Important words and concepts from Chapter 22,
Campbell & Reece, 2002 (3/25/2005):
by Stephen T. Abedon (abedon.1@osu.edu)
for Biology 113 at the Ohio State University
|
|
Course-external links are
in brackets Click [index] to access site index Click here to
access text’s website Vocabulary
words
are found below |
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IT CANNOT BE STATED TOO
STRONGLY THAT THE SIMPLEST THING THAT YOU CAN DO TO BETTER UNDERSTAND THE MATERIAL
PRESENTED IN THIS COURSE IS TO READ YOUR TEXTBOOK
IT ALSO CANNOT BE STATED TOO
STRONGLY THAT YOU WILL BE HELD RESPONSIBLE PRIMARILY FOR THESE NOTES ON EXAMS
THE ABOVE IS NOT A
CONTRADICTION—EXCELLENCE IS NOT ACHIEVED THROUGH A MINIMIZING EFFORT
SUCCESS IN BIOLOGY REQUIRES
MAXIMAL DEDICATION—DEDICATED STUDENTS READ THEIR TEXT BOOKS!!!!
|
The material we will
cover in Biology 114 is very much different from that covered in Biology 113,
particularly in terms of the perspective and approach of those who engage in
these difference aspects of biology. It is almost as though biology consists
of two very different sciences, a reductionist science that seeks to emulate
chemistry or physics (113), and a much more philosophical science that is
interested as much in the subtleties of history as it is in rigors of the
more exact physical sciences (114). This is not to say that we will not be
learning real science in Biology 114, but instead that the general approach
of learning that we will employ in Biology 114 will be different from that of
Biology 113. In Biology 113, basically, you sought to understand how a cell
works. Here we will deal with such squishy topics as why it is the cells that
we observe exist at all. Keep an open mind and study hard. By the end of this
term you will have gained an appreciation of the most important concept in
Biology: Darwinian evolution. |
(1)
Chapter title: Descent with Modification: A Darwinian View of Life
(a)
(i)
Get a feel for what it means for two organisms to be evolutionarily
related
(ii)
What do you think that means?
(b)
"The process of evolution
can be summarized in three sentences: Genes mutate. [gene: a hereditary unit]
Individuals are selected. Populations evolve." (Talk.Origins)
(c)
"Evolution refers to the processes that have transformed life on
Earth from its earliest forms to the vast diversity that characterizes it
today.
(d)
“Darwinism remains one of the most successful scientific theories ever
promulgated. There is hardly an element of humanity – not capitalism, not
gender relations, certainly not biology – that can be fully understood without
its help.” (Anonymous, Iconoclast of the Century. Charles Darwin (1809-1882) Time December 31, 1999, p. 186)
(e)
["Evolution is the
cornerstone of modern biology. It unites all the fields of biology under one
theoretical umbrella. It is not a difficult concept, but very few people -- the
majority of biologists included -- have a satisfactory grasp of it…
Misunderstandings about evolution are damaging to the study of evolution and
biology as a whole. People who have a general interest in science are likely to
dismiss evolution as a soft science after absorbing the pop science nonsense
that abounds. The impression of it being a soft science is reinforced when
biologists in unrelated fields speculate publicly about evolution."
(Talk.Origins)]
(f)
[“Mutation is a random process, and random processes do not, at least
on their own, generate complexity. Natural selection, however, is not a random
process. It is an ordering process, creating structure from noise and
increasing the degree of regularity in the biological system. Since complexity
is simply the length of a concise description of all the regularities in such a
system, natural selection, in conjunction with random mutation, can tend to
increase in complexity… The achievement of Darwinism is not that it explains
the origins of information, but that is explains the origins of complexity. And
it does so in terms of a completely natural process: random mutation
followed by non-random selection. Via such a process, the simple can
give rise to the complex: ‘from so simple a beginning endless forms most
beautiful and most wonderful have been, and are being, evolved’ (
(g)
[“Darwinian thinking is not confined to biology; it anchors a
naturalistic understanding of all complex order, even including our own
intelligence. Hence today, Darwinism is central to a thoroughly naturalistic
picture of the world.” Taner Edis (2001).
(h)
External links: [index]
(i)
[descent with modification: a
Darwinian view of life, Darwinism, evolutionary biology,
descent with modification
(Google Search)]
(ii)
[Teaching About Evolution and
the Nature of Science (National Academy Press)]
(iii)
[biology and evolutionary
theory (Talk.Origins)]
(iv)
[introduction to evolutionary
biology (Talk.Origins)]
(a)
(b)
Evolution, in its most general sense, is simply successive
change that occurs over time
(c)
In biology this change, ultimately, is that which occurs
within the collective genotypes found within a population of organisms
(d)
We observe this change as a change in the collective
phenotypes associated with a population of organisms
(e)
These changes can represent a change in the proportions of
existing variation within a population (due to natural selection, genetic
drift, or migration)
(f)
Or these changes can represent the introduction of new
variation into a population (mutation, migration, recombination)
(g)
For the most part, evolution is overall a destabilizing
process unless some mechanism exists whereby destabilizing influences are discarded;
that stabilizing influence, in biological systems, we call natural selection
(h)
[evolution (417,000
hits on April 1, 2000!) (Google Search)] [evolution is a fact and a
theory (Talk.Origins)] [evidence for evolution: an eclectic
survey (Talk.Origins)] [index]
DARWINISM
(3)
(a)
(b)
[Charles Darwin (Google Search)] [index]
(4)
The Darwinian “Controversy”
(a)
Darwinism is, of course, just about the most controversial subject
among non-biologists short of abortion, easy sex, and the morality of President
Clinton Bush
(i)
(one should, of course, qualify the above statement by noting that
these observations apply to the good ol’ enlightened U.S.A. while the rest of
the world finds threats of apoplectic extinction due to environmental
degradation or in the course of a hot war a tad more troubling than these other
issues, including any so-called controversy over the validity of Darwinian
evolution)
(ii)
I note this for the sake of
warning you about the lack of evolutionary sophistication presented by the
popular media, particularly in the
(iii)
If you’re into anti-intellectualism, you’re gonna love
anti-evolutionism
(b)
[“Scientists such as myself
must share the blame for the lack of public understanding of science. We need
to work harder to convey the correct information. Sometimes we don't succeed
very well but that does not mean that we are dishonest. On the other hand, the
general public, and creationists in particular, need to also work a little
harder in order to understand science. Reading a textbook would help.” (What is Evolution?)
