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.