Importantly, domestication is certainly an ongoing process, and the traits do not have to all arise concurrently. Given that the process has lasted several thousand years in many cases, with traits often considered to be selected and then bred into domestic animals throughout their domestication (as is often the case for example with colour; for example, different colour variants have been selected in different pig breeds [7]). Therefore, traits can certainly be considered part of the domestication phenotype even if they have slowly accumulated in a domestic species. For example, some of the biggest changes with domestic animals have occurred relatively recently during the domestication process. The split between layer (egg production) and broiler (meat production) chickens occurred less than 100 years ago and is accompanied by extreme changes in body size [8]; the huge variety of dog breeds is largely due to the Victorian-era breeding programmes [9]; and cattle have increased in size during the last 500 years after fluctuating since domestication [10]. So much so, that some researchers separate out domestication with improvement when it pertains to selection for specific production characteristics [11].

Lord et al. then used a restricted subset of domesticated species based on the presence of a wild comparison population and whether they are widely considered domestic. Unfortunately, there are many domestic species with a wild population that are not considered, including all domestic birds, sheep, mink, and others (Table 1). As they point out, characters attributed to the domestication syndrome vary between authors. Many of these cannot be considered central to the domestication syndrome, but must be rather species specific (for example, horn and tail traits). While many different traits have been