Page 74 - Environment: The Science Behind the Stories

Once we have a phylogenetic tree, we can map traits Hemignathus. These species are closely related in evolu-
onto the tree according to which organisms possess them, tionary terms, as indicated by the genus name they share.
and we can thereby trace how the traits have evolved. For They are more distantly related to honeycreepers in other
instance, phylogenetic research shows that birds, bats, and genera, but all honeycreepers are classified together in
insects are distantly related, with many flightless groups the family Fringillidae. This system of naming and clas-
between them. (Note in Figure 3.6 that birds and mammals sification was devised by Swedish botanist Carl Linnaeus
are separated on the tree and that insects are outside the tree.) (1707–1778) long before Darwin’s work on evolution.
Therefore, it is far simpler to conclude that these three very Today biologists use evolutionary information from phylo-
different groups evolved flight independently than it would genetic trees to help classify organisms under the Linnaean
be to conclude that the many flightless groups between them system’s rules.
each lost an ancestral ability to fly. Because phylogenetic
trees help biologists make such inferences about so many
traits, they have become one of the modern biologist’s most The fossil record teaches us about
powerful tools. life’s long history
Knowing how organisms are related to one another
also helps scientists to classify them and name them, so Scientists also decipher life’s history by studying fossils. As
that we can make sense of the life around us and commu- organisms die, some are buried by sediment. Under certain
nicate effectively. Taxonomists use an organism’s physical conditions, the hard parts of their bodies—such as bones,
appearance and genetic makeup to determine its species. shells, and teeth—may be preserved, as sediments are com-
These scientists then group species by their similarity into pressed into rock (pp. 55–56). Minerals replace the organic
a hierarchy of categories meant to reflect evolutionary rela- material, leaving behind a fossil, an imprint in stone of the
tionships. Related species are grouped together into genera dead organism (Figure 3.8, p. 76). In countless locations
(singular, genus), related genera are grouped into families, throughout the world, geologic processes across millions of
and so on (Figure 3.7). Each species is given a two-part Latin years have buried sediments and later brought sedimentary
or Latinized scientific name denoting its genus and species. rock layers to the surface, revealing assemblages of fossil-
For instance, the ‘akiapo¯la¯ ‘au, Hemignathus munroi, ized plants and animals from different time periods. By dating
is similar to other Hawaiian honeycreepers in the genus the rock layers that contain fossils, paleontologists (scientists

Domain: Eukarya

Kingdom: Animalia

Phylum: Chordata

Class: Aves

Order: Passeriformes

Family: Fringillidae CHAPTER 3 • Ev ol u T i on, Bi odiv ER si T y, A nd Po P ul AT i on E C ology

Genus: Hemignathus

Species: Hemignathus
munroi

Figure 3.7 Taxonomists classify organisms using a hierarchical system meant to reflect evolutionary
relationships. Species similar in appearance, behavior, and genetics (because they share recent common
ancestry) are placed in the same genus. Organisms of similar genera are placed in the same family. Families are
placed within orders, orders within classes, classes within phyla, phyla within kingdoms, and kingdoms within
domains. For example, honeycreepers belong to the class Aves, along with peacocks, loons, and ostriches.
However, the differences between these species, which have diverged across millions of years of evolution, are
great enough that they are placed in different orders, families, and genera. 73

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