PHylogENy: THE UNITy ANd dIvERSITy of lIfE 419
freshwater populations [6]. Eda is a classic example of adaptation
based on standing genetic variation: the gene tree of Eda is old,
even in populations that recently adapted to life in fresh water.
Much of the genetic divergence between marine and freshwater
populations of this species shows a similar pattern [20].
Darwin recognized that languages have diverged from com-
mon ancestors, and linguists have recently borrowed phylogenetic
methods from biology to trace language histories. Language trees,
in turn, have been used to trace the history of other aspects of
culture in these populations, in the same way that biologists use
DNA-based phylogenies to infer the evolutionary history of organ-
isms’ characteristics [23]. For example, diverse societies in the Aus-
tronesian language family originated in Taiwan more than 5000
years ago, and spread via the islands of Southeast Asia throughout
the Indian and Pacific oceans, from Madagascar to New Zealand
and Hawaii. Using a phylogeny based on languages in 84 societies,
Thomas Currie and colleagues tested several models of changes in
these cultures’ political organization (FIGURE 16.19) [9]. They con-
cluded that political organization increases in complexity by small
incremental changes, but can decrease by either small or large
steps. Because cultural inheritance follows different rules than genetic inheritance,
using phylogenetic methods to study the evolution of language and culture must be
done carefully—but it is exciting.Reconstructing ancestors
One of the most important uses of phylogenies is that they can enable us to trace
the evolution of organisms’ characteristics (see Chapter 2). For example, all ter-
restrial mammals are quadrupedal (walk on all four legs) except humans, the one
bipedal twig on the many branches of the mammalian tree. It is far more parsimo-
nious to suppose that the common ancestor of mammals was quadrupedal than
to suppose that it walked on two legs and gave rise to a great radiation of quadru-
pedal descendants, among which one reverted to the bipedal condition. In fact, we
can confidently say that all the common ancestors of the many clades of mammals
were quadrupedal, except the common ancestor of humans and extinct hominins
such as Australopithecus. That is, we can mentally reconstruct the state of a charac-
ter in extinct ancestors. You have encountered many examples in past chapters; for
example, we noted in Chapter 15 that primate ancestors of humans had tails and
Futuyma Kirkpatrick Evolution, 4e
Sinauer Associates
Troutt Visual Services
Evolution4e_16.18.ai Date 01-02-2017(B)Low-platedSCX
BLAU
FADA)
NOST
GJOG
LLOY
OMPL
NEU
NHR
NAKA
JAMA
AKMA
PAXL
WMSO
FRIL
LITC
PAXB
COND
WALL
JASE(A) BLAU
NOST
OMPL
SCX
FADA
PAXB
SRST
AKST
WALL
PAXL
COND
SFC
WMSO
FRIL
LLOY
NEU
GJOG
NHR
AKMA
NAVR
SRMA
JAMA
LITC
JASEHigh-platedAtlanticPaci cFIGURE 16.18 Gene trees provide evidence that adaptation in the
three-spined stickleback (Gasterosteus aculeatus) is based on standing
genetic variation. (A) Stained specimens show the ancestral, high-plated
morph, found in marine and some freshwater populations, and the
low-plated morph found in many freshwater populations in northern
Eurasia and North America. The low-plated phenotype is caused by
an allele of the Ectodysplasin (Eda) gene, which encodes a signaling
protein that is required for differentiation of ectodermal features. The
gene tree of Eda sequences at left shows that gene copies from all
high-plated fish form one clade (red) and that those from all low-plated
fish (blue) form another. This shows that all the low-plated copies have a
single origin, so copies of a low-plated allele must have been present at
low frequency in ancestral marine populations throughout the northern
oceans. The abbreviations designate collection localities. (B) A phylog-
eny of the populations based on single-nucleotide polymorphisms
(SNPs) at 25 other loci shows that several low-plated populations (blue)
have evolved independently. (After [6]; photos from [2].)16_EVOL4E_CH16.indd 419 3/22/17 1:33 PM