Chapter 2

Evolution

Evolution

• Both cultural and biological evolution interest anthropologists.

• Evolution is change in living organisms over time.

• Evolution is essentially the idea that new species develop from earlier species by

accumulated changes.

• This is sometimes referred to as "descent with modification".

• It is also sometimes called "microevolution".

• The idea of evolution was developed from many observations of life.

• It has been tested and challenged many times and in many ways, and has survived

largely intact.

• There are also many independent lines of evidence which are consistent with evolution

as a real process.

• There is NO observed evidence against evolution. Evolution therefore holds the high

status of near certainty: it is a scientific theory.

• This course is a science course and is a biological science.

• Therefore it presents scientific explanations from an evolutionary stance.

• I do not ask you to agree with the science of evolutionary theory but will ask you to be

able to explain this set of interpretations and to differentiate it from non-scientific

statements. This is important in that a 1985 survey determined that: Agree with evolution:

40%; Disagreed: 40%; and Not sure: 20%

Source: Flammer, L. (1999). “ENSI “ Retrieved from http://www.indiana.edu/~ensiweb/lessons/ev.not.html

Charles Darwin and the HMS Beagle

• Darwin did not come up with biological evolution out of the blue. His ideas were

strongly influenced by many thinkers from many different scientific disciplines.

• In this lecture, we will look into the following questions:

• 1) How did the theory of evolution come to be?

• 2) What was Darwin’s contribution to the theory of evolution? In other words, why

is he so famous? And

• 3) What has happened since Darwin in the development of our understanding of

evolution? Let’s start by going back to 1831 and joining Charles Darwin on the

HMS Beagle.

• In 1831, a young (22-year-old) Charles Darwin joined the crew of the HMS Beagle

for a five-year voyage around the world.

• The Beagle sailed from England, around the tip of South America, to the Galápagos

Islands, around the southern coasts of Australia and Africa, and back to England.

• During this journey, Darwin collected thousands of samples: plants, animals,

fossils, and rocks. He made careful and important observations about the organisms

he encountered.

• Darwin saw the importance of biological variation within a species.

• Most famous example is Darwin’s finches.

• Watch: What Darwin never knew: https://www.youtube.com/watch?v=kNPbjtej1Hk

Descent with Modification

• Evolution is change in living organisms over time.

• Evolution is essentially the idea that new species develop from earlier species by

accumulated changes.

• This is sometimes referred to as "descent with modification".

• It is also sometimes called "microevolution".

• The idea of evolution was developed from many observations of life.

• For instance, Darwin spent a considerable amount of time studying the plant and animal

life that inhabited the Galápagos islands.

• Darwin noticed that different kinds of birds—finches, in particular—were quite variable,

and different kinds of finches lived on different islands.

• But, their variation was not random:

• It appeared to vary according to the habitat in which they lived. In other words,

particular birds were adapted for very specific environments.

• The 13 different finch species that currently live on the Galápagos represent a kind of

rapid and prolific speciation known as an adaptive radiation.

• Darwin surmised that birds with certain physical features—those that allowed them to eat

certain foods in their environment—survived and reproduced.

• Through reproduction, they could pass on these physical features to their offspring, thus

increasing the frequency of these features in the overall population of birds.

• In different environments, different physical features would be favored and would be

“selected.” This idea, termed natural selection, is the driver of evolution.

Evolution: The Context for Darwin 1• 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.

• 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 and so to challenge this

perfection was to be anti-Christian.

• 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.

• Copernicus challenged the idea that the earth (geocentric) was the center of the universe.

• Galileo’s work supported the idea that the universe was a place of motion.

• In fact, challenges could get you dead.

• Watch: Galileo's battle for the heavens: https://www.youtube.com/watch?v=XCxkdR092c4

• James Ussher (1581-1656)

• Famous for his use of biblical text as basis to estimate age of earth.

• He determined that the world began on October 23, 4004 B.C.E.

