Download DARWIN`S STORY Charles Darwin was a very “atypical” scientist

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

Natural selection wikipedia, lookup

Theistic evolution wikipedia, lookup

Saltation (biology) wikipedia, lookup

Adaptation wikipedia, lookup

Transitional fossil wikipedia, lookup

On the Origin of Species wikipedia, lookup

The eclipse of Darwinism wikipedia, lookup

Koinophilia wikipedia, lookup

Introduction to evolution wikipedia, lookup

Transcript
DARWIN’S STORY
Charles Darwin was a very “atypical” scientist. He was a son of an English
country doctor. His mother died when he was eight years old and he was largely brought
up by his older sisters. Charles’ father, like most English fathers in the 1800’s, was a “no
nonsense” parent and talked his son into doing what he wanted him to do. This did not
always work out, however. Charles was enrolled in a “good” school, but did not apply
himself because he was bored. He was more interested in hunting, dogs, taking long
walks and collecting things like shells, moths, and butterflies.
“I will give proof of my zeal,” he wrote in his autobiography. “One day, on
tearing off some old bark, I saw two rare beetles, and seized one in each hand. Then I
saw a third new kind, which I could not bear to lose, so that I popped the one which I
held in my right hand into my mouth. Alas! It gave off some intensely acrid fluid, which
burnt my tongue so that I was forced to spit the beetle out, which was lost, as well as was
the third one.”
He tried medical school because his father wanted him to be a doctor, but was not
interested and became horrified when watching surgery. So his father sent him to
Cambridge University, hoping that he would become a minister. At this point, Charles
did not have a good self image since he seemed to never please his father and had failed
at living up to an older brother. He was, however, patient and unaggressive, but still
determined to do what he wanted to do.
While at Cambridge, he met people that were interested in science and natural
history, especially the study of plants (botany) and of geology. Charles wished that he
could get a respectable job in collecting plants and animals rather than be a minister at a
church. He did graduate, and right after graduation received a letter from his botany
professor saying that he had recommended him for the post of naturalist aboard H.M.S.
Beagle on a two year expedition to map the coast of South America and collect plants and
animals.
His father was against the idea, but told Charles that if he could find one
respectable person that agreed with Charles, he would let him go. Charles immediately
went to his uncle, Josiah Wedgwood, who was famous for his pottery works. Josiah
agreed that Charles should go on the voyage and was able to convince his father that it
was a good idea.
1
Before he sailed on the Beagle, Darwin believed that God created the
Earth and living things and that neither one changed. The earth was believed to be only six
thousand years old based on an interpretation of the earth's history in the Bible. Species are
exactly as they were created. The earth could change, but it changed by "catastrophes" such as
floods destroying the entire earth, mountains being raised in one day, and canyons opening at
once. These ideas were taken for granted by nearly everyone in Europe.
Earth
God
Both did
not change
Living Things
While he was on the Beagle, he become dissatisfied with his view of an unchanging
earth after reading Sir Charles Lyell's Principles of Geology. In this book Lyell showed that the
earth undergoes changes brought about by natural forces such as erosion. This happens over a
long period of time. (Evidence #1 “Old Earth”)
Lyell and Gerard Paul Deshayes (1797-1875) collected fossil shells from different layers
of rock. Back then, scientists could not tell the exact ages of the rocks, but many believed that
the oldest rocks were on the bottom and the youngest on the top since they could not think of a
way that the oldest rocks could be laid on top of the younger ones. They found that almost
2
all the fossils in the top layer belonged to species that were still living, while none of the fossil
species found in bottom layers were still alive today. They also found that the species on the
bottom were simpler then those on the top. (Evidence #2 “Fossils”) Darwin wondered how this
could be if God created all living things exactly like they are today. So he modified his view of
an unchanging earth to one of an earth that changes over long periods of time.
Earth which changes
God
Living Things Which Don’t Change
Captain Fitzroy, the commander of the Beagle, ran a tight ship. He wanted a naturalist
