Why Are Dogs' Ears Long? The Intersection of Evolution and Human Preference — The Latest Research Reveals the Blueprint

Why Are Dogs' Ears Long? The Intersection of Evolution and Human Preference — The Latest Research Reveals the Blueprint

The long ears of Basset Hounds and Bloodhounds that almost reach the ground. Just looking at them makes you want to touch them, succumbing to the "pressure of cuteness"—this feeling is introduced in the article with the term "cute aggression." However, this topic doesn't end with emotions alone. Researchers have directly pursued the question of "why do dogs have such varying ear lengths?" from the perspective of genomes (DNA information).


Chasing "ear length" instead of "ear shape"

Previously, research on dog ears tended to focus on whether they were erect or floppy, known as "ear carriage." However, this new study takes it a step further by specifically targeting the question of "what determines the 'length' of ears when comparing floppy-eared dogs?" This approach is novel.


The analysis included over 3,000 animals, not just dogs but also wolves and coyotes. First, floppy-eared dog breeds were classified into five categories from "short" to "long," and ear lengths were categorized by referring to breed standard images. Then, a genome-wide association study (GWAS) was conducted to find correlations on a whole-genome scale.


The shortcut was "near MSRB3"—and in an unexpected form

What Phys.org emphasizes is that a difference likely affecting ear length was found near the MSRB3 gene. Moreover, the researchers assumed that since they analyzed only floppy-eared dogs, "if everyone has floppy ears, the location should be the same." However, in reality, even among the same "floppy ears," additional differences that further divided ear length were found.


To break down the key points of the paper (Scientific Reports):

  • There is a strong signal associated with ear length near the area between MSRB3 and HMGA2 on canine chromosome 10 (CFA10).

  • That region is also a "known hotspot" related to whether ears are erect or floppy (ear carriage).

  • Therefore, researchers conducted analyses mixing erect and floppy ears, unraveling "ear carriage" and "ear size."


Particularly interesting is the "division of roles" within the same region, where two variations are related to ear carriage and one variation is related to ear length. The paper's summary explains that a "recombinant haplotype" with two variations strongly predicts floppy ears, and when the ear size variation is added, a "tri-allelic" combination becomes predominant in the largest floppy-eared breeds.


"It's all about the combination"—the "ear recipe" of dog breeds seen through haplotypes

Genes are often shaped not by a single switch but by a "combination of variations lined up nearby." This study exemplifies that, showing a tendency for specific haplotypes (linked types) to be almost fixed in longer floppy-eared breeds when organizing "three ear-related variations" for each breed.


The paper illustrates "breed differences" by showing, for example, that a type like "1|1|0|1" becomes almost fixed in frequency in the longest-eared group, while its frequency decreases in the shorter floppy-eared group. Additionally, it reports a contrast where strong selection signals are visible in this region for long floppy-eared breeds, while they are weaker for short floppy-eared ones. In essence, the visibly noticeable "long ears" may have their preference by humans etched into DNA.


Why is there a mention of humans?—The potential connection between "ears" and "hearing"

Another point Phys.org touches on is that MSRB3 is also related to human hearing impairments. Of course, it cannot be simply concluded that "long-eared dogs = poor hearing." However, if the same region is deeply involved in "ear shaping," it's always important to consider the possibility that when selecting for appearance through breeding, other traits (health risks or other characteristics) might be affected as well.


In fact, the introduction of the paper organizes examples where the size of the outer ear is often linked to temperature regulation (such as larger ears in hot regions to dissipate heat) and notes that genes related to ear size are known in livestock. It positions dogs as having been selected not only for function but also for "aesthetic preference." The results of this study can be said to have made that "aesthetic preference selection" visible through analysis.


The limitations of the study and the "next steps"

However, ear length cannot be completely explained by just three variations. The paper suggests that depending on the analysis method, biases in coat color might appear as apparent associations in other genetic regions (near RUNX3), highlighting the difficulty of trait analysis being influenced by "breed biases" or "co-selected traits." Therefore, the next step should be to advance to studies measuring ear length as a continuous quantity at the individual level, including analyses of structural variations (deletions, duplications, etc.), and functional experiments to determine how each variation works.


SNS reactions: "Pun in the title," "Ear thief," "Health concerns"

This topic, with its clear focus on "dog ears," is easy to consume with the typical SNS vibe. On Reddit's r/science, there were comments joking about the pun in the article's title, saying, "The paper is redacted because of that pun."
In the same thread, there was also a focus on the implications of the study, with some quoting a section of the article (differences near MSRB3 and the connection to human hearing) and commenting, "Interesting, but it's concerning that it might connect to human ear genes."


Additionally, as a related community, a subreddit about the "ear thief" meme was introduced, showing the atmosphere where scientific news can quickly become a meme when it leans towards "cuteness."

 
On the other hand, what UGA (the university's introduction article) and Phys.org emphasize is that understanding these genetic regions could help in the future with analyzing hereditary diseases and organizing the relationship between breeding and health. Beyond the "cute!" reactions on SNS, a more serious question remains: "How does choosing for cuteness relate to health?"


Summary: Ears are both a "symbol of cuteness" and a "fossil of selection history"

Dog ears are tools crafted by evolution and designs sculpted by human preference. This study suggests that the iconic feature of long floppy ears can be explained by genetic "combinations" centered around the MSRB3 vicinity, and it shows that these combinations are linked to the history (selection) of dog breeds.


The next question to ask is, "What else does that combination bring besides ears?" The science that dissected cuteness might be at the turning point towards the science that protects cuteness—and the study of dog ears might be at that crossroads.


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