Biology 1620 - Chapter 19

Darwin's observations

1) Variations exists. 2) Variations are heritable. 3) Species overproduce. 4) Competition for resources/not all offspring survive.

Darwin's Inferences

1. Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals. 2. This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations.

What are three key features of natural selection?

1. Natural selection is a process in which individuals that have certain heritable traits survive and reproduce at a high rate than do other individuals because of those traits. 2. Over time, natural selection can increase the frequency of adaptations that are favorable in a given environment. 3. If an environment changes, or if individuals move to a new environment, natural selection may result in adaptations to these new conditions, sometimes giving rise to new species

S. aureus and soapberry bugs provide examples that highlight three key points about natural selection. Explain the three key ideas.

1. Natural selection is a process of editing, not a creative mechanism. A drug does not create resistant pathogens; it selects for resistant individuals that are already present in the population. 2. In species that produce new generations in short periods of time, evolution by natural selection can occur rapidly-in just a few years (S. aureus) or decades (soapberry bugs). 3. Natural selection depends on time and place. It favors those characteristics in a genetically variable population that provide an advantage in the current, local environment. What is beneficial in one situation may be useless or even harmful in another. Beak lengths suitable for the size of the typical fruit eaten by members of a particular soapberry bug population are favored by natural selection. However, a beak length suitable for fruit of one size can be disadvantageous when the bug is feeding on fruit of another size.

Darwin set out to explain three key observations about life. What are those three observations?

1. Organisms are well suited (adapted) for life in their environments (Here and throughout this text, the term environment refers to other organisms as well as to the physical aspects of an organism's surroundings.) 2. The many shared characteristics (unity) of life. 3. The rich diversity of life.

Vestigial structures

A feature of an organism that is a historical remnant of a structure that served a function in the organism's ancestors; for example, skeletons of some snakes retain vestiges of the pelvis and leg bones.

Charles Darwin proposed that the mechanism of evolution is natural selection and that it explains how adaptations arise. What are adaptations? Give two examples of them.

Adaptations are inherited characteristics of organisms that enhance their survival and reproduction in specific environments. One example of an adaptation is the beak size of the finches found on the Galapagos Islands. The various beaks are adapted to the specific foods available on the finches' home islands. Some beaks are long and sharp, such as those of the common cactus finch and some beaks are narrow and pointed, such as what is found in the insect-eater, green warbler finch. Another example is the shape and colors that the Malaysian orchid mantis has in different environments. The color and shape of the mantis closely resembles the flower on which it rests, waiting for unwary prey to come within its reach.

Describe how analogous structures can arise and give an example.

Analogous structures, in species, share features because of convergent evolution. The analogous features share similar function, but not common ancestry. An example would be wings of birds and wings of insects.

Aristotle and Scala Naturae: view the origin of species

Aristotle viewed species as fixed (unchanging). Through his observations of nature, Aristotle recognized "affinities" among organisms. He concluded that life-forms could be arranged on a ladder, or scale, of increasing complexity, called the scala naturae. Each form, perfect and permanent, had its allotted rung on this ladder.

What role did Darwin's voyage on the HMS Beagle play in his thinking about life on Earth?

Being a skilled naturalist, Darwin observed and collected thousands of plants and animals. He described features of organisms that made them well suited to such diverse environments as the humid jungles of Brazil, the expansive grasslands of Argentina, and the towering peaks of the Andes. He also noted that the plants and animals in temperate regions of South America more closely resembled species living in South American tropics than species living in temperature regions of Europe. Furthermore, fossils he found, though clearly different from living species, distinctly resembled the living organisms of South America. Darwin also experienced geologic change firsthand when a violent earthquake shook the coast of Chile and he observed afterward that rocks along the coast had been thrust upward by several meters. He also found fossils of ocean organisms high in the Andes. He inferred that the rocks containing the fossils must have been raised there by many similar earthquakes. These observations reinforced what he had learned from Lyell: Physical evidence did not support the traditional view that Earth was only a few thousand years old. Darwin's observations on the Galápagos Islands also played a role in his thinking about life on Earth. Although the animals on the Galápagos resembled species living on the South American mainland, more of the Galápagos species were not known from anywhere else in the world. Darwin hypothesized that the Galápagos had been colonized by organisms that had strayed from South America and then diversified, giving rise to new species on the various islands.

What is biogeography?

Biogeography is the scientific study of the geographic distributions of species.

Organisms that are only distantly related can resemble each other. Explain convergent evolution.

