BY123 - Chapter 22 - Descent with Modification: A Darwinian View of Lie

Endemic

(adj.) native or confined to a particular region or people; characteristic of or prevalent in a field

There are four types of data that document the pattern of evolution

-Direct observations -Homology -The fossil record -Biogeography

Two examples provide evidence for natural selection:

-natural selection in response to introduced plant species, and - the evolution of drug-resistant bacteria

Darwin explained three broad observations

1. The unity of life 2. The diversity of life 3. The match between organisms and their environment

Within a few weeks of treatment with the drug 3TC, a patient's HIV population consists entirely of 3TC-resistant viruses. How can this result best be explained?

A few drug-resistant viruses were present at the start of treatment, and natural selection increased their frequency.

Natural Selection

A process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits.

Artificial Selection

Breeding organisms with specific traits in order to produce offspring with identical traits.

Embryological Homology

Comparative embryology reveals anatomical homologies not visible in adult organisms For example, all vertebrate embryos have a post-anal tail and pharyngeal arches

In the Darwinian view, the history of life is like a tree with branches representing life's diversity

Darwin reasoned that large morphological gaps between related groups could be explained by this branching process and past extinction events

Darwin's Hypothesis of Evolution

Descent with modification by natural selection explains the adaptations of organisms and the unity and diversity of life

Charles Darwin

English natural scientist who formulated a theory of evolution by natural selection (1809-1882)

During drought years on the Galapagos, small, easily eaten seeds become rare, leaving mostly large, hard-cased seeds that only birds with large beaks can eat. If a drought persists for several years, what should one expect to result from natural selection?

More small-beaked birds dying than larger-beaked birds. The offspring produced in subsequent generations have a higher percentage of birds with large beaks.

Which statement best describes the evolution of pesticide resistance in a population of insects?

Offspring of insects that are genetically resistant to the pesticide become more abundant as the susceptible insects die off.

What insight did Darwin gain from reading Thomas Malthus's essay on human suffering?

Organisms have the capacity to overreproduce.

Earth's continents were formerly united in a single large continent called _____________, but have since separated by continental drift

Pangaea

Which of the following is not an observation or inference on which natural selection is based?

Poorly adapted individuals never produce offspring. According to Darwin's description of natural selection, individuals who are poorly adapted are less likely to survive and therefore less likely to produce offspring. One of Darwin's observations was that there is heritable variation among individuals in a population. Individuals whose characteristics are best suited to the environment generally leave more offspring than those whose characteristics are less well suited. Individuals tend to produce more offspring than the environment can support, leading to a struggle for existence where only a fraction survive.

In a hypothetical environment, fishes called pike-cichlids are visual predators of algae-eating fish (i.e., they locate their prey by sight). If a population of algae-eaters experiences predation pressure from pike-cichlids, which of the following should least likely be observed in the algae-eater population over the course of many generations?

Selection for larger female algae-eaters, bearing broods composed of more, and larger, young

Inheritance of Acquired Characteristics

The hypothesis that organisms' bodies change during their lifetimes by use and disuse and that these changes are inherited by their offspring

In reassessing his observations, Darwin perceived ______________ to the environment and the origin of new species as closely related processes

adaptation

Homologous structures

are anatomical resemblances that represent variations on a structural theme present in a common ancestor. -Anatomical homology -Embryological homology -Molecular homology

Cuvier speculated that the boundaries between strata represent

catastrophic events

Convergent Evolution

evolution of similar, or analogous, features in distantly related groups Analogous traits arise when groups independently adapt to similar environments in similar ways

Ichthyosaurs were aquatic dinosaurs. Fossils show us that they had dorsal fins and tails, as do fish, even though their closest relatives were terrestrial reptiles that had neither dorsal fins nor aquatic tails. The dorsal fins and tails of ichthyosaurs and fish are

examples of convergent evolution, and adaptations to a common environment.

The study of _________ helped to lay the groundwork for Darwin's ideas

fossils

Molecular Homologies

genes shared among organisms inherited from a common ancestor

Evolutionary trees

hypotheses about the relationships among different groups Homologies form nested patterns in evolutionary trees Some homologies, such as the genetic code, are shared by all living things because they arose in the deep ancestral past Other homologies that evolved more recently are shared by only smaller branches of the tree of life.

