Many tame domesticated animals have a different appearance compared to their relatives in the wild, for example white patches in their fur or shorter snouts. Researchers have now for the first time shown that wild house mice develop the same visible changes — without selection, as a result of exposure to humans alone.
The significant part of the story is that the mice were not exposed to any kind of selection other than free handouts (although one suspects that mouse predators may have avoided the barn due to the common presence of humans).
A team of researchers led by Anna Lindholm from the Department of Evolutionary Biology and Environmental Studies at UZH has now also observed this phenomenon in wild mice (Mus musculus domesticus) that live in a barn near Zurich. Within a decade, this population of mice developed two of the distinct phenotypic changes: white patches in their otherwise brown-colored fur as well as shorter snouts. “The mice gradually lost their fear and developed signs of domestication. This happened without any human selection, solely as a result of being exposed to us regularly,” says Anna Lindholm. The evolutionary biologist has been studying the mice that live in the empty barn for about 15 years. These animals are regularly provided with food and water, and investigated by the researchers.
Now here is where it gets interesting:
It appears that a small group of stem cells in the early embryo — the neural crest — is responsible for these behavioral and physical changes that take place in parallel. The ear’s cartilage, the teeth’s dentine, the melanocytes responsible for the skin’s pigmentation, as well as the adrenal glands which produce stress hormones are all derived from these stem cells. The selection of less timid or aggressive animals results in smaller adrenal glands that are less active, and therefore leads to tamer animals. Changes in the color of fur and head size can thus be considered unintended side effects of domestication, as these traits can also be traced back to stem cells in the neural crest that were more passive in the early stages of development.
But how is that information that that should happen communicated to the relevant cells?
The observations of the study’s first author Madeleine Geiger increases the understanding of how house mice began to live in closer proximity to humans, attracted by their food, some 15,000 years ago. As a result of this proximity alone, the rodents got used to people and became tamer. “This self-domestication resulted in the gradual changing of their appearance — incidentally and inadvertently,” says Geiger. Evolutionary biologists assume that the development from wild wolf to domestic dog also initially began without the active involvement of humans. Wolves that lived near humans became less timid and aggressive — the first step in becoming domesticated. Paper. (public access) – Madeleine Geiger, Marcelo R. Sánchez-Villagra, Anna K. Lindholm. A longitudinal study of phenotypic changes in early domestication of house mice. Royal Society Open Science, 2018; 5 (3): 172099 DOI: 10.1098/rsos.172099 More.
Yes, certainly, but how? By what mechanism are these changes communicated to the stem cells? What is the cascade of events?
Under strict Darwinian natural selection, only the fittest life forms survive to breed. But these changes don’t especially render the mouse more fit or suggest that fitness played a role in how they came to be selected.
For one thing, most human interventions with wild mice have consisted of finding ways to rub them out.
See also: Basener stands his ground at Skeptical Zone: Fisher’s Darwinian theorem is clearly false.