onboard to collect more evidence that God created all living things at one time and that they
never changed. Darwin did not always discuss his ideas with Fitzroy since the Captain did not
like ideas that went against his own. He had mood swings and often dealt out unearned
punishment when he was angry. “He was,” wrote Darwin, “devoted to his duty, generous to a
fault, bold, determined and indomitably energetic. But his temper was a most unfortunate one. It
was usually worst early in the morning, and with his eagle eye he could generally detect
something amiss about the ship and was then unsparing in his blame.” It is a credit to Charles
that he could get along with a man like Fitzroy in cramped quarters in a bouncy, uncomfortable
little vessel for what turned out to be a five year voyage from 1831 to 1836.
God
Living things which don’t change
3
Even though he was sick most of the voyage, Charles still managed to collect a wide
variety of living things to take back to England. He went ashore every chance he had to make
geological observations and to collect specimens. He hired horses and guides, arranged for
camping trips into the interior of the continent, climbed mountains, and rented cabins for weeks
at a time.
As he collected, he become dissatisfied with his view of how a changing earth fit with
unchanging living things. If the earth changed, wouldn't living things also need to change in
order to survive? Many observations on his voyage led him to challenge his belief that living
things did not change over time. He observed the species on the Cape Verde Islands, off the
coast of Africa, and saw that the species there were not quite like those on the mainland. Along
the coast of Argentina, Darwin observed living armadillos. He also found fossils of some
extinct armadillos or glyptodonts. Here were two very strange similar animals, one living and
one extinct. How could he account for this? (Evidence #7 “The Succession of Types”)
4
A painting of the HMS Beagle in the waters of Murray Narrow, Tierra del
Fuego, the chilly southernmost tip of the South American continent
Darwin visited hundreds of miles of coastline in South America from
Brazil to Argentina. He saw many examples of the same species, but they were not exactly the
same from place to place. The farther apart the groups were located, the more different they
were. He had never seen this in England since England is small and the climate is basically the
same all over. (Evidence #8 Representative Types)
He visited the Galapagos Islands off the coast of Ecuador. He noticed tortoises living on
almost every island. But he also noticed that the tortoises were different from island to island.
Each seemed to fit into the environment of that particular island. Why was there one kind of
tortoise that had mysteriously become a dozen kinds?
He noticed the same thing with finches. They were similar, but different according to
their environment. One finch had a very big, heavy beak and ate seeds with tough outer
coverings. Another finch had a smaller beak and ate more easily cracked seeds. A third had a
long thin beak and ate insects. Another had a different bill and used a cactus needle to poke at
5
insect larvae in cracks in wood.
When he got back to England he discovered that he had collected thirteen species of
finches, all so closely related that it seemed almost that they might have had a common ancestor
and changed to use all the different kinds of food on the islands.
Other questions about the Galapagos bothered him. Why were there no mammals except
for one species of small rat? Why was there nothing but birds, reptiles and insects there? Why
was there only one kind of hawk, one dove, one owl, one snake?
When the Beagle reached New Zealand, he saw again fossils and living specimens of
many different kinds of birds, many that were flightless, eating many different kinds of things.
They ranged in size from giant moas that were twice the size of ostriches and laid eggs the size
of basketballs to small birds like the chicken-sized kiwi. There were no mammals.
While visiting Australia, Darwin saw many strange animals. Nearly all of them were
marsupials, mammals with pouches like kangaroos. There were marsupials that did the same
"jobs" of nearly every placental mammal in Europe. Large kangaroos did the same "job" as
cows, smaller kangaroos the same as sheep, while other marsupials did the “jobs" of rabbits,
dogs, wolves, porcupines, and monkeys. (Evidence #9 “Ocean Islands”)
Earth which changes
Causes
Living things to change
With this evidence, Darwin now believed that the environment caused changes in living
things. But he could not figure out how this could happen. In 1836, after he had returned from
