Is there a clear distinction between selective breeding and evolution?
I think it depends on what you mean by “evolution.” All sorts of things can evolve, but if you’re specifically referring to Darwinian evolution, natural selection can be contrasted with artificial selection.
Evolution is run by the fact that life forms that are better at survival in their local environment tend to have more offspring survive to reproductive age than life forms that are not equipped to handle the threats and challenges of their environment. As a result evolution ‘picks’ life forms that possess the traits that enhance survival odds.
Selective breeding is human run breeding plans designed to promote a certain trait that humans find desirable (increased milk or meat production, seedless plants, plants with more starch and calories, friendlier dogs, dogs that look a certain way, dogs good at hunting, etc).
Selective breeding tends to occur on much faster timescales than evolution by natural selection. Farmed chickens weigh about 4x what they weighed in the 1950s. They went from about 1kg to 4kg due to selective breeding. Evolution that fast likely wouldn’t happen with natural selection. Maybe in some massive environmental change that killed 95%+ of life forms except those able to handle the stressors, but thats probably about it.
Also with selective breeding you can pick traits that are bad for survival but good for the reasons you picked. Examples would be dogs that are bred to look a certain way, but have trouble breathing. Or chickens that are bred to have so much edible meat that their legs can barely support their weight.
I’d go with no clear distinction. Evolution is the differential survival of organisms with traits well suited for specific circumstances. In selective breeding, those circumstances are “what the breeder wants”. If circumstances changed, the advantageous traits may change (all people die off, kernals of wheat may have an advantage in becoming smaller and less energy-intensive, for example) but all evolution doesn’t have a long-term direction, it only “sees” the moment.
A major distinction is that in selective breeding, the process of breeding and the selection of breeding partners is intelligently controlled while in evolution it occurs among whatever life forms manage to survive and thrive in the current environment.
I don’t see a major distinction there. In one case external circumstances are causing selective pressure on variable traits, in the other case external circumstances are causing selective pressure on variable traits. Evolution is blind—it doesn’t care if it is a bird wanting a tasty moth (so the moth becomes camouflaged) or a farmer wanting a tasty apple (so the apple becomes sweeter).
The major distinction is that one is being controlled and the other is not. Would you say there is no major distinction between a person driving a car and it rolling down a hill with no driver?
Evolution is blind. But selective breeding isn’t. One will produce what you want it to. The rest it’s essentially random chance if you get what you want.
If humans interfere with natural selection by, say, breeding heavier chickens that can’t stand on their own feet, then those humans will probably take good care of those chickens, at least until they make some more chickens. Thus, those chickens that have the human-desired trait have a survival advantage over those chickens that don’t.
This is substantially the same as “natural selection”, the only difference being that it is human-directed (which we can argue is “natural” or not in this context), and being directed, it works much faster.
But the “survival of the fittest” (for the human-decided value of “fit”) is still the principal of evolution. So I think @Darren_Garrison has it right.
Selective breeding is done with the end point in mind, Evolution is not. That’s the essential difference. I also agree that, in principle, all that is really different is that the selective pressure is a human preference rather than unthinking natural environments.
I thought evolution was just, per wiki, “the change in the heritable characteristics of biological populations over successive generations.” (In college, the version I heard was “change in allele frequencies over time, full stop.”) That it’s what’s happening, is all, regardless of whether it’s happening in response to selective breeding.
This must be qualified to make clear that evolution is the differential survival of variant life forms within an interbreeding population. If by “life forms” you mean different species, then your description is wrong.
Evolution is not the survival of one species at the expense of another species.
Suppose (say) Impala and Springbok coexist in a similar ecological niche in a certain area. If all current Impala are better equipped to survive in that environment than all Springbok, the Springbok may die out. But if that’s all that happens, no variant life form exists that did not exist before, so nothing has evolved. All that has happened is that the Impala are still alive while the Springbok are dead.
If, on the other hand, a slightly better digestive enzyme arises within the Impala population in one mutant Impala, then the advantage that this new variant enzyme confers on mutant Impala over other Impala may cause the mutation to spread to fixation within the Impala population. If so, the Impala population has changed - it has evolved.