Evolution: The Context for Darwin 2

• The Judeo-Christian view of the world held that the Earth was quite young (~6,000 years old).

Species had all been created by God and these species were unchangeable (immutable).

• However, scientists in the eighteenth and nineteenth centuries began to change this way of

thinking. They began to collect evidence that, in fact, the Earth was quite old (millions of years

old), and that the Earth’s surface and its plants and animals have changed considerably over

time.

• Evidence for these revolutionary ideas came from many different scientific arenas. We will look

at how Darwin was influenced by new discoveries in the following sciences:

• Geology: The study of the Earth and its processes.

• Paleontology: The study of fossils.

• Taxonomy and systematics: The study of organisms, their classification, and relationships to

one another.

• Demography: The study of populations.

• Evolutionary biology: The study of how organisms change over time.

• The idea of evolution was developed from many observations of life.

• It has been tested and challenged many times and in many ways, and has survived largely

intact.

• There are also many independent lines of evidence which are consistent with evolution as a

real process.

• There is NO observed evidence against evolution. Evolution therefore holds the high status of

near certainty: it is a scientific theory.

Evolution & Geology

• James Hutton (1726–1797)

• Our species has figured out that the planet Earth is 4.6 billion years old. But, in the 1600s,

any suggestions that the Earth was more than just a few thousand years old were not only

considered incorrect but blasphemous.

• However, this way of thinking began to change in the eighteenth century thanks, in part, to

the work of the Scottish geologist James Hutton, He introduced two concepts:

1. Hutton recognized that wind and rain caused erosion and formed sand, small rocks, and

soil. These particles could then be redeposited, forming the layered pattern of rock we call

strata.

2. Hutton’s ideas of geological strata and time depth rely on the assumption that the processes

that occur today are the same ones that have occurred in the past. This is known as

uniformitarianism, an idea that is widely accepted in all scientific fields today.

• Charles Lyell (1795–1875)

• A lawyer, geologist, and, for Charles Darwin’s friend and mentor.

• 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 work suggested that small biological changes could add up over time. His work

strongly influenced Charles Darwin.

• Hutton’s ideas were soon tested by Lyell, who confirmed that it would take millions, not

thousands, of years for the Earth’s geological strata to form.

Evolution & Paleontology

• Robert Hooke (1635–1703)

• Not only is the Earth old, but there were once organisms that populated the Earth that no

longer exist.

• Robert Hooke invented the microscope, and examined fossil wood under his new device.

• He noted that the cellular structure of the fossil wood was the same as wood that exists

today.

• In other words, he discovered that fossils were the remains of things that were once

alive.

• Georges Cuvier (1769–1832)

• Over 100 years later, the French naturalist Georges Cuvier made two other important

observations.

• He proposed that fossils were from organisms that no longer existed. This idea, which

sounds quite obvious today, was not at all at the time.

• Cuvier also discovered that different fossils could be found in different geological strata.

• If geological strata were layered by age, with the older sediments deeper and the

younger ones more superficial, then the different fossils in the different layers of rock

could demonstrate evolutionary change.

• Multiple disasters resulted in the repopulation of regions by newly created organisms

• Introduced the idea of catastrophism to explain this fossil record. He proposed that the

different layers represented groups of organisms that had been wiped out in a series of

catastrophic events

Evolution & Taxonomy/Systematics

• 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.

• Carolus Linnaeus (1707-1778)

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

• Prior to Cuvier’s work on fossils, the great Swedish naturalist Carolus Linnaeus devised a

system for naming and classifying all living organisms.

• 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 also included humans in the classification system

• Homo sapiens is the scientific name for humans. 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.

• Linnaeus also devised a hierarchical classification scheme in which all living organisms could

be placed within a kingdom, phylum, class, order, family, genus, and, finally, species.

Evolution & Demography

• Thomas Malthus (1766-1834)

• Darwin’s great insight of natural selection was strongly influenced, oddly, by an

economist.

