Can domestic breeding be considered evolution?

Question

Domestic breeding of animals (and plants) by humans seems to match some of the definitions of evolution I have been able to find:

• "a process that results in heritable changes in a population spread over many generations." (the TalkOrigins website)
• "cumulative inherited change in a population of organisms through time leading to the appearance of new forms" (Merriam-Webster)
• "Changes in the heritable attributes of populations of organisms over time" (this SE's 'evolution' tag info)

But other definitions seem to be less of a fit:

• "the way in which living things change and develop over millions of years" (Cambridge)
  (domestic breeding does not take millions of years)
• "The process by which different kinds of living organism are believed to have developed from earlier forms during the history of the earth" (Oxford)
  (Does breeding lead to different 'kinds' or organisms?)
• "The gradual development of more complex organisms from simpler ones" (Chambers)
  (Breeding may not result in more complex organisms)

I've seen people argue that domestic breeding can not be considered evolution, because domestic breeding:

1. does not involve natural selection
2. doesn't direct towards 'fitness'
3. does not lead to new species
4. decreases, rather than increases, the size of the gene pool (is this actually true?)
5. does not (or may not) lead to more complex organisms

I was not able to find whether or not there is a general consensus among experts from relevant fields on whether domestic breeding can be considered evolution. Is there?

EDIT: I've made the list of arguments I've heard against calling it evolution a bit clearer, and also added an extra one.
EDIT 2: Added why the second set of definitions seem to exclude domestic breeding as evolution

Answer 1

Yes, selective breeding results in evolution.

Definitions of evolution

I don't understand why you say that for 3 of the definitions you found, selective breeding would not be considered as evolution. To me, all of these definitions match with the idea that selective breeding results in evolution. If you think otherwise, can you please explain why?

There are a number of related definition out there, some of them being more clear and straight forward than others. The simplest definition is probably the classical population genetics definition which says

Evolution is a change in allele frequency over time.

See wikipedia > allele. You might want to have a look at How to define evolution? too.

Under this definition, any event of death or birth in a population is evolution as it affects allele frequency. In the human species for example, that means an evolution happens about 254 times per second (computed from these numbers from ecology.com)!

Specific statements

All these statements are stupid and none-sense! The easiest is probably for you to just have a look at an intro course to evolutionary biology (such as Understanding Evolution by UC Berkeley for example) and you will be able to refute those statements yourself.

Let's go through these statements...

1. There is no natural selection

First, evolution is much more than just natural selection. There is genetic drift, mutations, gene flow and plenty of interacting processes.

Second, it is silly to separate natural selection from artificial selection (aka. selective breeding). The only difference between these two is that in artificial selection someone is willingly affecting the environment of the individual to affect selection pressures. This is really it.

Note, btw, you never totally get rid of natural selection. Under selective breeding you may affect the environment but some things will remain the same. For example, a mutation causing the cell membranes to be extremely unstable will not be selected for whether under an artificial setting or a natural one.

2. It doesn't direct towards 'fitness'

The claim is unclear. What is "it" and assuming it refers to a population, then what does it mean a population is directing toward "fitness"?

Fitness is a function of survival and fecundity. Each genotype is associated to a particular fitness in a specific environment. Ignoring stochastic processes such as genetic drift, the mean fitness of a population is increasing from one generation to the other by the amount of the additive genetic variance. This is true for (artificial or natural) selection.

The only thing to consider is that the environments under which this happen is different. Under selective breeding, the population evolves to a higher fitness for the specific environmental conditions set by the farmer (or who ever who selectively breed). It is possible (and quite common in fact) that genotypes associated with a high fitness under one environment has a low fitness under another environment.

3. It does not lead to new species

In short, 1) it does lead to new species 2) the concept of species is often meaningless as poorly defined 3) evolution > speciation. In more details, below..

1. It does lead to new species. Different lineages of cabbage are considered different species. Cows and ox are different species. Pigs and boars are often considered different species. While wolves and dogs are considered same species, some lineages within this species (such as a Chihuahua and a Great Dane) are, I think, reproductively isolated. You might also want to have a look at the post Have we ever observed two drosophila lineages that evolved reproductive isolation in labs?

