Jurmain et al.

Chapter 2

Development of Evolutionary Theory

Evolutionary Theory Misconceptions about evolution result from the poor quality of education (particularly science

education) in the U.S.

In the United States, evolution is considered to run counter to religious beliefs and is often

denigrated as being “only” a theory.

Evolution is, in fact, a scientific theory that has a wealth of support and is the unifying

theory of the biological sciences, including bioanthropology.

By the end of this course, due to studies in evolution, students will learn what we know to be

true n science:

1. Earliest human ancestors evolved from a species that lived 6 to 8 million years ago.

2. Humans separated from the last common ancestor with monkeys some 20 million years

ago.

Focus questions:

• What are the basic premises of natural selection?

• What were the technological and philosophical changes that led people to accept notions of

evolutionary change?

• Before we begin with the history of evolutionary thought, let’s review the worldview of

evolutionists:

• Evolution is a theory that has been tested and has been supported by a mounting body of

genetic (and other) evidence.

• As a theory it has stood the test of time and continues to grow.

• Evolution takes time; hence, the appearance of a new species is rarely witnessed.

Brief History of Evolutionary Thought• Evolutionary principles were developed in western Europe, made possible by

scientific thinking dating to the 16th century.

• Western science, however, borrowed ideas from Arab, Indian, and Chinese

cultures where notions of biological evolution had already developed.

• During the Middle Ages, the western worldview was that the world is static

(not changing).

The meant that the idea of fixity of species dominated understanding. Fixity

of species is the idea that all living species do not change once they are

created.

Also, the Earth was ‘full’; there was no room for any new species to be

created.

Further, the Aristotle’s vision of the Great Chain of Being stated that all

species are organized in a hierarchy, with humans at the top and so on down

the Chain.

• The universe was perceived as being part of the Grand Design, created as

recently as 4004 B.C.E.

• Overall, this all culminated into the idea of the Argument from Design

(life engineered by a purposeful God):

• God had created everything in perfect form

• To challenge this perfection was to be anti-Christian.

The belief that the earth was very young, coupled with the notion of fixity of

species, was a significant obstacle to the development of evolutionary

thought.

The Scientific Revolution• The Scientific Revolution came to be for many reasons, but among the most important was the

European discovery of North and South America

• In Europe, the scientific revolution developed as fundamental ideas of the earth and the biological

world were overturned. 2. Europe made scientific advances due to:

Discovery of the New World.

Circumnavigation of the globe.

Emerging intellectual ideas

• Challenges to traditional beliefs wherein Aristotle had taught that the sun and planets existed in a

series of concentric spheres that revolved around the sun.

• Further, Aristotle had taught that the sun and planets existed in a series of concentric spheres that

revolved around the sun.

• In 1514, Copernicus argued that the earth was not the center of the universe (geocentric)

• In the 1600s, Galileo Galilei restated Copernicus concepts’ and was sentenced to house

arrest. Learn more by watching the NOVA show

• The laws of physics, motion, and gravity were developed throughout the 16th and17th centuries.

• Invention of scientific instruments, including the microscope.

Precursors to the Theory of Evolution 1

• The first step to the development of any new science is to go through a phase that is descriptive; if

you do not know what you have, it is hard to discuss it.

• As a result, many of the early naturalists are known for their contributions to descriptive

biology

• The early researchers continued to view the world from a fixity of species perspective and

were interested in describing the Argument by Design.

• John Ray (1627-1705)

• Introduced the concept of species as based on reproductive success

• He realized that groups of organisms could be differentiated based on the ability to reproduce

with each other (or not).

• Today we call this idea the Biological Species Concept (BSC)

• The BSC can be defined in terms of reproductive capability.

• If organisms from two populations are capable of breeding naturally and can produce

fertile offspring, they are classified in the same species.

