What Is Macroevolution?
While microevolution refers to changes in the allele frequencies of populations, macroevolution focuses on the formation of new species (speciation) and on the evolutionary relationships 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 response to environmental changes. The accumulation of small changes from generation to generation may transform an ancestral 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.
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 mammals. 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.
Today, humans are the only primate existing globally. We inhabit every continent, including areas as inhospitable as the icy Antarctic or the scorching Sahara Desert. This extended geographic range reflects the adaptability of Homo sapiens. By comparison, our relatives in the hominoid superfamily live in very circumscribed areas of the Old World tropical rainforest. Chimpanzees, bonobos, and gorillas can be found only in portions of Central, East, and West Africa. Orangutans are limited to the trees on the Southeast Asian islands of Sumatra and Borneo. Gibbons and siamangs swing through the branches of a variety of Southeast Asian forests.
Such comparisons between humans and the other primates appear natural to biologists and anthropologists today, because they accept that modern humans, apes, and monkeys are descended from the same prehistoric ancestors. However, a century and a half ago, when Charles Darwin published On the Origin of Species (1859), this notion was so controversial that Darwin limited himself to a single sentence on the subject. Today, anthropologists, as well as the global scientific community in general, accept that human origins are revealed in the evolutionary history of the primates. We now know that much of who we are, as culture-bearing biological organisms, derives from our mammalian primate heritage.
Although many of the primates discussed in this chapter no longer exist, their descendants (as we discussed in Chapters 3 and 4) now live in South and Central America, Africa, Asia, and Gibraltar at the southern tip of Spain, and in zoos and laboratories all over the world. The successful adaptation of the primates largely reflects their intelligence, a characteristic that provides for behavioral flexibility. Other physical traits, such as stereoscopic vision and a grasping hand, have also been instrumental in the success of the primates.
Why do paleoanthropologists attempt to recreate primate evolutionary history from ancient evidence? The study of these ancestral primates gives us a better understanding of the physical forces that caused these early creatures to evolve into today’s primates. It gives us a fuller knowledge of the processes through which an insecteating, small-brained mammal evolved into a toolmaker, a thinker, a human being. In addition, the continued
Macroevolution Evolution above the species level. speciation The process of forming new species. isolating mechanism A factor that separates breeding populations, thereby preventing gene flow, creating divergent subspecies and ultimately (if maintained) divergent species. cladogenesis Speciation through a branching mechanism whereby an ancestral population gives rise to two or more descendant populations.
Survival of our species and of our world now depends on understanding evolutionary processes and the way all organisms interact with their environment.
World History