2. The question of whether selective breeding lead to speciation or not does not matter much on the question of whether it leads to evolution. Speciation is one outcome of evolution but is definitely not the same as evolution. Evolution does not need to lead to speciation. For example, evolution of the lactase gene in humans (see this post) did not lead to any speciation. It is still an evolutionary process.

3. The concept of species is mainly arbitrary. If you want to understand the concept of species, have a look at the post How could humans have interbred with Neanderthals if we're a different species?.

4. It decreases, rather than increases, the size of the gene pool (is this actually true?)

The term "size of the gene pool" is very undefined. I suppose, it just means genetic diversity, aka. expected heterozygosity.

All act of selection, whether artificial or natural, decreases genetic diversity. This is correct. Mutations is the fundamental process increasing this genetic diversity and selection selects the variants associate with the highest fitness.

Because, the selection pressures imposed under selective breeding are often extreme, the decrease of genetic diversity via selection is often faster in selective breeding than in nature.

Note however, that if we split a lineage in two and select the two populations under different optimas, then the total genetic diversity will increased (the within-population genetic diversity will still decrease). As such, via selective breeding we created a gigantic diversity of dogs and a fantastic diversity of cabbage but each cabbage lineage (e.g. brussel sprouts) and each dog lineage (cocker spaniel) have very low genetic diversity.

What the claim is suggesting is that because selection is often stronger (and therefore change in allele frequencies is faster) under selective breeding than in natural environments, we should not consider artificial selection as resulting in evolution? How silly is that!

Answer 2

The answer is "yes". Evolution is defined as a change in heritable characteristics of a population over generations, and to me, there is no reason not to define domestic animals as populations.

The statements you list can all be refuted:

1. Part of the selection human-driven, part "natural". You cannot control all genes.

2. The concept of fitness talks about offspring and contribution to the gene pool. Humans enhancing the fitness of desired individuals should also count as fitness. It is just the "human selection" that partly drives the evolution (i.e. human selection works as an environment).

3. Dog, chicken, cow are all species created by domestic breeding. They are all considered species by some biologists.

4. Strong selection pressure sometimes decreases the size of the gene pool, but again if you take dogs as an example: they are likely genetically more diverse than wolves. There are so many factors involved in domestic breeding that you cannot say that it decreases the size of the gene pool. It can go both ways.

But again, evolution is a human-created concept to understand our surroundings. If somebody wants to think that humans should not be a driving factor in evolution, that is fine for me.

Next logical question would be whether gene-manipulation is evolution. I will leave that for someone :)

Answer 3

There is not consensus among scientists, that human sciences of should be equaled to natural sciences.

Scientists don't agree if pets and farm stock are new species, and we all agree, domestic animals are in a different, recent, group to all other and selection processes. It's Yes and No andwer. It shares and conflicts with evolution and seems to deserves a human sciences category of it's own.

"Evolution of the chihuaha specif traits from the wolf", wouldn't qualify for a science journal.

Survival of the funny looking animal, for a dominant species, that has a large brain, that devises breeding methods. Contrary to survival of the fittest. It's a form of evolution that was seen only 50k years from 4 billion, that's 0.00125% of evolutionary history. You can compare it to evolution of captive algea used by coral, and ant-aphid relationships.

Darwin studied the topic for decades, and in the actual title of his book he wrote "Natural" selection, so he clearly made a mental difference between human and wild, natural processes.

The difference of the concepts is similar to human geography and physical geography. They are described by different books.

To make a language's semantics clear, it's best not to group different groups of processes with the same word, when new semantics be invented where a discussion is required to differentiate the two.

It's the only form of evolution that uses artificial foods, artificial walls and fences, artificial mating, to make funny looking animals for amusement, and social animals companionship and work.

The result is generally low fitness, stamina, immune system, fainting goats, deaf dogs, dogs that can't breathe well due to snout length, dogs which are tremendously unfit. and animals that are fit for human amusement.