HUMAN BIOLOGY

450 Chapter 23

Tarsiers

New World

monkeys

Old World

monkeys Gibbons Orangutans Gorillas Humans

Lemurs, lorises,
galagos

Chimpanzees,

bonobos

Hominins

Hominoids

Anthropoids Figure 23.15 The primates include several

nonhuman species. As the diagram shows,

bonobos and chimpanzees are our closest

primate relatives. Like us, bonobos walk

upright. (© Cengage Learning)

forest for insects, seeds, buds, and eggs. Between 54 and

38 million years ago, some primates were living in the

trees—a habitat where natural selection would strongly

favor some traits over others.

precision grip and power grip The first mammals

spread their toes apart to help support the body as they

walked or ran on four legs. Primates still spread their toes

or fingers. Many also make cupping motions, as when a

monkey lifts food to its mouth. Other hand movements

also developed in our ancient tree-dwelling relatives.

Changes in hand bones allowed fingers to be wrapped

around objects (that is, prehensile hand movements were

possible), and the thumb and tip of each finger could touch

(opposable movements).

evolution from a Human perspective

Domain Eukarya

Kingdom Animalia

Phylum Chordata

Class Mammalia

Order Primates

Family Homininae

Genus Homo

Species sapiens

(only living species of this genus)

Table 23.1 Classification of Humans

Bruce Coleman Ltd./Photoshot

23.8

n Like other life forms, we humans have a well-defined place

in the evolutionary scheme of things.

The scientific name for the human species is Homo sapiens.

Scientific names for organisms are always shown in italic

type. In a binomial system devised centuries ago, the name

has two parts. The first part is the genus name. A genus

(plural: genera) encompasses all the species that are similar

to one another and distinct from others in certain traits.

The second part of the name indicates the particular spe-

cies within the genus.

Species are organized into a hier-

archy of groupings. Table 23.1 lists

them, using humans as the example.

Each group above the genus level

includes a larger array of organisms

that share more general features.

Each lineage of life forms has its defining traits. We

humans share certain characteristics with other primates

(such as being land dwellers). At the same time, we differ in

major ways from other primate lineages, such as the New

World monkeys. We are genetically closer to the great apes

and closest to the chimpanzees and bonobos (Figure 23.15).

Five trends mark human evolution

Primates evolved from ancestral mammals more than

60 million years ago. Fossils suggest that the first primates

resembled small rodents. They may have foraged in the

genus All the species that

are similar to one another

and distinct from others with

respect to certain traits.

Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).