(Talk.Origins)]
(c)
[Darwinism and God (Google Search)] [index]
(5) Darwinism encompasses two ideas, one explaining the other
(a)
(b)
Darwinism encompasses two distinct ideas
(i)
The origin of biological diversity via evolution
(ii)
The mechanisms of evolutionary change (specifically via Natural Selection)
(c)
By far and away, the majority of evidence for Darwinism supports the
former assertion (the existence of evolution, i.e., the origin of biological
diversity via evolution); an assertion which, in fact, predates Darwin
(d)
The latter tenet (ii) is less well-supported than the former (i), but
nevertheless is sufficiently robustly supported to be considered a scientific theory---a hypothesis that explains broad arrays of
data with exceptional clarity
(e)
[origin of biological diversity,
evolution and "scientific
theory" (Google Search)] [index]
(6) Darwinism as the foundation of biology
(a)
(b)
Any time you generalize from one organism to another (e.g., from a fetal
pig to a human) you are assuming evolutionary relationships
(c)
Any time you speculate on the function of a biological structure, you
are speculating on natural selection (otherwise you would
have to assume lack of function, in which case you would not be able to
speculate on function)
(d)
It is difficult to imagine biology as a coherent discipline absent
Darwinism and, in fact, biology did not exist as a coherent discipline prior to
the advent of Darwinism
(e)
[Darwinism as the foundation of
biology (Google Search)] [what is Darwinism?
(Talk.Origins)] [index]
HISTORY OF DARWINISM (AND
EVOLUTIONARY THINKING)
(7) Darwinism's
historical context (Origin of Species)
(a)
The advent of Darwinism is
typically traced to 1859, the year of the publication of Charles Darwin's The Origin of Species
(i)
(the full title of this text, by the way, is On the Origin of Species by Means of Natural Selection, or The
Preservation of Favored Races in the Struggle for Life)
(b)
What Darwin did in this text is essentially to synthesize (i) the
then-current understanding of geology, the diversity of life, and the
domestication of plants and animals, with (ii) the contention of Malthus that populations
are limited in size by external factors (e.g., food supply)
(c)
The roots of Darwinism are found
in many individuals. We will limit our discussion to the contributions of
(ii)
Lyell
(iv)
Malthus
(v)
Wallace
|
A Brief
History of Evolutionary Thought – Supplemental Table |
||
|
Person |
Dates |
Concept |
|
Aristotle |
384-322
B.C.E. |
Scala
Naturae
|
|
|
|
Natural
Theology |
Carolus Linnaeus |
1707-1778 |
Taxonomy
(biology) |
|
Georges
Cuvier |
1769-1832 |
Catastrophism
(geology) |
|
James
Hutton |
1729-1797 |
Gradualism
(geology) |
|
Charles
Lyell |
1797-1875 |
Uniformitarianism
(geology) |
|
Jean
Baptiste Lamarck |
1744-1829 |
Adaptation
(biology) |
|
Thomas
Malthus |
1766-1834 |
Limits
(economics/biology) |
|
Charles
Darwin |
1809-1882 |
Natural
Selection (biology) |
|
Alfred
Russel Wallace |
1823-1913 |
Natural
Selection (biology) |
(d)
Generally, it is worth noting that
(e)
See Figure 22.1, The
historical context of
(f)
However, "The Origin of
Species convinced most biologists that species are
products of evolution, but
(i)
The popularity of this latter aspect of
(ii)
In
(g)
[darwinism history (Google Search)] [The Origin of Species
(full text of first edition) (Talk.Origins)] [Darwin's precursors and
influences (Talk.Origins)] [index]
(8)
(a)
Carolus Linnaeus was the developer of the science of taxonomy
(b)
He was the inventor of binomial nomenclature
(e.g., Escherichia coli) and higher
taxonomic descriptors
(c)
He was a grouper of organisms according to phenotypic resemblance (recall that evolution is
typically observed in populations as differences in or changes in phenotypic
resemblance)
(d)
Linnaeus essentially defined modern biological diversity according to
phenotypic relationships
(e)
Linnaeus was not an evolutionist
(f)
However, the explanation that phenotypic relationships exist due to
evolutionary (i.e., "blood") relationships is one of the triumphs of Darwinism
(i)
(this, by the way, is the answer to the question I posed at the top of
this page: Get a feel for what it means for two organisms to be
evolutionarily related. What do you think that means? It means that two
organisms are related by blood, just as you are related by blood to your
parents and siblings or, more distantly, to your first, second, third, etc.
