Transcript What Is a Species?

What Is a Species?
PHIL 225
EVOLUTIONARY REASONING
JULIE YOO
APRIL 21, 2014
Sections of this Presentation
 The “Species Problem”: Introduction
 Nominalism v Realism
 The Species Problem: A Problem of Definition
 Definitions: N/S Conditions
 The “Species Problem”: An Illustration
Essentialist
 Biological
 Ecological
 Cladistic

 The “Species Problem”: Conclusion?
Sections of this Presentation
 The “Species Problem”: Introduction
 Nominalism v Realism
 The Species Problem: A Problem of Definition
 Definitions: N/S Conditions
 The “Species Problem”: An Illustration
Essentialist
 Biological
 Ecological
 Cladistic

 The “Species Problem”: Conclusion?
The “Species Problem”: Introduction
 Biologists classify animals into species.
The “Species Problem”: Introduction
 Biologists classify animals into species.
 This is important because we gain a better
understanding of the things we study through their
classifications.
The “Species Problem”: Introduction
 Chemistry: Periodic Table of Elements
The “Species Problem”: Introduction
 Physics: Standard Model of Subatomic Particles
The “Species Problem”: Introduction
 Biology:
?
 But we run into significant complications when it
comes to the biological definition of species.
 And this in itself raises a problem – the problem of
Nominalism v Realism.
Sections of this Presentation
 The “Species Problem”: Introduction
 Nominalism v Realism
 The Species Problem: A Problem of Definition
 Definitions: N/S Conditions
 The “Species Problem”: An Illustration
Essentialist
 Biological
 Ecological
 Cladistic

 The “Species Problem”: Conclusion?
Nominalism v Realism
 Consider these two groupings of objects:
A
B
Nominalism v Realism
 Are A and B equally coherent ways of classifying
objects?
A
B
Nominalism v Realism
 Consider another example: Are A and B equally coherent
ways of classifying objects?
tuna
salmon
cod
trout
catfish
A
4 ft tuna
4 ft ape
4 ft tomato vine
4 ft mountain lion
4 ft rose bush
B
Nominalism v Realism

Both groups have members that share some feature
in common.
All the member of A are fish.
 All the members of B are 4 feet tall.

 If you were given the task of taxonomizing the
natural world – listing all the groupings that make
sense – would you equally include A and B?
Nominalism v Realism
 If you think that only A should be recognized, then
you are probably a realist.
 If you think that A and B are equally viable, then you
are probably a nominalist.
Nominalism v Realism
Realism
Nominalism
•
There IS a correct way of
grouping organisms.
•
There is NO correct way of
grouping organisms.
•
That grouping reflects the
existence of the organisms’
shared intrinsic features.
•
There are no shared intrinsic
features that belong to
organisms.
•
Species are real fixtures of
nature.
•
Species are a function of how
humans want to group things.
Nominalism v Realism
 If there is no settled view about the concept of a
species, we can’t be sure whether it is a product of
our minds (nominalism) or a real feature of nature
(realism).
Nominalism v Realism
 If there is no settled view about the concept of a
species, we can’t be sure whether it is a product of
our minds (nominalism) or a real feature of nature
(realism).
 Why are there no settled views about this?
Sections of this Presentation
 The “Species Problem”: Introduction
 Nominalism v Realism
 The “Species Problem”: A Problem of Definition
 Definitions: N/S Conditions
 The “Species Problem”: An Illustration
Essentialist
 Biological
 Ecological
 Cladistic

