Why Selective Breeding is a Bad Way to do Genetic Engineering

by GeneSmith2 min read5th Mar 202114 comments

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Human GeneticsWorld OptimizationWorld Modeling
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A Brief Intro

During any conversation about genetic engineering, people inevitably bring up worries about eugenics movements of the past and often use the cruelty, bad science, and objective failure of these efforts as an example of why we shouldn't ever try anything remotely related again. In this short post, I'm going to summarize why I think selective breeding of humans is bad both from a moral perspective and ineffective as a means of improving human genes.

Selective breeding at its core involves taking organisms that score well on some test of desirable traits and enabling them to reproduce at higher rates than organisms that score poorly. Despite its many flaws, this technique has lead to amazing gains in both agriculture and animal husbandry, and allowed domesticated corn crops to undergo this incredible transformation over the last few thousand years. Picture showing corn at various stages of natural selection

But despite the amazing performance on crops, there are reasons this technique would not work very well on humans.

Humans are Slow Breeders

Every generation that you selectively breed an organism you get some gain in a particular trait. The faster reproduction happens, the faster you see improvements in the trait(s) under selection. Humans are extremely slow-breeding animals. Though humans are capable of reproducing sometime in early adolescence, most humans today opt to wait until their 20's to 30's to have children. This is a very very long time if you want to do selective breeding.

Selective Breeding Leads to an Undesirable Reduction in Genetic Diversity

Genetic diversity is valuable. Because selective breeding can only work by throwing entire organisms out of the gene pool, it naturally ends up reducing a lot of desirable genetic diversity. Even organisms that don't score well overall will still have many good genes. With selective breeding, there is no way to keep this valuable genetic diversity unless one were to select the best X% from every lineage in a population.

Selective Breeding Creates a Single Point of Failure

The right to reproduce is foundational to all modern societies. Even in societies that do place restrictions on reproduction, such as China with its one-child policy, the restrictions are not total: each couple can still have a single child. In order to make any notable gains in desirable traits from selective breeding, one must necessarily only allow a small portion of the population to reproduce. This would require an incredible concentration of power in the regulatory authority, and the pressure on regulatory officials from powerful people who want to be able to have children would be immense. I see rampant corruption as nearly inevitable in such a system.

Not only that, but concentrating power in this way creates a single point of failure. It is not too difficult to imagine such a system becoming corrupted by discriminatory ideology. In fact, you don't even have to imagine it because this type of failure was exactly what happened in Nazi Germany before and during World War II when they implemented a eugenics program based on racist ideology and belief in a fictional Aryan "master race".

Selective Breeding is Cruel

For myself personally, this is the most compelling reason to not use selective breeding: it is a cruel judgment upon those who, through no fault of their own, happen to draw the short stick in the genetic lottery. The desire to see some part of ourselves live on past our death is nearly universal, and the most common realization of this desire is through having children. Restricting this ability, even if it would result in future generations more capable of carrying on the human legacy, would be an enormous price to pay.

Though we may recognize that certain genes confer advantages to an individual, we must not confuse human ability with human value. As humanity enters the age in which we will be able to rewrite our genetic source code, I think this is one of the most important lessons for us to remember.

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In order to make any notable gains in desirable traits from selective breeding, one must necessarily only allow a small portion of the population to reproduce. 

It's unclear to me that this is true. It might very well be possible to have people who aren't in the selective breeding group to have one child per couple and the selective breeding group have more children then that.

Though humans are capable of reproducing sometime in early adolescence, most humans today opt to wait until their 20's to 30's to have children. 

You can harvest male sperm faster then that and put it in sperm banks. Male sperm is also much more easy to scale. 

This is a good point, though even with one child you'd have a significantly lower per generation gains. I'd have to model this to get a clear idea of how it would function. I guess part of my theory here is that parents would still have to raise their own children, which would limit the number of offspring high-scoring individuals could have.

I did some quick maths and determined that if one were selecting strictly for a single trait and were to take the top 11% of scorers and that entire group was to have 10 children each (while the rest of the population was to have 1 child), your population would have an average trait score 2/3rds of one standard deviation above the previous population's mean. Not a trivial difference, but not that great.

Furthermore, if this was really being done you'd end up with a highly hierarchical society where all those who were not among the top scoring fell further and further behind. In fact, this will likely be a problem even in what I would consider well designed genetic engineering schemes, though the gap in those schemes would be more generational.

I think this is missing the very critical understanding that selective breeding is completely unavoidable.  Not every possible pairing occurs, and those that do occur produce different amounts of offspring.  Both of these factors are controlled by human choice.  

