the period of darwinism (1859-1882)€¦ · the development of evolutionary theory since darwin –...

The period of Darwinism (1859-1882)

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T h e d e v e l o p m e n t o f e v o l u t i o n a r y t h e o r y s i n c e D a r w i n – D a r w i n i s m

www.evolution-of-life.com Marcus Hammann (corresponding author)

The period of Darwinism (1859-1882)

Exercise 1 (home group, individual work):

Read the following text carefully. Your task is to fill in the missing words and phrases, which

you know from your biology lessons. If you need help, you can...

• …go back in the text or

• …read further.

If you have problems understanding the text, write down your questions!

Charles Darwin was an enthusiastic natural scientist.

He tried to write down all his observations of animals

and plants and sought to explain them. After his

expedition on the Beagle (fig. 1), which took five

years, Charles Darwin recognized that there had to be

an explanation other than creation by God for the

diversity of life and for the similarities he observed

between the organisms.

In 1837 Darwin wrote down the theory of descent

with___________________________ for the first time in

his notebooks. The name of the theory derives from the

Latin descendere (i.e. to descend) and means that

organisms descended from a common ancestor and

changed. Darwin developed this theory by collecting

fossils and animals. He noticed that he could reproduce

lines of related organisms by arranging them in such a way that there were very few

modifications from one organism to the next.

Fig. 1: The research ship: the Beagle. © CNDP, 2009

Fig. 2: Darwin collected animals. © CNDP, 2009

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In the same year, Darwin described the theory of

__________________________________________ of all

organisms. Later he also included human beings – to the

horror of many. However, Darwin initially wrote down

this idea only in his notebooks. It was essential for him that

all organisms on earth have a common origin.

In 1838, Darwin explained the change of the species by means of the theory of

______________________________. He was inspired to do so, when he read a book from

Thomas R. Malthus about human population:

“[F]ifteen months after I had begun my systematic

enquiry, I happened to read for amusement Malthus

on Population, and being well prepared to appreciate

the struggle for existence which everywhere goes on

from long-continued observation of the habits of

animals and plants, it at once struck me that under

these circumstances favorable variations would tend

to be preserved, and unfavorable ones to be destroyed.

The result of this would be the formation of a new

species.” (Darwin, 1859)

Moreover, Charles Darwin published an additional theory in his important publication ‘On the

origin of species’ (1859): the theory of ____________________________. It says that the

change of species takes place in small steps (gradually) and not in saltations (leaps). Darwin

deduced gradualism from an old tradition in Natural Philosophy, according to which there are

generally no saltations (leaps) in nature.

However, also other researchers made contributions to the development of evolutionary

theory, especially Henry W. Bates and Ernst Haeckel.

Fig. 3: Darwin draws a phylogenetic tree. © CNDP, 2009

Fig. 4: An example of the struggle for existence. © CNDP, 2009


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Fig. 5: A drawing from Henry W. Bates. (in: Linn. Soc. 23:495-566, 1862; Source: www.wikipedia.org)

In 1862, Henry W. Bates observed in the Amazon

region that edible butterflies imitate the coloration of

poisonous or inedible butterflies, when both species

occur in the same habitat. He termed this phenomenon

____________________. When the appearance of

poisonous butterflies varied geographically, Bates

discovered the same variations among edible

butterflies. Mimicry means imitation.

In 1866, Ernst Haeckel described the

_____________________________________:

“During its rapid and short development, the

organic individual repeats the most important

modifications its ancestors had to pass through

during their slow and long-lasting

paleontological development according to the

laws of inheritance and adaptation.”

Five years later Charles Darwin published a further

theory. He developed the theory of

_______________________________________,

with the intention to explain characteristics like the

gorgeous tail of the peacock. At first sight it seems to

be disadvantageous for the peacock, but it is favored

by the peahens. The theory of natural selection was

not a sufficient explanation for this phenomenon.