 The “Species Problem”: Conclusion?
The “Species Problem”: A Problem of Definition
 The problem is mainly definitional/conceptual for
the biological term, “species.”
The “Species Problem”: A Problem of Definition
 The problem is mainly definitional/conceptual for
the biological term, “species.”
 We have many definitions of the term, “species,”
making it hard to know who’s got it right when he or
she groups organisms into a species.
The “Species Problem”: A Problem of Definition
The Spectrum of Species Concepts:
•Agamospecies concept
•Biological species concept
•Cladistic species concept
•Internodal species concept
•Morphological species concept
•Non-dimensional species concept
•Cohesion species concept
•Composite species concept
•Ecological species concept
•Evolutionary significant unit
•Evolutionary species concept
•Genealogical concordance concept
•Recognition species concept
•Genetic species concept
•Genotypic cluster concept
•Hennigian species concept
•Reproductive competition concept
•Successional species concept
•Taxonomic species concept
•Phenetic species concept
•Diagnosable phylogenetic SC
•Monophyly phylogenetic SC
•General phylogenetic SC
•Polythetic species concept
The “Species Problem”: A Problem of Definition
 How does this pose a problem?
The “Species Problem”: A Problem of Definition
 How does this pose a problem?
 Let’s look at an example with the many definitions of
“democracy”: A “democracy ” is where:
1. everyone gets to vote on a leader who chooses the laws OR
2. everyone decides what the laws should be OR
3. everyone gets equal opportunity OR
4. everyone has the freedom to pursue his or her goals OR
5. (and more)
The “Species Problem”: A Problem of Definition

Illustration of Problem: Even though everyone
may have the same term, “democracy,” in mind,
different definitions of this concept can lead to
conflict.

The laws of the chosen leader (first definition)
could very fail to line up with the laws that the
community agrees upon (second definition).
The “Species Problem”: A Problem of Definition
 Before we look at why we are in this predicament
with Biology, we need to understand what a
definition is.
Sections of this Presentation
 The “Species Problem”: Introduction
 Nominalism v Realism
 The Species Problem: A Problem of Definition
 Definitions: N/S Conditions
 The “Species Problem”: An Illustration
Essentialist
 Biological
 Ecological
 Cladistic

 The “Species Problem”: Conclusion?
Definitions: N/S Conditions
 Q: What is a definition?
Definitions: N/S Conditions
 Q: What is a definition?
 A: A definition consists of the necessary and
sufficient conditions for the application of the term.
Definition of a “dozen”: being a dozen = being twelve
Being twelve is BOTH necessary and sufficient for being a dozen.
Definition of a “sister”: being a sister = being a female sib
Being a female sibling is BOTH necessary and sufficient for being a sister.
Definitions: N/S Conditions
In a definition, we have a necessary condition (N) and a
sufficient condition (S) for the term being defined.
X is sufficient (S) for Y = being X guarantees being Y
X is necessary (N) for Y = being X is conceptually
required for being Y (where “conceptual requirement”
means that there is no way to be X without being Y)
X is N and S (B) for Y = each guarantee and conceptually
require the other (there is an equivalence in this
situation)
Warning: These notions have technical meanings. Do not be tempted to apply your everyday understandings
of these notions when using these terms in their technical sense.
Definitions: N/S Conditions
elephant
S
animal: (being an elephant guarantees
being an animal)
animal
N
elephant: (being an animal is required
for being an elephant;
nothing can be an elephant
unless it is also an animal)
being a dozen
being a sister
B
B
being twelve
being a female sibling
Definitions: N/S Conditions
 Q: How do we know when we have a good
definition?
Definitions: N/S Conditions
 Q: How do we know when we have a good
definition?
 A: This is much harder to answer than knowing
when a definition is in trouble.
Definitions: N/S Conditions
 Q: How do we know when we have a good
definition?
 A: This is much harder to answer than knowing
when a definition is in trouble.
 A definition is in trouble when it faces a
counterexample, which can happen when:
the definition is NOT SUFFICIENT: just because something
satisfies the definition does not mean we have a species
 the definition is NOT NECESSARY: there can be a species without
satisfying the definition

Sections of this Presentation
 The “Species Problem”: Introduction
 Nominalism v Realism
 The Species Problem: A Problem of Definition
 Definitions: N/S Conditions
 The “Species Problem”: An Illustration
Essentialist
 Biological
 Ecological
 Cladistic