Having said that - it may certainly be the case that the existence of a competing Springbok population creates greater selective pressure on the Impala population (and vice versa), causing both the Impala population and the Springbok population to evolve more quickly. It may be the case that the existence of Springbok competing for the same food sources makes the novel digestive enzyme that arises in the Impala population more important for Impala that carry it, conferring a greater advantage over other Impala. But evolutionary change takes place within a population. In other words, this:
Evolution in wild animals produces traits that are beneficial to the animals.
Selective breeding in domesticated animals produces traits that are beneficial to humans.
I think the OP is slightly mis-phrased. The distinction the OP is asking about is between natural selection and artificial selection. In both cases the population is evolving (by definition). So the question really is about the character of the evolution that takes place in each case, whether there are fundamental qualitative differences.
In the most fundamental sense of the population genetic principles involved, as others have argued, there is no difference. In both cases, all mutations arise naturally, and we see changes in allele frequency in the population influenced by external selective pressure, leading to a change in phenotype. The basic principle is exactly the same.
Whereas direct genetic modification - mutagenesis, transgenics, introducing genetic changes that do not arise through natural mutation - is fundamentally different from “natural” evolution.
I’m not exactly sure what the OP is after, but I imagine that selective breeding more often results in more inbreeding and monoculture, resulting in higher probability of genetic diseases and disease.
Obviously, it’s not always the case – population bottlenecks can result in the same problems. But the only way to reliably get changes on human timescales is through inbreeding.
So, it’s possible that genetic analysis could often determine whether an organism is the result of artificial vs. natural selection.
Well, evolution is driven by natural selection while selective breeding is artificial selection. Here, “artificial” means that human is making the decision as to which animals breed and which don’t, not in the sense of “artificial colorings and flavorings”. So as far as that goes, there’s an important distinction.
However, there’s no distinction in the way that the organism’s dna mutates, or how the traits are inherited, or how the animal reproduces or grows. This works the same in artificial vs. natural selection.
There are 2 qualifiers to this:
- Artificial selection can develop variations more quickly because humans are going to be more aggressive in culling out the undesirables and mating the desirables as often as possible.
- However, as far as producing an actual new species that’s fertile only to its same type… even the most aggressive selection process would take minimum tens of thousands of years to do. Humanity could conceivably do this, but it would require us to sustain a generational attention span much longer than anything we’ve ever attempted. It’s extremely hard to compete with natural selective processes that run unattended for millions of years.
Think of dogs… humans started deriving dogs from wolves something like 100,000 years ago. True, we’ve made the animals look far different than any natural process has done to wolves in the meantime. But genetically, anatomically, and physiologically, dogs are just a specialized type of wolf, they’re cross-fertile with wolves, etc. So we’d have to work a long time to do the same things that natural selection does over millions of years.
I would say that humans are part of the other organism’s environment. We’re natural. Yes, we think and form goals, but those are natural, too. Just as one wouldn’t say “Selection by which things get eaten doesn’t count as natural selection”, so too we also shouldn’t say “selection by which things humans like doesn’t count as natural selection”.
Agreed
Dogs have not evolved. ‘Breeds’ just represent variants in the worldwide dog population. There has been no speciation, so were all dogs released and allowed to breed naturally, the population morphology would revert to some common mutt whose characteristics are suited to the current environment.
But if all dogs but Saint Bernards and Chauhahas were euthanized, and those released, interbreeding (probably) wouldn’t happen. Dogs are a ring species.
Were your scenario to take place, there would be a progression toward the mean in both populations eventually resulting a merger.
Creating speciation by isolating two populations is Lamarkism.
Nobody can stop you from using words in whatever eccentric way you want, but the entire field of evolutionary biology is decisively clear that that when humans do it, we call it artificial selection.
Also not a correct definition. Lamarckism is the mostly discredited theory that when an organism changes in its lifetime due to its environment, the offspring inherits that change. (i.e. a giraffe stretches its neck by reaching into tall trees, and then passes that stretch to its offspring).
I say “mostly discredited” because the study of epigenetics has shown that Lamarck was accidentally correct in a very narrow, microscopic sense, but that’s out of scope for this topic.