Removing ambiguity from the biological species concept

Area of Science:

• Evolutionary Biology
• Systematics
• Philosophy of Science

Background:

• The biological species concept (BSC) is widely used but suffers from ambiguity, especially concerning gradual evolutionary changes.
• Existing interpretations of the BSC struggle with phenomena like gradual reproductive isolation and introgression.

Purpose of the Study:

• To syntactically reinterpret the biological species concept (BSC) in four distinct ways.
• To identify a more suitable interpretation of the BSC that can accommodate gradual evolutionary processes.

Main Methods:

• Syntactic analysis of the biological species concept (BSC).
• Evaluation of four different interpretations based on their applicability to evolutionary scenarios.
• Assessment of how each interpretation handles gradual reproductive isolation and introgression.

Main Results:

• The "fully restricted" interpretation is inapplicable during gradual evolution.
• The "cohesion relaxed" and "fully relaxed" interpretations are too broad.
• The "isolation relaxed" interpretation allows for non-discrete, overlapping species, effectively handling gradual evolution and introgression without subjectivity.

Conclusions:

• A "relaxed isolation" interpretation of the BSC offers an objective and naturalistic framework for defining species.
• This interpretation resolves long-standing issues with the BSC, including ring species, phyletic species, and syngameons.
• Precision in defining the terms of the BSC is key to overcoming its inherent ambiguities.