 The “Species Problem”: Conclusion?
The “Species Problem”: Illustrations
 Every proposed definition of “species” seems to face
counterexamples. The proposed definitions are
either insufficient or unnecessary or fail on both
counts.
The “Species Problem”: Illustrations
 Every proposed definition of “species” seems to face
counterexamples. The proposed definitions are
either insufficient or unnecessary or fail on both
counts.
 To illustrate, let’s look at some definitions and the
counterexamples they face.
Essentialist Species Concept
 Biological Species Concept
 Ecological Species Concept
 Cladistic/Phylogenetic Concept

Sections of this Presentation
 The “Species Problem”: Introduction
 Nominalism v Realism
 The Species Problem: A Problem of Definition
 Definitions: N/S Conditions
 The “Species Problem”: An Illustration
Essentialist
 Biological
 Ecological
 Cladistic

 The “Species Problem”: Conclusion?
The “Species Problem”: Illustrations
Essentialist Species Concept
A
Family
Genus
(share A but differ in
B and C)
Species
(share AB, but differ
in X, Y, and Z)
ABX
AB
AC
ABY
ABZ
The “Species Problem”: Illustrations
Essentialist Species Concept
 S is a species [Essentialist Species Concept] = all and
only members of S permanently having the same
distinguishing feature. In other words:

Species are uniform: If S is a species, all members of S resemble
each other exactly.

Species have clear boundaries: If S is a species, there is a fact of
the matter about when some individual does or does not belong to
S.

Species do not change: If S is a species, there is some feature(s)
unique to all members of S that the members have at all times.
The “Species Problem”: Illustrations
Essentialist Species Concept
 Essentialist Species Concept is not necessary because
there can be species that fail to satisfy this concept:

Species are uniform: If S is a species, all members of S resemble
each other exactly. COUNTEREX: differences within species

Species have clear boundaries: If S is a species, there is a fact of
the matter about when some individual does or does not belong to
S. COUNTEREX: hybridization

Species do not change: If S is a species, there is some feature(s)
unique to all members of S that the members have at all times.
COUNTEREX: speciation
The “Species Problem”: Illustrations
Essentialist Species Concept
 The fact of speciation is reason enough to reject the
Essentialist Species Concept.
Sections of this Presentation
 The “Species Problem”: Introduction
 Nominalism v Realism
 The Species Problem: A Problem of Definition
 Definitions: N/S Conditions
 The “Species Problem”: An Illustration
Essentialist
 Biological
 Ecological
 Cladistic

 The “Species Problem”: Conclusion?
The “Species Problem”: Illustrations
Biological Species Concept
 The Biological Species Concept can accommodate all
three counterexamples to the Essentialist Species
Concept.
 Classic Statement of the Biological Species Concept:
“Species are groups of actually or potentially
interbreeding natural populations, which are
reproductively isolated from other such groups.”
(Mayr, 1942)
The “Species Problem”: Illustrations
Biological Species Concept
 S is a species [Biological Species Concept] =
Members of S can produce reproductively viable
offspring; if organisms cannot produce
reproductively viable offspring, they belong to
different species.
 Illustration: Cats and lizards cannot create offspring
so they count as different species, and while horses
and zebras can create offspring, the offspring cannot
reproduce.
The “Species Problem”: Illustrations
Biological Species Concept
 The Biological Species Concept is not necessary,
because there are species that fail to satisfy the
concept.
The “Species Problem”: Illustrations
Biological Species Concept
 The Biological Species Concept is not necsesary,
because there are species that fail to satisfy the
concept.
 COUNTEREX: asexual organisms
The “Species Problem”: Illustrations
Biological Species Concept
 COUNTEREX: asexual organisms