• Thomas Malthus wrote An essay on the principle of population that laid the

foundation for many of Darwin’s ideas.

• Malthus observed that humans often have more than two offspring.

• If parents (two people) continued to have more than two children, then the

population of humans would grow.

• In fact, Malthus argued that the growth could be exponential, resulting in

billions and billions of humans in a short period of time.

• Although Malthus observed that human population did not grow without

limit.

• Why not? Because there is not enough food for everyone. Populations are

limited by their resources. This concept is called the Malthusian curve

• Therefore, there is a struggle for existence, with only certain individuals

surviving and reproducing. 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.

Evolution & Transformation of Life Forms

• It is a common misunderstanding that Charles Darwin “invented” evolution. But, the idea

that living organisms have changed over time was already around in Darwin’s time.

• Jean-Baptiste Lamarck (1744-1829)

• The French scientist Jean-Baptiste Lamarck argued that plants and animals had changed

over time, or evolved.

• What Darwin contributed to science was not just the evidence that life on Earth had

evolved, but he proposed a mechanism for how this can happen: natural selection.

Lamarck also proposed a mechanism: Inheritance of acquired characteristics.

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

• In the Lamarckian view:

1. Changes in an individual's physical organs, due to the so-called Law of use or disuse

(organs are strengthened by use or weakened by misuse)

2. During the individual's lifetime, can somehow be transmitted to the next generation

due to inheritance of acquired characteristics.

• 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.

What Darwin Borrowed

• From the work done by the great geologists Hutton and Lyell, Darwin knew that the Earth was

quite old and that natural processes often occur gradually Earth old

• Darwin read the work of Cuvier, and recognized that many of the fossils that he collected while

sailing around the world resembled living forms.

• From Malthus, Darwin began to recognize the importance of reproduction, variation, and

population-level thinking

• And from Linnaeus and Lamarck, Darwin realized that life was clustered into related, nested

hierarchies, and that it had changed over time.

• These ideas led to his two great realizations:

1. All life on Earth is related through common ancestry. More related organisms share a more

recent common ancestor.

2. The mechanism for evolutionary change is natural selection. All he had to do now was

publish these ideas.

• The basic processes of natural selection:

1. All species produce offspring at a faster rate than food supplies can increase

2. Except for identical twins, no two individuals are exactly alike.

3. In each generation, more individuals are produced than can survive.

4. Individuals that possess certain traits have an advantage over those that do not.

5. The environment determines whether a trait is beneficial.

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

7. Over time, successful variations accumulate in a population, and a new species may appear.

8. Geographical isolation may lead to the formation of a new species.

Darwin’s Theory of Evolution

• Charles Darwin (1809-1882)

• Natural selection can only operate if there is variation.

• If every member of a species is the same size, or the same color, or has the

same-sized beaks, then how can certain individuals survive and not

others?

• Darwin talked to the idea of struggle for existence.

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

fittest.

• Alfred Russell Wallace (1823-1913)

• In 1858, Charles Darwin received a startling letter from the naturalist

Alfred Russel Wallace. He wrote to Darwin and proposed a mechanism for

evolution that was strikingly similar to Darwin’s own ideas.

• Like Darwin, Wallace made many of his observations on islands—in

Wallace’s case, the Indonesian archipelago.

• In 1858, They agreed to jointly present their findings to the Linnaean

Society of London in July 1858.

• The origin of species, according to Darwin and Wallace, is explained:

Species are mutable (not fixed) and they evolve from each other.

• Darwin and Wallace view of evolution: That environment acted to change

populations of organisms over time through natural selection: Differential

reproduction PLUS differential survival.

• Environment favors individuals with long necks.

• Those individuals more likely than others to have offspring.

An Example of Natural Selection

• An example of natural selection

• Perhaps the most famous example of how natural

selection works is that of the peppered moths in

England.

• The variation in the species is found in their

coloration: light and dark.

• Prior to the Industrial Revolution, the majority were

light-colored, allowing them to camouflage

themselves among the lichens.

