STUDY GUIDE: CHAPTER 13 How Populations Evolve
BIOLOGY: Concepts and Connections by Campbell et al. 6th edition, 2008. Benjamin
Cummings Publishers.
Intro.: The blue-footed booby--a bird of the Galapagos Islands, feeds on fish in the
waters near the shore.
Garnered the name “booby” from the British seamen—“stupid”—can be easily
approached and killed.
Awkward on land due to webbed feet—yet very graceful swimming under the
water, where it catches fish.
Evolutionary adaptations include salt-secreting glands in eye sockets, webbed
feet, nostrils that close when it dives under water.
Evolution: Inherited change in organisms over time. This is a unifying theme for
all the fields of biology.
13.1 A sea voyage helped Darwin frame his theory of evolution.
Darwin visited the Galapagos Is., relatively isolated 600 mi. off the west coast of South
America, between 1831 and 1836.
At this time, the generally held belief: Earth was about 6,000 yrs. old and that species are
unchanging.
Some of the ideas that Darwin was aware of:
1) French naturalist Georges Buffon studied fossils, suggested in 1766 that certain
fossil forms might be ancient forms of certain living things.
2) In early 1800’s Jean Baptiste Lamarck suggested that best explanation for above
is that species evolve. He proposed that by using body parts in certain ways an
individual may develop traits which are passed on to its offspring: “Inheritance of
acquired characteristics.”
Darwin’s 5-yr trip was on the HMS Beagle, a survey ship.
Darwin was a naturalist, and spent most of his time on shore in South America,
Galapagos Is., etc. exploring and collecting plants, animals, fossils, etc. He wondered
why fossils of South America were more similar to South American plants/animals than
those of other continents.
While on the Beagle, Darwin read Charles Lyell’s Principles of Geology. This led him to
understand that natural forces gradually change Earth’s surface, indicating Earth was very
old. Darwin saw that fossils of marine snails found on mountaintops had arrived there
thru upheavals of the earth’s surface that occurred over long periods of time.
Darwin wrote an essay of his evolutionary concept in 1840’s – delayed publishing it.
But in mid 1850’s another British naturalist, Alfred Wallace, sent him a manuscript
describing an identical theory of evolution.
In 1858, colleagues of Darwin presented both men’s works to a scientific group.
However, little happened until 1859 when Darwin published On the Origin of Species by
Means of Natural Selection. This book is a strong argument for evolution, based on
much evidence and careful logic.
EVOLUTION IS THE GREAT UNIFYING THEORY OF BIOLOGY. Its theme
relates anatomy (study of physical structure of organisms) with such field as genetics,
comparative embryology, comparative molecular biology, and taxonomy (the branch of
biology concerned with naming, describing and classifying organisms).
13.2 Darwin proposed natural selection as the mechanism of evolution.
Much of The Origin of Species Charles Darwin devoted to theorizing how living
organisms adapted to their environment.
1. He recognized all species produce excessive numbers of offspring beyond that which
can survive.
2. Individuals of a population vary extensively in their characteristics and that many of
the varying traits are inherited.
3. Each environment has only limited room for each species: those that survive and
produce the most offspring tend to be those best suited for the particular habitat they fit
into. Sometimes major environmental changes result in extinction, the irrevocable loss
of a species.
Natural Selection: differential, or unequal, success in reproduction by individuals.
One of Darwin’s supporting ideas was that of artificial selection—the selective breeding
of domestic plants and animals. For ex. how the dog breeds vary from their origin, the
wolf. Another ex. is the variety of common garden vegetables which have been
developed from a weed, the wild mustard.
13.3 Scientists can observe natural selection in action.
Evolution of insecticide resistance:
A small amount of insecticide when first applied may kill 99%. The few
survivors have a resistance which before was not an advantage—now they breed with
other resistant individuals, and 2nd insecticide application is made. Many fewer insects
die, and quickly a resistant population develops.
An insecticide doesn’t create resistant individuals, instead selects for resistant
ones which were already present. Natural selection works as an editing mechanism to
select the most fit individuals.
13.4 The study of fossils provides strong evidence for evolution.
Fossil record: the ordered array in which fossils appear within layers or strata of
sedimentary rock. Fig. 13.4G: rock strata of Grand Canyon.
Fossil record provides strong evidence of evolution. It shows a historical sequence:
fossils which are least like today’s life are found in older strata, those most like modern
forms are in newer strata.
Prokaryotes: oldest known fossils—3.5 billion yr old.