Fig. 6: Each column shows three embryonic steps of development of a species. Considering the first line reveals that the different species are very similar to each other in the beginning of the embryonic development. (Haeckel, 1874; Source: www.wikipedia.org)

Fig. 7: Darwin assumed that females have apparently a sense of beauty. © CNDP, 2009


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Exercise 2 (expert group, teamwork)

Check your cloze texts and your reading comprehension for correctness. Subsequently answer

the following questions:

a) Which term (that Darwin himself never used) is used for Darwin’s first theory of 1837

as it is known today? You know this term from class.

_____________________________________________________________________

_____________________________________________________________________

b) Why do nonpoisonous butterflies imitate the coloration of poisonous butterflies? Why

was Charles Darwin encouraged by these findings?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

c) Why couldn’t Charles Darwin explain the gorgeous tail of the peacock by natural

selection? Find another explanation for the gorgeous tail of the peacock!

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

d) Give further examples for characteristics that developed by means of sexual selection.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________


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Exercise 3 (expert group, individual work)

Copy the terms you filled into the gaps of the cloze text (everything that is underlined) onto

the ‘milestone-cards’ (see last page of the material). There is one card for each milestone from

the period of Darwinism.

Exercise 4 (home group, teamwork):

Each of you is asked to present the milestones of his/her period to the other team members by

attaching the milestone-cards chronologically to the time bar. The expert for the period of

Darwinism starts. For each milestone-card, the expert explains, which person arrived at which

insight by which means and how the insight changed evolutionary theory. Afterwards, the

next expert follows until the time bar is completed.


After completing the time bar, your team creates a concept map with as many connections as

possible.

1.) Choose at least 12 milestones from the time bar (each period should be included).

2.) Write down the term from each milestone on a piece of paper.

3.) Arrange the pieces on a blank sheet so that the milestones which have a close

connection lie close to each other. Consider what kind of relationship exists between

the different milestones.

The following advices my help you:

The relation between two terms can be that …

… one term is an example of the other term (i.e.: mimicry is an

example of natural selection)

… one term is part of the other term in the sense of a whole – part

relationship (i.e.: chromosomes contain genes)

… terms are superordinate or subordinate concepts (i.e. mutation

and selection are evolutionary factors)


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4.) If you are satisfied with the arrangement of the milestones and the relations between

them, glue the pieces of paper on the blank sheet.

5.) Now draw arrows between the terms.

6.) Describe the relationship above the arrows.


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The period of Neo-Darwinism (1883-1907)

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T h e d e v e l o p m e n t o f e v o l u t i o n a r y t h e o r y s i n c e D a r w i n – N e o - D a r w i n i s m


Fig. 1: The procedure of Weismann’s experiment. He repeated this experiment 19 times. The offspring of the subsequent matings provided the basis for the next experiment.

The period of Neo-Darwinism (1883-1907)




• go back in the text or

• read further or

• regard the figures carefully.


The term Neo-Darwinism was coined on the occasion of

the revolutionary findings of the scientist August

Weismann. In 1882, August Weismann declared that

there is no _____________________________________

____________________________________________.

August Weismann conducted a spectacular experiment

(see fig. 1), in order to test his hypothesis. He repeated

the experiment over several generations of mice.

In contrast, Charles Darwin believed in the idea, that

acquired traits can be inherited; an idea that was first

formulated by Jean-Baptiste de Lamarck around 1800.

But how did August Weismann explain the findings of

his experiments? He did further research. In 1885 he

discovered that germ line cells are separated from

somatic cells (body cells) very early in the embryonic

development. Accordingly, he postulated the division

between____________________________________.

But how did Weismann explain variability? He assumed _______________________ during

the sexual reproduction to be the solution. He postulated maternal and paternal genetic

material is combined in the form of particles. Figure 2 shows a drawing by August Weismann.


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It illustrates how he imagined the process of inheritance. Today we know that the process of

inheritance is much more complicated. August Weismann had no knowledge of

chromosomes and crossing-over. However, the scientist recognized correctly, that sexual

reproduction is the cause of individual differences, which are the basis for natural selection.

Weismann’s assumption represented another breach with traditional concepts in 1886. In that

time many biologists believed that inheritance works like the coalescence of liquids.

According to this idea, sexual reproduction leads to the uniformity in a species, but not to

variability.

