What is a species? And how are biological species related to the philosophical ideas of essential natures and natural kinds? Is there such a thing as a human nature?

Required

• Mayr, What is a Species, and What is Not? Also here.
• Background Tutorial: Ridley, The Idea of a Species
• Stanford Encyclopedia of Philosophy: Species (Ereshefsky)

Recommended

• Ereshefsky, M. (1992). Eliminative pluralism. Philosophy of Science, 671-690.
• Griffiths, P. E. (1999). Squaring the circle: natural kinds with historical essences. Species: New interdisciplinary essays, 208-228.
• Hull, D. L. (1980). Individuality and selection. Annual Review of Ecology and Systematics, 11, 311-332.

1. What is a species? Why is it important that we consider organizing the biological world into species?
2. What are the differ criteria for species membership that biologists consider?
   1. Morphological
      1. Group membership based on morphological similarity (though not essentialism)
      2. But similar to whom? Is this an objective relationship? How do we handle disagreements? Doesn't connect well with evolutionary theory.
   2. Biological
      1. Membership determined by reproductive isolation: members can successfully interbreed (need to consider actual and possible linkages)
      2. Explains the relatedness of members from an important evolutionary perspective, like gene flow.
      3. But what about plants where reproductive isolation is weak? Or asexual species?
      4. What about historical possibilities of interbreeding? Or species that could but don't?
      5. How to handle ring species?
   3. Phylogenetic
      1. Taxonomy should accurately reflect geneology. To be members of the same species, members must share common descent
      2. Necessary, but not sufficient
      3. But how do we detect speciation events (branches on the tree of life)?
      4. “[T]he most plausible account of species is that they are lineages between speciation events. The biological species concept, perhaps supplemented by the ecological species concept or by something else, reemerges as an account of speciation” (Sterelny and Griffiths, p. 192).
   4. Others
3. How is the idea of a species related to the philosophical idea of an essential nature? How does it diverge from traditional philosophical conceptions of essentialism?
   1. Species as types or kinds of organisms
   2. Can we find essential properties that define the species? Are there necessary and sufficient conditions?
      1. An essential property is one that without it the individual would not exist.
      2. Necessary condition: x can be an F only if it meets the necessary condition.
      3. Sufficient condition: meeting the sufficient condition is enough for x to be an F.
   3. There are problems with typological thinking in biology
      1. What traits are necessary? Can't we always think of exceptions? The boundaries don't seem to be sharp.
      2. Evolutionary thinking must consider gradualism and variation.
4. Are species themselves individuals?
   1. Hull and Ghislen argue that species are themselves evolutionary units
   2. Species are spatiotemporally continuous
   3. The organism/species relationships is like part/whole, not member/class.
   4. Species are not subject to scientific laws (assuming laws apply to classes of individuals)
   5. Search for an essence (like a human nature) to a species seems to be misguided.
5. Should we be pluralists? The many species definitions are all acceptable (correct) relative to different needs for explanation.
   1. Is there an ideal species (concept)?
   2. Kitcher argues for two concepts based on proximate/ultimate distinction.
      1. Proximate: look to structural similarities (species as classes or kinds)
      2. Ultimate: look to genealogical (species as individuals)

William Blake
From Auguries of Innocence

To see a world in a grain of sand,
And a heaven in a wild flower,
Hold infinity in the palm of your hand,
And eternity in an hour.
A robin redbreast in a cage
Puts all heaven in a rage.
A dove-house fill'd with doves and pigeons
Shudders hell thro' all its regions.
A dog starv'd at his master's gate
Predicts the ruin of the state.
A horse misused upon the road
Calls to heaven for human blood.
Each outcry of the hunted hare
A fibre from the brain does tear.