cousins)
(g)
For example, Linnaeus' system would group the various species of dogs into a higher taxonomic category
on the basis of shared phenotypic characteristics
(i)
[that taxon, by the way, is called family Canidae, the canines
(Google Search)]
(h)
Darwinism would argue that dogs share certain phenotypic
characteristics with each other but not with other groups of organisms (e.g.,
horses) due to a closer blood relationship between dogs than between dogs and other
organisms (again, such as horses)
(i)
“To
(i)
[lions and tigers are members of order Carnivora, family Felidae, the
cats (Google Search)]
(ii)
[horses are members of order Perissodactyla,
the odd-toed ungulates, family Equidae (Google Search)]
(j)
[Carolus Linnaeus (Google Search)] [popular groups on the tree
(The Tree of Life)] [index]
(9)
Lyell, Charles (1797-1875)
|
What we see around us
predominantly are those things that are most easily created, given existing
raw materials and processes, and those things that are sufficiently durable
that, once created, they hang around for a while. What we do not see are
things that are rarely created or very fragile. Thus, the world is populated
by relatively inert, readily created chemicals such as water, nitrogen gas,
and carbon dioxide; constantly created but highly reactive chemicals such as
molecular oxygen; rocks due to their durability and abundance; soil (or sand)
due to the propensity for rocks to be converted into smaller rocks; and the
products of both geological processes and natural selection. |
(a)
Lyell was a geologist
(b)
The arguments of Lyell employed by
(i)
Geological processes of the past resemble (in a physical sense) the
geological processes of today
(ii)
These processes would have to have been going on for a very long time
to result in the Earth we observe today
(c)
Thus, the surface of today's earth is the cumulative product of the
gradual expression of the same physical processes we observe today
(d)
See Figure 22.3, Formation
of sedimentary rock and deposition of fossils from different time periods
(e)
This is essentially Darwinism as applied to geology: Long time frames
with net loss of that which is most easily lost and retention of that which is least easily lost
(f)
This is neither the first nor the last time that geology and Darwinism have intercepted
(g)
[Charles Lyell, gradualism and geology,
uniformitarianism (Google Search)] [index]
(10)
Lamarck, Jean Baptiste (1744-1875)
(a)
Lamarckism is a forerunner of Darwinism
(b)
Lamarckism is very similar to Darwinism in terms of the first tenet of Darwinism,
the origin of biological diversity by means of evolution
(c)
Lamarckism, however, lacks the robust explanation for why evolutionary
change occurs that Darwinism employed (i.e., natural selection)
(d)
Note that this distinction is not terribly large: Lamarckism
essentially employed ideas of adaptation though failed to articulate
that evolutionary adaptation is derived from differential reproductive
success
(e)
Lamarckism is also known for its (now considered to be incorrect) idea
of acquired characteristics: That individuals can acquire characteristics
during their lives that they are then able to pass down to their offspring
(f)
Keep in mind in understanding Darwinism historically
that Darwinism and Lamarckism are not incompatible theories
(g)
Instead, it is Lamarckism and Mendelism that are incompatible, and Darwinism
was derived independent of knowledge of Mendelian genetics
(h)
Though Lamarck, for historical reasons, would not have understood it in
these terms, Lamarck's “inheritance of acquired characteristics idea” posits
essentially protein to DNA information flow; Mendelism, however, is consistent
only with DNA to DNA (or, more generally, nucleic acid to nucleic acid)
information flow along with the nucleic acid to RNA to protein flow of
transcription and translation
(i)
“Even though the Lamarckian theory of evolution is ridiculed by some
today because of its erroneous assumption that acquired characteristics are
inherited, in Lamarck’s time that concept of inheritance was generally accepted
(and, indeed, Darwin could offer no acceptable alternative)… In retrospect,
Lamarck deserves much credit for his theory, which was visionary in many
respects: in its claim that evolution is the best explanation for both the
fossil record and the current diversity of life, in its recognition of the
great age of Earth, and especially in its emphasis on adaptation to the environment as a primary product of evolution.”
(p. 417, Campbell et al., 1999)
(j)
["Biology came of age as a
science when Charles Darwin published "On the Origin of Species."
But, the idea of evolution wasn't new to Darwin. Lamarck published a theory of
evolution in 1809. Lamarck thought that species arose continually from
nonliving sources. These species were initially very primitive, but increased
in complexity over time due to some inherent tendency. This type of evolution
is called orthogenesis. Lamarck proposed that an organism's acclimation to the
environment could be passed on to its offspring. For example, he thought
proto-giraffes stretched their necks to reach higher twigs. This caused their
offspring to be born with longer necks. This proposed mechanism of evolution is
called the inheritance of acquired characteristics. Lamarck also believed
species never went extinct, although they may change into newer forms. All
three of these ideas are now known to be wrong." (Talk.Origins)]
(k)
[“In retrospect, Lamarck deserves much credit for his theory, which was
visionary in many respects: in its claim that evolution is the best explanation
for both the fossil record and the current diversity of life; in its
recognition of the great age of Earth; and especially in its emphasis on adaptation
to the environment as a primary product of evolution.” p. 431, Campbell
& Reece, 6th edition, 2002]
(l)
FAQ: 1. If populations adapt to their environment isn't it the same
as: they become better to fit such environment? Yes, though it could be
that better fit means better able to compete with their ancestral genotypes
rather than translating to an increase in stable population densities. 2.
why is the inheritance of acquired characteristics not true? What is the mechanism?