Adaptation

inherited characteristic that increases an organism's chance of survival (From studies made years after Darwin's voyage, biologists have concluded that this is what happened to the Galápagos finches)

Strata

layers of sedimentary rock

Direct Observations

observing phenomena using the five senses; capturing information by watching participants

Fossils

remains or traces of organisms from the past, usually found in sedimentary rock, which appears in layers called strata

Vestigial Structures

remnant of a structure that may have had an important function in a species' ancestors, but has no clear function in the modern species.

The Greek philosopher Aristotle viewed species as fixed and arranged them on a

scala naturae (ladder or scale increasing in complexity)

Anatomical Homology

similar body structures among different species from a common ancestor

Homology

similarity resulting from common ancestry

The bacteria Staphylococcus aureus has developed resistance to some antibiotic drugs. How did this resistance come about?

some members of the bacteria populations possessed some sort of genetic variation for antibiotic resistance that was selected for when the bacteria was exposed to the drugs. An example of ongoing natural selection that dramatically affects humans is the evolution of drug-resistant pathogens (disease-causing organisms and viruses). This is a particular problem with bacteria and viruses because resistant strains of these pathogens can proliferate very quickly. Consider the evolution of drug resistance in the bacterium Staphylococcus aureus. About one in three people harbor this species on their skin or in their nasal passages with no negative effects. However, certain genetic varieties (strains) of this species, known as methicillin-resistant S. aureus (MRSA), are formidable pathogens. The past decade has seen an alarming increase in virulent forms of MRSA such as clone USA300, a strain that can cause "flesh-eating disease" and potentially fatal infections. How did clone USA300 and other strains of MRSA become so dangerous? The story begins in 1943, when penicillin became the first widely used antibiotic. Since then, penicillin and other antibiotics have saved millions of lives. However, by 1945, more than 20% of the S. aureus strains seen in hospitals were already resistant to penicillin. These bacteria had an enzyme, penicillinase, that could destroy penicillin. Researchers responded by developing antibiotics that were not destroyed by penicillinase, but some S. aureus populations developed resistance to each new drug within a few years. How did these resistant strains emerge? Methicillin works by deactivating a protein that bacteria use to synthesize their cell walls. However, different S. aureus populations exhibited variations in how strongly their members were affected by the drug. In particular, some members were able to synthesize their cell walls using a protein that was not affected by methicillin. These members survived the methicillin treatments and reproduced at higher rates than did other members. Over time, these resistant individuals became increasingly common, leading to the spread of MRSA. The S. aureus example highlights two key points about natural selection: First, natural selection is a process of editing, not creating. A drug does not create resistant pathogens; it selects for resistant pathogens that are already present in the population. Second, natural selection depends on time and place. It favors those characteristics in a genetically variable population that provide advantages in the current local environment. What is beneficial in one situation may be useless or even harmful in another.

Carolus Linnaeus is considered to be the founder of __________, and he __________.

the binomial classification system; thought that resemblances among different species reflected the pattern of their creation

Biogeography

the scientific study of the geographic distribution of species, provides evidence of evolution

Paleontology

the study of fossils, was largely developed by French scientist Georges Cuvier

The Fossil Record

•Fossils can document important transitions -For example, the transition from land to sea in the ancestors of cetaceans

Natural Selection: A Summary

•Individuals with certain heritable traits survive and reproduce at a higher rate than other individuals •Natural selection increases the match between organisms and their environment over time •If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species

Lamarck's Hypothesis of Evolution

•Lamarck hypothesized that species evolve through use and disuse of body parts and the inheritance of acquired characteristics •The mechanisms he proposed are unsupported by evidence

Natural Selection in Response to Introduced Species

•Natural selection does not create new traits, but edits or selects for traits already present in the population •The current, local environment determines which traits will be selected for or selected against in any specific population

The Evolution of Drug-Resistant Bacteria

•The bacterium Staphylococcus aureus is commonly found on people •One strain, methicillin-resistant S. aureus(MRSA) is a dangerous pathogen •Resistance to penicillin evolved in S. aureus by 1945, two years after it was first widely used •Resistance to methicillin evolved in S. aureusby 1961, two years after it was first widely used