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BIO 4113 – Evolutionary Biology
Introduction
“….a beautifully simple and easily
understood idea – evolution by
natural selection – can be
scientifically tested in all these
fields. It is one of the most powerful
ideas in all areas of science, and is
the only theory that can seriously
claim to unify biology.”
Evolution: change in living things by
descent with modification.
The change may be range from
DNA sequences to behavior.
Evolution depends on external environmental
change and on random genetic changes.
That means that the future course of
evolution is unpredictable, unless we can
specify future conditions.
Another aspect: evolution of life has
proceeded in branching pattern, with the
tremendous variety of modern species being
descended from a common ancestor.
Adaptation – a critical concept.
Living things show adaptations.
Natural Selection: Simply put, some kinds of
individuals in a population tend to contribute more
offspring to the next generation than do others.
Provided that the offspring resemble their parents,
any attribute of an organism causing it to leave
more offspring than average will increase in
frequency in the population over time. The
composition of the population will then change.
Some History
Diderot
Maupertuis
Darwin was not the first to question
the idea that species were fixed,
although it was certainly the
commonly held belief at his time.
The French naturalist Jean-Baptiste
Lamarck put forward the idea that
species changed over time in 1809 in
his book Philosphie Zoologique. His
process, though, was very different
from that imagined by Darwin fifty
years later. Lamarck suggested the
idea of transformism. He did not
suggest that lineages branched and
went extinct.
Lamarck’s Theory actually had two parts:
1. Transformism
2. Inheritance of Acquired Characteristics.
Friction between Lamarck and
the highly influential Georges
Cuvier had a great influence on
thinking through the early part of
the 19th Century.
Cuvier
Charles Darwin
1809-1882
Shrewsbury,
England
Charles Darwin was born on February 12, 1809, in
Shrewsbury, England. Interestingly, another man
was born on the same day in a log cabin in
Kentucky. That man was Abraham Lincoln.
The Darwin family home was called “The
Mount”. It was here that Darwin was born, and
where his father practiced medicine.
Charles
father, Robert
Waring
Darwin, was a
prominent
physician in
Shrewsbury.
Erasmus Darwin (1731-1802
Organic life beneath the shoreless waves
Was born and nurs’d in ocean’s pearly caves:
First forms minute, unseen by spheric glass,
Move on the mud, or pierce the watery mass;
These, as successive generations bloom,
New powers acquire and larger limbs assume;
Whence countless groups of vegetation spring,
And breathing realms of fin and feet and wing.
Shrewsbury
School
Charles was educated at home until the age of nine.
He then attended Shrewsbury School, a boarding
school located about a mile from his home, until he
was sixteen.
In 1825, Charles entered the University of
Edinburgh in Edinburgh, Scotland, to study to
become a physician.
“The instruction at Edinburgh was
altogether by lectures, and these were
intolerably dull, with the exception of
those on chemistry….to my mind there
are few advantages and many
disadvantages in lectures as
compared with reading…. Dr. _____
made his lectures on human anatomy
as dull as he was himself, and the
subject disgusted me.”
Charles Darwin 1876
In 1827, Charles gave
up the study of
medicine and began
studying for a career
in the clergy at
Christ’s College of
Cambridge University.
During his time at
Cambridge, Darwin was
an “adequate” student,
but busied himself with
many other activities. He
became fascinated with
natural history. He was
particularly fascinated
with the intrigued by the
enormous diversity of
beetles.
Darwin was influenced
by a Professor of Botany
(and clergyman), John
Stevens Henslow.
Henslow persuaded
Darwin to become
interested in Geology.
“I fully believe a better man
never walked this earth.”
Charles Darwin to Joseph Hooker
regarding John Stevens Henslow.
John Henslow
1851
Henslow arranged
for Darwin to
accompany Adam
Sedgwick on a field
trip studying the
geology of Wales in
1831. This
stimulated Darwin’s
interest in geology.
Adam Sedgewick
In 1831, Henslow arranged for Darwin to
be interviewed for a position on board
the HMS Beagle
Darwin was interviewed
by Robert Fitzroy, and
was offered a position
as a “volunteer”
naturalist on board the
Beagle.