• Example: the mule

• The result of breeding a donkey with a horse is the infertile mule

• Assumes two organisms either belong to same species or not (mutually exclusive), but

this may not be always clear:

• Example: gypsy moths: far away populations produce infertile offspring, closer together

produce fertile offspring

• Also recognized that species can share characteristics. He grouped them into what he called

the same genus (plural is genera).

Precursors to the Theory of Evolution 2• Carolus Linnaeus (1707-1778)

He proposed a theory of the inheritance of acquired characteristics, in which an animal’s body

parts are altered through use or disuse.

• These altered characteristics are transmitted to their offspring.

• Although this is biologically impossible, he is credited with being the first to recognize the

importance of the interaction between organisms and their environment in the evolutionary

process.

• A Swedish naturalist who developed a method of classifying plants and animals.

• In Systema naturae, first published in 1735, he standardized Ray’s use of genus and species

terminology and established the system of binomial nomenclature.

• He standardized the genus and species into this binomial nomenclature

• He added to more levels of classification: class and order

• He also included humans in the classification system

• Homo sapiens (note that the genus is capitalized, the species is not; also in italics).

• Including humans was controversial as most thought of humans as separate from other living

organisms.

• He did create a set of racial groups within the listing wherein he put Europeans at the apex

and Africans at the base.

He grouped humans into his classification system

• Homo sapiens is the scientific name for humans

• This was a controversial position at the time; it countered the idea that humans were special,

made in the image of the Christian deity

Precursors to the Theory of Evolution 3• Erasmus Darwin (1731-1802)

• Charles Darwin’s grandfather.

• Physician, poet, and leading member of an intellectual community in England

• In a poem, expressed the view that life had originated in the seas and all species descended from

a common ancestor.

• Charles read his grandfather’s writings, but how much he was influenced by them is unknown.

• Georges-Louis Leclerc de Buffon (1707-1788)

• Was an 18th century thinker who believed that living forms changed in response to the

environment yet still rejected the idea that one species could give rise to another.

• He stressed the importance of the dynamics between nature and living forms in Natural History

(1749).

• He also stated that the external environment and living organisms are in a relationship that explains

the changing nature of species.

• His idea was that species changed gradually, influenced by the local environment

• He influenced two important naturalists: Georges Cuvier and Jean-Baptiste Lamarck.

• He did not adhere to the concepts of perfection in nature nor in the concept that nature had a

goal. He talked to the idea that the universe is changeable.

• Georges Cuvier (1769-1832

• Was a French vertebrate paleontologist who was an opponent of Lamarck’s evolutionary ideas

• Was adamant about the fixity of species, but he introduced the concept of extinction to explain the

existence of hitherto unknown fossil forms.

• Introduced the idea of catastrophism to explain the fossil record. Multiple disasters resulted in the

destruction of old life forms, and the newer forms were the result of creation events.

Precursors to the Theory of Evolution 4• Jean-Baptiste Lamarck (1744-1829)

• First scientist who codified his beliefs into a system that attempted to explain evolution.

• He is credited with being the first to recognize the importance of the interaction

between organisms and their environment in the evolutionary process.

• Thought physical alteration occurred because of bodily needs (called besoin)

• Basic idea was the inheritance of acquired characteristics (use-disuse theory) where a

trait acquired during lifetime is based down to offspring.

• An example is the giraffe: having stripped the leaves from the lower branches of a

tree, the animal tries to reach leaves on upper branches.• The neck becomes slightly longer. • The longer neck is passed on to offspring.

• Epigenetics: Environment CAN alter gene expression; not itself genetics.

Lamarck’s view of evolution:

The individual changes and

then transmits that change to

offspring.

Precursors to the Theory of Evolution 5• Thomas Malthus (1766-1834)

• An English clergyman and economist.

• Author of an essay, An essay on the principle of

population,

• Was arguing for limits of human population

growth, not concerned with how species

changed.

• Thought the limits for populations to increase

is controlled by availability of resources.

• Concerned with relationship of human

population growth to food supplies. Malthusian curve

• He noted that population sizes increase exponentially but food supplies remain

stable (see Malthusian curve).