It would have to be phenotype impacting on genotype specifically so that
physiological or morphological adaptations translate into a genetic
perpetuation of, say, larger muscles on the children of blacksmiths. There just
isn't any sensible way that one could picture information moving about in that
manner. Confusingly, though, it clear that the ability of individual organisms
to adapt physiologically or morphologically to their environments is a product
of natural selection. Furthermore, it is clear that natural selection does
allow phenotype to influence genotype, particularly within populations and
across generations. But inheritance of acquired characteristics would be as
though changing one's hair color resulted in a change in the hair color of
one's offspring. Biological systems just don't work that way. 3. If the
individuals that have the proper trait for certain environment have more
chances to successfully reproduce than those who don’t have that trait, isn't
it the same as 2? Not quite. Only if the trait has an underlying genetic
basis such that possessors of the trait do possess that basis and
non-possessors don't. To a degree, both blacksmiths and non-blacksmiths have
the potential to have the same genetic potential to have well-muscled arms.
Therefore, even if there is selection for well-muscled arms, this does not
necessarily translate into a change in allele frequency (unless, of course,
that people genetically predisposed to having well-muscled arms tend to become
blacksmiths, but that would imply a priori genetic distinctions rather than
physiological adaptation resulting in genetic change). 4. In our notes it
says: at least some of the differences between individuals which impact
survival and fertility are heritable; isn't this the same as characteristics or
traits that are passed from parents to offspring? Yes. But note that not
all phenotypic differences are heritable. Phenotype is more than just a
consequence of underlying genotype.
(m)
[Jean Baptiste Lamarck,
Lamarckism (Google Search)] [index]
(11)
Wallace, Alfred (1823-1913)
(a)
Wallace independently derived Darwinism
(b)
Darwin's and Wallace's theories were first presented to the public more
or less simultaneously in 1858
(c)
Darwin's name is better recalled than Wallace's as a consequence of
Darwin's extremely robust support and further development of the theory
(besides, Darwin had and then sat on the idea long before Wallace derived his
very similar ideas)
(d)
[Alfred Russel Wallace
(Google Search)] [index]
(12)
Malthus, Thomas (1766-1834)
(a)
Malthus proposed the idea of limits on population growth
(b)
Essentially all populations
are capable of growing exponentially
to an infinite size but don't only because of environmental limits
(c)
These limits include such things as food supply, supply of fresh water,
supply of breathable air, etc.
(d)
Any species will eventually reach the limits of its
environment
and then stop growing in numbers
(e)
This implies that the intrinsic ability of organisms to grow typically
exceeds their observed rate of growth
(f)
In other words, in a world of limits, organisms typically either die before
their time or don't make as many babies as they otherwise may be genetically
capable of producing
(g)
[Note that there are a number of individuals around who claim that Malthus was wrong
and that, therefore, populations (particularly human) can continue to grow
because limits may always be overcome, given sufficient evolutionary or
cultural progress—don’t believe these zealots: they are radical non-biologists
who seek to screw, typically for personal gain, you and your descendants out of
an earthly future!]
(h)
[Thomas Malthus (Google Search)] [An Essay on the Principle of
Population (Mathus’ essay on population) (Ed Stephan)] [index]
SELECTION (AND DARWINISM
CONTINUED)
(13) Descent with
modification
(a)
(b)
Darwinism additionally argues that many of the changes that occur do so
for specific reasons; that is, modification over time is not necessarily
completely random
(c)
If we divide organisms into species, we can
follow the evolution of species through time such that multiple, related species collapse into individual ancestral species as we
go back in time (the ancestral dog, the ancestral horse, the ancestral ape,
etc.)
(d)
Ultimately, if we go back far enough in time, all living (i.e., extant) species may be collapsed into a single, universal ancestral species (which in all
likelihood was a bacterium)
(e)
Thus, the relationships between species may be visualized as a tree
which progressively branches with time, with the tree growing taller but more
and more diverse (bushier) with time
(f)
Typically branches end in extinction, but all living (i.e., extant)
organisms can trace their descent (ascent if we use the tree analogy) through
branches, none of which ended solely in extinction
(g)
Note, however, that: "Evolution is not
progress. Populations simply adapt to their current surroundings. They do not
necessarily become better in any absolute sense over time. A trait or strategy that
is successful at one time may be unsuccessful at another." (Talk.Origins)
(h)
[descent with modification
(Google Search)] [image: summary of evolution as
a process (blurry) (Evolution -- The Evidence)]
[index]
|
“What if you could travel in time and visit with |
(a)
"…frequently, people use
the word evolution when they really mean natural selection…" (Talk.Origins)
(b)
The non-random motivator of evolution we call natural selection
(c)
Natural selection simply is the idea that when organisms within
environmentally limited populations
die, or don't make as many babies as they otherwise could, they are dying or
not making babies non-randomly
(d)
Particularly, those organisms that are less able to survive or make
babies die at a faster rate or make fewer babies than those organisms that are
better able to survive and make babies
(i)
Note that the key word or phrase here is not “dying” but instead is
“making babies”
(ii)
Though we typically think of natural selection as a mechanisms of
selective death, in fact the sole reason that selective death impacts on the
evolution of populations is because dead organisms can’t make babies
(iii)
Don’t forget this idea; in biology it is the making of babies that is
everything and we survive only to maximize our reproductive output thereby
maximizing the representation of our alleles within our population
(e)
In other words, environmental limits cause a lack of population growth, but these limits impact on
individuals differently
(f)
Natural selection is another name for these differential impacts of
environmental limits
(g)
In addition, Darwinism employs the idea that at least some of the
differences between individuals, which impact their survival and fertility, are
heritable
(h)
Thus, limits dictate that some (typically many) will die (or will make
fewer babies) and genetic differences bias these deaths toward genotypes (a very key word) that are less hardy (or fertile)