Fig. 2: Original drawing from August Weismann. He supposed that maternal and paternal parts will be inherited as solid particles. (Fig. from A. Weismann: ”Essays upon heredity“ Vol. I & II, 1889)


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Fig. 3: Evening primrose. De Vries reproduced the Mendelian experiments with this plant. (Thomé, 1885; Source: www.wikipedia.org)

The scientist Hugo de Vries rediscovered Mendel’s laws

around 1900 and popularized them. Thereby he became the

founder of genetics. He reproduced the Mendelian

experiments with the evening primrose (fig. 3) and explained

the appearance of new variants after crossbreeding with the

theory of ______________________. De Vries felt confident

that his discovery of spontaneously occurring modifications in

the genetic material – and not natural selection – explained

the change of species. The next years Charles Darwin’s theory

of natural selection receded into the background, while Hugo

de Vries’ theory was mistaken to be the main mechanism of

evolution. Later it became apparent that mutations cannot

completely account for evolutionary the change in species,

but additional evolutionary mechanisms have to take effect, i.e. natural selection.

In 1896, Henri Becquerel discovered radioactivity. This

discovery enabled Marie and Pierre Curie in 1902 to determine

geological time spans just like using a clock. In 1906 it was

possible for the first time to determine the approximate age of

the earth by radioactive measurements. They calculated that the

earth is _____________________ years old. This finding

surprised many scientists, because most of them estimated the

age of the earth to be at the most a few thousand years, whereas

Charles Darwins assumptions, however, were confirmed. He

would have been very happy about this insight.

Fig. 4:Our globe. (© Paul Schubert, earthe_01, CC-Lizenz (BY 2.0) http://creativecommons.org/licenses/by/2.0/de/deed.de; Source: www.piqs.de )



http://creativecommons.org/licenses/by/2.0/de/deed.de�

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a) Describe the process of August Weismann’s experiment with mice. What was the

finding of his experiment?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b) How does August Weismann explain this result?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

c) What causes variability according to the hypothesis August Weismann’ formed in

1886? What fact was he not aware of in this time? Discuss the misconceptions of

Weismann and explain his misunderstandings about the mechanism of inheritance.

Think of meiosis!

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

d) Why was Hugo de Vries mistaken when he supposed that mutations are solely

responsible for the development of new species?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

e) Why would Charles Darwin – if he would have been alive at that time – have been

very happy about the discovery in 1906? (If you cannot find the solution yet, ask the

expert of Darwinism later in the home group.)

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________


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the period of Neo-Darwinism.









possible.









example of natural selection).


relationship (i.e.: chromosomes contain genes).


and selection are evolutionary factors).


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The period of Neo-Darwinism and Population

Genetics (1908-1930)

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T h e d e v e l o p m e n t o f e v o l u t i o n a r y t h e o r y s i n c e D a r w i n – P o p u l a t i o n G e n e t i c s


The period of Neo-Darwinism and Population Genetics

(1908-1930)







In the early 20th century, the integration of Mendelism and Darwinism started. The

rediscovery of Mendel’s laws around 1900 displaced the theory of natural selection by

Charles Darwin. In 1908, Godfrey H. Hardy and Wilhelm R. Weinberg established the

basis for this important integration of theories independent of each other.

In 1908, Hardy attended a conference, at which the frequency of recessive characters was

discussed. The scientist Yule stated that recessive factors (today better known as alleles) will

disappear in the course of a few generations even if natural selection is absent because

dominant factors (alleles) will establish themselves at any rate. Hardy disagreed with Yule’s

statement, but he was not able to disprove it. He was quite unhappy about this. In the same

year, he managed to develop a mathematical formula (see fig. 1). It says that allele

frequencies in “ideal populations”, which means in the absence of factors like selection or

mutation, will remain constant by means of random recombination (see example in fig. 1).

This principle was later called the ______________________________distribution.


