Chapter 20: Development of Evolutionary Thinking

What is the fundamental organizing principle of Biology?

Evolutionary science.

How do genetic basis of inheritance, molecular biology, developmental biology, and evolutionary biology provide a better understanding of organisms?

Together, they provide a better understanding of an organism's function and its relationship with its physical and biotic environment.

When did evolutionary thinking emerge as a significant school of thought?

In the nineteenth century in Europe, specifically gaining significance at the end of the eighteenth century.

Who independently described natural selection as the major basis of biological evolution?

Charles Darwin and Alfred Russel Wallace.

When was the field of evolutionary science firmly established?

Not until Charles Darwin and Alfred Russel Wallace independently described natural selection in 1858, providing an explanation for how species change and new species evolve.

What is the definition of biological evolution?

Biological evolution occurs when specific processes cause the genomes of organisms to differ from those of their ancestors.

What acts as raw materials for evolution?

Genetic changes, phenotypic alterations, and the environment.

What is Scala Naturae?

The entire natural world arranged as a single continuum in a hierarchical ladder of all matter and life, as decreed by God.

What is Natural Theology?

The belief that each organism was specially created by God, species would never change or become extinct, and new species would never arise.

What was a goal of natural theologists?

To name and catalog all creations, merging Aristotle's Scala naturae and the Great Chain of Being.

How did the Great Chain of Being illustrate nature's hierarchy?

As a series of steps: stone, flame, plant, animal, man, heaven, angel, God.

What was the limitation of the Great Chain of Being for classifying life's diversity?

It provided a fixed hierarchy, but was not very useful for classifying life's diversity at a finer scale.

When was the birth of Taxonomy and systematics?

In the 1600s.

What is Taxonomy?

The branch of Biology that classifies organisms.

Who organized all living things known at that time into a nested hierarchy of groups or taxa?

Carl Linnaeus.

What is the Binomial system of nomenclature?

The modern system of naming organisms using two parts: Genus species.

What did Linnaeus believe about the classification of plants and animals?

He believed they had been created by God and could be placed into natural groups revealing God's divine plan.

What is the significance of the 15th-18th century in the history of science?

Modern science came of age, with scientists proposing mechanistic theories to explain physical phenomena.

Who proposed the heliocentric model?

Nicolaus Copernicus.

Who formulated the theory of universal gravity and invented calculus?

Isaac Newton.

Who is regarded as the "Father of Modern Philosophy" and made important connections between geometry and algebra?

René Descartes.

Who established the importance of observation, experimentation, and inductive reasoning?

Francis Bacon.

Scientific Method process.

Generally involves observation, asking a question, forming a hypothesis, making predictions, experimentation, analyzing results, and checking if data supports the hypothesis.

What new disciplines promoted a growing awareness of change in living forms, challenging Natural Theology?

Biogeography, Comparative morphology, and Paleobiology.

What is Biogeography?

The branch that studies the world distribution of plants and animals.

What puzzling questions did biogeography raise for natural theology?

Why did some species have limited geographical distribution, why were species from far-flung locations similar, and where did all the new species fit in Scala naturae.

What is Comparative morphology?

The comparison of the morphology or anatomical structures of organisms.

What similarities were observed in comparative morphology (e.g., forelimbs)?

Similarities in body plans, construction using similar tissues, and homologous traits having developmental similarity.

What are homologous traits?

Characteristics that are similar in two species because of genes they inherited from a common ancestor.

What was the natural theologists' counter argument to morphological similarities despite different functions?

Body plans were perfect and there was no need to invent a new plan for every species; the creator used the same materials.

What did George-Louis Buffon observe that puzzled natural theology?

The existence of body parts with no apparent function, like the two toes on pigs' feet that don't touch the ground.

What are vestigial structures/organs?

Useless parts or tissues that had some function in ancestral organisms, or traits/organs that have lost all or most of their original functions through evolution.

Examples of vestigial structures in humans.

Coccyx (tailbone), vermiform appendix, wisdom tooth.

What is Paleobiology?

The study of fossils.

What is stratification in geology?

The horizontal layering of sedimentary rocks.

What pattern was observed in the fossil record regarding rock layers?

