Encyclopedia of Evolution.pdf - Online Reading Center

Dobzhansky, Theodosius
Mice have two genes (more properly, transcription units) for globin
proteins, which have resulted from a duplication of a single gene. Each
of the genes has three very similar coding regions, and two introns in
the same locations between the coding regions; in the β globin gene,
one of the introns is much longer than the corresponding intron in the
α globin gene. Humans also have α and β globin genes very similar to
those of mice and in addition have genes for δ, Gγ, Aγ, and ε globins that
are nearly identical to the β globin gene and resulted from duplication.
Numbers inside the boxes represent the number of nucleotides in the
coding region or the intron. (Redrawn from Freeman and Herron)
gene has duplicated several times during animal evolution,
producing a whole family of globin genes (see figure on page
136). One of them is myoglobin, which is found in muscles;
two others are the components of hemoglobin, the protein
that carries oxygen gas in the red blood cells. The gene duplication
that produced the α and β genes occurred early in vertebrate
evolution; all vertebrates have both of these genes,
except hagfishes, which are descendants of one of the earliest
divergences in vertebrate evolution. Fetal hemoglobin, slightly
different from adult hemoglobin, is encoded by yet another
gene in this complex. If the duplicated gene has no promoter,
it becomes part of the noncoding DNA.
DNA in Evolution
Not only are the physical characteristics of organisms, such as
humans, encoded within the DNA but also many behavioral
characteristics. Individual human behavior is strongly influenced
by the levels of brain chemicals such as neurotransmitters
and neuropeptides. Individual humans differ in the levels
of these chemicals, which causes some people to eat more than
others, or to seek adventure more than others. In part, the levels
of these chemicals are determined by things that happen
during the individual’s lifetime—environmental factors, education,
reinforcement of behavior by habit. But they are also
strongly influenced by control sequences of DNA that regulate
the transcription of the genes and the manufacture of the
proteins. Many aspects of human behavior, including sexual
orientation, have a genetic as well as an environmental component.
While genes are not known to ever force an individual
to do something (to eat more or less, or to seek more or less
stimulation), they definitely influence human inclinations (see
essay, “How Much Do Genes Control Human Behavior?”)
DNA provides raw material for evolution by reliably
passing genetic traits to the next generation and by allowing
limited mutations. Gene duplication also contributes raw
material to the evolutionary process. Even noncoding DNA
can contribute to evolution if it alters the transcription of
genes or is reactivated and becomes a gene. All of this contributes
to the stability and variability of genetic information
that must be present in populations for evolution to occur.
Geneticists have analyzed DNA, and proteins, and traits, and
found that wild populations contain a great deal of variability.
This confirms what Darwin established in his landmark
1859 book (see origin of species [book]), but the basis
of which he did not understand. Modern evolutionary science
therefore represents a convergence of Darwinian natural
selection, Mendelian genetics (see modern synthesis), and
the chemistry of DNA.
Further Reading
Ast, Gil. “The alternative genome.” Scientific American, April 2005,
58–65.
Chiu, Lisa Seachrist. When a Gene Makes You Smell Like a Fish…
And Other Amazing Tales About the Genes in Your Body. New
York: Oxford University Press, 2006.
Freeman, Scott, and Jon C. Herron. “Mutation and Genetic Variation.”
Chap. 4 in Evolutionary Analysis, 3rd ed. Upper Saddle
River, N.J.: Pearson Prentice Hall, 2004.
Lynch, Michael, and John S. Conery. “The evolutionary fate and consequences
of duplicate genes.” Science 290 (2000): 1,151–1,155.
Maynard Smith, John, and Eörs Szathmáry. The Origins of Life:
From the Birth of Life to the Origins of Language. New York:
Oxford University Press, 1999.
Rice, Stanley, and John McArthur. “Computer analogies: Teaching
molecular biology and ecology.” Journal of College Science
Teaching 32 (2002): 176–181.
Russo, V. E. A., et al., eds. Development: Genetics, Epigenetics and
Environmental Regulation. New York: Springer, 1999.
Watson, James D., with Andrew Berry. DNA: The Secret of Life.
New York: Knopf, 2003.
Dobzhansky, Theodosius (1900–1975) Russian-American
Evolutionary geneticist Theodosius Dobzhansky was one
of the principal architects of the modern synthesis in which
Mendelian genetics was united with Darwinian natural
selection (see origin of species [book]) to form the modern
theory of evolution.
Born January 25, 1900, Dobzhansky was a teenager during
the tumultuous time of the Russian Revolution. Imme-