Parthenogenesis
Fission
Budding
Sporulation
(and more …)
The “Species Problem”: Illustrations
Biological Species Concept
 The Biological Species Concept may also not be
sufficient, because there are organisms that satisfy
the concept and yet may belong to different species.
 COUNTEREX: polar bears and grizzly bears can
interbreed successfully but they seem to be different
species.
Sections of this Presentation
 The “Species Problem”: Introduction
 Nominalism v Realism
 The Species Problem: A Problem of Definition
 Definitions: N/S Conditions
 The “Species Problem”: An Illustration
Essentialist
 Biological
 Ecological
 Cladistic

 The “Species Problem”: Conclusion?
The “Species Problem”: Illustrations
Ecological Species Concept
 This last problem for the Biological Species Concept
is a motivation for the Ecological Species Concept.
The “Species Problem”: Illustrations
Ecological Species Concept
 This last problem for the Biological Species Concept
is a motivation for the Ecological Species Concept.
 S is a species [Ecological Species Concept] =
Members of share a cluster of morphological features
due to their adaptation to their specific ecological
niches.
The “Species Problem”: Illustrations
Ecological Species Concept
 Problem: This last illustration may, however, be its
very downfall.
 If there can be organisms that satisfy Ecological
Species Concept and yet count as different species,
then this concept may be not sufficient.
The “Species Problem”: Illustrations
Ecological Species Concept
 COUNTEREX: Lions and tigers could be grouped
into the same species under the Ecological Species
Concept, but they belong to diverging branches ofa
common ancestral line, which seems to indicate that
they are different species.
The “Species Problem”: Illustrations
Ecological Species Concept
 If there can be organisms that satisfy Ecological
Species Concept and yet count as different species,
then this concept may be not sufficient.
Sections of this Presentation
 The “Species Problem”: Introduction
 Nominalism v Realism
 The Species Problem: A Problem of Definition
 Definitions: N/S Conditions
 The “Species Problem”: An Illustration
Essentialist
 Biological
 Ecological
 Cladistic

 The “Species Problem”: Conclusion?
The “Species Problem”: Illustrations
Cladistic/Phylogenetic Species Concept
 This problem for Ecological Species Concept can be
accommodated by the Cladistic/Phylogenetic
Species Concept.
 S is a species [Cladistic/Phylogenetic Species
Concept] = S is a distinct branch among possibly
several others that all shoot off from a common
evolutionary line.
The “Species Problem”: Illustrations
Cladistic/Phylogenetic Species Concept
 COUNTEREX: Phylogenetically distinct species may
occupy the same ecological niche (which takes us
back to the Ecological Species Concept) and some of
them can interbreed (taking us back to the Biological
Species Concept).
Sections of this Presentation
 The “Species Problem”: Introduction
 Nominalism v Realism
 The Species Problem: A Problem of Definition
 Definitions: N/S Conditions
 The “Species Problem”: An Illustration
Essentialist
 Biological
 Ecological
 Cladistic

 The “Species Problem”: Conclusion?
The “Species Problem”: Conclusion?
 Each concept/definition has both pros and cons in
that they can accommodate some (though not all) of
the facts.
The “Species Problem”: Conclusion?
 Each concept/definition has both pros and cons in
that they can accommodate some (though not all) of
the facts.
 There are conflicts among biologists about which
facts are the most relevant.
The “Species Problem”: Conclusion?
 Each concept/definition has both pros and cons in
that they can accommodate some (though not all) of
the facts.
 There are conflicts among biologists about which
facts are the most relevant.
 This has made some philosophers skeptical about the
very notion of a species, pulling them in the direction
of Nominalism.
The “Species Problem”: Conclusion?
 But Nominalism seems to ignore the possibility that
there are real, intrinsic features and divisions in
nature that are there regardless of the concepts we
use.
The “Species Problem”: Conclusion?
 But Nominalism seems to ignore the possibility that
there are real, intrinsic features and divisions in
nature that are there regardless of the concepts we
use.
 Which means that the “Species Problem” is a
problem.