If humans had not bred the dogs themselves, they would have had quite a difficult time figuring out that a tiny Chihuahua and a giant Great Dane are in fact related, scientists said.
Jack Tseng, a palaeontologist at the American Museum of Natural History in New York, said that if a biologist came from a society that had never been associated with dog breeding, he or she would immediately think that various dogs are in fact different species.
To determine whether an animal belongs to a certain species, scientists usually look at genetics and anatomy, Tseng said. When comparing different breeds of dogs, anatomy is often times not very helpful due to the animals’ various sizes and shapes.
For instance, although dog’s teeth have similar structure, they also come in a lot of sizes (depending on the breed), which would make it difficult to determine that they are in fact the same species, according to Mr. Tseng.
Dogs are an excellent example of how animals can have the same genetic blueprint, belong to the same species and yet look so different, he added.
What tells us that dogs are the same species is genetic analysis. Dogs and gray wolves (Canis lupus) share most of the same genes, so by those standards they could be considered the same species.
However, scientists say that dogs are in fact a subspecies of Canis lupus familiaris, a distinct species from the wolf due to some different gene variants called alleles. An allele can be defined as one of a number of alternative forms of the same gene or same genetic locus (the specific location or position of a gene).
For example, a variant of the gene IGF1 is linked with body size. According to a study published in the journal BMC Biology in 2010, one of the IGF1 variant that is associated with small body size in dogs cannot be found in wolf populations.
Another piece of evidence that shows all dogs are in fact the same species is that technically, different breed can reproduce with one another. Of course, that may not be possible in all cases because some breeds are dramatically different in size – such as a Chihuahua and a Great Dane, according to Tseng.
That being said, domestic dogs are also able to breed successfully with wolves, Tseng. Although that might suggest that they should be classified as the same species, there are still some subtle difference is the anatomy of wolves and dogs. Compared with wolves, dogs have more raised, prominent foreheads and they also tend to have more crowded teeth and shorter faces.
According to Tseng, both dogs and wolves have the same number of teeth, but dogs’ teeth are sometimes smaller in size so they can all fit in the smaller space.
Based of genetic data, specifically mitochondrial DNA – that gets passed down to the offspring through the maternal line – indicates that all dogs are the same species. There is a possibility that wolves are too, but from a societal standpoint, dogs and wolves are without a doubt significantly different, Tseng said.
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