Download Species concepts Patterns of Evolution Evidence in Homology and

Biol 4974/5974 Evolution
Species concepts; patterns and evidence
8/22/2013
Species concepts
Patterns in and evidence of Evolution
Learning goals
Understand:
• Changing views of species through time.
• Linnaeus and binomial species names and classification.
• Species concepts: morphological, biological, evolutionary, and
phylogenetic.
• That similar structures in organisms arise through three
evolutionary processes: homology, parallelism, and
convergence.
• Comparative embryology and fossils as evidence of
relationships among organisms and evolution.
Changing view of species
• 4th and 5th centuries BCE, Plato and
Aristotle: idealist species concept.
• Each species was a product of
creation and had a special purpose.
• Steps from least perfect to most
perfect.
• Teleology What does this mean?
• “Natural science became interwoven
with religion.”
• Manifested in the Great Chain of
Being (Scale of Nature, Ladder of
Nature).
1
Biol 4974/5974 Evolution
Species concepts; patterns and evidence
8/22/2013
18th century view
Views were growing more sophisticated:
Georges Buffon (Georges-Louis Leclerc) (1707-1788): species
were the biological units. Contribution?
• Species were defined by reproductive isolation (were fertile or
sterile offspring produced?)
• Buffon accepted individual variation within species.
• Ultimately, he did not believe that species change.
• If species are fixed, how could new species arise?
• What reasons did he give? p. 21, 24.
18th-19 century
Jean-Baptiste de Lamarck (1744-1829)
• Subscribed to the Great Chain of Being but
thought species evolved from other
species. Species did not go extinct.
• Branching inheritance depicted. Clearly
different routes to perfection.
• Believed that organisms could evolve over
time, and work up the Scale.
• Lamarc provided a mechanism for change
(Principle of use and disuse; Inheritance of
acquired characters), which was later
discredited. How did these work?
Fig. 2.2
Linnaeus: modern systematics
• Carl von Linnė(1697-1778) or Linnaeus’ work was a
revolutionary step in our understanding of species.
• Provided a basis for describing species and noting
prominent features.
• Binomial nomenclature. Please define.
• Species relationships based on morphological features
Established hierarchies of relationship: Orders, classes,
etc.
• He also acknowledged varieties or races, which means that
he understand variation within species.
2
Biol 4974/5974 Evolution
Species concepts; patterns and evidence
8/22/2013
Figure 02.F08: The nested taxonomic categories traditionally used to classify fruit flies and
humans.
Current species concepts (Table 2.1)
Morphological species: “Unites individuals that share more
characteristics (features) with one another than they do with any
other organism.” These individuals would be considered a single
species.
• Objective, quantitative methods are used today. How?
Biological species: “Based on the inability of individuals in
populations to interbreed with individuals in other populations
to produce viable offspring.”
• Ernst Mayr proposed this concept in 1942. He defined species
essentially as interbreeding or potentially interbreeding
groups of populations that are isolated by other groups by
absence of gene exchange. What about hybrids?
• Applies to sexually-reproducing species—not clones or singlecell organisms.
Current species concepts, continued
Evolutionary species: Based on “evolutionary isolation” from
other species. Proposed by George G. Simpson (1961), who
stated, “an evolutionary species is a lineage (p. 32) evolving
separately from others with its own unitary evolutionary role
and tendencies.”
• May be difficult to identify when speciation is complete.
Phylogenetic species (phylospecies, cladospecies): “Ancestordescendant relationships define lineages of organisms.” E. O.
Wiley reworked Simpson’s definition to “a single lineage of
ancestral descendant populations of organisms which maintains
its identity from other such lineages and which has its own
evolutionary tendencies and historical fate.”
3
Biol 4974/5974 Evolution
Species concepts; patterns and evidence
8/22/2013
Similar adaptations: patterns of evolution
Figure 03.F06: Homology, parallelism, and convergence diagrammed for two species (1, 2) that
share a similar phenotypic character (phenotype a, b, c).
Figure 03.F07: Skeletal structures of the forelimbs of representative terrestrial vertebrates to
show the homology among bones at different levels in the limbs.
Figure 03.B01_01: Vestigial (non-functioning) structures found in humans.
Adapted from Romanes, G. J. Darwin, and After Darwin. Open Court, 1910.
4
Biol 4974/5974 Evolution
Species concepts; patterns and evidence
8/22/2013
Figure 3.F08: Comparison of insect and bird wings to show their analogy
Fig. 3.3 Parallel evolution of “wolf” phenotype.
Fossil marsupial from Miocene in Patagonia.
Extinct Tasmanian marsupial wolf.
Placental North American wolf.
Fig. 3.4. Convergent evolution between species of two
different families of plants.
North American Cactaceae, saguaro
North African Eophorbiaceae
5
Biol 4974/5974 Evolution
Species concepts; patterns and evidence
8/22/2013
Comparative embryology as evidence
• Comparative embryology from Karl von Baer (1792-1876):
showed similarities in embryonic development among very
different vertebrates.
• From this, Ernst Haeckel (1834-1919) developed his
biogenetic law: In short, ontogeny recapitulates phylogeny.
• We now know that only early developmental stages are
repeated, using shared genes and gene networks.
• Later stages differ because of developmental changes.
• Regardless, embryology supports a common ancestry and
common descent.
Fossil record provides evidence
• Discovery of fossils has been a major
source of information supporting evolution.
• Helps us understand the relationships
among organisms as well.
• Fossil record was beginning to develop in
the mid-19th centrury.
• Fossils with mixed traits, such as
Archaeopteryx, represented transitional
species.
• Complete evolutionary sequences of fossils
were powerful confirmation of evolution
and descent with modification, e.g., the
evolution of horses.
Figure 03.F14: Evolutionary relationships among various lineages of horses, with emphasis on
North American and Old World groups.
(Adapted from MacFadden, B. J. Fossil Horses: Systematics,
Paleobiology and Evolution of the Family Equidae. Cambridge University Press, 1992.)
6