Evolution, 4th Edition

Several texts on population genetics give the cur-

rent view of the field. John Gillespie’s Popula-

tion Genetics: A Concise Guide (Johns Hopkins

university Press, Baltimore, MD, 2004) is con-

cise and accessible. D. l. Hartl and A. G. Clark’s

Principles of Population Genetics (Sinauer

Associates, Sunderland, MA, 2007) is a more

detailed exploration. The more recent text by

R. Nielsen and M. Slatkin, An Introduction to

Population Genetics: Theory and Applications

(Macmillan Education, 2013), emphasizes how

the principles of population genetics are ap-

plied to data, including in the study of human

evolution. Brian and Deborah Charlesworth’s

Elements of Evolutionary Genetics (Roberts

and Co., Greenwood Village, Co, 2010) is an

advanced but definitive summary of the field

of evolutionary genetics.

Molecular evolution is among the fastest moving

areas of biology. The data, analyses, and data-

collection technologies change so rapidly

that any review we suggest here will soon be

dated. Given that caveat, we recommend R.

Nielsen’s review “Molecular signatures of nat-

ural selection” (Annu. Rev. Genet. 39: 197–218,

2005) for those interested in learning more

about how we use genetic data to find evi-

dence of adaptation. “Strength in small num-

bers” by S. Tishkoff (Science 349: 1282–1283,

2015) and “Signals of recent positive selection

in a worldwide sample of human populations”

by J. K. Pickrell and colleagues (Genome Res.

19: 826–837, 2009) give nice summaries of ad-

aptation in humans.

for a broader perspective on what genetic data

can tell us about adaptation, “Molecular span-

drels: tests of adaptation at the genetic level”

by R. D. H. Barrett and H. E. Hoekstra (Nat.

Rev. Genet. 12: 767–780, 2011) and “Commen-

tary: When does understanding phenotypic

evolution require identification of the underly-

ing genes?” by M. D. Rausher and l. f. Delph

(Evolution 69: 1655–1664, 2015) give thought-

ful perspectives on a complex topic.

PRoBlEMS AND DiSCuSSioN ToPiCS

1. if the egg-to-adult survival rates of genotypes
   A 1 A 1 , A 1 A 2 , and A 2 A 2 are 90 percent, 85 percent,
   and 75 percent, and their fecundities are 50, 55,
   and 70 eggs per female, respectively, what are
   the absolute fitnesses (W) of these genotypes?
   using A 1 A 1 as the fitness reference, what are
   the relative fitnesses (w)? if the frequency of the
   A 2 allele is p = 0.5, what will be its frequency
   one generation later? What will be the allele
   frequency when the population reaches equilib-
   rium (stops evolving)?


2. How rapidly would a large population adapt to
   an environmental change if an advantageous
   allele were already present at low frequency
   (say, 1 percent), compared to the situation where
   it adapts by a newly arisen mutation at that locus?
   Would both of these events be accompanied by
   a selective sweep? Would they both be detect-
   able by studying variation in the DNA sequence
   near the locus after adaptation occurred?


3. Describe a situation in which evolution does not
   occur even though natural selection is acting on
   a genetically variable character. (Assume that
   genetic drift is not occurring.)


4. imagine a population in which the survival of
   A 1 A 1 homozygotes is 80 percent as great as that
   of A 1 A 2 heterozygotes, while the survival of A 2 A 2
   homozygotes is 95 percent that of the heterozy-
   gotes. What is p, the frequency of the A 2 allele,

at equilibrium? Now suppose the population has

reached this equilibrium, but that the environ-

ment then changes so that the relative fitnesses

of A 1 A 1 , A 1 A 2 , and A 2 A 2 become 1.0, 0.95, and

0.90. What will p be in the adults after one gen-

eration of selection in the new environment?

5. Suppose a species has two generations per year,
   that adult survival rates of genotypes A 1 A 1 , A 1 A 2 ,
   and A 2 A 2 are identical, and that the fecundity
   values are 50, 55, and 70 in the spring genera-
   tion and 70, 65, and 55 in the fall generation,
   respectively. Will polymorphism persist, or will
   one allele become fixed if fecundity values are
   unchanged for many years? What if the fecun-
   dity values are 55, 65, 75 in the spring and 75, 65,
   55 in the fall?


6. What hypotheses could account for the observa-
   tion that more genes have experienced recent
   adaptive evolution in the chimpanzee genome
   than in the human genome?


7. Do you expect that natural selection acting
   within a species would increase the population
   size of the species? Do you expect that it would
   increase the rate at which new species arise, thus
   increasing the number of species?

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