Encyclopedia of Evolution.pdf - Online Reading Center

coevolution
descent, and that scientists had been studying evolution all
along without knowing it.
Cladists pay close attention to the occasional differences
between cladistic and traditional classification systems. One
significant example of these differences is the reclassification
of the flowering plants. Traditionally, all flowering plants
were classified as either monocots or dicots. More recent
analysis indicates that the monocots are a monophyletic
group but the dicots are not. The monocots are one branch
from within the dicots; therefore “dicot” is a paraphyletic
group (see figure on page 76). Cladistics has shown that the
monocot/dicot dichotomy that every college biology student
learns is an oversimplification.
Perhaps the main advantage of cladistics in evolutionary
science is that it allows investigations to proceed without having
detailed knowledge of which ancient species, represented
today by fossils, were or were not ancestral to which modern
species. For example, the existence of Homo Habilis about
two million years ago is well known. However, scientists
cannot know if H. habilis represented the actual ancestral
population from which the modern human species evolved,
or whether modern humans evolved from another population
similar to H. habilis. With cladistics, research can continue
despite this uncertainty.
The cladistic method has received some experimental
confirmation. Evolutionary microbiologist Daniel Hillis
grew cultures of viruses in his laboratory, allowing them
to undergo mutations and evolve into different lineages. He
knew precisely what the pattern of evolutionary branching
was for these viruses. He then performed cladistic analyses,
using DNA base sequences. The resulting cladogram closely
matched the evolutionary pattern that had actually occurred.
Some creationists (see creationism) have pointed to cladistics
as an example of evolutionists starting to lose faith in
evolutionary science. When a cladistic approach was used in
classifying organisms in the British Museum of Natural History
in 1981, some creationists hailed it as the first step in
the death of evolutionary assumptions, and some evolutionary
scientists also worried that this was what was happening.
Cladists are quite certain that all of life represents one
The dicots are a paraphyletic group of flowering plants because the
monocot lineage is excluded from it. The term dicot is used descriptively
but is not a phylogenetic classification.
immense pattern of branching from a common ancestor, just
as all evolutionists since Darwin have assumed.
Cladistics has also proven its worth in the study of evolutionary
medicine. Cladograms regularly appear in articles
published in such journals as the Journal of Emerging Infectious
Diseases, published by the National Institutes of Health.
Epidemiologists routinely perform cladistic analyses on strains
of diseases, in order to determine which strains are most
closely related to which others, in the hope of deducing where
new strains of diseases originated. This knowledge helps in the
production of vaccines, to control the spread of the disease,
and to predict the emergence of new diseases. It was cladistic
analysis that allowed epidemiologists to identify that the strain
of anthrax that was used in bioterrorist attacks in the United
States in 2001 came from within the United States. Cladistics
has also revealed the origin of HIV (see AIDS, evolution
of). Cladistics has proven not only a revolutionary technique
within evolutionary science but has allowed evolutionary science
to produce practical benefits to humankind.
Further Reading
Baum, David A., et al. “The tree-thinking challenge.” Science 310
(2005): 979–980.
Cracraft, Joel, and Michael J. Donoghue. Assembling the Tree of
Life. New York: Oxford University Press, 2004.
Foer, Joshua. “Pushing PhyloCode.” Discover, April 2005, 46–51.
Freeman, Scott, and Jon C. Herron. “Reconstructing evolutionary
trees.” Chap. 14 in Evolutionary Analysis, 3rd ed. Upper Saddle
River, N.J.: Pearson Prentice Hall, 2004.
Hillis, Daniel M., et al. “Experimental phylogenies: Generation of a
known phylogeny.” Science 255 (1992): 589–592.
Nikaido, M., A. P. Rooney, and N. Okada. “Phylogenetic relationships
among cetartiodactyls based on insertions of short and long
interspersed elements: Hippopotamuses are the closest extant
relatives of whales.” Proceedings of the National Academy of Sciences
USA 96 (1999): 10,261–10,266.
Stanford, Alice M., Rachel Harden, and Clifford R. Parks. “Phylogeny
and biogeography of Juglans (Juglandaceae) based on matK and ITS
sequence data.” American Journal of Botany 87 (2000): 872–882.
Stewart, Caro-Beth. “The powers and pitfalls of parsimony.” Nature
361 (1993): 603–607.
coevolution Coevolution occurs when the evolution of
one species influences, and is influenced by, the evolution
of another species. Probably every species has experienced
coevolution, since every species exists in a web of ecological
relationships. In the general sense, every species coevolves
with every other species. In the specific sense, the term coevolution
is usually restricted to important and specific relationships
between species that influence the evolution of each of
them, rather than the diffuse background of ecological relationships.
For example, many plants have evolved the ability
to compensate for the loss of tissue to herbivores, and
herbivores have evolved the ability to digest plants, but this
interaction is usually considered too diffuse to qualify as
coevolution. Coevolution occurred when plants evolved the
ability to produce toxins, and herbivores evolved the ability