Final answer:
The most popular method of species concepts is the Biological species concept, which bases species identification on breeding capabilities and reproductive isolation. However, it can be difficult to apply with fossils, and modern biology often employs other methods like the phylogenetic species concept for such cases.
Step-by-step explanation:
The most popular method of the species concepts is Option 2: the Biological species concept. This concept distinguishes species based on their reproductive isolation from each other, meaning that if two organisms are capable of breeding and producing fertile offspring, they are considered to be the same species. Despite its widespread acceptance, this definition can be difficult when looking at species over time, particularly with fossil records where breeding capabilities can't be observed. Phylogenetic species concept, however, identifies species based on their smallest distinct groupings with a unique common ancestor, making it particularly useful in fossil differentiation where morphological characters are preserved.
Furthermore, the Biological species concept relates to a species' reproductive strategies, habitat, and behavior, which includes how they obtain resources and care for their young. It is often contrasted with other concepts, like the morphological, phylogenetic, and ecological species concepts, each having its own utility depending on the context and information available. In modern biology, it is important to classify living things to understand relationships, behaviors, and evolutionary processes. The Linnaean system of classification and binomial nomenclature, like genus Homo and species sapiens for humans, underpins how we name and categorize species.