Convergent evolution is the independent evolution of similar features in different lineages. The marsupials of Australia are distinct from another group of mammals—the eutherians, or placental mammals—few of which live in Australia. Some Australian marsupials have eutherian look-alikes with superficially similar adaptations. For instance, a forest-dwelling Australian marsupial called the sugar glider is superficially very similar to flying squirrels, gliding eutherians that live in North American forests. But the sugar glider has many other characteristics that make it a marsupial, much more closely related to kangaroos and other Australian marsupials than to flying squirrels or other eutherians. Although they evolved independently from different ancestors, these two mammals have adapted to similar environments in similar ways.

How would Georges Cuvier have explained the appearance of the record of life shown in the rock strata?

Cuvier observed that the older the stratum, the more dissimilar its fossils were to current life-forms. He also observed that from one layer to the next, some new species appeared while others disappeared. He inferred that extinction must have been a common occurrence, but he staunchly opposed the idea of evolution. He advocated catastrophism, the principle that events in the past occurred suddenly and were caused by mechanisms different from those operating in the present. Cuvier speculated that each boundary between strata represented a catastrophe, such as a flood, that had destroyed many of the species living at that time. Such regions, he reasoned, were later repopulated by different species immigrating from other areas.

Lyell and Hutton gave Darwin "the gift of time." How would time play an important role in Darwin's development of a theory of evolution?

Darwin agreed that if geologic change results from slow, continuous actions rather than from sudden events, then Earth must be much order than the widely accepted age of a few thousand years. It would, for example, take a very long time for a river to carve a canyon by erosion. He later reasoned that perhaps similarly slow and subtle processes could produce substantial biological change. However, Darwin was not the first to apply the idea of gradual change to biological evolution.

Define evolution broadly, and then give a more specific definition that came about after the field of genetics was better understood.

Evolution is broadly defined as descent with modification, a phrase Darwin used to summarize the process by which species accumulate differences from their ancestors as they adapt to different environments over time. Evolution can also be defined as a change in the genetic composition of a population from generation to generation

James Hutton: ideas strongly influenced Darwin's thinking

Hutton proposed that Earth's geologic features could be explained by gradual mechanisms still operating today, such as valley formed by rivers.

Evolution is not "just a theory." Explain the difference between the scientific meaning of the term "theory" and the way the term is used in everyday language.

In everyday language, a theory is a hypothesis, guess, or speculation but in the scientific meaning, a theory is much more comprehensive than a hypothesis. A theory, such as the theory of evolution by natural selection, accounts for many observations and explains and integrates a great variety of phenomena. Such a unifying theory does not become widely accepted unless its predictions stand up to thorough and continual testing by experiment and additional observation.

How does the scientific meaning of "theory" differ from the common vernacular meaning?

In everyday language, a theory is a hypothesis, guess, or speculation but in the scientific meaning, a theory is much more comprehensive than a hypothesis. A theory, such as the theory of evolution by natural selection, accounts for many observations and explains and integrates a great variety of phenomena. Such a unifying theory does not become widely accepted unless its predictions stand up to thorough and continual testing by experiment and additional observation.

Explain the process of natural selection.

In the process of natural selection, individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits.

___________ do not evolve. ___________ evolve.

Individuals, Populations

Although Lamarck's mechanism of evolution does not explain the changes in species over time, his thinking has been influential. What is the importance of his ideas?

Lamarck recognized that the match of organisms to their environments can be explained by gradual evolutionary change rather than special creation.

Carolus Linnaeus: view the origin of species

Linnaeus adopted a nested classification system, grouping similar species into increasingly inclusive categories. Linnaeus, adhering to the Old Testament belief that all species were designed by God, did not ascribe the resemblances among species to evolutionary kinship, but rather to the pattern of their creation.

Charles Lyell: ideas strongly influenced Darwin's thinking

Lyell incorporated Hutton's thinking into his principle of uniformitarianism, which states that mechanisms of change are constant over time. Lyell proposed that the same geologic processes are operating today as in the past, and at the same rate

How did MRSA become so dangerous? Explain the evolution of MRSA's resistance to methicillin.

MRSA became dangerous because, over time, doctors used a variety of antibiotics, such as penicillin, to combat MRSA. Each time a new antibiotic was used to fight the disease, some S. aureus populations had resistance to the new drug. In 1959, doctors used the powerful antibiotic methicillin. Members of the S. aureus population that were resistant to methicillin reproduced at higher rates, leading to the spread of methicillin-resistant S. aureus (MRSA).

Antibiotic resistance has become a serious medical concern and is an example of evolution in bacteria. Your text explores this problem with a look at antibiotic resistance in MRSA. What do the initials MRSA mean?