Your points make more sense if you talk about WHO is doing the selection.  There is no "we" in this, there are only billions of individuals, all doing some amount of selection.  Some imposed coordination would be problematic, but that's because the imposition is evil, not because of selection itself.

I didn't see the need to clarify because I've never heard anyone use the term "selective breeding" in the context of individual mate selection. Of course you're correct that individual choices about whom to reproduce with affect trait selection, but I don't think many people find the ability to choose one's own spouse problematic.

The right to reproduce is fundamental.

It might be that creating new consciousnesses is a fundamental right, but merely stating it is just sweeping a (tricky) subject under the rug. And even rights have limits when they collide with other rights. Imagine someone has a genetic trait that condemns their offspring to constant excruciating pain. How about the right not to be born just to suffer?

Selective Breeding is Cruel

For myself personally, this is the most compelling reason to not use selective breeding: it is a cruel judgment upon those who, through no fault of their own, happen to draw the short stick in the genetic lottery.

How about people who are not attractive then?

Though we may recognize that certain genes confer advantages to an individual, we must not confuse human ability with human value.

Differences in ability already lead to different opportunities for breeding offspring. Should we correct that too?

It might be that creating new consciousnesses is a fundamental right, but merely stating it is just sweeping a (tricky) subject under the rug. And even rights have limits when they collide with other rights. Imagine someone has a genetic trait that condemns their offspring to constant excruciating pain. How about the right not to be born just to suffer?

You're right, there are definitely some corner cases in the "right to reproduce" where we might make exceptions, such as extreme suffering of the offspring. I'm going to change the wording of the original post because it came across as more absolutist than I meant it to be.

How about people who are not attractive then?

Frankly I agree that unattractive people are not treated well by our society. It is one of many unfortunate things about the current state of the world. It would be nice if everyone was attractive, just like it would be nice if everyone was intelligent and had low risk of lung cancer. We should work to fix such issues.

But we have a choice to make about how we pursue genetic engineering, and I was merely trying to make the point that CHOOSING to pursue it via selective breeding would introduce additional cruelty into the world not already present.

One don't need to limit breeding ability to get genetic selection: just move those who you not interesting on into outside world. For example, i want to breed dogs who are good to live in mountains. I put a group of dogs on a mountain. As generations pass, those dogs which are good in living in the mountain will remain there and even move higher, and those who are not good in it, will move to live in plains. Those who live in plains may even have higher number of children.

As a side note, here's the succinct algorithm I thought of the "clean up" the human genome.

For each allele:

       Sample across the population, find the prevalence of different versions of the allele

       Expected : most alleles are going to be either [99% version A][1% or slightly mutated A]

        Take version A, the other versions are incorrect

       Some Alleles will be in the form of [40% version A][50% version B] [10% mutated versions of A or B]

        In this case, look at the data and try to see if A or B is statistically correlated with a desirable trait.  If you               can't determine, choose the version the parents of this designer baby have.

 

And that's it.  You don't need to know what most of the genes do.  Statistically speaking you are going to almost always be right with this algorithm, the resulting baby will not be uber but will not have as many problems as baseline humanity, because by simple probability, most mutations are neutral or deleterious, and a significantly beneficial mutation will have a prevalence greater than 1%.

You're right that most de novo mutations are harmful, but I don't think this strategy is necessarily optimal. There's no guarantee that rare alleles are harmful.

In this case, look at the data and try to see if A or B is statistically correlated with a desirable trait

This is more or less what I think the correct approach is, but you're glossing over a lot of detail. There are big questions around HOW to do this, to what degree desirable traits are heritable, as well as tradeoffs inherent in the human genome where the answer as to which variant is the "better" cannot be given an unqualified answer.

I am not saying the algorithm is optimal. But it's safe. Suppose you find a rare allele that your protein folding model predicts improves function. Why didn't nature pick it? There may be a long term problem you can't model, while picking the majority allele is a less risky choice.

Basically, nature only cares about what works over a reproductive lifetime. But nature has information you won't have in any feasible computer model as it is sampling from actual lives.

It may be safe from an individual perspective, but if you always pick the more common allele, you are converging towards the modal genome, which would be a world where everyone is a clone of everyone else.

Genetic diversity is valuable both as a hedge against disease and because it lends itself to specialization, which is an important part of the modern economy.

This post isn't wrong, but I doubt anyone today (except a few crazy people) disagree with it. Do you think there is a significant risk of a large-scale human eugenics program happening before direct genetic modification becomes cheap enough to make this irrelevent?

No. I wrote this as a reference post for another larger post I'm writing on the topic of human genetic engineering. I will link to this as a brief summary of why I think other approaches to genetic engineering are better.

This was written as more or less a reference post for a larger post I'm writing on the topic of human genetic engineering.