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“Survival of the cutest” backs up Darwin, scientists say

Jan. 22, 2010
Courtesy Univers­ity of Man­ches­ter
and World Science staff

Do­mes­tic dogs have fol­lowed their own ev­o­lu­tion­ary path, twist­ing Dar­win’s di­rec­tive “sur­vival of the fittest” to their own needs – and have proved him right in the pro­cess, ac­cord­ing to a new stu­dy.

The stu­dy, pub­lished in The Amer­i­can Nat­u­ral­ist on Jan. 20, com­pared the skull shapes of do­mes­tic dogs with those of dif­fer­ent spe­cies across the or­der Car­niv­o­ra, the wider line­age that in­cludes dogs, cats, bears, weasels, civets and even seals and wal­rus­es.

An Af­ghan dog (black) with a Chi­hua­hua (white.) (Cour­tesy U.S. NHGRI)
The analysis found that the skull shapes of do­mes­tic dogs var­ied as much as those of this whole group, and that the ex­tremes of di­vers­ity were far­ther apart in do­mes­tic dogs than in the rest of the or­der. For in­stance, the dif­fer­ence in skull shape be­tween a Col­lie and a Pe­king­ese ex­ceeds that be­tween a cat and a wal­rus.

“Do­mes­tic dogs are boldly go­ing where no self re­spect­ing car­ni­vore ev­er has gone be­fore” in terms of skull shape, said Chris Klin­gen­berg of The Univers­ity of Man­ches­ter in the U.K., a co-author of the stu­dy.

“We usu­ally think of ev­o­lu­tion as a slow and grad­u­al pro­cess,” added Ab­by Drake of the Col­lege of the Holy Cross in Worces­ter, Mass., also a co-author. “But the in­cred­i­ble amount of di­vers­ity in do­mes­tic dogs has orig­i­nat­ed through se­lec­tive breed­ing in just the last few hun­dred years, and par­tic­u­larly af­ter the mod­ern pure­bred dog breeds were es­tab­lished in the last 150 years.” By con­trast, the Car­niv­o­ra as a whole date back at least 60 mil­lion years.

“Do­mes­tic dogs don’t live in the wild so they don’t have to run af­ter things and kill them—their food comes out of a tin and the tough­est thing they’ll ev­er have to chew is their own­er’s slip­pers,” Klin­gen­berg said. “So they can get away with a lot of varia­t­ion that would af­fect func­tions such as breath­ing and chew­ing and would there­fore lead to their ex­tinc­tion.”

Nat­u­ral se­lec­tion—the set of en­vi­ron­men­tal pres­sures that drives spe­cies to evolve as they adapt to meet the rig­ors of sur­vival—has been re­laxed for pet dogs, he added. In its place is “ar­ti­fi­cial se­lec­tion,” in which hu­mans ma­ni­pu­late ev­o­lu­tion to ob­tain shapes that breed­ers favor, such as a “cute” ap­pear­ance. “Dogs are bred for their looks, not for do­ing a job, so there is more scope for out­land­ish varia­t­ions,” said Drake.

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Domestic dogs have followed their own evolutionary path, twisting Darwin’s directive “survival of the fittest” to their own needs – and have proved him right in the process, according to a new study. The study, published in The American Naturalist on Jan. 20, compared the skull shapes of domestic dogs with those of different species across the order Carnivora, the overarching lineage that includes dogs, cats, bears, weasels, civets and even seals and walruses. It found that the skull shapes of domestic dogs varied as much as those of this whole group, and that the extremes of diversity were farther apart in domestic dogs than in the rest of the order. For instance, the difference in skull shape between a Collie and a Pekingese exceeds that between a cat and a walrus. “We usually think of evolution as a slow and gradual process,” said Abby Drake of the College of the Holy Cross in Worcester, Mass., one of the researchers. “But the incredible amount of diversity in domestic dogs has originated through selective breeding in just the last few hundred years, and particularly after the modern purebred dog breeds were established in the last 150 years.” By contrast, the Carnivora as a whole date back at least 60 million years. “Domestic dogs are boldly going where no self respecting carnivore ever has gone before” in terms of skull shape, said Chris Klingenberg of The University of Manchester in the U.K., a co-author of the study. “Domestic dogs don’t live in the wild so they don’t have to run after things and kill them—their food comes out of a tin and the toughest thing they’ll ever have to chew is their owner’s slippers. So they can get away with a lot of variation that would affect functions such as breathing and chewing and would therefore lead to their extinction.” Natural selection—the set of environmental pressures that drives species to evolve as they adapt to meet the rigors of survival—has been relaxed for pet dogs, he added. In its place is “artificial selection,” in which humans manipulate evolution to obtain “various shapes that breeders favour.” “Dogs are bred for their looks, not for doing a job, so there is more scope for outlandish variations,” added Drake.