MRSA is methicillin-resistant Staphylococcus aureus, a flesh-eating strain of bacterium.

Explain the role of fossils in rock strata as a window to life in earlier times.

Many fossils are found in sedimentary rocks formed from the sand and mud that settle to the bottom of seas, lakes, swamps, and other aquatic habitats. New layers of sediment cover older ones and compress them into superimposed layers of rock called strata. The fossils in particular strata provide a glimpse of some of the organisms that populated Earth at the time that the layer formed.

Do antibiotics cause bacteria to become resistant? Explain your response.

No. A drug does not create resistant pathogens; it selects for resistant individuals that are already present in the population.

Fossil record

Possible examples include fossils showing that ancestors of cetaceans had hind limbs.

Biogeography

Possible examples include the creation of the evolutionary tree of horses, based on fossil locations

Direct observations of evolutionary change

Possible examples include the evolution of MRSA or the change in beak size in soapberry bugs.

Homology

Possible examples include the similarities between mammalian forelimbs

Homologous structures

Structures in different species that are similar because of common ancestry; for example, the similarity of mammalian forelimb bone structure suggests that these organisms share a common ancestor.

Convergent evolution might be summarized like this: Similar problem, similar solution. Can you give two examples of convergent evolution?

Sugar glider and the flying squirrel, and the evolution of wings in birds and bats.

Why are the Galápagos Islands often cited as being critical to Darwin's development of the idea of descent with modification?

The Galapagos Islands are a group of volcanic islands located near the equator about 900 km west of South America. Darwin collected many types of mockingbirds, though similar to each other yet seemed to be different species. Some were unique to individual islands, while others lived on two or more adjacent islands. Furthermore, although the animals on the Galápagos resembled species living on the South American mainland, most of the Galapagos species were not known from anywhere else in the word. Darwin hypothesized that the Galapagos had been colonized by organisms that had strayed from South America and then diversified, giving rise to new species on the various islands. With these observations, he was able to summarize his view of life: unity in life, accumulated adaptations that fit the organism's specific ways of life, and accumulated differences of organisms can be seen.

The Old Testament: view the origin of species

The Old Testament holds that species were individually designed by God and therefore perfect. Organisms have remarkable ways in which they are well suited for life in their environment, which can be interpreted as evidence that the Creator had designed each species for a particular purpose.

How is the concept of biogeography supported by continental drift and the presence of endemic species?

The geographic distribution of organisms is influenced by many factors, including continental drift, the slow movement of Earth's plates over time, and the presence of endemic species, species that are found nowhere else in the world. We can use our understanding of evolution and continental drift to predict where fossils of different groups of organisms might be found. Predictions of divergence time for numerous species based on anatomical and sequence data often corroborate the estimated events related to biogeography. Temporal estimations of land mass connections that enabled land animals to travel between them correspond to fossil evidence of endemic species found on both land masses.

Use and Disuse (Lamarck)

The idea that parts of the body that are used extensively become larger and stronger, whereas those that are not used deteriorate.

What is the pattern of evolution?

The pattern of evolutionary biology is revealed by data from many scientific disciplines, including biology, geology, physics, and chemistry.

What is the process of evolution?

The process of evolution consists of the mechanisms that produce the observed pattern of change.

Explain why the statement that a monkey is more evolved than a mouse is incorrect.

The traits that are present in monkey's have evolved to increase survival and reproduction in their specific environment. Same for a mouse. The traits that are required to survive and reproduce for a monkey are different from a mouse. Thus, both are equally evolved to succeed in their respective environments.

Why do scientists consider vestigial structures evidence for evolution?

They provide evidence of homologous structure. Structures that organisms share due to common ancestry. Whales still have pelvic bones because a common ancestor had them.

Inheritance of acquired characteristics (Lamarck)

This idea states that an organism could pass these modifications of use and disuse to its offspring.

If a person scatters a handful of garden pea plant seeds in one area, how would natural selection work in this situation?

Variation in traits would lead to differences in survival and reproduction, which would lead to unequal reproduction. Only those individuals that were able to survive and reproduce would pass genes to next generation. Frequency of those genes would increase over generations

It is important to remember that differences in heritable traits can lead to differential reproductive success. This means that the individuals who have the necessary traits to promote survival in the current environment will leave the most offspring. How does differential reproductive success affect the match between organisms and their environment?

When such advantages increase the number of offspring that survive and reproduce, the traits that are favored will likely appear at a greater frequency in the next generation.

Which scientific concept did Charles Darwin and Alfred Wallace independently discover?

natural selection