Captain Robert Fitzroy of
the HMS Beagle
The Beagle sailed
from Plymouth
harbor on
December 27,
1831.
The Beagle spent five years
circumnavigating the globe.
South
American
sketch
from
Beagle
voyage
The Beagle’s primary mission was
mapping and exploring the coast of
South America.
On the voyage, Darwin read
Lyell’s Principles of Geology.
It persuaded him that the
earth was very ancient.
Charles Lyell
Author of Principles of Geology
The
Galapagos
Darwin was particularly influenced by
observations made in the Galapagos Islands,
some 500 miles off the coast of Ecuador.
Pinnacle Rock
The Galapagos are
a group of volcanic
islands, isolated
from the South
American
mainland.
The islands are
inhabited by a
diverse group of
organisms that
differ from those
found on the
mainland.
Marine iguana
Darwin’s
Finches
On his return, Darwin married his cousin
Emma Wedgewood. They had ten
children, with seven surviving to adulthood.
Charles with his
daughter
In 1842, the Darwins moved to
Down House in Kent, about sixteen
miles from London. Darwin never
left the British Isles again.
He spent much of
his time in his
study, working on
his ideas.
Darwin’s
microscope
Darwin became one
of the world’s
leading authorities
on a wide range of
topics, including
barnacles……
…. and volcanic
islands.
“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 favourable
variations would tend to be
preserved and unfavourable
ones to be destroyed.”
Darwin, on reading Malthus’ Essay on
the Principle of Population in 1838.
Thomas Malthus
In 1844, Darwin received a manuscript
from Alfred Russell Wallace, a young
naturalist who was working in the Malay
Archipelago.
Darwin moved rapidly, and Origin of
Species was published in 1859
The monumental new idea in Origin of
Species was not the idea that species
had evolved. The enormous step that
Darwin took was the suggestion of a
mechanism by which evolution could
take place.
Darwin’s ideas
were immediately
controversial in
the public eye,
although most
scientist’s were
quickly convinced
of the validity of
his arguments.
One of the better arguments against
Darwin’s theory was that it lacked a
satisfactory theory of heredity. In
fact, Darwin preferred a “blending”
theory of inheritance. In truth, such
a mechanism of inheritance would
work against evolution by natural
selection.
A more popular objection had to do
with the role of chance, and the
difficulty of making big jumps on
the basis of chance and natural
selection alone. A comparative
anatomist named George Mivart
published a book in 1871 in which
he listed a number of structures
that would be maladaptive in their
early stages. Wing, for example.
Some biologists tried to get around the
difficulty by thinking of a process other than
natural selection that could work in the early
stages of a new structure or organ. They fall
in the area of “directed mutation”. The idea is
that offspring tended to differ from their
parents in a particular direction. In other
words, early birds would tend to produce
offspring with more developed wings, even
though there was no advantage to it.
Lamarckian.
In the 1880’s,
Lamarckian
inheritance was
largely debunked
through the
experiments of
August Weismann.
His work led to a
rediscovery of the
work of….
….Gregor Mendel.
Early on, the effect of Mendel’s
work was to cast doubt on
Darwin’s theory. The early
Mendelian geneticists like Hugo
de Vries and William Bateson
opposed natural selection. They
thought that evolution proceeded
in big jumps powered by
macromutations. Big difference
between parent and offspring.
On the other hand, another school of geneticists
called themselves biometricians. They were led
by Karl Pearson. Biometricians looked at small
differences between individuals instead of large.
Source of much of biological statistics. Saw
evolution as more of a statistical shift of the whole
population instead of the production of an entirely
new type of organism by macromutation. They
tended to be more sympathetic to Darwin than the
Mendelians.
The Modern Synthesis
Theodosius Dobzhansky immigrated from Russia in
1927 and began studies on evolution in fruit flies.
The question of how
species originate was
investigated by Ernst Mayr.
George Gaylord Simpson argued that the evidence in
the fossil record was consistent with the population
genetic mechanisms of the modern synthesis.
Stephen Jay Gould