There are some breeders of Shetland that feel that too much selective breeding toward specific wool types, horn phenotypes, colors, patterns, etc. could cause Shetlands to lose their natural hardiness, thriftiness, easy lambing, adaptability and longevity. Some breeders try to select for these traits. However, as breeders, we still have favorites in the flock based on friendliness, phenotype, bloodlines, etc, and we do give care to sick and needy animals. We are bound by what is humane and responsible. We deworm. We cull rams that have fatal horns. We build shelters for the sheep to escape the elements. We have breeding schemes. We manage a flock, we selectively breed according to a Standard, therefore we manage the genetics and the very essence of the sheep. Even if we select for specifically "natural" traits, we are still confined by the limits of the 1927 Standard. A good shepherd must cull even his hardiest sheep if it doesn't fit the breed. We practice Artificial Selection.
Even sheep on Foula, considered to be the most "natural" and unselected of the shetland breed, are subject to some human selection.
"Natural traits" are relative to the Animals Selected by Nature, animals that are naturally selected.
Fitness, also called Darwinian fitness, encompasses the ability to survive to reproductive age, success at finding a mate/s and producing offspring. Basically, the more offspring an individual makes during its lifetime, the greater its biological fitness. The better "fit" it is to it's environment, the more likely it is that it will produce offspring.
- If populations of animals at the mercy of Natural Selection are more "fit" than those who are Selectively Bred by humans, could Natural Selection be simulated?
- Can one simulate Natural Selection while conforming to the specifications of a Standardized Breed?
Those questions came about during a discussion I had a while back over this question:
Are Wild animals are more "fit" than their Domestic counterparts, more likely to better adapted to their environment genotypically and phenotypically, and more likely to live longer, and produce "biologically stronger" offspring than those in a domestic (farm), and further on, industrial (mega-farms)?
Here's an outline of a simulation of Natural Selection I put together at work one night post-discussion, the context being with Shetland Sheep. I had to try and make sense of my own scribbles, so if it's a little rough, I'm sorry.
Natural Selection also varies due to a number of factors:
Environment- Changes in the environment cause changes in the population. Changes in the population cause changes in the environment. There is always a response somewhere. The more common traits in the population are traits that best fit the population to the environment. Natural selection is not so much random in that sense, on a large scale, however, but may be slightly random in regard to specific animals.
Mutations- Mutations may occur causing randomness, genetic variation, traits that may not typically occur in that population in response to that environment. This aspect of Natural selection is quite random. I will try to simulate both randomness and non-randomness.
Selecting the Founder Animals:
Randomly- all animals are chosen randomly. Bottleneck. This would be the most "true".
Variation- start off with the greatest range of variation you can find. You must choose good and bad, defective, old, young, polled, horned, patterned, solid, extension, spotted, everything. I don't see how this one can be easy, or fun.
Intermediate- As close to middle-spectrum as possible. Would be very fun to watch "drift" over the course of time.
Best- choose the very best examples of the breed you can find. These would be animals that had been Selectively bred for generations. This one would would also be fun to watch, as reversion or evolution could potentially occur.
Natural selection involves no deworming or extra feeding for animals that need it, so you'd have to get rid of the that.
Breeding Season would consist of one ram with all the ewes, so as to know the parentage of the lambs, and best gather data from this entire thing. The ram would have to be selected randomly from a group of rams. Writing each ram's name on a slip of paper and drawing from a hat would probably be the most random way of choosing. In a natural environment, the ram that creates the most offspring, is the one that is the most productive. This doesn't necessarily mean the ram is the most dominant ram, or that that ram is the most suited for it's environment. It's the ram that bred with the most ewes and/or produced the most lambs. That's something you can't really predict, or determine prior to lambing, so in that sense, randomness is "true" in this situation.
I am not sure how long the ram would have to be kept with the ewes for, as you could keep him until lambing to ensure all the ewes are bred, but then that might allow some genetics to pass on that may not have, had the ram not been able to reach/breed with these ewes/ the ewes had not cycled at the same time as the ram. Your best bet, if you wanted to be the most "true", would be to leave the ram in with the ewes for entire year. This way, if the ram does not breed with the ewes, it is not because you removed him.
There'd also have to be some form of culling. In wild populations, the size of the population fluctuates in response to the environment, predators, fertility, etc If there was no culling, your population would expand exponentially until the culling took place by itself, which would not end well for you.
In a Domestic situation, people tend to keep the ones they like, save the sick from dying, keep a few pets, and sell all the ones they no longer want in their flock's gene pool. The people select for certain things, and their flock changes because of it.
Culling in the wild is done somewhat randomly. The animals that are least suited for the environment will typically die off first, then the old or sick or disabled (natural causes), then, any that die off due to accidents (falling off a cliff, eating something poisonous, running in front of a car, drowning, getting stuck in a mud bog, being crushed by a boulder, lightning strike, etc.), and then any that are killed by predators. In this case, random culling in the situation would be okay, though not necessarily 'true'.
Again, draw names from a bag, the first however many drawn are kept, the ones not drawn, are culled. This process would be the same with the rams. After the first cull cycle, your population should have changed either very little or quite a lot, in response to what has happened. Your flock may have more genetics from the first breeding ram, or it may not. Instead of drawing a set number, possibly just reach in and grab a handful, that will determine your population size. The more you grab, the higher the population, the more likely for genetic diversity. The less you grab, the lower the population, the more likely for genetic drift to occur over time.
If populations of animals at the mercy of Natural Selection are more "fit" than those who are Selectively Bred by humans, could Natural Selection be simulated?
-Yes, and no. You can create a situation in which genetic drift will occur, but it is not exactly by natural means. Therefore, not exactly natural selection. There is far too much randomness, and the process is far too quick for increased fitness ("stronger animals") to be viable.
Can one simulate Natural Selection while conforming to the specifications of a Standardized Breed?