See Figure 13.4H
Basilosaurus: an extinct whale with hind legs. Modern whales don’t have rear flippers,
but skeleton reveals bones of rear legs and pelvis. An earlier whale predecessor actually
may have been able to crawl out on land, perhaps dividing its time between land and
aquatic environment.
13.5 A mass of other evidence validates the evolutionary view of life.
Every aspect of life show signs of evolutionary change.
Biogeography: study of the geographic distribution of species. Darwin noted that
animals on the Galapagos Is. resembled those of mainland South America more than
those of distant island archipelagos—evolved from common ancestors from nearby
mainland, not from other island forms.
Comparative Anatomy: the comparison of body structures in different animals. Fig.
13.5A
Similarity in characteristics that result from common ancestry is known as a homology.
Although used for different purposes, and differing in outward appearances, whale’s
flippers have homologous structures with human arm.
Homologous structures are structures that may have different functions on different
animals/plants but are structurally similar.
Comparative embryology: study of structures that appear in embryonic development.
“Gill pouches” appear in early embryos of fish, frogs, snakes, apes—in all vertebrates.
In all but fish develop into structures other than gills.
Molecular biology: study of the molecular basis of genes and gene expression.
The amino acid sequence of polypeptide chains of common proteins (ex. hemoglobin, the
molecule that carries oxygen in the blood) is more similar btw. man and rhesus monkey
than between man and lamprey, a fish. Fig. 13.4B
13.6 Homologies indicate patterns of descent that can be shown on an evolutionary tree.
Darwin showed that the history of organisms could be shown as a tree. Multiple
branches come off a single trunk to show the hypothetical relationship of ancient life to
more modern life forms. This is still used by biologists, called an evolutionary tree,
although it is usually turned sideways (Fig. 13.6).
13.7 Populations are the units of evolution.
In the evolution of insecticide of resistance, we saw how evolution works through a
succession of generations.
Population: a group of individuals of same species living in the same place at same time.
It is the smallest unit that can evolve—the individual can’t.
Populations can be isolated from the rest of the species and evolve into a new species or
die out completely.
Mussels: native mollusks of various species found in our rivers in Indiana. Most have
suffered from polluted streams and consequently the only ones remaining are in isolated
sections of the streams having the best habitat and water quality.
The fanshell and rabbitsfoot are two species that were common in our rivers 200 years
ago. They now exist in only a few locations in Indiana or elsewhere in the U. S.
Frequently such species are unable to evolve fast enough to stay up with the
changing environment. That is why the U. S. and world are rapidly losing thousands of
species. The trend seems to be getting worse as years go by.
13.8 Mutation and sexual reproduction produce genetic variation, making evolution
possible.
We saw why genetic variation occurs in chapter 8. Now we see why it occurs: Variation
provides for a reshuffling of alleles of various genes, resulting in traits in adults varying
and new combinations occurring in young individuals that will allow the better adapted
ones to produce more offspring.
New alleles arise by mutation. Mutation: a change in the nucleotide sequence.
13.9 The Hardy-Weinberg equation can be used to test whether a population is evolving.
The Hardy-Weinberg equilibrium, a principle named for two scientists who developed
it independently in 1908, states that the frequency of each allele in the population will
remain constant unless acted upon by outside forces. Fig. 13.7B shows that the alleles for
webbed vs. unwebbed feet of blue-footed booby will remain constant from one
generation to next if this difference does not affect survival and reproductive rates.
The recombination of alleles in second generation in Fig. 13.7B gives same allele
frequency: 0.8W to 0.2w.
Note that the two allele frequencies sum to 1.0, when there are only 2 alleles:
W allele (freq. p) + w allele (freq. q) =1.0
Or p + q = 1.0
13.10 The Hardy-Weinberg equation is useful in public health science.
You can figure out what proportion of population carries a deleterious allele, such as that
for PKU or phenylketonuria (the condition where the body accumulates too much
phenylalanine, a certain amino acid).
PKU is caused by a recessive allele, and one PKU occurrence takes place in 10,000
births, giving a frequency of q2 = 0.0001 for the homologous recessive individuals.
Therefore, the occurrence of the recessive allele, q, in the U. S. population is the square
root of 0.0001, or 0.01. The frequency of the dominant allele, p, equals 1 – q, =0.99.
The frequency of carriers, heterozygous individuals with one recessive allele, is
2pq, which is 2 x 0.99 x 0.01 = 0.0198. Thus, we learn that about 2% (actually 1.98%) of
the U. S. population carries the PKU allele.
End Chapter 13 here.