “Survival of the Fittest”. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [April 27, 2021, 5:20pm UTC](https://boards.straightdope.com/t/genes-and-heritability/940862/7 "2021-04-27T17:20:23Z")
> [@Machine\_Elf](#): > > He goes on to claim that the “activation” of genes somehow makes them more likely to be passed on to offspring. This does make sense in a population/evolution sense. A beneficial gene that is activated would have higher odds of spreading in the population as those individuals would get the benefits and increase their survival. ---
**Author:** ![echoreply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/echoreply/32/3641_2.png) [@echoreply](https://boards.straightdope.com/u/echoreply)\ **Post date:** [April 27, 2021, 5:31pm UTC](https://boards.straightdope.com/t/genes-and-heritability/940862/8 "2021-04-27T17:31:48Z")
Genes are activated and deactivated all of the time in response to environmental factors. That’s one of the ways gene regulation and such works. In environment X, activate gene Y to produce protein Z, etc. Gene Y is always present, but sometimes it is turned off. I don’t think that’s what he’s talking about, though. I think he did just poorly talk about natural selection. If some people have a gene that produces that muscle during development, and that gives them an advantage in reproduction, then that gene will tend to become more common. If the extra muscle is neither an advantage or disadvantage, then the gene will assort randomly. It may by chance disappear, or it may stick around forever not hurting or helping.