This is my attempt to explain punctuated equilibrium vs. phyletic gradualism and how both ideas contribute to the controversy of what constitutes a species.

1. The Species Problem
How it Affects Paleontology
“
“The boundaries of the species, whereby
men sort them, are made by men.”- John
Locke

2. What is a Species?
• A species is “the fundamental
taxonomic unit in nature” (39.)
• Species “recognize each other.”
• Proof of this “recognition” is
displayed in reproductive
habits, or the potential for
interbreeding.

3. Species of Lilies

4. Variation in a Single Butterfly Species
Kingdom - Animalia
Phylum - Arthropoda
Class - Insecta
Order – Lepidoptera
Family- Nymphalidae Species
Genus-Agrias
Agrias

5. What is phylogeny?
Loosely (according to the dictionary)
phylogeny is the evolutionary history of a
group of organisms as depicted in their family
tree or “cladogram.”

6. A Basic Cladogram

7. Two Concepts of Species (p 39)
• Morphological • Biological Species
Species  Population array
Diagnosible cluster  Actual
Pattern of ancestry interbreeding
Self contained OR
group  Potential
“beyond which interbreeding
there is not”  Reproductive
(Eldredge and Cracraft) isolation

8. These opposing ideas break into
two camps:
Phyletic Gradualism Punctuated Equilibrium
• Often favored by • Makes more sense in
biologists and life the context of
scientists paleontological
• Speciation is studies
slow, uniform and • Most species exhibit
gradual little net evolutionary
change

9. A paleontological
study of speciation
in favor of phyletic
gradualism.

10. Scientists Today…
-Tend to adhere to a biological
concept of species.
-This can pose a problem for
Paelontologists.

12. There are at least 24 different
species concepts and none of
them can be applied to all
organisms that have ever lived.
(Hey, J. 2001 qtd in Techne)

14. How do Paleontologists Know?
• Fossils cannot demonstrate
interbreeding or the lack
thereof.
• Therefore, typological
(morphological) species
divisions make the most sense.

15. Potential Problems
Sexual Dimorphs Ontogeny
(developmental stages)
Recent reconstruction
of Pterodactyls

16. Modern Sexual Dimorphs

17. Modern Insect Ontongeny

18. Is Time on our Side?
Paleontologists have a
different perspective than
biologists.

20. TIME
Key Word
anagenesis-gradually changing
from one form to another

22. Determining a “Cut Off”
GAPS IN RECORD VS CONTINUOUS SERIES
• Artificial  First Specimen?
• Convenient  Halfway through?
New Problem: Pseudoextinction

24. What is “Pseudoextinction?”
• Parent species go extinct as new
species evolve in succession
• Not the same as extinction.
• Part of the evolutionary species
concept.

25. Trilobite Family Tree

26. Take your Pick!
• General
paleontologists will
find the evolutionary
species concept (a
lineage that evolves
separately with
separate lineages and
• Biostratigraphers tendencies) more
make use of many practical
fine species divisions
to date layers of
stratigraphy.

27. A Solution to the Mayhem
Punctuated Equilibrium to the Rescue!
• Phyletic gradualism(gradual
transformation among species) is actually
not that common in the fossil record.
• Actually, fossil records appear to remain
static and relatively unchanged throughout
paleo reconstructions for the most part.

29. Punctuated Equilibrium
• Most large species populations do
not evolve in any direction.
• Fossil populations remain in stable
equilibrium for long periods,
• Punctuated by the introduction of
a new species formed in an isolated
area (and then migrated back to
main group.)

31. Eldredge and Gould
Stephen J. Gould Niles Eldredge
There is very little proof of anagenetic
transformations taking place.

32. Exception:
Biostratigraphy

33. Exception:
George Simpson of Columbia
University says,
“The state of rest is the exception
and it seems that some restraint
or force must be required to
maintain it."

34. Main Idea
Anagenetic continua are rare, and thus
species division is not as complicated as
it seems.
Nietzche says, “Out of chaos comes order.”
Punctuated Equilibrium simplified the
species problem significantly.

36. Sources:
"Biostratigraphy." Harvard University Museum of Comparative Zoology. Harvard
University, 2004. Web. 7 Sep 2011.
<http://www.mcz.harvard.edu/Departments/InvertPaleo/Tren
ton/Intro/GeologyPage/Sedimentary%20Geology/biostrat.htm
Crampton, , James. Gale, A. "A plastic boomerang: speciation and
intraspecific evolution in the Cretaceous bivalve Actinoceramus."
Paleobiology 31.4 (2005): 559-577. BioOne. Web. 7 Sep 2011.
<http://www.bioone.org/doi/abs/10.1666/04003.1>.
Phylogeny. (2012, April 14). Retrieved from www.dictonary.com
Prothero, Donald. Bringing Fossils to Life. 2nd ed. NY: McGraw-Hill, 2004.
39-45. Print.
Punctuated Equilibrium." Wikipedia. Online. 2011. Print.
<www.wikipedia.com>.
Unknown. (Image Creator). (2012). Phylogenetic tree of life. [Print Photo].
Retrieved from http://en.wikipedia.org/wiki/Phylogenetic_tree