in a given environment
(i)
Evolutionary change via natural selection: Darwinism
(i)
Populations are consequently modified over time as those genotypes less
capable of surviving or reproducing are culled from these environments (and the
alleles underlying these culled genotypes as a result decrease
in frequency)
(j)
"The environment (acts) upon the inherited variations manifest in
any population, favoring the survival and reproductive success of some
individuals over others. Natural
selection edits populations." (p. 409, Campbell, 1996; emphasis mine)
(k)
["natural selection"
and evolution (Google Search)] [index]
(a)
“The result of natural selection is evolutionary adaptation, a
prevalence of inherited characteristics that enhance organisms’ survival and
reproduction in specific environments.” (p. 428, Campbell & Reece, 2002)
(b)
(c)
Natural selection assures that populations
adapt to their environment
by culling those individuals who are phenotypically
less-well suited to surviving and reproducing in that environment
(d)
Thus, because many phenotypes reflect underlying genotypic differences, over time populations typically become
overall better at surviving and reproducing in a given, unchanging environment
(i.e., better adapted genotypes preferentially survive)
(e)
We describe this process as adaptation (in particular, evolutionary
adaptation)
(f)
We describe those heritable phenotypes
associated with increasing survival or reproductive potential as adaptations
(g)
Darwinism thus involves an adaptation by
populations to local environments via the process of natural selection
(h)
Nevertheless, keep in mind that "natural selection is situational:
What works best in one environmental context may be less suitable in some other
situation." (p. 409, Campbell, 1996)
(i)
“We must distinguish between adaptations an organism acquires by its
own actions, and inherited adaptations that evolve in a population over many
generations as a result of natural selection.” (p. 444, Campbell et al.,
1999); the former is physiological adaptation
or morphological adaptation while the latter is evolutionary adaptation and
only the latter involves changes in allele frequencies
(i)
(though note that this is confusing because the ability of an organism
to physiologically adapt is, in fact, itself a product of natural selection,
i.e., is itself an evolutionary adaptation—get it? if no, press here for further discussion of this concept)
(j)
["A trait's current
utility is not always indicative of its past utility. It can evolve for one
purpose, and be used later for another. A trait evolved for its current utility
is an adaptation; one that evolved for another utility is an exaptation. An
example of an exaptation is a penguin's wing. Penguins evolved from flying
ancestors; now they are flightless and use their wings for swimming."
(Talk.Origins)]
(k)
[adaptation and evolution
(Google Search)] [the evolution of improved fitness by random mutation
plus selection (The Talk.Origins)]
[index]
(a)
Selection may be somewhat “artificially” divided into two types
(ii)
Artificial selection
(b)
Natural selection is where environmental
limits are defined by nature
(c)
Artificial selection is where environmental limits are defined by man;
that is, artificial selection is selection imposed by man rather than by nature
(d)
Otherwise there exist no fundamental difference between the two
processes
(e)
Artificial selection is responsible for the phenotypic diversity and
change from ancestral, wild populations
observed in domesticated organisms
(f)
Note that in addition to purposefully applied artificial selection,
much domestication actually occurs via a process of natural selection inadvertently imposed by man, e.g.,
(i)
Guinea pigs sure look cute, but they also don't bite; a possible
explanation for the latter is because guinea pigs that bite became dinner at a
higher rate than guinea pigs that don't bite (yes, guinea pigs apparently were
initially domesticated as a source of food)
(ii)
Domestic animals (such as guinea pigs) tend to have huge litters,
presumably because man has eliminated many of the environmental limits that prevent wild populations from
raising large numbers of offspring simultaneously
(iii)
Again guinea pigs, they are not terribly good at escaping from
pens/cages, presumably because those that were good at escaping were lost from
the domesticated populations (i.e., the escapees took their escape-motivating
alleles with them)
(iv)
Etc.
(g)
See Figure 22.11, Artificial
selection
(h)
Thus, again, there exists no fundamental difference between natural
selection and artificial selection: both involve differential survival (or
reproductive success) based on genotypic differences,
between individuals, that impact on phenotypes; the
major difference is that when humans are attempting to modify a character via a
breeding program, that selection is termed artificial selection whereas all
other examples of selection are termed natural selection (though note that artificial
selection regimens also typically involve selective matings (i.e., non-random
mating), which explains in part why artificial selection appears to operate so
much more rapidly than natural selection)
(i)
[artificial selection,
domestication (Google Search)] [index]
(a)
Ernst Mayr has collected a series of observations and inferences that
he used to dissect Darwinism into component parts that summarizes many of our
above discussions:
(i)
Observation 1: high reproductive potential
(ii)
Observation 2: stable population sizes
(iii)
Observation 3: resource limits
(iv)
Inference 1: struggle for existence
(v)
Observation 4: variation within populations
(vi)
Observation 5: variation is heritable
(vii)
Inference 2: differential reproductive success
(viii)
Inference 3: evolution
(b)
See this dissection on page
420-421 (reproduced below and in outline above—you should understand this logic)
|
Logic of Darwinism (supplemental discussion) |
|
Observation 1
|
Populations
tend to have high reproductive
potentials |
|
Observation
2 |
Populations
tend to be stable in size |
|
Observation
3 |
Environments
tend to possess limited resources |
|
Inference
1 |
There
exists a struggle for existence |
|
Observation
4 |
There
exists phenotypic variation within
populations |
|
Observation
5 |
Some
phenotypic variation is heritable |
|
Inference
2 |
Within
populations there is differential
reproductive success that is influenced by phenotypic differences between
individuals |
|
Inference
3 |
Differential
reproductive success leads to a decline in frequency genotypes that underlie
phenotypes that are less fit to the environment and a corresponding increase
in frequency of genotypes that underlie phenotypes that are more fit to the
environment: Darwinian Evolution |
(c)
You should know and understand this dissection "of the logic of
(d)
“Summarizing
(i)
Natural selection is
differential success in reproduction (unequal ability of individuals to survive and
reproduce).