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Fig. 1: Example of use for the formula of Hardy and Weinberg.

p² + 2pq + q² = 1

frequency of frequency of frequency of genotype BB genotypes Bb and bB genotype bb


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Fig. 2: Drosophila with red eyes. (© André Karwath, CC-Lizenz (BY 2.0) http://creativecommons.org/licenses/by/2.0/de/deed.de; Source: www.wikipedia.de )

Two years later, Thomas H. Morgan and his team studied the

inheritance of white eyes in Drosophila (fig. 2). The team discovered

that ________________________ are responsible for the inheritance.

But soon a problem occurred: there were more character states than

chromosomes. Thomas H. Morgan did further research and succeeded in

solving the problem. The solution consisted in

____________________________. Thomas Morgan had to define

them exactly because until then they were simply known as “units of

heredity”.

In 1928, the scientist Frederick Griffith investigated the bacterium Streptococcus

pneumoniae, which causes pneumonia in mammals. He worked with two different strains.

The so-called S-strain (S means smooth) of the bacterium Streptococcus pneumoniae is

characterized by a mucic capsule, which surrounds two connected cells. The other so-called

R-strain (R means rough) has no mucic capsule. Griffith was surprised that he was able to

obtain living pathogenic cells from the dead mice in experiment 4. The mice had obtained a

mixture of pathogenic cells killed by using heat and living harmless cells (fig. 3). Griffith

concluded that some chemical substance from the pathogenic cells had changed (transformed)

the harmless cells. Thus, Griffith discovered the phenomenon of _______________________.

Fig. 3: Frederick Griffith’s experiment. He drew his conclusions from experiment 4.




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Sixteen years later, in the year 1944, Oswald T. Avery continued the experiment from

Griffith. Avery succeeded in identifying the mysterious chemical substance, which

transformed the harmless cells into pathogenic cells in the 4th experiment. He discovered the

mysterious molecule responsible for inheritance: ___________. He made this discovery by

relating his experiments to already existing findings of Frederick Griffith.

Fig. 4: The experiment from Oswald T. Avery. He related his experiments to the findings of Frederick Griffith from the year 1928.


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a) Imagine you are Godfrey Hardy and would like to persuade scientists like Yule that

recessive and dominant alleles alone do not trigger evolution. Interpret figure 1 in

order to support your argumentation.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b) How did Thomas H. Morgan solve the problem that there are more character states

than chromosomes?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

c) Describe Frederick Griffith’s experiments. What happened in experiment 4 (fig. 3) so

that the R-cells killed the mice?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

d) Using figure 4, explain, how Oswald T. Avery discovered the mysterious molecule of

inheritance.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________


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the period of population genetics.




Darwinism starts. For each milestone-card the expert explains, which person arrived at which





possible.















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The period of Evolutionary Synthesis

(1930-1950)

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T h e d e v e l o p m e n t o f e v o l u t i o n a r y t h e o r y s i n c e D a r w i n – E v o l u t i o n a r y S y n t h e s i s


Fig. 1: The fan-out of a peacock. (© Josi, Pfau, CC-Lizenz (BY 2.0) http://creativecommons.org/licenses/by/2.0/de/deed.de; Source: www.piqs.de )

The period of Evolutionary Synthesis (1930-1950)





• …read further or

• …regard the figures carefully.


Six prominent scientists, Theodosius G. Dobzhansky, Ernst Mayr, George Simpson,

Julian S. Huxley, Bernhard Rensch and George L. Stebbins, have been particularly

involved in further developing evolutionary theory. Their findings have been united in the

period of evolutionary synthesis (Synthesis = combination).

In the beginning of this time period, Ronald A. Fisher focused on sexual selection. Whereas

Charles Darwin was able to observe sexual selection only,

Fisher was now able to explain this evolutionary factor. He

revealed that both the female trait ’preference‘ and the male

trait ’ornament‘, i.e. the peacock’s tail, are coded genetically.

Based on this assumption, he proposed the

_________________-process. This hypothesis describes that

male ornaments become bigger and/or more conspicuous by

an automatism.