Relatively small and simple fossils appeared in deeper layers, while more complex fossils appeared in the layers above them.

Who was a founder of paleobiology and realized fossil layers represented organisms from successive times?

Georges Cuvier.

What is Catastrophism?

The theory that each layer of fossils represents creatures that had died in a local catastrophe (e.g., floods), causing abrupt changes between geological strata.

Who proposed Gradualism?

James Hutton.

What is Gradualism?

The idea that slow, continuous physical processes, acting over long periods of time, produced Earth’s geological features; variations come about gradually.

Who proposed Uniformitarianism?

Charles Lyell.

What is Uniformitarianism?

The geological processes that sculpted Earth’s surface over long periods are exactly the same as the processes observed today.

Who proposed the most significant pre-Darwinian evolutionary hypothesis?

Jean Baptiste de Lamarck.

Lamarck's theory overview.

Life was driven from simplicity to complexity; species change over time in response to environments, and acquired characteristics are passed on.

What metaphysical principle did Lamarck believe caused organisms to become better suited to their environments?

A perfecting principle.

Lamarck's mechanisms of evolutionary change.

1. Principle of use and disuse. 2. Inheritance of acquired characteristics.

What is the Principle of use and disuse?

Body parts grow in proportion to how much they are used, and structures not used get weaker and shrink.

What is the Inheritance of acquired characteristics?

Changes an organism acquires during its lifetime are inherited by its offspring.

What was a major downfall of Lamarck's theory regarding acquired characteristics?

Structural changes acquired during an organism's lifetime are not inherited by the next generation.

When did Charles Darwin embark on the voyage of HMS Beagle?

In 1831.

What was Captain Robert Fitzroy looking for when he invited Darwin on the Beagle voyage?

An unofficial naturalist and a gentleman for companionship to avoid depression on the long journey.

What type of specimens did Darwin collect during his voyage?

Fossils of extinct mammals, birds, barnacles, plants.

What geological observations did Darwin make in South America?

Recognized layers of rock that formed gradually and were reworked into mountains/valleys, observed shoreline uplift after an earthquake.

Darwin's observation about fossils resembling organisms in the same region.

Fossils like glyptodonts resembled living organisms like armadillos in the same region.

Darwin's reasoning for fossils resembling living organisms in the same region.

Living armadillos may be living descendants of the extinct glyptodonts.

Darwin's observation about animals in different South American habitats.

Animals encountered in different South American habitats clearly resembled each other, but differed from species in similar habitats on other continents (e.g., nutria vs beaver).

Darwin's reasoning for why animals in different South American habitats resembled each other.

They had inherited their similarities from a common ancestor.

Darwin's observation about the distribution patterns on the Galapagos Islands.

Many species resembled those on the distant South American mainland, but varied slightly from island to island.

Darwin's hypothesis about Galapagos species origins.

The plants and animals of the Galapagos islands were descended from a South American ancestor, and each species had changed after being isolated on a particular island.

Darwin's observation about Galapagos finches.

Great variability in bill shapes among finches from different islands.

Darwin's questions about Galapagos finches.

Why did finches on nearby islands differ slightly, and how did these different species arise?.

What common knowledge and hypotheses did Darwin use to develop his theory?

Selective breeding/Heredity, artificial selection, the struggle for existence, and natural selection.

Darwin's observation about offspring production.

Most organisms produce more than one or two offspring.

Darwin's observation about population size.

Populations do not increase in size indefinitely.

Darwin's observation about resources.

Food and other resources are limited for most populations.

Darwin's observation about individual characteristics.

Individuals within populations exhibit variability in many characteristics.

Darwin's observation about inheritance of variations.

Many variations appear to be inherited by subsequent generations.

Darwin's inference about competition.

Individuals in a population compete for limited available resources.

Darwin's inference about hereditary traits enabling survival/reproduction.

If certain hereditary traits enabled some individuals to survive and reproduce more than others, those traits would become more common in the next generation.

What is Natural Selection, according to Darwin's first fundamental insight?

The environment selects on variation in the traits of individual organisms because some variants are more successful at surviving and reproducing.

What is the concept of Common Ancestry, according to Darwin's second fundamental insight?

