Nature vs. Nurture

Hui Zhou raised some interesting points in the comments to my 15 mile race results post. He even when on to write about some of our very divergent views on this issue. I made a comment about not having natural aptitude for running. The crux of Hui’s argument was this “So, when you say “natural aptitude”, do you recognize the snowball effects of pure experience? How much in us are real natural? or is it just experience difference matters?” For me, the answer is a bit of both.

I run a genetics research lab and am firmly convinced by the data I see daily that genes (nature) have a huge impact on physical and behavioral phenotypes. However, even genetically identical individuals can have significant variation both behaviorally and physically that is typically written off as either environmental (nurture) or stochastic effects. In general, I tend to view most traits as continuums (tall–short; fat–thin; strong–weak; smarter–dumber). Some of these we can change with training and practice, whereas others we cannot. I would love to be taller but it simply is not something I can change. I used to have a martial arts teacher that tried to teach us to fight strategically rather than with brute force. Just about every class he would remind us that “there will always be someone who is faster, smarter, stronger and better looking.”

So when I say I have “no natural aptitude” for running it is because genetically I am more endomorphic than ectomorphic like “natural runners.” The skeletal structure of my hips is wider than most great female runners. Sure, I have legs and can train. So, I do have some innate capacity for running but I don’t think this will get me to the front of the pack, even if I keep striving at it. Conversely, I may end up being able to run faster and further than someone with a natural aptitude for running who never trained to run. But I think that the point where the training will plateau is largely driven by “natural aptitude.”

So Hui, we may not come to agreement on this but I thank you for an interesting discussion.


Edit to address Hui’s comment below:

Hui, I’m not sure that I agree that running fast and far was one of the essential characteristics of our survival and evolution. I might instead say that using our brains to hide and avoid having to run fast and far might have provided an even greater advantage. But lets stick with running for now.

Human beings have about 20,000 to 30,000 genes encoded by our 3 billion DNA base pairs. On average, every 1000 base pairs there is a polymophism or variation between just about every person on the planet. This is a significant amount of variation between individuals. I’m not sure how many genes are involved in running performance but let’s assume that this number is between 10 and 100. There are 1000’s of different proteins needed to make up our muscles and bones so this is a very low estimate. Now let’s assume that most of the variants work pretty well (not a disease state) with differences in function for a single gene/protein being between 0.5 and 10 percent. That is, each one is between 90 and 99.5% as good as another. The real variation happens when individuals get all of the optimal or suboptimal versions. I’ve put together a very quick table that shows the impact of this effect depending on how much variation there is between each version and how many genes play a role in the trait of interest.

number of genes
gene variance 10 25 50 100
99.5% 95.11% 88.22% 77.83% 60.58%
99.0% 90.44% 77.78% 60.50% 36.60%
98.0% 81.71% 60.35% 36.42% 13.26%
95.0% 59.87% 27.74% 7.69% 0.59%
90.0% 34.87% 7.18% 0.52% 0.00%

So if the genes variants are substantially similar, and very few genes are involved I should be 95% as good as olympic runners. If there are more genes involved, you can see how, just by the random chance of gene assortment, I can very quickly become an innately bad runner.

Obviously, the chance of getting all of the bad genes is quite remote (it requires your parents carry them and transmit them, etc.). Let’s assume that there are only 2 versions of each gene and that each gene is equally common in the population. Now let’s assume I had average parents who had one good copy and one less good copy of each of the genes. If I use the example where only 10 genes are involved in running performance, the chance of inheriting both bad copies (the less good copy from each parent) is (0.25)^10 or 1 in 1,048,576. The chances of inheriting all of the good copies is identical. Thus, in my opinion, elite atheletes will be rare. Most of us can do OK. And some group of people will have utterly no capacity for athletic performance.

Here ends my lovely lesson in genetics for the day. Hope this clarifies a bit where I am coming from.

