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

The Species Problem

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

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Page 1: The Species Problem

The Species Problem

How it Affects Paleontology

““The boundaries of the species, whereby men sort them, are

made by men.”- John Locke

Page 2: The Species Problem

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.

Page 3: The Species Problem

Species of Lilies

Page 4: The Species Problem

Variation in a Single Butterfly Species

SpeciesAgrias

Kingdom - Animalia Phylum - ArthropodaClass - InsectaOrder – LepidopteraFamily- NymphalidaeGenus-Agrias

Page 5: The Species Problem

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.”

Page 6: The Species Problem

A Basic Cladogram

Page 7: The Species Problem

Two Concepts of Species (p 39)

• Morphological SpeciesDiagnosible

clusterPattern of

ancestrySelf contained

group“beyond

which there is not” (Eldredge and Cracraft)

• Biological Species Population

array Actual

interbreeding

OR Potential

interbreeding

Reproductive isolation

Page 8: The Species Problem

These opposing ideas break into two camps:

Phyletic Gradualism

• Often favored by biologists and life scientists

• Speciation is slow, uniform and gradual

Punctuated Equilibrium

• Makes more sense in the context of paleontological studies

• Most species exhibit little net evolutionary change

Page 10: The Species Problem

Scientists Today…

-Tend to adhere to a biological concept of species.

-This can pose a problem for Paelontologists.

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Page 12: The Species Problem

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)

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Page 14: The Species Problem

How do Paleontologists Know?• Fossils cannot demonstrate interbreeding or the lack thereof.

• Therefore, typological (morphological) species divisions make the most sense.

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Potential Problems

Sexual Dimorphs

Recent reconstruction of Pterodactyls

Ontogeny (developmental

stages)

Page 16: The Species Problem

Modern Sexual Dimorphs

Page 17: The Species Problem

Modern Insect Ontongeny

Page 18: The Species Problem

Is Time on our Side?

Paleontologists have a different perspective

than biologists.

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Page 20: The Species Problem

TIME

Key Word

anagenesis-gradually changing from one

form to another

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Determining a “Cut Off”

GAPS IN RECORD VS

• Artificial• Convenient

CONTINUOUS SERIES

First Specimen? Halfway

through?

New Problem: Pseudoextinction

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Page 24: The Species Problem

What is “Pseudoextinction?”

• Parent species go extinct as new species evolve in succession

• Not the same as extinction.

• Part of the evolutionary species concept.

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Trilobite Family Tree

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Take your Pick!

• Biostratigraphers make use of many fine species divisions to date layers of stratigraphy.

• General paleontologists will find the evolutionary species concept (a lineage that evolves separately with separate lineages and tendencies) more practical

Page 27: The Species Problem

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.

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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.)

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Eldredge and Gould

Stephen J. Gould Niles Eldredge

There is very little proof of anagenetic transformations

taking place.

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Exception:Biostratigraphy

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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."

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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.

Page 36: The Species Problem

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