Imagine an island that is suddenly populated with one hundred couples, each with a unique last name. No couple has the same last name. Further, they continue the tradition of the females taking the male’s last name upon marriage. As these couples reproduce, their children will marry one another. Couple A1 has a couple of boys who marry the girls from Couple C2. This is not a controlled experiment, so nature can take its course and people are free to marry who they like.
Obviously, some couples will have all girls and some couples will have no children, but infertility and a lack of interest in children is not that common, so the number of childless couples will be quite small. At the same time, “Fertile Myrtle” is not an unusual phenomenon either and some men have a near uncontrollable sex drive. That means there will be quite a few big families to counter the infertile couples and those couple that choose not to reproduce.
If all couples have one male child and one female child, both of whom make it to sexual maturity and reproduce, then the population remains stable. The number of last names will also remain constant, as each male heir will continue the family name. Given this is a small island, a few extra children, or the “heir and spare” model will make sure that the family names live on, and the population remains steady. In this scenario, we can come back in a dozen generations and things are about the same.
If each generation has 10% of the females unable to bear children, it will take about twenty generations before almost everyone has the same last name. The decline in last names happens fast initially. Something similar happens if 10% of the couples have only female children that make it to adulthood. Throw in the fact that each generation may not have enough females for all the males and the decline of last names will progress toward one single last name.
Obviously, lots of couples will have all boys or all girls. Since this island does not have video games or feminism, getting busy with the opposite sex will be the main form of entertainment. That means some couples will have lots of kids, but others will be more restrained and have one or two kids. The bigger the family, the lower the odds of having all girls or all boys, but it happens. If that is just ten percent of the result, we still end up with one last name in twenty generations.
Why would anyone care about this? Well, it is a good way to understand how a trait can flow through a population, resulting in a unique population. Instead of last names, let us use a pronounced brow ridge, indicating high intelligence. If this is a trait passed through the male line of the A1 family, and that family has plenty of males each generation, then that male trait will become ubiquitous in twenty generations like we saw with the last name idea.
Since a prominent brow line is desirable, men with it will have a greater chance to reproduce, increasing the spread of those genes. On the other hand, let us say the one guy in our one hundred founding couples with the brow ridge drowns while out for a swim, before he had kids. That means this highly desirable trait, both from a biological as well as reproductive reason, is removed from the gene pool forever. Our island will be full of homely dumb people.
This is a simplified and rather crude way of illustrating how a desirable trait can flow through a population. This is how we have so many dog breeds. Humans short-circuited nature, through selective breeding, thus selecting for specific traits. After enough generations, one breeder ended up with Great Danes, while another ended up with Dachshunds, so to speak. A famous example of this is the creation of a domesticated foxes by a Russian geneticist named Dmitry K. Belyaev.
Another way of understanding this is to imagine our island paradise flourishing with a high fertility rate over many generations. Then resource scarcity sets off competition among the islanders, eventually leading to a tyrant. He correctly sees that the issue is the left-handed and has all of them killed. In future generations, anyone found to be left-handed is killed. It will not take long, in fact it could literally happen overnight, for the population to lose the left-handed trait.
This is a good way to understand the natural diversity of people. When modern humans emerged from Africa, the most likely origin, we carried almost all of the traits present in humans today. As people spread out around the globe, nature found some traits much more useful in the new environment, so those traits thrived. Nature also found some traits deleterious and strongly selected against them. Overtime, we got the diversity of man we see today that tracks with geography.
It is why the phrase “scientific racism” indicates stupidity. Just as there is great diversity in the domestic dog, there is diversity in humans. Denying observable reality is a few clicks less reasonable than witchcraft or astrology. It also means multiculturalism is, in effect, a war on nature, as it is an effort to obliterate human diversity. Mixing everyone together into a gray slurry is just a primitive minded war on nature, which we have decided is immoral. it is is also suicidal.