Illuminating our world: an essay on the unraveling of the species problem, with assistance from a barnacle and a goose.

In order to plan for the future, we must understand the past. This paper investigates the manner in which both naturalists and the wider community view one of the most intriguing of all questions: what makes a species special? Consideration is given to the essentialist view-a rigid perspective and ancient, Aristotelian perspective-that all organisms are fixed in form and nature. In the middle of the 19th century, Charles Darwin changed this by showing that species are indeed mutable, even humans. Advances in genetics have reinforced the unbroken continuum between taxa, a feature long understood by palaeontologists; but irrespective of this, we have persisted in utilizing the 'species concept'-a mechanism employed primarily to understand and to manipulate the world around us. The vehicles used to illustrate this journey in perception are the barnacle goose (a bird), and the goose barnacle (a crustacean). The journey of these two has been entwined since antiquity-in folklore, religion, diet and even science.