All species have descended from one or a few common ancestors; species sharing recent ancestry tend to resemble one another.

How does natural selection allow species to change and diverge?

By favoring individuals well adapted to their environments, leading to evolutionary divergence over time.

What is Descent with modification?

The evolutionary alteration and diversification of ancestral species; species diverge from a common ancestor, accumulating differences over time.

What was a problem with Darwin's views that was later resolved?

He used complex characteristics but lacked the genetic basis of heredity to fully explain variation and inheritance.

Who studied simple characteristics in pea plants and proposed factors (genes) control the expression of traits?

Gregor Mendel.

What is "Mutationism"?

An early 20th-century idea that evolution occurs in spurts induced by chance appearance of "hopeful monsters," not gradual change.

Who identified that genes are present in chromosomes?

T. H. Morgan.

What field links the ideas of Mendel and Darwin and recognizes the importance of genetic variation?

Population genetics.

What is the Modern Synthesis?

A unified theory of evolution (1930s-1940s) integrating data from various fields (biogeography, morphology, embryology, paleontology, taxonomy).

Principles embraced by proponents of the Modern synthesis.

Focus on gradual evolutionary change within populations, consider natural selection the primary mechanism, and support Darwin's gradualism.

What are the two basic levels of evolutionary change identified by Modern Synthesis?

Microevolution and Macroevolution.

What is Microevolution?

Describes small-scale genetic changes in populations in response to specific environmental shifts (e.g., shift in finch bill size).

What is Macroevolution?

Describes larger-scale evolutionary changes in species and more inclusive groups (above the species level).

How does Macroevolution result from Microevolution?

Macroevolution results from the gradual accumulation of microevolutionary changes.

What is a key point about variation and natural selection?

Natural selection does not create variation or new genetic traits; it selects for genes already present.

How are new genetic strains added to a population?

Through mutation and horizontal gene transfer.

Evidence for evolutionary change comes from many disciplines, including:

Adaptation by Natural Selection, The Fossil Record, Historical Biogeography, Comparative Morphology, and Molecular Techniques.

Example of natural selection operating on a short time scale.

The development of pesticide resistance in insects or antibiotic resistance in bacteria.

How does the fossil record document evolutionary change?

It documents continuity in morphological characteristics, providing evidence of ongoing change in biological lineages.

What fossil is considered a basic common ancestor of modern birds?

Archaeopteryx lithographica.

How does Historical Biogeography support Darwin's theory?

Geographical distributions of plants and animals are consistent with descent with modification, showing species on a continent are related and often distinct from others.

How does Comparative Morphology support evolution?

Analyses of living and extinct organisms reveal homologous traits, reflecting inheritance from common ancestors and divergence over time.

How do molecular techniques contribute to understanding evolution?

Provide powerful tools for exploring all aspects of life, including genome-level alterations and genetic changes.

Hox gene process in limb development.

In reptiles, mammals, birds, Hoxc6 expressed alone causes limb buds to develop; when Hoxc6 and Hoxc8 are expressed together, only ribs develop.

Role of Hox gene expression in snake limb loss.

In snakes, a mutation caused Hoxc8 expression to extend forward in the body, preventing limb bud formation where forelimbs would develop.

ZRS/shh gene process in limb development.

ZRS (Zones of polarizing activity Regulatory Sequence) is an enhancer for the sonic hedgehog gene (shh), which produces a protein that triggers limb growth.

Role of ZRS/shh in snake hindlimb loss.

Most recently evolved snakes have a less functional ZRS, leading to a lack of shh expression and therefore no hindlimb development. Primitive snakes (boas/pythons) retain some ZRS function, resulting in vestigial hindlimbs.

Woolly mammoth cold adaptation genes/parts.

Differences in about 1600 genes coding for proteins involved in metabolism of fats/sugars, development of skin/hair, size of sebaceous glands, and immune system responses to cold viruses.

Which specific gene variant contributed to the woolly mammoth's cold tolerance?

A variant TRPV3 gene, which is less active than in elephants and is involved in temperature sensation, hair growth, and fat storage.

What is Orthogenesis?

An early 20th-century idea that evolution produces new species with the goal of improvement, derived from Scala Naturae.