The genes for the female trait ‘preference’ and the genes for the male trait ‘ornament’ are

genetically associated, because females with a ‘preference’ for conspicuous ornaments mate

with appropriate males and therefore the offspring bears both traits. Furthermore, he

explained that once a male trait becomes too big and/or conspicuous, it will be restrained by

other selection processes (i.e. increased conspicuousness for predators, increased

susceptibility to disease). Fishers’ hypothesis on the runaway-process is able to account for

the evolution of ornaments which are bigger and/or more conspicuous than required in the

attempt to survive.



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Fig. 3: Processes of anagenesis and cladogenesis.

Another important component of evolutionary biology was Ernst Mayrs’ definition of the

biological__________________________ in 1942. Ernst Mayr was not the first scientist who

dealt with this issue. However, in contrast to the morphological species concept, he

emphasized the common gene pool (total number of all genes in a population) and the

reproductive isolation of a species (fig. 2).

Charles Darwin, the prime father of the evolutionary theory, used the term species but never

defined it.

In 1947, Bernhard Rensch studied the origin of new species (speciation). He differentiated

two processes (fig. 3): the evolutionary change of various characteristics in each descendant

(____________________) und the branching of a lineage into two or more descendant lines

(____________________). Rensch came to this conclusion due to the discovery of fossils,

which document these two processes of evolution. Furthermore the scientist explained the

branching of two species by the mechanism of geographical isolation. This evolutionary

mechanism cannot be attributed to

mutation, recombination and

selection and was first described by

Ernst Mayr. Charles Darwin also

considered geographical isolation to

be a mechanism of speciation, but

rejected this idea later. Today,

additional mechanisms of speciation

have been described by researchers.

Fig. 2: Very similar but still different: Willow Warbler (left; © Jörg Kretzschmar, 2009) and Chiffchaff (right; ©א,

2008, CC-Lizenz (BY 2.5) http://creativecommons.org/licenses/by/2.5/de/deed.de; Source: www.wikipedia.de)



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The mechanism of ____________________________ was first described by Sewall Wright

in 1931 and was integrated into evolutionary theory in 1950. Wright’s discovery is also

named Sewall-Wright-effect and characterizes the random fluctuation in the frequency of

alleles. Therefore, the Sewall-Wright-effect is an evolutionary factor, which is independent of

natural selection. The process described by Wright is especially important for small

populations, where random changes in the frequency of alleles have serious influence.

In the middle of the 20th century the contributions of the aforementioned scientists were

integrated in _____________________________. This great theory combines classical

Darwinism and modern findings of genetics, population genetics and systematics. Genetic

drift, moreover, was identified as an additional evolutionary factor.

According to evolutionary synthesis, mutation and recombination constantly cause genetic

variations, whereas selection and genetic drift constrain these. The geneticist Theodosius

Dobzhansky declared in these days: “Nothing in biology makes sense except in the light of

evolution.”


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a) Ronald A. Fisher explained that a male ornament trait, which becomes too

“expensive”, will be constrained by other selection processes. Which costs has a

peacock to bear in his natural environment due to his ornate train?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b) Do organisms, which look externally similar, necessarily belong to the same species,

according to Ernst Mayr’s biological species concept?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

c) Why is the evolutionary factor discovered by Sewall Wright independent of natural

selection?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

d) Explain the citation of Theodosius Dobzhansky using the example of sexual

dimorphism.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________


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the period of the evolutionary synthesis (just the two discoveries from Bernhard Rensch have

to be noted on one card!).









possible.















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The period of the Enhanced Evolutionary Eynthesis (from 1950) (Part 1)

1 T h e d e v e l o p m e n t o f e v o l u t i o n a r y t h e o r y s i n c e D a r w i n – E n h a n c e d E v o l u t i o n a r y S y n t h e s i s 1


Fig. 3: Structure of DNA. (Courtesy of Apers0n; Source: www.wikipedia.org)

Fig. 1: Homologous structures: Front limbs of salamander, turtle, crocodile, bird, bat, whale, mole, human (from left to right). (Wilhelm Leche, 1909; www.wikipedia.org)

The period of the Enhanced Evolutionary Synthesis (from 1950)

(Part 1)




• go back in the text or

• read further.


The zoologist and marine biologist Adolf Remane

established in 1952 the three main

_________________________________________. They

are a practical tool for research on phylogenetic

relationships because they enable the researcher to

differentiate between homologous and analogous traits.

