Chapter 5

Macroevolution and the Early Primates

Chapter Outline

What Is Macroevevolution? When and Where Did the First Primates

Appear, and What Were They Like? When Did the First Monkeys and Apes

Appear, and What Were They Like?

Macroevolution

Over time, macroevolutionary forces produce new species from old ones.

Macroevolution focuses upon the formation of new species and on the evolutionary relationships between groups of species.

Isolating mechanisms can separate breeding populations and lead to the appearance of new species.

Isolating Mechanisms

Geographical Anatomical structure Social and cultural concepts

Cladogenesis

Isolating Mechanisms In branching evolution, isolating mechanisms

separate breeding populations, creating divergent subspecies and then divergent species.

Geographical, biological, or social isolating mechanisms block gene flow between groups, contributing to the accumulation of genetic mutations in each population.

Biological isolating mechanisms include phenomena such as the sterility of hybrid offspring.

Anagenesis and Convergence Anagenesis

– When natural selection, over time, favors some variants over others.

– Creates a change in a population’s average characteristics.

Convergence– Occurs when two unrelated species

come to resemble each other owing to functional similarities.

Anagenesis

Continental Drift

Primate Evolution

Primates arose from a branching of mammalian forms that began more than 100 million years after the appearance of the first mammals.

Most ecological niches that mammals have since occupied were– preempted by reptiles – nonexistent until flowering plants became

widespread about 65 million years ago.

Ancestral Features Features in the Eocene genus Adapis are found in

prosimians today. Like modern lemurs, it has a postorbital bar, a bony ring around the eye orbit. Note that the orbit is open behind the ring.

Primate Evolution

Geological changes in the orientation and position of the earth’s continents affected the global climate.

This played a key role in the evolution and distribution of the primates.

The first primates were arboreal insect eaters and the characteristics of all primates developed as adaptations to this early way of life.

Early Primates

The earliest primates developed 60 million years ago in the Paleocene epoch.

They were small arboreal creatures. Diverse prosimianlike forms were common in

the Eocene across what is now North America and Eurasia.

By the late Eocene, 45 million years ago, small primates combining prosimian and anthropoid had emerged.

Location of Hominid Fossils

Primate Evolution

By the late Eocene small primates combining lemurlike and tarsierlike features with those in monkeys and apes developed.

In the Miocene epoch, apes proliferated and spread over many parts of the Old World.

Ancestors of large apes and humans appeared by 16 m.y.a. and were widespread as recently as 8 m.y.a.

Primate Evolution

Details of dentition suggest that hominines arose from these earlier apes.

Some populations lived in parts of Africa where pressures existed to transform a creature just like it into a primitive hominine.

Other populations remained in the forests, developing into today’s bonobo, chimpanzee, and gorilla.