(ii)
Natural selection occurs
through an interaction between the environment and the variability inherent
among the individual organisms making up a population.
(iii)
The product of natural
selection is the adaptation of populations of organisms to their
environment.
(e)
Evolution by natural selection is
essentially an interplay of an organism’s genotype with an organism’s
environment whereby the product of this evolution is a phenotype that allows
the possessing organisms to more closely “fit” their environment such that
these organism’s reproductive success is greater than it would have been had
natural selection not been operating; this is essentially a feedback loop
between a population and its environment that is analogous (same idea,
different mechanism) as the feedback loops that we studied in Chapter
18 (i.e., operons)
(f)
[Ernst Mayr (Google Search)] [index]
EVIDENCE OF EVOLUTION AND
NATURAL SELECTION
(a)
"Scientists do not accept (Darwinism) solely on the face of its
logic but because it has been confirmed repeatedly by the hypothetico-deductive approach." (p.
409, Campbell, 1996)
(b)
Keep in mind as we walk through the evidence for Darwinism that some of
the evidence is for the idea of descent with modification (evolution) while other is evidence for the
occurrence of natural selection
(c)
Evidence for Darwinism may be subdivided into
(i)
Evidence for the occurrence of evolution in extant populations
(ii)
Evidence of the occurrence of natural selection in extant populations
(iii)
Evidence from biogeography
(iv)
Evidence from the fossil record
(v)
Evidence from comparative anatomy
(vi)
Evidence from comparative embryology
(vii)
Evidence from molecular biology
(viii)
Etc.
(d)
Keep in mind also that though much of this evidence is for the
existence of evolution rather than for the existence of natural selection;
still the typically most robust way to understand evolution is as mechanisms
driven to a considerable extent by the non-random processes of natural
selection (that is, to explain adaptation one must come up with some
explanation for non-random, particularly directed evolutionary change and
natural selection is by far and away the most plausible and robust explanation)
(e)
["Microevolution can be studied directly. Macroevolution
cannot. Macroevolution is studied by examining patterns in biological
populations and groups of related organisms and inferring process from pattern.
Given the observation of microevolution and the knowledge that the earth is
billions of years old -- macroevolution could be postulated. But this
extrapolation, in and of itself, does not provide a compelling explanation of
the patterns of biological diversity we see today. Evidence for macroevolution,
or common ancestry and modification with descent, comes from several other
fields of study. These include: comparative biochemical and genetic studies,
comparative developmental biology, patterns of biogeography, comparative
morphology and anatomy and the fossil record." (Talk.Origins)]
(f)
[Evidence Darwinism
(Google Search)] [index]
(a)
Evolutionary change is easily observed in extant (i.e., currently
existing) populations
as changes in genotypes that occur over time
(b)
The hard part is attributing that change to natural selection
(c)
Your text examines one such attempt on pp. 437-438 (Campbell &
Reece, 2002)
(d)
Other changes that are consistent with a natural selection cause
include:
(i)
The evolution of antibiotic-resistant bacteria
(ii)
The evolution of antiviral-resistant viruses
(iii)
The evolution of insecticide-resistant insects
(iv)
The evolution of toxin-resistant organisms (i.e., about toxic waste
dumps)
(v)
Industrial melanism (the evolution of darker moths in the face of
smoke-blackened trees and birds which hunt visually)
(vi)
Sickle cell anemia (selected for by resistance to malaria)
(vii)
Predator selection on guppies
(viii)
Evolution of sex ratios
(ix)
Cancer progression
(x)
Evolution of pathogen virulence
(xi)
Etc.
(e)
You will note, of course, that many of these evidences have man at
their centers; this is because natural selection is most easily observed in the
face of relatively straightforward environmental change and if there is one
thing man is good at, it is totally screwing up the environment in relatively
straightforward ways
(i)
(e.g., air pollution, water pollution, deforestation, desertification,
improper use of antimicrobials, over-use of pesticides, over-hunting,
elimination of species, conversion of complex ecosystems
into extremely simple ones, e.g., irreplaceable wet or wood lands into parking
lots, etc.)
(f)
[extant species (Google Search)] [index]
(a)
Biogeography is the study of the geographical distribution of species
(b)
“
(c)
Species are distributed neither evenly nor randomly across the globe
(d)
Instead, related species tend to be more geographically closer to one
another than are less-related species doing similar jobs in similar environments
(e)
“…most island species are closely related to species from the nearest
mainland or neighboring island. This explains why two islands with similar
environments in different parts of the world are populated not by closely
related species but by species taxonomically affiliated with the plants and
animals of the nearest mainland, where the environment often is quite different.”
(p. 441, Campbell & Reece, 2002)
(f)
As one edition of your text has put it (p. 423, not sure which edition)
(i)
"Why are the tropical animals of
(ii)
"Why are two islands with similar environments in different parts
of the world not populated by closely
related species but by species taxonomically affiliated with the plants and
animals of the nearest mainland, where the environment is often quite
different?"
(iii)
Etc.
