Visualizing Environmental Science

150 CHAPTER 6 Ecosystems and Evolution

Evidence for evolution

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Human

Humerus

Ulna

Carpals

Radius

Metacarpals

and

phalangeses

Horse Cat Bat

Similarities among organisms demonstrate how they

are related. These similarities amongfourvertebrate

limbs illustrate that, while proportions of bones have

changed in relation to each organism’sway of life, the

forelimbs have the same basic bone structure.

a. The Fossil Record b. Comparative Anatomy

Fossils deposited in rock layers, which can be dated, show how organisms

evolved over time.This well-preserved snake fossil from the Messel Pit,

a significant fossil site near the village of Messel, Germanyyy, dates from

47 million years ago. The ancient snake bears both similarities to and

differences from snake species living today.

© Jonathan Blair/Corbis

Adapted from Figure 15.13 on p. 244, in S. A. Alters and B. AltersBiology:

Understanding Life, Hoboken, NJ: John Wiley and Sons, Inc. ( 2009 ).

or changes in DNA. Mutations provide the genetic vari-

ability on which natural selection acts during evolution.

Some new traits may be beneficial, whereas others may

be harmful or have no effect at all. As a result of natural

selection, beneficial strategies, or traits, persist in a popu-

lation because such characteristics make the individuals

that possess them well suited to thrive and reproduce.

In contrast, characteristics that make the individuals that

possess them poorly suited to their environment tend to

disappear in a population.

A vast body of evidence supports evolution, most

of which is beyond the scope of this text. This evidence

includes observations from the fossil record, com-

parative anatomy, biogeography (the study of the geo-

graphic locations of organisms), and molecular biology

(Figure 6.19). In addition, evolutionary hypotheses are

tested experimentally.

On the basis of these kinds of evidence, virtually all

biologists accept the principles of evolution by natural

selection, although they don’t agree on all the details.

They try to better understand certain aspects of evolu-

tion, such as the role of chance and how quickly new

species evolve. As discussed in Chapter 1, science is an

ongoing process, and information obtained in the future

may require modifications to certain parts of the theory

of evolution by natural selection.

1. What is evolution?


2. What four phenomena or conditions are the
   basis of natural selection?


3. Which types of evidence support evolution?

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