his voyage on the Beagle, Darwin read Reverend Thomas Malthus' “An Essay on Population.”
Malthus said that there was so much misery and hunger in England during the Industrial
Revolution because there were too many people for the food supply. Some had to go hungry and
die since there was not enough for all. (Evidence #10 “Malthus on Population Growth”) This
idea led Darwin's thoughts to a possible way for the earth to change and living things to change
along with it.
Darwin's Model of Evolution through Natural Selection focused on
6
populations, groups of the same species of living things. It says that there are many more living
things born in a population than can survive. Each member of a species is a little different from
each other. (Evidence #12 “Variation”) As the earth changes, the living things that have
characteristics best suited or adapted to the new environment will live long enough to reproduce.
(Evidence #11 “Adaptation.”) These characteristics that help them survive will be passed on to
their kids. Most of the time, the living things that are not best adapted will die out before they
have a chance to reproduce. After a great amount of time, populations can change so much that
the two populations cannot breed with each other. A new species has developed or, as we call it
in life science, evolved.
This differed from Lamarck since Darwin was looking at a group (population) and not
just an individual like Lamarck was. Lamarck was concerned mostly with the struggle for
getting food, where Darwin also considered other survival advantages such as keeping away
from predators and adjusting to the temperature. Lamarck did not tie survival to reproduction.
Darwin said that those that were the best adapted would survive to reproduce.
The Galapagos were a wonderful example of how evolution works. The living things on
the islands were similar to South American species which suggests that they had migrated to the
islands. But they were different enough from their South American relatives to suggest that they
had changed after their arrival. The Galapagos were volcanic and had at one time been clean
unmarked slates. Everything that arrived on them had to come from somewhere else. Each
island at some point in its history had been invaded by a few tortoises. Each tortoise was slightly
different. They formed a breeding group with each island having differences in their breeding
groups. Gradually each group became different from each other and by the time Darwin arrived
in the islands, each had its own tortoise. (Evidence #9 “Ocean Islands)
Darwin also looked at other pieces of evidence. Some species have vestigial (“leftover”)
organs that do not do anything. Why would whales and pythons have pelvis (hip) and femur
(thigh) bones if they do not have legs? Maybe these were “leftovers” from an ancestor in their
past. (Evidence #3 “Vestigial Organs”) Why do embryos of different vertebrates look so
much alike if they did not have an ancestor in common in the past? (Evidence #5 Embryology)
Why would there be homologous structures, parts of the body which are similar from species to
species? For example, the arms of humans, wings of bats, flippers of whales, front legs of
horses and lions all have the same bones in the same relative places. Wouldn’t they have to
have a common ancestor for them to be this way? (Evidence #4 Homologous Structures)
7
Darwin looked at pet pigeons and dogs and saw that when people picked which pigeon or
dog reproduced, they could get a wide variety of features. He also found that people
would choose the “best” animals or plants and breed them for the next generation. So
over time a farmer could get cows that gave more of milk if in each generation he bred
the cows that were the best milk producers. (Evidence #6 Animal and Plant Breeding
or Artificial Selection)
Darwin did not discover any totally new facts or “missing pieces" that would allow
him to recognize how species came into being. No one before him seemed to recognize
the significance of the ideas and see a pattern to explain them. It is similar to what
happens when a "puzzle picture” suddenly changes appearance and you can see a
different figure than what you did before. Darwin saw beyond the creationist idea of a
young earth that was created perfectly at the beginning.
Seeing this picture as a
rabbit prevents a person
from seeing the picture as a
duck facing In the opposite
direction.
Darwin married his cousin, Emma Wedgwood. They had ten children. He became sick,
probably because of a parasite that he had picked up in the tropics on his voyage on the Beagle.
Emma took care of him in their house in the village of Down In Kent, only twenty miles from
London.
Darwin thought and wrote about his ideas in his diary and in letters to friends for many