(g)
The answer is that environments are not necessarily populated by the
organisms best suited to those environments because organisms are typically
limited in their ability to traverse geographical barriers including great
distances
(h)
Instead, new environments tend to be inhabited by less well-adapted
organisms coming from geographically close environments, and then natural selection in time assures an evolution of organisms
better adapted to what had been new environments
(i)
“Although such biogeographical patterns are incongruous if one imagines
that species were individually placed in suitable environments, they make sense
in the historical context of evolution. In the evolutionary view, we find
modern species where they are because they evolved from ancestors that
inhabited those regions.” (p. 423, Campbell et al.,
1999)
(j)
See Figure 22.15, Different
geographic regions, different mammalian “brands”
(k)
See Figure 22.16, The
evolution of fruit fly (Drosophila)
species on the Hawaiian archipelago
(l)
[biogeography (Google Search)] [index]
(a)
The fossil record records a very evolutionary view
of life complete with the descent of modern forms from
archaic forms via numerous evolutionary transitions
(b)
Note that the fossil record is much less able to confirm the existence
of natural selection
(c)
However, the fossil record is perfectly consistent with an evolutionary
interpretation of life (note that this statement is somewhat tautological since
evolutionary theory was developed in part as an explanation for what we observe
in the fossil record)
(d)
See Figure 22.7, Decent with
modification
(e)
See Figure 22.17, A
transitional fossil linking past and present
(f)
See also Figure 24.24 (on p.
481), The branched evolution of horses
(g)
[fossil record (Google Search)] [index]
HOMOLOGIES
(a)
The more closely related two organisms are, the more similar tend to be
their phenotypes (this too is a somewhat tautological
statement since degrees of evolutionary relationships are often determined via
phenotypic comparisons)
(b)
More interestingly, seemingly unrelated organisms often show underlying
phenotypic similarities that suggest evolutionary relatedness
(c)
Phenotype comparisons can be grouped under a number of headings
including
(iii)
Molecular
evolution
(d)
Concepts relevant to such comparisons include
(i)
Homology
(iii)
Vestigial organs
(e)
[phenotypic similarity
(Google Search)] [index]
(a)
A homology is a characteristic of two organisms which are similar as a
consequence of shared ancestry (i.e., the characteristic is also found in the
common ancestor)
(b)
The wings of birds are homologous structures among birds because the common ancestral
bird presumably had wings
(c)
The wings of birds and bats are not a homology because the common
ancestor to birds and bats (a very early reptile) lacked
wings (though, it should be pointed out that much of the underlying anatomy of
bird and bat wings consist of numerous homologies since the common ancestor to
birds and bats had reptilian forelimbs, and wings in both taxa evolved as modified reptilian forelimbs, though modified
in different ways)
(d)
“Surely, the best way to construct the infrastructure of a bat’s wing
is not also the best way to build a whale’s flipper. Such anatomical
peculiarities make no sense if the structures are uniquely engineered and
unrelated… Such anatomical signs of evolution are called homologous structures…
For example, the human knee joint and spine were derived from ancestral
structures that supported four-legged mammals. Almost none of us will reach old
age without experiencing knee or back problems. If these structures had first
taken form specifically to support our bipedal posture, we would expect them to
be less subject to injury. The anatomical remodeling that stood us up was
apparently constrained by our evolutionary history.” (p. 439, Campbell &
Reece, 2002)
(e)
The near-universal commonality of the genetic code (i.e., codon
designations) is a homology, one presumably consistent with the existence of an
extinct universal ancestor
(f)
So, in short, a homology is a trait (i.e., a
variation on a character) that is shared by two organisms
particularly because the common ancestor of those two organisms also possessed
this trait
(g)
Homologies tend to be associated with additional homologies (the
existence of a homology predicts additional homologies)
(h)
“Homologies form a layered pattern, with all life sharing the deepest layer
and each smaller group adding fresh homologies to those they share with larger
groups.” (p. 439, Campbell & Reece, 2002)
(i)
Analogies (i.e., products of convergent evolution), by contrast, tend
to predict only additional functional similarities (i.e., additional analogies;
e.g., flippers predict streamlining) and not similarities between underlying
structures only tangentially related to function
(j)
[homology, homology -jonathan -wells
(Google Search)] [index]
(a)
A homologous structure is simply an anatomical (i.e., structural)
characteristic that serves as a homology
(b)
[Body parts in different
organisms that have similar bones and similar arrangements of muscles, blood
vessels, and nerves and undergo similar embryological development, but do not
necessarily serve the same function; e.g., the flipper of a whale and the
forelimb of a horse (OnLine Biology Book)]
(c)
Wings can be homologous structures (e.g., among birds)
(d)
Nucleotide
sequences, which can also be similar due to descent and thereby homologies, are
not anatomical structures and therefore are not called homologous structures (which, however, doesn’t mean
that nucleotide sequences cannot be examples of homologies)
(e)
Proteins, on the other hand, can possess homologous structures
(f)
See Figure 22.14, Homologous
structures: anatomical signs of decent with modification
(h)
[homologous structures,
homologous structures
-jonathan -wells -denton -god (Google Search)] [index]
(a)
In comparing the anatomy of organisms, one typically compares these organisms
in terms of their similarities and differences
(b)
“Descent with modification is evident in anatomical similarities
between species grouped in the same taxonomic category. For example, many of
the same skeletal elements make up the forelimbs of humans, cats, whales, bats,
and all other mammals, although these appendages have very different functions.