Homologies can be used to make inferences about kinship

(fig. 1).

One year later James Watson and Francis Crick

succeeded in clarifying the structure of DNA. At that

time, the molecular components were already known.

The discovery of the structure of DNA was possible

due to the method of X-ray crystallography. Francis

Crick was already familiar with this technique

because he had investigated protein structures this

way. Crick introduced Watson to X-ray

crystallography after Watson persuaded him that it is a worthy method for

analysing the structure of DNA. A photograph of crystalline DNA

Fig. 2: X-ray photograph of DNA. (Courtesy of the National Institute of Health; Source: www.wikipedia.org)




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triggered an important insight (fig. 2). The photo was a result of the research of the X-ray

expert Rosalind Franklin, who started her work in 1951 at the same college as Watson and

Crick. From the photo, Watson concluded that the shape of a DNA molecule is a

_________________________ (fig. 3). The researcher had seen X-ray photos of other helical

molecules before. Subsequently, Watson and Crick reconstructed the exact plan of a DNA

molecule with the aid of handmade wire models and finally published the DNA structure in

1953.

Linus Pauling and Emile Zuckerkandl first postulated the

concept of the ________________________________ in 1961.

The discovery displays a measuring tool for estimating

evolutionary distances. The basis for this concept is the

following correlation: The longer two systematic entities are

separated, the bigger is the number of differences in nucleotides

and changes in amino acids. The molecular clock corresponds

with mutation rates of single genes or with differences between

sequences in single proteins. This technique cannot be applied

in every case, because not all genes or proteins possess a reliable average evolutionary rate.

Therefore this method is hardly ever exact. The clock can be adjusted by the fossil record and

enables the researcher to estimate e.g. at which time a specific speciation event took place.

Even insights from geology played an important role for developing evolutionary theory

further. In 1962, geology was revolutionized by the theory of

______________________________. The theory comprised the movement of plate tectonics

and the forces which affect it. Furthermore, the theory explains the distribution of volcanoes,

earthquakes, mountains, rock formations and the structures of the sea floor. The formation of

these large-scale geological structures can be accounted for by the movement of the tectonic

plates. As early as 1915, Alfred Wegener postulated the theory of continental drift based on

his observation that the continents surrounding the Atlantic fit together like a puzzle. His

theory was not accepted at that time because his assumptions on the driving force of plate

tectonics proved wrong. Wegener hypothesized the tidal forces of the moon and the sun to

cause this movement.

Fig. 4: An illustration of the discovery from Pauling and Zuckerkandl. (Courtesy of Apers0n and Trojan respectively; Source: www.wikipedia.org)





Fig. 5: Convection. A comparison. (The numbering belongs to exercise 2c).

In 1962, Harry Hess and Robert Dietz found a plausible explanation for the driving force of

plate tectonics, which is still accepted today. Hess and Dietz realized that convection (lat.

convehere = to convey) in the mantle of the earth can passively pull and push the continents

(see fig. 5).

Another problem in evolutionary biology was the

explanation of altruistic (unselfish) behavior. Already

in the 19th century Charles Darwin, the father of

evolutionary theory, described leaving (direct)

offspring as the highest aim in life for each

individual. But he would not have been able to

explain, why Belding’s Ground Squirrels take a high

risk of dying, when they warn other members of their

species against predators. The animals utter a shrill

warning cry, which does not only inform other

members of their species about danger but also

informs predators about the position of the alerter. Today it is known that the animals only

risk their life when they are surrounded by closely related members of their species. For the

relatives the chance of survival is increased enormously by the warning cry.

Fig. 6: A Ground Squirrel watches for predators. (© Ute Steinbrecher, Wachposten, CC-Lizenz (BY 2.0) http://creativecommons.org/licenses/by/2.0/de/deed.de; Source: www.piqs.de )





The behavior of Belding’s Ground Squirrel can be explained by the so-called kin selection. In

1964, William Hamilton developed a formula in order to predict under which circumstances

unselfish behavior occurs. The basis for the formula and therefore the cause for altruistic

behavior were already known in 1964: unselfish behavior depends on the degree of

relationship. If the degree of relationship is known, it is possible to decide, if

_______________________________ exists or not, due to the Hamilton-formula. Kin

selection is a kind of natural selection because it increases the likelihood of passing on one’s

genes (contains in the close relatives) to the next generation.

