Every few years, stories about the endangerment of the redhead population surface the internet. The proposed reasons for this are diverse, from climate change to rejecting redhead sperm donors. And where does the truth lie? These types of stories usually come up just to cause a commotion.
Let's start from the end: the likelihood of the redhead gene to disappear is nearly zero. Even if one day a deadly virus will emerge, killing all redheads on Earth, this still would not wipe out the redhead gene, and sooner or later a new freckled ginger baby will come into the world. In order to understand why, we have to jump into the depths of natural selection and genetic heredity.
Every property in our body, such as the color of our hair, shape of our nose and even sensitivity to fava beans, is encoded in a genetic unit called a gene. Every gene is comprised of two DNA segments called alleles – one of which came from our mother, and the other from our father.
Alleles can be dominant or recessive. Just like people, the dominant ones are expressed at the expense of the recessive ones. The allele encoding ginger hair is recessive, so if I were to inherit the ginger gene from my mother and a dominant allele for black hair from my father, I would have black hair, since that is the allele that would be expressed. Only if I were to inherit two ginger alleles from my parents, they would be expressed and I would have ginger hair.
Throughout the evolutionary process certain traits undergo natural selection. Some traits disappear, while others thrive and are passed on to future generations. However, the selection can only be applied to expressed traits. Therefore, dominant traits undergo natural selection more simply, and thus can disappear more easily. Recessive traits, in contrast, can remain "dormant" for many generations, and they will affect the individual's fitness to procreate only in the few cases in which they are expressed.
Let's return to the example of the theoretical virus that only attacks redheads: the virus basically applies selective pressure on the ginger trait – only people expressing this trait would be afflicted and would not be able to pass on their alleles to their offspring. In contrast, those who are not redheads but carry the ginger allele (e.g., those with one ginger allele and one black allele) would be immune to the disease and could pass on the ginger allele to the next generation. In this manner, the ginger allele remains protected inside the DNA of its carriers.
When selection is applied against dominant traits that are always expressed, there is a higher chance that the trait will disappear. In contrast, if all people expressing a recessive allele die, the allele may become very rare in the population. So, the recessive allele may have a very small prevalence, but will almost never disappear completely.
This evolutionary mechanism does indeed make sure that redheads do not disappear from the face of the Earth. However, it poses a problem when it comes to genetic diseases. Recessive diseases are much more difficult to eradicate, since there are families, sometimes entire communities, that some of their members are carriers of the disease without expressing any symptoms, so they can still pass it on to their offspring.
Translated by Elee Shimshoni