Surely, the best way to construct the infrastructure of a bat’s wing is not
also the best way to build a whale’s flipper. Such anatomical peculiarities make
no sense if the structures are uniquely engineered and unrelated. A more likely
explanation is that the basic similarity of these forelimbs is the consequence
of the descent of all mammals from a common ancestor.” (p. 424, Campbell et al.,
1999)
(c)
See Figure 22.14, Homologous
structures: anatomical signs of decent with modification
(d)
See also Figure 24.18 (on p.
477), A range of eye complexity among mollusks
(e)
Of particular interest when attempting to determine evolutionary
relationships are similarities known as homologies
(f)
["Groups of related organisms are 'variations on
a theme' -- the same set of bones are used to construct all vertebrates. The
bones of the human hand grow out of the same tissue as the bones of a bat's
wing or a whale's flipper; and, they share many identifying features such as
muscle insertion points and ridges. The only difference is that they are scaled
differently. Evolutionary biologists say this indicates that all mammals are
modified descendants of a common ancestor which had the same set of
bones." (Talk.Origins)]
(g)
[comparative anatomy
(Google Search)] [index]
(a)
Homologous structures are not necessarily useful
to a recipient organism
(b)
A structure that is expensive to make or to sustain, but which truly
makes no positive impact on survival or reproductive success will not be
selected for (indeed, may be selected against) and therefore will ultimately
may be lost via evolution (i.e., via natural selection
or via genetic drift)
(c)
In the mean time, the structure is retained as a vestigial,
constituting for us a example of structural evidence of shared ancestry
(d)
For example, vestigial rear legs in some snakes and in transitional
whale ancestors are homologies shared with more-fully legged ancestral species
(e)
It is very important to keep in mind and then remember that vestigial
structures are homologous structures, i.e., structures that are
no longer used and have degenerated but nevertheless are similar to structures possessed
by other organisms particularly because a shared ancestor possessed these
structures
(f)
The important question, then, is why would an organism possess a
useless structure? The answer is that vestigial structures represent evidence
for the occurrence of decent with modification, i.e., the utilization of a
structure by an ancestor that is no longer utilized by a descendant
(h)
[vestigial structures
(Google Search)] [a wonderful debate on the
illogic of a creationists position on vestigial structures (Darwin Campfire Chat)]
[index]
(a)
The embryos of organisms are loaded with homologous structures and, of
even greater interest (since we would expect similar adults to have similar
embryonic features), embryos are loaded (at least superficially) with vestigial
structures, e.g., gills on human fetuses
(b)
Thus, even when adult organisms are superficially very different, loads
of homologies can still be located in embryos via comparative embryos (i.e.,
comparing embryos)
(c)
“Comparative embryology often establishes homology among structures,
such as the gill pouches, that become so altered in later development that
their common origin is not apparent by comparing their fully developed forms.”
(p. 425, Campbell et al., 1999)
(d)
See also Figure 24.19b,
Allometric growth, Comparison of chimpanzee and human skull growth
(e)
["Closely related organisms share similar
developmental pathways. The differences in development are most evident at the
end. As organisms evolve, their developmental pathway gets modified. An
alteration near the end of a developmental pathway is less likely to be
deleterious than changes in early development. Changes early on may have a
cascading effect. Thus most evolutionary changes in development are expected to
take place at the periphery of development, or in early aspects of development
that have no later repercussions. For a change in early development to be
propagated, the benefit of the early alteration must outweigh the consequences
to later development. ¶ Because they have evolved this way, organisms pass
through the early stages of development that their ancestors passed through up
to the point of divergence. So, an organism's development mimics its ancestors
although it doesn't recreate it exactly… ¶ Natural selection can modify any
stage of a life cycle, so some differences are seen in early development… There
are differences in the appearance of early vertebrate embryos. Amphibians
rapidly form a ball of cells in early development. Birds, reptiles and mammals
form a disk. The shape of the early embryo is a result of different yolk
concentrations in the eggs. Birds' and reptiles' eggs are heavily yolked. Their
eggs develop similarly to amphibians except the yolk has deformed the shape of
the embryo. The ball is stretched out and lying atop the yolk. Mammals have no
yolk, but still form a disk early. This is because they have descended from
reptiles. Mammals lost their yolky eggs, but retained the early pattern of
development. In all these vertebrates, the pattern of cell movements is similar
despite superficial differences in appearance. In addition, all types quickly
converge upon a primitive, fish-like stage within a few days. From there,
development diverges." (Talk.Origins)]
(f)
[comparative embryology
(Google Search)] [index]
(a)
Much inference of evolutionary relatedness these days is done, when
possible, via comparisons of nucleotide (or
amino acids) sequences
(b)
The use of these techniques are very common and can be found in such
areas as
(i)
The designation of the mitochondrial Eve
(ii)
Tracking the AIDS epidemic
(iii)
The relationship between humans and apes
(iv)
Etc.
(c)
“If two species have libraries of genes and proteins with sequences of
monomers that match closely, the sequence must have been copied from a common
ancestor. If two long paragraphs are identical except for the substitution of a
letter here and there, we would surely attribute them both to a single source.”
(p. 425, Campbell et al., 1999)
(d)
See Table 22.1, Molecular
data and the evolutionary relationships of vertebrates
(e)
[molecular evolution
(Google Search)] [index]
VOCABULARY
(29)
Vocabulary [index]
(a)
Adaptation
(c)
Biogeography
(b)
Darwin, Charles
(c)
Darwinism as the foundation of biology
(d)
Darwinism
encompasses two ideas, one explaining the other
(e)
Darwinism's
historical context
(k)
Homology
(o)
Lyell, Charles
(v)
Wallace,
Alfred