Two years later, the zoologist Willi Hennig elaborated on the principle of

_______________________________________, he had first described in 1950. This

principle represents an application of Darwin’s theory of common descent to the discipline of

systematics. Willi Hennig defined systematic groups as groups of organisms which share a

common ancestor as well as all descendants of this ancestor. In contrast to this, classical

systematics before Hennig often described groups, which did not comprise all descendants of

a common ancestor (see fig. 7).

Fig. 7: A cladogram.







a) Read up on the criteria of homology by Adolf Remane and give one example for each.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b) Specify the components of a DNA molecule.

_____________________________________________________________________

_____________________________________________________________________

c) Explain the meaning of convection flow. Thereto, cut the pieces of the sentences on

the page 8 and arrange them so that they are in accordance with the numbers in figure

5.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

d) Explain why altruistic behavior is finally selfish.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

e) Explain by means of figure 7, why reptiles do not exist as a systematic group in

phylogenetic systematics.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________







the period of the enhanced evolutionary synthesis (part 1).









possible.

















Hot material moves upward from the

mantel of the earth …

… heats up and moves

upward again.

Through convection water moves from the bottom to

the surface …

Where tectonic plates converge the cooler plate will submerge under the

upper one...

…and leads to the origin and separation of tectonic plates.

… cools down, moves sideward and sinks

down…

… and submerge in the mantle of the earth, where it melts and the hot melted

material moves upward again.


The period of the Enhanced Evolutionary Synthesis (from 1950) (Part 2)

1

T h e d e v e l o p m e n t o f e v o l u t i o n a r y t h e o r y s i n c e D a r w i n – E n h a n c e d E v o l u t i o n a r y S y n t h e s i s 2


The period of the Enhanced Evolutionary Synthesis (from 1950)

(Part 2)







In the 1960s, the Japanese scientist Motoo Kimura investigated the degree of genetic

variance in natural populations. He critically looked at the common assumption that

mutations are either disadvantageous or advantageous because it contradicts the possibility of

a great number of variations. Kimura applied a method, which enabled him to investigate the

variance between individuals on the level of proteins. It turned out that the amino acid

sequences of proteins in one population differed more often than previously assumed. Thus,

Kimura concluded that most changes in the DNA do not have any influence on the survival

and the reproduction rate of an organism. In other words, Kimura found out that most

mutations are neutral. In 1968, he published his theory of ___________________evolution.

This discovery did not contradict to the concept of natural selection, but rather added to

existing evolutionary concepts. Not every mutation leads to phenotypical changes, which are

subject to selection.

Although Watson and Crick had analyzed the structure of DNA in the 1950s, it remained

unclear, how this structure encodes information. Theoretical considerations suggested that

three nucleotides contribute the information for one amino acid. Marshall Nirenberg and

Heinrich Matthaei first succeeded in 1961 in synthesizing triplets (consisting of three

nucleotides) outside a cell. They found out that RNA-triplets consisting of Uracil-nucleotides

encode the amino acid phenylalanine. Soon they were able to synthesize RNA-triplets with

nucleotide sequences in any combination.


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Fig. 1: Illustration of the preparation. A total of 20 test-tubes are filled with the defined components. Each test-tube contains another radioactive labeled amino acid.

Fig. 2: The course of the test runs by Marshall and Nirenberg using the example of the triplet UUG. Two from a total of 20 experiments are illustrated (see arrow). The content of each test-tube will be filtered.

The following figures illustrate an experiment for

identifying the amino acid which is encoded by the

triplet UUG. The preparation for the experiment is

shown in figure 1. Then, 20 test-tubes are filled

with defined components, with each test-tube

containing different radioactively labeled amino

acids. The test-tubes are left standing some time,

so that the UUG-triplets can attach to the

corresponding amino acid and to the ribosome.

