LINEAGE-THINKING, OR THE CONCEPTUAL NON-NECESSITY OF SPECIES AND ITS IMPLICATIONS

The species problem is a long-standing biological debate on the delineation and nature of species. New insight on the problem can be gained by considering the paleontological dimension and conceptualizing species as a part of continuous lineages. Lineages are essentially continuous phenomena, extending from the origin of life until either the present or the extinction of the lineage—linked by the transmission of the genetic code. Continuous phenomena are found elsewhere in nature, notably color and light. Any subdivision of continuous phenomena are, at best, semi-arbitrary. The decision that makes the arbitrary break in the continuous lineage resides in the head of the decision-maker, not in the objective world. Thus species as segments of lineages compels the realization that species themselves are arbitrary and not a feature of the objective world. This position is referred to as weak species nominalism.

The implications of this position are numerous. Species function in biological thought essentially as poor proxies for morphological or genetic disparity; the concepts of diversity and disparity are indistinguishable. Macroevolution needs to be reconceptualized, as its conceptualization as evolution above the species level leaves its domain subjective. Biodiversity tallies need to be reassessed and replaced with measures of morphological or genetic difference. Conservation needs to ground its priorities on more concrete assessments involving measures of disparity. Taxonomy, surprisingly, changes most in its conceptualization rather than practice; pointing out interesting segments in the lineages of life.