• Inspired both Charles Darwin and Alfred Wallace in their separate discoveries of natural

selection.

• The idea of population-resources being linked was extended to all organisms by Darwin

and Wallace.

• Malthus is considered the father of demography.

• He influenced a group who came to be called social Darwinism

• Social Darwinists were concerned with the overpopulation of the lower classes.

Precursors to the Theory of Evolution 6• Charles Lyell (1797-1875)

• A lawyer, geologist, and, for Charles Darwin’s friend and mentor; he is considered the

founder of modern geology.

• Before meeting Darwin in 1836, Lyell had earned acceptance in Europe’s most

prestigious scientific circles, thanks to his praised Principles of geology, published

during the years 1830–1833.

• His ideas provided the deep time necessary for biological evolution to have occurred.

Proponent of theory of uniformitarianism.

• The theory that the earth’s features are the result of long-term natural processes (i.e.

wind, water erosion, local flooding, frost, decomposition, volcanoes, earthquakes, and

glacial movements) that continue to operate in the present as they did in the past.

• Proposed by James Hutton, he demonstrated that uniform processes could account for

present geological features.

Mary Anning (1799-1847)

• She discovered the first fossilized Pleiosaurus (ocean-dwelling reptile) while exploring

near her home in Dorset, England.

• Became known as one of the world’s leading “fossilists.”• When her father died, Anning began collecting and selling marine fossils to support her

family.

• Because of her gender, she was not allowed into the inner circles of British naturalists.

Even so, her fossils were sought by many of these same men, including Lyell.

The Discovery of Natural Selection 1

• Social context

• A concept of evolution was prevalent in European scientific circles at the time.

• There was a growing Reform Movement in England to undo the inequalities of the class system.

• Evolutionary ideas were seen as related to these types of reforms and were socially feared by

certain groups.

The idea of transmutation is the shift of one type of species into another over time.

• Many of the early transmutationists were strongly anti-Christian.

• This set the tone of the discussion for many by the time that natural selection was suggested

• Charles Darwin (1809-1882)

He proposed the first credible mechanism for evolutionary change, natural selection, in On the

Origin of the Species (1859).

After graduating from Cambridge University, where he studied theology but also cultivated his

interests in natural science and geology, he was recommended to join the five-year expedition of

the HMS Beagle.

Darwin began the voyage as a believer in the fixity of species, but his observations of, among other

things, fossils of giant ancient versions of living animals and varieties of Galápagos finches

eventually convinced him to the contrary.

After his return to England in October 1836, Darwin began to formulate the theory of natural

selection based on what he had observed, especially of Galapagos finches.

He began experiments in selective breeding with domesticated animals ,developing and testing

the theory of natural of selection. Darwin saw the importance of biological variation within a

species.

He wrote summaries of his ideas by 1844, but felt he needed more evidence before he published.

The Discovery of Natural Selection 2• Charles Darwin (continued)

• Charles Darwin formulated theory of natural selection.

• Darwin talked to the idea of struggle for existence.

• The idea that in each generation more offspring are born than survive to

adulthood, coupled with the notions of competition for resources and

biological diversity led to the theory of evolution.

• He wrote,“ It at once struck me that under these circumstances favourable

variations would tend to be preserved, and unfavourable ones to be

destroyed.”• FYI: Herbert Spencer (not a biologist) coined the phrase survival of the

fittest.

• Alfred Russel Wallace (1823-1913)

Developed his own theory of natural selection after collecting bird and

insect specimens in Southeast Asia. Suggested species descended from other

species (speciation) and new species were influenced by environmental

factors.

• Wallace published a paper on speciation and soon sent another paper to

Darwin in 1858.

• As a result, he presented joint paper, coauthored with Darwin, on

evolution and natural selection to the Linnean Society of London. Little

notice was taken.• Next, in 1859 Darwin published his On the origin of species, and an uproar began that continues

today.

