Chapter 22 (3)

__ are a potent force in shaping the adaptations of their food source. The __ is most likely to feed on prey individuals that are least able to avoid detection, escape, or defend themselves. As a result, such prey individuals are less likely to reproduce and pass their traits to their offspring than are individuals whose traits help them evade predators.

For many years, __ has studied the impact of predators on guppies, small freshwater fish that you may know as aquarium pets. (p.460- 461)

An example of ongoing __ that affects our own lives dramaticaly is the evolution of drug- resistant __ (disease-causing organisms and viruses). This is a particular problem with bacteria and viruses that reproduce rapidly, because individuals that are resistant toa particular drug can increase in number very quickly.

Researchers have developed numerous drugs to combat this __, but using these medications selects for viruses resistant to the drugs. A few drug-resistant viruses may be present by chance at the beginning of treatment. Those that survive the early doses reproduce, passing on the __ that enable them to resist the drug. In this way, frequency of resistant viruses increases rapidly in the population.

Scientists designed __ tointerefere with __. HIV uses this enzyme to make a DNA version of its RNA genome, which is then inserted into the DNA of the human host cell. Because the __ molecule is similar in shape to the __- bearing nculeotide of DNA, HIV's __ picks up a __ moleucle instead of a C-bearing mucleotide and inserts the __ into a growing DNA chain. This error terminates further elongation of the DNA and thus blocks reproduction of HIV.

The __- resistant varieties of HIV have versions of __ that are able to discriminate between the drug and the normal __- bearing nucleotide. These viruses have no advantage in the absence of __, in fact, they replicate more slowly than viruses that carry the typical version of __. But once __ ius added to their environment, it becomes a powerful selecting force, favoring the survival of resistant viruses.

Two key points about natural selection.
1) __: A drug does not create resistant pathogens; it selects for resistant individuas that were already present in the population
2) __: It favors those characteristics in a genetically variable population that provide advantage in the current, local environment. What is beneficial in one situation may be useless or even harmful in another.

A second type of evidence for evolution comes from __. The __record shows that past organisms differed from present-day organisms and that many species have become extinct. __ show the evolutionary changes that have occ urred over time in various groups of organisms.

Over longer time scales, __ document the origins of major new groups. (p. 462)

In addition to providing evidence of how life on Earth has changed over time- __- the fossil record also can be used to test evolutionary hypotheses arising from other kinds of evidence. (p. 462)

A third type of evidence for evolution comes from analyzing similarities among different organisms. __ is a process of descent with modification: Characteristics present in an ancestral organism are altered (by __) in its descendants over tme as they face different environmental conditions. As a result, related species can have characteristics with an underlying similarity even though they may have very different funcitons. Such similarity resulting from common ancestry is known as __.

The view of evolution as a remodeling pocess leads to the prediction that closely related species should share similar features- and they do. Of course, closely related species share the features used to determine their relationship, but they share many other features. Some of these shared features make little sense except in the context of __.

Organisms with such striking anatomical resemblances would be highly unlikey if these structures had arisen anew in each species. Rather, the underlying skeletons of the arms, forelegs, flippers, and wings of different mammals are __ that repesent variations on a structural theme that was present in their common ancestor.

Comparin g early stages of development in different animal species reveals additional anatomical __ not visible in adult organisms. Fror example, at some point in their development, all vertebrate embryos have a tail located __ to the anus, as well as structures called __ that develop into structures with very different functions, such as gills in fishes and parts of the ears and throat in human and other mammals.

Some of the most intriguing homologies cocern "leftover" structures of marginal, if any, importance to the organism. These __ are remnants of features that served important fuctions int eh organism's ancestors.

Biologists also observe similarities among organisms at the mollecular level. All forms of life use the same genetic language of __ and __, and the _- is essentially universal. Thus, it is likely that all species descended from common ancestors that used this code.

Some __, such as the genetic code, are shared by all species because they date to the deep ancestral past. In contrast, __ characteristics that evolved more recently are shared only within smaller groups of organisms.

__ form a nested pattern: All life shares the deepest layer, and each succesive smaller groups adds their own __ to those they share with larger groups. This nested pattern is exactly what we'd expect to result from __ from a common ancestor.

Biologists often represent the pattern of descent from common ancestors and the resulting homologies with an __, a diagram that reflects evolutionary relationships among groups of organisms. (p.464)

True or False:
Mammals are closer to amphibians than birds.
True False

__ are hypotheses that summarize ur current understanding of patterns of descent. Our confidence in these relationships, as with any hypothesis, depends on the strength of the supportive data.
-- In some cases, the tree is supported by a variety of independent data sets, including both anatomical and DNA sequence data. As a result, biologists feel confident that it accurately reflects actual evolutionary history.

ALlthough organisms taht are closely related share characteristics because of common descent, distantly related organisms can resemble one another for a different reason: __, the independent evolution of similar features in different lineages.

An example would be the distinction between __ and __.

__ complete their embryonic deverlopment in the uterus whereas marsupials are born as enbryos and complete their development in the uterus, whereas __ are born as embryos and complete their development in an external pouch

A fourth type of evidence for evolution comes from __, the geographic distribution of species. The geographic distribution of organisms is influenced by many factors, ncluding __, the slow movement of Earth's continents over time. About 250 million years ago, these movements united all of Earth's landmasses into a single large continent, called __, which began to break apart about 200 mil years ago.

We can use our understanding of _- and __ to predict where fossils of different groups of organisms might be found. Evolutionary biologists have constructed __ for horses based on anatomical data. Based on these trees and ont he ages of fossils of horse ancestors, researchers estimate that present-day horse species originated 5 mil years ago in N. America.

We can use our understaning of evolution to explain __. For example, islands generally have many species of plants and animals that are __, which means they are found nowhere else in the world. Yet, as Darwin described in The Origin of Species, most island species are closely related to species from the nearest mainland or a neighboring island.

TRUE OR FALSE:
He explained this observation by suggesting that islands are colonized by species from the nearest mainland. These colonists eventually give rise to new species as they adapt to their new environments. Such a sprocess also explains why two islands with similar environments in different parts of the world are populated not by closely related species but rather by species that resemble those of the nearest mainland, where the environment is often quite different.
True False

Some people dismiss Darwin's ideas as "just a __." However, the pattern of __- the observation that life has evolved over time- has been documented directly and is supported by a great deal of evidence. In addition, Darwin's explanation of the process of __- that __ is the primary cause of the observed pattern of evolutionary change- makes sense of massive amounts of data. The effects of __ also can be observed and tested in nature.

The scientific meaning of the term __ is very different from its meaning in everyday use. the colloquial use of the word __ comes close to what scientists mean by a hypothesis. In science, a __ is more comprehensive than a __. A __, such as Darwin's __ of evolution by natural selection, accounts for many observations and explains and integrates a great variety of phenomena. Such a unifying __ does not become widely accepted unless its predictions stand up to thorough and continual testing by experiment and additional observation.

The skepticism of scientists as they continue to test theories prevents these ideas from becoming __. For example, although Darwin th ought that evolution was a very slow process, we now know this isnt true. New species can form in relatively short periods of time. Furthermore, evolutinary biologists now recognize that __ is not the only mehanism responsible for evolution. Indeed, the study of evolution today is livelier than ever as scientists find more ways to test the predictions of Darwin's theory.