How you know a terrier and a poodle belong to the same species?

Terriers and poodles belong to the same species because they can interbreed and produce fertile offspring, which is a key criterion for species classification. Both are members of the Canis lupus familiaris species, sharing the same genetic lineage. Additionally, they exhibit similar physiological and behavioral traits typical of domestic dogs, despite their different appearances and temperaments. Genetic analyses further confirm their classification within the same species.