Natural Selection 1

Darwin envisioned natural selection as a process in which individuals with favorable

variations survive and reproduce at a higher rate than those with unfavorable variations.

The basic processes, as he understood them, are as follows:

1. All species are capable of producing offspring at a faster rate than food supplies

increase.

2. There is biological variation within all species.

3. In each generation more offspring are produced than survive, and because of limited

resources, there is competition among individuals.

4. 4. Individuals who possess favorable traits have an advantage; they have greater fitness

because favorable traits increase the likelihood that they will survive to adulthood and

reproduce.

5. The environmental context “determines” whether or not a trait is beneficial.

6. Traits are inherited and passed on to the next generation. Because individuals who

possess favorable traits contribute more offspring to the next generation, over time

those favorable traits become more common in the population. Individuals who

produce more offspring at a higher rate have greater reproductive success.

7. Over long periods of geological time, successful variations accumulate in populations,

resulting into later generations being distinct; thus new species appear.

8. Geographical isolation may lead to the formation of new species because over time

populations in distinct areas face different selective pressures.

Natural Selection 2

• Natural selection in action

• Gradualism was Darwin’s view on how species occur.

• Over long periods of geological time, successful variations accumulate in a population

• Later generations may be distinct from ancestral ones, or a new species can appear.

• Key concept: Natural selection operates on individuals, but it’s the population that evolves

• Famous examples of natural selection:

• Again, Darwin finches on the Galapagos.

• The example of dog breeding.

• Industrial melanism as evidenced by the peppered moths.

Prior to the 19th century in England, the most common variety of peppered moth was a mottled

gray color. During the day, the moths would rest on the lichen-covered tree trunks and their

coloration provided camouflage.

Due to changes driven by industrialization, coal dust covered the tree trunks, killed the lichen, and

the mottled gray moths became more conspicuous and targeted by birds and over time the moths’

(subjective to selective pressures) numbers dwindled. Darker moths then became more common.

Once the coal pollution was cleaned up, the gray moths multipled again.

• Antibiotic resistance today

• Evolutionary change through natural selection

1. A trait must be inherited in order to have importance in natural selection.

2. Natural selection cannot occur without variation in inherited characteristics.

3. Fitness is a relative measure that will change as the environment changes.

Natural Selection 3

• Natural selection and reproductive success

Natural selection acts through not only differential death rates, but also through differential

fertility rates.

This leads to a differential net reproductive success.

Fitness, as a term in biology pertains, to natural selection, a measure of relative

reproductive success of individuals.

The terms genetic fitness, reproductive fitness, and differential reproductive success are

also used.

• Fitness can be measured by an individual’s genetic contribution to the next generation

compared to that of other individuals. The terms fecundity and fertility are important here.

• Fecundity refers to the ability to conceive and produce healthy offspring.

• We should ask if a person is fecund, not fertile.

• The book uses the term fertility and so in not correct.

• Fertility refers to the number of live offspring produced by an individual An animal that

gives birth to more young passes its genes on a faster rate than one that bears few

offspring.

• Fitness is measured on a scale from 0 (zero) to 1 (one).

• The record for the most live births by a single woman is 69 so she had a value of 1

(female). Of these, 67 lived past infancy.

• Her husband married again and had 18 children with his second wife. His total was 89

births, with 87 surviving so he had a value of 1 (male).

Opposition to Evolution 1

• Constraints on 19th century evolutionary theory

Darwin did not know how favorable traits were passed from generation

to generation Darwin argued that natural selection acts on variation

within species, yet could not explain the source of this variation.

No-one in the 19th century understood the actual source of variation.

• 19th century scholars believed inheritance was a blending process in

which parental characteristics were mixed to produce intermediate

expressions in offspring. This is the source of concepts like ‘bad

blood’ and ‘blue blood’.

• Gregor Mendel had worked out the modern principles of heredity, but

his work was not recognized until the beginning of the 20th century

• The modern understandings of inheritance

• Only with the discovery of Mendel’s work did the mechanism become

clear

• In 1953, the structure of deoxyribonucleic acid (DNA) was

discovered.

