Evolution

Question 1

Evolution

Answer 1

“descent with modification” - Darwin

Darwin never used the word evolution in the first edition of The Origin of Species.

The phrase refers to the view that all organisms are related through descent from an ancestor that lived in the remote past.

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 .

Evolution can be viewed as both a pattern and a process.

Question 2

taxonomy

Answer 2

The branch of biology concerned with classifying organisms.

Carolus Linnaeus developed the binomial format for naming species (for example, Homo sapiens).

Question 3

fossils

Answer 3

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

Question 4

Paleontology

Answer 4

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

Cuvier speculated that the boundaries between strata represent catastrophic events.

Question 5

natural selection

Answer 5

A process in which individuals with favorable inherited traits are more likely to survive and reproduce.

Question 6

Darwin explained three broad observations:

Answer 6

The unity of life.

The diversity of life.

The ways organisms are suited to life in their environments.

Question 7

artificial selection

Answer 7

Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits.

Question 8

Darwin drew two inferences from two observations:

Answer 8

Observation #1: Members of a population often vary in their inherited traits.

Inference #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.

Observation #2: All species can produce more offspring than the environment can support, and many of these offspring fail to survive and reproduce.

Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations.

Note that individuals do not evolve; populations evolve over time.

Natural selection can only increase or decrease heritable traits that vary in a population.

Adaptations vary with different environments.

Question 9

New discoveries continue to fill the gaps identified by Darwin in The Origin of Species.

Four types of data document the pattern of evolution:

Answer 9

Direct observations:

• Two examples provide evidence for natural selection:
  1) Natural selection in response to introduced species and the evolution of drug-resistant bacteria.
  2) Soapberry bugs using their “beak” to feed on seeds within fruits.

Homology: is similarity resulting from common ancestry.

The fossil record: The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time.
Fossils can document important transitions.
-For example, the transition from land to sea in the ancestors of cetaceans.

Biogeography: the scientific study of the geographic distribution of species, provides evidence of evolution.

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

An understanding of continent movement and modern distribution of species allows us to predict when and where different groups evolved.

Question 10

Homologous structures

Answer 10

Anatomical resemblances that represent variations on a structural theme present in a common ancestor.

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

Question 11

Vestigial structures

Answer 11

Remnants of features that served a function in the organism’s ancestors.
-Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor

Question 12

Evolutionary trees

Answer 12

Diagrams that reflect hypotheses about the relationships among different groups.

Homologies form nested patterns in evolutionary trees.

Evolutionary trees can be made using different types of data, for example, anatomical and DNA sequence data.

Question 13

Convergent evolution

Answer 13

The evolution of similar, or analogous, features in distantly related groups

Analogous traits arise when groups independently adapt to similar environments in similar ways.

Convergent evolution does not provide information about ancestry.

Question 14

Endemic

Answer 14

Species are species that are not found anywhere else in the world.

Islands have many endemic species that are often closely related to species on the nearest mainland or island.

Darwin suggested that species from the mainland colonized islands and gave rise to new species as they adapted to new environments.

In the Galápagos Islands, Darwin discovered plants and animals found nowhere else on Earth.

Question 15

Speciation

Answer 15

The process by which one species splits into two or more species, is at the focal point of evolutionary theory.

Speciation forms a conceptual bridge between microevolution and macroevolution.

Question 16

Microevolution

Answer 16

Consists of changes in allele frequency in a population over time.

Question 17

Macroevolution

Answer 17

Refers to broad patterns of evolutionary change above the species level.

Macroevolution is the cumulative effect of many speciation and extinction events.

Question 18

Species

Answer 18

Latin word meaning “kind” or “appearance”.

Biologists compare morphology, physiology, biochemistry, and DNA sequences when grouping organisms.

Question 19

biological species concept

Answer 19

States that a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with members of other such groups.

Gene flow between populations holds a species together genetically.

Question 20

Reproductive isolation

Answer 20

The existence of biological factors (barriers) that impede two species from producing viable, fertile offspring.

Reproductive isolation can be classified by whether factors act before or after fertilization.

Question 21

Hybrids

Answer 21

The offspring that result from mating between different species.

Gene flow can occur between morphologically and ecologically distinct species
-For example, grizzly bears and polar bears can mate to produce “grolar bears”.

Question 22

morphological species concept

Answer 22

The morphological species concept defines a species by structural features
-It applies to sexual and asexual species but relies on subjective criteria.

Question 23

ecological species concept

Answer 23

The ecological species concept defines a species in terms of its ecological niche.
-It applies to sexual and asexual species and emphasizes the role of disruptive selection.

Question 24

Speciation can take place with or without geographic separation.

Speciation can occur in two ways:

Answer 24

1) Allopatric speciation

2) Sympatric speciation

Question 25

Allopatric (“Other Country”) Speciation

Answer 25

In allopatric speciation, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations.
-For example, the flightless cormorant of the Galápagos likely originated from a flying species on the mainland.

Separated populations may evolve independently through mutation, natural selection, and genetic drift.

Reproductive isolation may arise as a by-product of genetic divergence.
-For example, isolated populations of mosquitofish have become reproductively isolated as a result of selection under different levels of predation.

Regions with many geographic barriers typically have more species than do regions with fewer barriers.

Reproductive isolation between populations generally increases as the distance between them increases.

Reproductive barriers are intrinsic to the organisms themselves; physical separation alone is not a biological barrier.

Question 26

Sympatric (“Same Country”) Speciation

Answer 26

In sympatric speciation, speciation occurs in populations that live in the same geographic area.
Sympatric speciation can occur if gene flow is reduced by factors including:
-Polyploidy
-Sexual selection
-Habitat differentiation

Question 27

Sexual Selection

Answer 27

Sexual selection can drive sympatric speciation.

Sexual selection for mates of different colors has likely contributed to speciation in cichlid fish in Lake Victoria.

Question 28

Habitat Differentiation

Answer 28

Sympatric speciation can also result from the appearance of new ecological niches.

• For example, populations of the North American maggot fly (Rhagoletis pomonella) can live on native hawthorn trees, as well as more recently introduced apple trees.
• Flies that use different host species experience both habitat and temporal isolation

Question 29

Allopatric and Sympatric Speciation: A Review

Answer 29

In allopatric speciation, geographic isolation restricts gene flow between populations.

Reproductive isolation may then arise as a by-product of genetic changes resulting from divergent natural selection, genetic drift, or sexual selection.

Even if contact is restored between populations, interbreeding is prevented.

In sympatric speciation, a reproductive barrier isolates a subset of a population without geographic separation from the parent species.

Sympatric speciation can result from polyploidy, natural selection, or sexual selection.

Question 30

Punctuated equilibria

Answer 30

Describes these periods of apparent stasis punctuated by sudden change.

The fossil record includes examples of species that appear suddenly, persist unchanged for some time, and then disappear.

The interval between speciation events can range from 4,000 years (some cichlids) to 40 million years (some beetles), with an average of 6.5 million years.