4 comments on “Nature vs. Nurture
  1. Hui Zhou says:

    Let me know whenever you get tired of my argument 🙂
    genes. Certainly I can’t, won’t deny genetic roles. A monkey can never remotely compete with a human. However, for any given species, I don’t think there is any significant portion of them are genetically doomed to underperform the rest.
    First lets get genetic defects out of the way. There is alway certain amount born with genetic deseases, and those are rare and gets excluded quickly by evolution. And there are possibility of genetic defects that outperform the rest of species, those are pioneers of the evolution, and is even more rare. And for the rest of the species, they all survive and gets inherited generations after generations. I tend to think about evolution as a filtering process. Any underperforming genes will lose its population after each generation, and after millions of years (or should we look at a even more grand scale?) of evolution process, our survival ability is as pure as 24k gold. Certainly there is still infinity variations among one species, but can I say that all these variations are not related to their survival abiblity?
    So I won’t argue that we are born with various physical shapes, but the reason all these variations get passed down the evolution path is because they doesn’t determine that one group of people with one shape will systematically underperform in a ability that related to survival, directly or indirectly.
    Then the question is which ability is related to survival and which is not. I think any judgement that reaches specie-wise recognition is about an ability that relates to suvivial. We all recongize running faster and longer is better than running slower and short. So running is an ability that relates to human suvival and I think our potential on it is about the same, despite what body shape in your dna.
    Sidenotes: Running faster may not be as related to our survival as 5000 years ago, but I think for a species and evolution, 5000 years is just too short to look at. After another 5 million years, the dominating species on earth may no longer have functional legs. 🙂 Guess will they try to have a race on legs?
    Sidenote2: So is bodyshape and obesity. It certainly may well have some relationship, but the determining factor is others. Bodyshape plays negligible roles. — just my opinion, not thoroughly reasoned.
    By the way, don’t you think techniques and body balancing and blood circulation (what is the word?) plays a much important role than body shape?
    You may say that because one can use training to overcome one’s inherent disadvantage so those genes gets passed down the evovlution path. But look at the number of generations and amount of samples in each generation, any systematic error (here, underperforming genes) after such amount of filtering, it will show up. So if one body shape systematically runs slower or shorter than others, considering running being a critical ability in ancient survival, the portion of such genes, if still exist today, should be very rare. The reason that we still have significant portion of each body shape in each race, it just means the role of body shape plays a negligible role in the performance of running.

  2. Cathy says:

    Hi Hui
    I’ve addressed some of your comments by editing the original post. I wanted to put in a table and was not sure typepad would let me put it here.
    Please don’t get me started on Obesity. We are designed for famine and there is simply too much food around right now. However, most other species know when to stop eating.

  3. Hui Zhou says:

    —“Please don’t get me started on Obesity. We are designed for famine and there is simply too much food around right now. However, most other species know when to stop eating”
    :)Sorry, can’t resist.
    Most other species don’t know when to stop eating. But most of them are limited by environment. Lions don’t know how to raise lambs, and lambs are eating as much as they can and don’t know how to eat food with much higher nutrition density. We, on the other hand, lacks this limit, unless we were restricted in poor Africa.

  4. Hui Zhou says:

    Now back to your article.
    I raise two points here:
    1. I think the genes that related to running is far greater than 100. As we start think about the process, running really is a full body – mind activity, especially for marathon, and almost every of our body/mind function can come critical during the running process, right? Maybe you disagree, but would you agree that there are much more than 100 critical genes involved in one’s natural ability in running?
    Now assume it is random distributed and each of these critical genes contributed equal, it will be a gaussian distribution, the odds of extreme born excellent is very rare, so is extreme born poor. Let’s use 100 genes as an example, then around 99% of the population will have 40-60 good genes (asuming each gene is either good or bad), which is to say, given a group of 100 people, I should have confidence that my born abiity is as good as at least 98 others. — I can’t help realizing that my math get pretty rusty now 🙂
    So I won’t deny your calculation in the table, but if you are lucky enough to have the numbers in your table, you should have the confidence of buy a lottery and win it.
    2. Then there is the question how much role of the variance of each gene plays. You made a guess from 0.5% to 10%, my guess is much smaller, let’s say less than 0.01%. My reason is the evolution filtering process. By each generation, the unfavorable genes gets filtered off by certain percentage. No matter how inefficient this filtering process is, by millions of years of path under one environment, the gene variance that effects our ability become so small that I felt confident enough to guess — <0.01%
    --abount the role of running in our survivial during evolution. Of course using our mind to circumvent physical inability plays essential role in survivalship. But lets give it an average. on average, one human has the equal chance of successful hiding and circumven physical by using tools and strategies, but there is always situation that one have to resort to running, running to catch prey and running from predators. So if there are genes that systematically renders one's inability to run fast enough, the population that hosts that gene will have a higher chance of die before raising next generation; thus the overall population percentage that hosts that gene shrinks. And imagine repeating this process millions of times.
    And remember, we are looking at a scale of million years and even 5000 thousand years ago, imagine how often one would rely on running to get survive.
    But it certain is not true not any more. It is fun to imagine what the dominant species on earth would look like 5 million years later. 🙂