Evolution: A Primer by Meg Dickson
There are a lot of different ways for humans to define the term species; the most famous one is the Biological Species Concept (BSC). This idea states that a species is a group of organisms that can breed with one another and produce viable, fertile offspring - meaning, children that live, and then can reproduce themselves. This method is mostly used in modern biology in almost every context, and is typically what is taught in schools.
This is not our only species concept. There’s also the Morphological Species Concept (MSC). This is also known as the Phenetic or Typological species concept. This designates that a group of organisms with specific, fixed morphology or phenotypes (aka overall similarity) designate a species. This was used by Linneaus to classify species back in the day, but now is mostly used only by paleontologists to classify species of extinct species by looking at fossils, since we can’t exactly see which fossils interbred with each other.
There is also the Phylogenetic Species Concept (PSC). This is, to put it bluntly, the smallest group of organisms that are evolving independently from all other groups. In short, it’s the smallest possible “clade.” More on cladistics later in this essay (because I’m telling you, this thing is going to be very, very long,) but this concept is honestly only used in phylogenetics and is not entirely helpful in any other context.
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