• This was followed by even more advances in the field of genetics,

including the sequencing of the human genome.

• With the discovery of the structure of DNA came the understanding

of the entire genetic makeup of an individual (genome) or species.

• Human and chimpanzee genomes were sequenced in 2003 and 2005,

respectively.

Opposition to Evolution 2 Religion and science concern different aspects of the human experience, and they are not inherently

mutually exclusive categories. Today, evolution is considered to be a fact by most biologists.

Darwin’s formulation of evolution was offensive to some Christians and some Muslims.

Yet, evolutionary theories are accepted, in part, by the Catholic Church and most mainstream

Protestants. See chahttp://www.pewforum.org/religious-landscape-study/views-about-human-

evolution/

Most fundamentalists reject all scientific explanations of evolution.

A brief history of opposition to evolution in the United States

After WWI conservative Christians in U.S. revived “traditional values” and avoided mention of

Darwinism in public schools.

“Scopes Monkey Trial,” involved John Scopes who was arrested and tried for teaching evolution

Creationists have dropped the term “creationism” in attempts to mask their fundamentalist

ideologies with less religious-sounding terms such as “intelligent design theory.”

• These groups argue that creation science and intelligent design (ID) are as much a scientific

endeavor as is evolution, and suggest scientific evidence to support creationist views.

• ID is not science, however. Creationists argue their view is absolute and fallible, which is

counter to science which seeks testable hypotheses

Almost half of all Americans believe that evolution does not occur. Some reasons:

1. Evolution is complex and is not easily explained.

2. Relation between science and religion has never been easy.

3. Also, most cultures do not emphasize the biological continuity.

Opposition to Evolution 2

• Five (5) myths about evolution

• Myth 1: Evolutionary theory denies the existence of God.

• Response 1: In fact, science does not ask these questions, so the debate does not really center

here.

• Myth 2: Evolutionary theory claims life is one huge, incredible accident.

• Response 2: Just the opposite. There are very specific mechanisms of evolution that we will

discuss in later chapters.

• Myth 3: A scientific debate exists concerning the existence of evolution

• Response 3: According to Pew Research (2014) “" While 98% of scientists connected to the

American Association for the Advancement of Science say they believe humans evolved over

time, only two-thirds (66%) of Americans overall perceive that scientists generally agree about

evolution …” (Source: http://www.pewresearch.org/fact-tank/2017/02/10/darwin-day/)

• Myth 4: Evolutionary theory preaches progress.

• Response 4: “Evolution is not progress. Populations simply adapt to their current

surroundings” (Colby, 1996)

• Myth 5: Evolutionary theory says humans are ‘just animals’.

• Response 5: Of course humans are animals; it is the just part that is in error. All animals have

unique evolutionary histories, and among those for humans is the use of culture to adapt. No

other species is as good at it as we are. But, all species are unique and this is important to note.

• Great website to read more: https://evolution.berkeley.edu/evolibrary/misconceptions_faq.php

Kinds of Evidence for Evolution

1. Fossil record

• The fossil record gives evidence for species loss, introduction and change.

• Gaps in the fossil record are due to a lack of data collection. We will see many

examples of fossil discoveries this quarter where former gaps are being filled.

2. Chemical and anatomical similarities: All living organisms share either DNA or

RNA

3. The structural similarities of anatomy among closely related organisms

• Homologous organs are those that come from shared evolutionary history

(forelimbs of humans, whales, dogs, and birds)

• They differ from analogous organs which are those that result from convergent

evolution (wings of insects and of bats)

• Vestigial organs argue against a Grand Design (appendix for instance)

4. Geographic distribution

• Absent of many species in isolated places

• In these same isolated places other species, seen nowhere else, exist.

5. Genetic changes in living organisms over many generations discussed earlier

Source: O’Neil, D. (2010). Evidence of evolution. Retrieved from http://anthro.palomar.edu/evolve/evolve_3.htm