years. He also discussed them with a few scientific friends, Asa Grey, Charles Lyell and Joseph
Hooker. No one is sure why he did not publish his ideas before 1859, but it may have been
because he feared the controversy that would follow the publication. Charles was a man that
liked to avoid arguments.
He may also have delayed publishing his ideas because he recognized that evolution
could not be observed directly, unlike many other models in science. He showed scientific
caution and thought that his model would not be backed by other scientists unless he had
collected an overwhelming amount of evidence to support his model.
In 1858 Darwin received a letter from Alfred Wallace, a young naturalist collecting
specimens in the East Indies. Wallace had hit on an idea of natural selection in the struggle for
existence that sounded almost exactly like that of Darwin's. Darwin and Wallace were thinking
about the same problem-how new species can arise in nature-and the same explanation occurred
to both of them at the same time.
8
Charles Darwin
Alfred Wallace
Darwin's friends backed his claim to the idea of natural selection since they had letters
that he had written to them about the idea as early as 1844. Since Darwin was sick and also grief
stricken from his infant son's death, Hooker and Lyell made a joint announcement of Darwin's
and Wallace's ideas at a scientific meeting of the Linnaean Society on July 1, 1858.
Darwin worked for over a year on a book to explain his ideas. He wrote many chapters
with evidence from paleontology, geographical distribution, and the likenesses among species to
support his idea. It was a long, slow process since Darwin was often sick.
In 1859 the first edition of The Origin of Species By Means of Natural
9
Selection or the Preservation of Favoured Races In the Struggle For Life was published. Many
important scientists were very supportive of the book. T.H. Huxley said, "How obvious. How
stupid of me not to have thought of it myself.” Wallace said “I never could have approached
the completeness of his book. I really feel thankful that it has not been left to me to give the
theory to the world.” Wallace and Darwin stayed friends throughout their lifetime.
Many people that did not understand science misread the book and objected to it. This
included many church people of the day along with a few scientists who could not abandon their
Creationist beliefs.
The theory of evolution by natural selection is now the backbone of biology. Some
changes and additions have been added since Darwin published his book, The Origin of Species
in 1859.
One of the weak links in Darwin's theory was that he could not explain the variation
found in living things. Gregor Mendel, the man who proposed the idea of dominant and
recessive “factors” or genes, read a copy of Darwin's book and wrote in the margin of his copy
how his own work supported that of Darwin's. They never met and Darwin may have never
heard of Mendel's theory since no one supported Mendel's findings until after Mendel’s death.
The evidence now shows that many differences in individuals are caused by genes found
in the nucleus of cells and that these genes are passed on from parents to children. Darwin never
thought to look into cells. He thought that each part of the body sent particles called gemmules
through the blood to the reproductive organs and these would come together to form either the
egg or the sperm.
New characteristics can come from mutations, changes in a gene.
These changes then can be handed down from generation to generation if they help the organism
to survive. If the change is very harmful, the organism will die before it has a chance to
reproduce. Other changes don't cause any change at all in survival advantages. This synthesis
(putting together) of two areas of biology, genetics and evolution, was a major step forward in
figuring out a better model of what goes on in the world of living things.
Scientists have also found many more fossils that show organisms that are in between
two groups. For example, Archaeopteryx was found in 1861. It had a skull like a bird, but teeth
like a reptile. A long bony tail like a reptile was present, but so were feathers. This was a form
in between reptiles and birds.
10
Evolution is so important to biologists that in 1973, Theodosius Dobzhansky
wrote an essay titled, “Nothing In Biology Makes Sense Except In the Light of
Evolution.” Without evolution, biology is just a collection of facts that are interesting
and curious, but make no meaningful picture as a whole. They are like pieces of a puzzle
that make a pretty design when not assembled, but make a brilliant picture when pieced
together.
11
12
13