Reading the book how the mind works Pinker talked about how our brain tripled in size in about 2 million years. He also mentions how in that timeline there was enough time for our brain size to triple, shrink back down again, regrow, etc and possibly do that several times.
Seeing how 2 million years equates to about 100,000 generations I am sure he is right. Even a growth of 1% or shrinkage of 1% a year should, I assume, be possible per generation. So how much more selective pressure does intentional selective breeding put on organisms vs. natural selection?
I know foxes can be turned into dogs in 20 generations doing this, we have a lot of experience with agriculture and pets being bred for certain traits.
I don’t know if this question has a factual answer, but how much more pressure on trait development does controlling breeding with an end goal have on evolution vs. natural selection which seems like it would only have minor effect.
In natural selection, not everyone is going to be killed by X before they breed, and many organisms will be killed by something other than X, and some will be killed by X after they breed, so the traits to combat X are not going to grow extremely fast. however if you want to create resistance to X intentionally you just get a giant pool and mate the best ones at that, then repeat generation after generation).
I assume with selective breeding the risk for unhealthy side effects is higher, since you do not have as long a timeline to weed out the errors that come along with trait changes.
Tripling in size over 1 million years is an average increase of about 0.0001% per year. If you could increase by 1% per year, you would triple the size in a little more than 100 years.
Natural selection favors fertility over many generations. Selective breeding favors any trait in a short time frame. We have no idea of what 2 million years of selective breeding will produce, but we know it produces results in a much shorter time span or people stop doing it.
A dog can produce 2 litters a year that can breed in 9 months, a human can’t duplicate that even if we harvest eggs and sperm and breed in labs. I believe humans contain the genes for dramatic changes but it will take a long long time to realize anything substantial.
Take as an example the races of man. If we accept that we started from a bottleneck population about 70,000BC, then it took less than 70,000 years for different people in different areas to develop adaptions useful to their environment.
Asian/Siberian peoples and eskimos have flat noses to avoid frostbite in winter, while Europeans developed facial hair to a greater extent to get the same protection… Northerners have lost their skin pigment (assuming coming from Africa that was the starter position). This allows that population less shielding of the body from vitamin D production from the weaker sunshine during winter in higher latitudes. I read that the Indians of the Andes were starting to show significant adaption to high altitude living. And so on…
Evolution takes in the whole picture. Selective breeding risks the breeder ignoring linked detrimental characteristics. Ask dog owners - some breeds are “high strung” like some horses -which means they can fly off the handle irrationally like “special” humans. Some fancy dogs are prone to hip problems. A friend of mine with Dalmatians (the dogs) swore they were the dumbest things on four feet. Modern pigs, for example, have been bred as huge fast-growing meat factories to the detriment of brains - they have to be restrained lest the mother rollover on her litter, for example. Heritage breeds were almost as smart as a smart dog.
In selective breeding we substitute human support to protect badly adapted animals from the consequences of their genetic shortcomings, so the breeding cycles can focus exclusively on one set of characteristics. In evolution, the selection is much more general, so charcteristics evolve much more gradually.
Plus, its not about “how fast?” or growth rates. The current popular theory is that a lot of evolutionary change in species happens in spurts, very fast when the ecological niche a species occupies changes, or new ones open up. Rather than the brain growing .001% a year for a million years, perhaps it doubled in 10,000 years when the time was right - when suddenly brainpower conferred a greater advantage. (Perhaps when well-organized cooperative hunting meant far better results, or complex language offered more opportunities forconveying plans to others.)
Both are equally fast, with change only occurring each generation. Selective breeding just looks fast because it’s under conscious, planned direction and therefore any changes are consistently towards the planned goal. Most of the time natural selection just “jitters in place” for lack of a better phrase; it has no particular direction so it isn’t noticeably moving.
In cases where there is a strong direction being imposed on natural selection it can result in dramatic changes just as fast as selective breeding. The peppered moth being a commonly used example of this.
We often think of dogs, cats, livestock, and rats to be the main animals that live around humans. The Stone martin from europe is something I have wondered about geneticaly. From the little I have found on them they appear to live almost exclusively around human settlements. I wonder how much they have changed in the past 10,000 years.
Yes but if we were intentionally trying to breed bigger or smaller brains, I would assume an increase or decrease of 1% per generation would be possible with selective breeding. I don’t know why I said 1% a year.
The trouble with selection, is you only select for one trait, typically As an example, racehorses are selected for speed - with a fairly aggressive breeding program. What we don’t select for, except in extreme cases, is the concurrent development needed to support that speed. Quite frequently you hear of a horse shattering a leg or an ankle, because we don’t select on bone density needed to support that speed, except to shoot the ones that fail spectacularly.
You don’t hear about cheetahs regularly breaking their legs. We might have been able to breed a slightly faster animal if we concentrated on speed and nothing else, but mother nature has taken her time and created an animal that not only is spectacularly fast, but has the internal infrastructure - so to speak - to support that action. Mother nature isn’t holding time trials and running stud farms; a cheetah does not have to be fastest on the continent to get offspring, they just have to be as fast or faster than their fast-food lunch.
I was warned by the President (? Something or other) of the Golden Retriever Society of America to “run, not walk” from breeders who announce they are exclusively “white”/cream Goldens.
A good breeder will breed for everything: conformation, character, true to type, etc. Focusing focus on coat is still not compatible, in the main, with the other characteristics good breeders strive for.
However, and more focused on OP, I think British Goldens have a much more solid genetic history of cream-colored Goldens than present currently in the New World. Goldens were originally bred in England in the late 19th century.
Natural selection can work very slowly or very quickly. Selective breeding is generally going to be more speedy, but not necessarily always more speedy. And then there’s genetic engineering, which is a whole different thing, and can produce crazy things (like glowing mice) that might never be able to be produced by selective breeding.
Nm, I can think of a case myself, sort of. Race horses haven’t gotten any faster despite years of selective breeding. They aren’t really bred for speed, they’re bred to win races, and since they are filled with genes from past Derby winners it’s probably all an illusion.
Yup. Maize is the most dramatic example I know. It looks no different now than it did in your childhood, but it looks an awful lot different than it did 3000 years ago.
I don’t understand the question. It assumes that all selective breeding proceeds at the same pace. Since we know that’s not true, then some instances will, of course, produce results more slowly than others. It’s all relative (said Einstein to Darwin. )
Shoud have thought more about this. We do plenty of selective breeding that is not intensive selective breeding. If a dog breeder doesn’t get improved traits in a couple of generations they’ll go in another direction. Farmers planting grains won’t see such immediate signs of success, but they’re not going to stop growing wheat that doesn’t improve year by year.
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