• During the Industrial Revolution, the trunks of the

trees became heavily covered in soot and the dark-

colored moths predominated.

Light and dark moths

• Once the coal burning practices subsided, the light-colored moths increased in

numbers.

• Several points can be drawn from this set of observations:

• There are not ‘good’ and ‘bad’ traits, it depends on the environment.

• Evolution is not unidirectional; it responses to changing conditions.

• Variation among a species is critical to survival as environments do change.

• Another observation to keep in mind is that the peppered moths studies illustrate how

the scientific method can be used to explain observations.

Mechanisms of Inheritance 1

• Gregor Mendel (1822–1884)

• Variation is a fundamental tenet to natural selection.

• During Darwin’s time, it was thought that offspring were a 50-50 blend of their

parents.

• This idea, known as blended inheritance, was quite a problem for natural selection

because it would dilute favorable adaptations, limiting the power of selection to cause

evolutionary change.

• Little did Darwin know that an Augustinian monk named Gregor Mendel was doing

experiments with pea plants that would refute the ideas of blending inheritance and lay

the foundation for modern genetics.

• Mendel bred more than 28,000 pea plants and very carefully mapped how traits like

flower color and position, pea color and shape, and plant height passed from generation

to generation.

• He discovered that traits were inherited discretely, though units ultimately called

genes. These genes can come in different versions, called alleles.

• Often one version could exert dominance over another version, which would be

called recessive.

• The two versions, one from the mother and one from the father, did not blend.

Mechanisms of Inheritance 2

• Let’s look at a way to model a cross-breeding experiment: The Punnett square.

• Imagine that Mendel breeds a tall pea plant with a short one.

• According to the ideas of blending inheritance, all of the offspring should be intermediate

in height.

• But, instead of these being plants of intermediate height (if blended), Mendel measured

these plants and found all were tall. The allele BIG T is dominant over the little t.

• Now, let’s breed these plants together. Mendel bred thousands of plants and found that that

three of every four plants (75%) were tall, and 25% were small. There was no in-between

height.

• Tall, which we call the phenotype (the term for what the organism looks like as a result of

this gene).

• And they had the allele combination of either TT or Tt, which we call the genotype (the

actual code for a specific gene).

• The small ones could only have the genotype tt, because little t is recessive.

• Heritability is the proportion of total variance in a phenotypic trait that is attributable to genetic

variation in a specific population. Formulae (A high value means more contribution of

genetics):

• Total variation = genetic variation + environmental variation

• Heritability = (genetic variation/total variation)

• Points to remember: 1) Heritability can differ between populations; 2) It can change in the

same population over time; and 3) Because it is measured at the population level it is not

applicable to an individual’s phenotype.

Model of A Dominant/Recessive Trait

Causes of Evolution

• Bringing the two together

• Mendel’s work on inheritance provides an understanding for how variation arises and is passed

from generation to generation.

• Darwin’s work provides an understanding for how that variation leads to differential survival

and reproduction.

• Together, these two big ideas of inheritance and natural selection can be combined into an

evolutionary synthesis.

1. Natural selection is one cause of evolution. But where does variation originate?

2. Mutation is the source of new variants.

• This observation was provided by the great biologist Thomas Hunt Morgan.

• Morgan worked with fruit flies, and was particularly interested in their chromosomes.

• Morgan discovered that a gene could change spontaneously, something called a mutation.

• A mutation could lead to a new variant, like the different eye colors, or the four-winged fly

shown to the far right on this slide.

• If beneficial, this mutation could spread to future generations, making mutation an important

cause of evolutionary change.

3. Gene flow is the spread of genes from one gene pool to another.

• It is also known as admixture.

• This process can introduce variants into a population that were previously either quite rare or

absent altogether.

4. Genetic drift happens when populations are quite small, and gene frequencies change because of a

random drifting effect.

The Discovery of DNA

• It is important to understand that many traits that natural selection acts on are coded for by genes.

