123CHAPTER 6
Macroevolution and
the Early Primates
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When and Where Did the First Primates
Appear, and What Were They Like?
Fossil evidence indicates that the earliest primates began to develop around 65 million years ago
(mya), when the mass extinction of the dinosaurs opened new ecological opportunities for mam-
mals. By 55 mya, primates inhabited North America and Eurasia, which at that time were joined
together as the supercontinent Laurasia and separated from Africa. The earliest primates were
small nocturnal insect eaters adapted to life in the trees.
What Is Macroevolution?
While microevolution refers to changes in the allele frequen-
cies of populations, macroevolution focuses on the formation
of new species (speciation) and on the evolutionary rela-
tionships among groups of species. Speciation may proceed
in a branching manner, as when reproductive isolation of
populations prevents gene flow between them, leading to the
formation of separate species. Alternatively, in the absence
of isolation, a species may evolve without branching in re-
sponse to environmental changes. The accumulation of small
changes from generation to generation may transform an an-
cestral species into a new one.
When Did the First Monkeys and Apes
Appear, and What Were They Like?
By the late Eocene epoch, about 40 mya, diurnal anthropoid
primates appeared. Many of the Old World anthropoid
species became ground dwellers. By the Miocene epoch
(beginning 23.5 mya), apes were widespread in Asia, Africa,
and Europe. While some of these hominoids were relatively
small, others were larger than present-day gorillas. Sometime
between 5 and 8 mya, a branch of the African hominoid line
became bipedal, beginning the evolutionary line that later
produced humans.