Chapter 17, Problem 21A

Summary Introduction

To differentiate:

Typological species concept and the phylogenetic species concept.

Introduction:

It is not easy to define a species. Organisms that are different species according to one definition might be same species according to different definition. Definitions change as knowledge increases. The concept of species today is much different from what it was 100 years ago. There are three main species concepts; biological species concept, typological species concept and the phylogenetic species concept.

Answer to Problem 21A

Typological species concept was given by Aristotle and Linnaeus. It is based on the idea that species are not changing, distinct and natural types and is based on physical similarities of organisms. This is not very reliable as species change over time.

Phylogenetic species concept is based on evolutionary history of organisms. It defines species in terms of populations and ancestry. It is more reliable as it accounts for extinct species also.

Explanation of Solution

Typological species concept−This concept was given by Aristotle and Linnaeus. They considered species as a distinctly different group of organisms based on physical similarities. It is based on the idea that species are not changing, distinct and natural types. The type specimen was an individual of the species that best displayed the characteristics of that species. When another specimen was found that varied significantly from the type specimen, it was classified as different species. It has a limitation as we now know that alleles produce a wide variety of features within a species so members of some species display wide variations. Also the species change over time. Hence this concept is not much in use.

Phylogenetic species concept−This classification is based on evolutionary history of organisms. It defines species in terms of populations and ancestry. According to this concept, two or more groups that evolve independently from an ancestral population are considered as different species. It defines a species as a cluster of organisms that is different from other clusters and shows evidence of pattern of ancestry and descent. It has only one limitation that it cannot define those species whose evolutionary history is not known but it can account for extinct species.