• Genes are discrete units packaged on things called chromosomes, which reside in the nucleus of

your cells.

• These chromosomes are made, in part, of a chemical called deoxyribonucleic acid, or DNA.

• Your somatic DNA could stretch to 6 feet when the cell is performing normal functions.

• A chromosome is composed of a DNA molecule and associated proteins.

• There are 2 types of chromosomes:

• Autosomes (or autosomal chromosomes) carry genetic information that governs all

characteristics except primary sex determination.

• Sex chromosomes are the X and Y chromosomes.

• In 1953, British scientists James Watson and Francis Crick, using detailed microscopic images taken

by Rosalind Franklin, discovered the structure of DNA, and it is the structure that helps reveal how

DNA works.

• They never gave Franklin credit.

• Watch: Secret of Photo 51: https://www.youtube.com/watch?v=Vw8Wrr-ykFc

• Following this discovery, scientists have figured out how the DNA molecule codes for particular traits

(or phenotypes).

• And it is the structure of the molecule that helps explain how we each have a copy of DNA in all of

our trillions of cells. Scientists have also been able to count the differences in the DNA code

between different species to estimate how closely related different organisms are, and how long

ago they shared a common ancestor.

• This is possible because all life, from humans to chimpanzees, dogs, mice, fish, mushrooms, and

bananas, contain a DNA code written in the exact same chemical alphabet.

Science and Religion 1

• For some people, evolution represents an argument against their belief in the sudden creation of

all life by a creator

• One response was to devise creation science to communicate their teachings in the context of

scientific study.

• Not necessary, science and religion are two worldviews that are not in conflict, so no need to

validate religion in the guise of science.

• Both worldviews are valid.

• Where the difficulty arises in when supporters of faith-based worldviews insist that their

explanations are scientific, but then do not adhere to the processes. For instance,

creationists argue their view is absolute and fallible, which is counter to science which

seeks testable hypotheses.

• Creation science: Devised by opponents of evolution to communicate their teachings in

the guise of scientific study. Creation science is not supported by factual evidence.

• Intelligent design (or intelligent design creationism): An approach stressing the idea that

the biological world was created by an intelligent entity, although “God” is not generally

specified directly as the creator.

• Tries to divorce intelligent design for objections regarding the establishment of

religion under the First Amendment.

• Basic concept is that there are certain characteristics of biological organisms that are

too complex to explain through natural selection (irreducible complexity)

Science and Religion 2

• Stance of most scientists:

• Religion and science concern different aspects of the human experience, and they

are not inherently mutually exclusive categories.

• Belief in God does not exclude the possibility of biological evolution;

acknowledgement of evolutionary processes doesn’t preclude the existence of God.

• Stance of religious groups:

• Evolutionary theories are not rejected by all religions or by most forms of

Christianity.

• Some groups do struggle with evolutionary ideas and include Christian

fundamentalists and those who support scientific creationism or intelligent design.

• Those in this later group argue that creation science and intelligent design (ID) is

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.

Science and Religion 3

• One of the greatest controversies regarding education in the United States and other parts of

the world is the teaching of evolution.

• One noticeable casualty of the debate over teaching evolution has been the erosion in

science education.

• Creationism has not gone away despite legal and theological objections. Many favor

teaching of intelligent design as an alternative to evolutionary theory.

• Famous trials over teaching evolution:

• The most famous example of a court case linked with evolution was the Scopes Monkey

Trial (1925, Tennessee)

• Despite a recent Dover school board resolution favoring intelligent design, a subsequent

court challenge reversed the ruling. The presiding judge stated intelligent design was not

a science.

• Kansas State Department of Education (2005) determined that teaching evolution and

intelligent design must be given equal time in their instruction.

• One response was by an Oregon State University student, who wrote a letter to this

school board. This sparked the Flying Spaghetti monster movement.

• In 2007, the Board rejected this policy (unrelated to the letter)

Science and Religion 4

• 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