a. Biological diversity is defined as the number of different species of organisms we have observed (Figures 2.1, 2.2, 2.3).

b. The field of systematics or taxonomy focuses on the naming and categorizing of organisms into species and other groups.

c. The modern theory of evolution addresses questions of diversity, and the study of evolution begins by identifying and systematizing the world of organisms.

a. Artificial selection can occur either intentionally or accidentally.

b. Artificial selection preserves desirable features or rejects undesirable ones.

c. Natural selection is the molding of organisms by nature, without foresight or purpose.

a. Essentialism is the long-held view that every member of a species has the same underlying or basic features, and that each species is unique.

b. This typological view of species de-emphasized the importance of variation (Figure 2.7), and hindered the development of the evolutionary concept.

c. Misconceptions concerning the age of the earth and postulates such as catastrophism both served to further hinder the advancement of the idea of evolution (Figure 2.8).

d. Charles Lyell's Principles of Geology shaped the modern view that both living and nonliving elements of the earth have changed constantly and uniformly over time.

a. The fossil record continues to supply the main evidence for evolution (Figure 2.9):

b. Comparative anatomy, the analysis of anatomical features in various organisms, has produced strong evidence to support the evolutionary concept of continuity with modification (Figures 2.10 and 2.11).

c. Additional support for evolution comes from observing homologous features among various groups of organisms.

d. Homologous features have similar functions or occupy similar positions and result from common ancestry.

e. Analogous features have similar functions but different origins.

a. In 1834, Robert Chambers proposed that evolution occurred, but he could not account for its mechanism.

b. Charles Darwin and Alfred Wallace focused on populations of organisms and noted the following:

c. The principle of natural selection can be summarized by four points:

d. Lamarck's failed theory relies on the postulate that organisms can pass on acquired modifications (Figure 2.12).

a. Evolution and natural selection are only possible because organisms can reproduce. The hereditary mechanism must be very stable but must also allow for change.

b. A model will be used in this text to represent the main features of genetic systems.

c. Organisms are genetic systems because of reproduction and inheritance (Figure 2.13).

d. An organism's genome is defined as its encoded genetic information.

e. There is an important connection between structures and functions of biological molecules, including DNA (Figure 2.14).

a. Each organism contains a genetic program that determines its structure and function.

b. The concept of the genome might be illustrated by a comparison to a computer's program (Figure 2.15).

c. A virus is not an organism, but contains a genome which can redirect the functions of other organisms.

a. An ecosystem is a community of organisms together with its physical environment.

b. A community is a group of different organisms that live in the same area and interact in various ways (Figure 2.16).

c. Ecology is the study of relationships within ecosystems, including those among the members of the community and those between the community and the physical environment.

d. Members of a community exchange energy and are thus interdependent (Figure 2.17).

e. Human beings are an integral part of their ecosystems and should realize their intimate connection therewith.

f. Evolution can be best understood by viewing it in an ecological context.

g. As a result of adaptation, each organism is shaped for its ecological niche in a community.

h. An organism's niche includes not only where it lives, but how it lives, or its role in the ecosystem.

a. All organisms have life cycles by which they produce new generations (Figure 2.18).

b. Asexual reproduction involves the simple division of cells without combination.

c. Sexual reproduction involves fertilization, whereby different cells (or their equivalents) are combined.

d. A species can have organisms at different stages of their life cycle that present very different morphologies.

e. A species can be defined as a group of organisms that both reproduce only with one another and are isolated (reproductively) from all other similar groups.

a. Exponential growth is typical of organisms growing in good surroundings without any limitations, with no lack of food or space, and with no predators to eat them.

b. Environmental limitations restrict the growth of populations when resources such as living space, nutrients, and energy are limited.

c. The growth of a population will level off at the point where the environment can no longer support unhindered growth. This maximum point on the growth curve is called the carrying capacity.

d. Reverend Thomas Malthus (1766—1834) put forth the Malthusian principle, which states that the number of individuals in a population will increase faster than the food supply.

e. Darwin was greatly influenced by this principle and the concept that, in a competition for space and food, only the fittest survive.

a. Evolution is a change in a population of organisms from generation to generation, not a change in an individual. The product of evolution is defined by individuals that are different from their ancestors.

b. Mutations are small changes in the structure of the DNA molecules that constitute the genome (Figure 2.19).

c. Genetic variation is the raw material upon which natural selection operates.

d. Fitness measures an individual's ability to produce viable offspring.

e. The English peppered moth, Biston betularia, is a classic illustration of natural selection operating over a very short period of time (fifty years), and also illustrates the concepts of differential survival and differential reproduction (Figure 2.20).

f. Natural selection can be thought of as a kind of editing process, in which the best features of each organism are developed, while the less suitable features are discarded (Figure 2.21).

a. All organisms are opportunists that are said to develop strategies for survival.

b. These strategies are not the result of any grand scheme, but are driven by random evolutionary forces.

c. The French biologist Jacques Monod characterized this process as one of chance and necessity.

a. A central question in evolution is "Why do some organisms resemble one another more closely than they do others?".

b. Phylogeny provides the answer to this question by proposing how similar organisms could have evolved from common ancestors (Figure 2.22).

c. Phylogenetic trees illustrate relationships among various groups of organisms.

a. The classification of species into a hierarchy of groups is a work in progress (Figure 2.23).

b. The hierarchy of categories from most to least inclusive are: kingdom, phylum, class, order, family, genus, and species.

c. This textbook follows a taxonomy of five kingdoms:

d. The domain concept, which separates the Archaebacteria from the Eubacteria and from the eucaryotes, will be explored in Chapters 6 and 29.