Afterwards, the main test run starts, composed of a

maximum of 20 experiments (see figure 2).

Next, the contents of each test-tube are filtered.

The special filter retains only the ribosome and the

attached components. Then, analyses of all 20 test-tubes reveal, in which test-tube

radioactively labeled amino acid are retained.


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Fig. 3: The theory of endosymbiosis.

Nearly at the same time the scientist Har Gobind Khorana succeeded in synthesizing longer

RNA-fragments outside the cell. Thus, the three scientists gained further insights into the

nature of the codons. Thus the whole ________________________________ could be

decoded in 1966.

The genetecist Lynn Margulis rediscovered the ________________________________ in

1970. The theory was originally formulated by the Russian Merezhkowsky, who published it

in 1910 without attracting further interest. The theory of endosymbiosis explains that

chloroplasts and mitochondria of the eukaryotes are descendants from freely living

prokaryotes, which entered the host cells through endosymbiosis at some point in the course

of evolution.


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In 1977, Frederick Sanger developed the method of

__________________________________. This method enabled researchers to determine the

nucleotide sequence of a DNA molecule. The result is the sequence of the DNA strand which

is complementary to the template.

The basis of this method is the random assembly of a modified nucleotide (ddATP, ddCTP,

ddTTP or ddGTP) during DNA-replication. It provokes the termination of the synthesis of the

amplified strand, because the 3’-OH-end for the attachment of the next nucleotide is lacking.

This results in many DNA fragments of different length, which can be separated by size

through gel electrophoresis. Radioactive bands can be made visible (fig. 4) through

autoradiography.

Fig. 4: The method of DNA sequencing according to Frederick Sanger.


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Fig. 5: A Drosophila wild type B Drosophila mutant, bearing two instead of one pair of wings. © Markus Tögel, Werner Mangerich, Prof. Dr. Achim Paululat (University of Osnabrück), 2010

A B

Another important step in the further development of evolutionary theory was the integration

of the developmental biology, which deals with the development from the zygote to the

complete organism. In 1980, the scientists Edward Lewis, Eric Wieschaus and Christiane

Nüsslein-Volhard discovered the so called homeotic genes, which control embryonic

development. These genes determine where, when and how specific segments of the body,

like e.g. eyes or extremities, develop in an organism. Edward Lewis found the first of these

genes when he investigated a Drosophila mutant bearing two instead of one pair of wings

(fig. 5). Meanwhile, ________________________________ have been found in many

different species. It became clear that particular nucleotide sequences (so-called

‘homeoboxes’) of these genes are identical or very similar in many species.

In 1982, John Maynard Smith made another important contribution. He applied the game

theory, commonly used in economics, in order to explain behavioral patterns from an

evolutionary perspective. Often, it can be observed that individuals of a species use different

behavioral strategies in identical contexts. The game theory allows for predicting, when

alternative behavioral strategies can exist in parallel and when one strategy displaces the

other. Strategies, which stand up to alternative behavioral strategies and resist change, are

called ________________________________ (ESS). By means of applying game theory and

identifying evolutionary stable strategies it was possible to explain behavioral strategies,

which had hitherto been unable to explain from the perspective of individual selection alone.


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a) Because of the nature of the genetic code some point mutations do not result in a

different gene product. Use the codon table to find out, at which positions of a

nucleotide triplet neutral mutations can occur! Give an example.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

b) Which amino acid is encoded by the triplet UUG? How did Nirenberg and Matthaei

discover this? Explain how the experiment was conducted with the aid of the text and

the figures.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

c) Use figure 3 to explain, how the theory of endsymbiosis explains the formation of

cells with mitochondria and chloroplasts.

_____________________________________________________________________

_____________________________________________________________________

____________________________________________________________________

_____________________________________________________________________

d) Use the example of the fly with two pairs of wings in order to explain the function of

homeotic genes.

_____________________________________________________________________

_____________________________________________________________________

____________________________________________________________________


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the period of the enhanced evolutionary synthesis (part 2).









possible.















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the period of darwinism (1859-1882)€¦ · the development of evolutionary theory since darwin –...

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