Download The Darwin theory of Natural Selection

Year 12 Biology 9.3 Blueprint for Life
Evolution and Natural Selection
Evolution’, ‘natural selection’, ‘Charles Darwin’ and ‘survival of the fittest’ are now common terms heard
not only in high school or university classrooms but in everyday households around the globe. What do
these terms mean to you?
This familiarity is understandable considering that Darwin’s theory of evolution was not only one of
the most controversial of the nineteenth century, but also one of the most important as it attempted
to answer one of the most baffling questions of all time – where do the variety of living things
originate from? After 150 years, aspects of evolution by natural selection are still under debate in the
scientific community due to the nature of Science to continually question in order to continually gain
knowledge. Many religious academic institutions across the United States refuse to teach evolution
and many outright attack it in favour of creationism. So who was Darwin, what did he propose, and
what modern day evidence do we have both for and against evolution by natural selection?
The Wallace theory of Natural Selection
I was born in Wales and had no formal education but was a keen naturalist all my life. As a young man I
taught in a school until my mid 20s before I took off – in 1848 - on a specimen collecting trip to the
Amazon. Unfortunately all my notes and specimens were destroyed. I travelled again in 1854, this time
to Indonesia on a trip that lasted 8 yrs. I published an essay in 1855 entitled On the Law which has
Regulated the Introduction of New Species which attracted little notice from the scientific
community other than from one fellow named Charles Darwin.
After more study I attempted to explain the variety in species by suggesting the theory of Natural
Selection – I didn’t know that Darwin had independently come to the same conclusions as I. In 1858 I
published, an essay entitled On the Tendency of Varieties to Depart Indefinitely from the Original
Type which I sent to Darwin for his opinion. He was taken aback by the coincidence that by studying
the natural world, we had both reached the same conclusions about the origin of different
organismsOur two papers were read at the Linnean Society in 1858. Darwin was such an excellent
naturalist that I wrote a book Darwinism (1889) on his theories.The theory of Natural Selection
states that organisms with low relative fitness (ability to survive within a certain set of conditions)
are reduced in number within a population as they are least likely to survive
The Darwin theory of Natural Selection
In 1831, at 22, I set sail with the Beagle (my Uncle Wedgwood – of pottery fame- helped fund my trip)
under Captain Fitzroy. As the Captain was not allowed to socialize with his staff, I suspect I was
invited on board to keep him company and stop him from going mad –like the previous captain. We
sailed to South America. When we landed I hired locals to assist me in collecting many specimens new
to science, including many fascinating fossils.I first conceived my ideas of Natural Selection, the
‘struggle for survival’ when visiting the Galapagos Islands. I noticed that individuals better suited to
their environment survived at a greater rate than those who were less suited. Natural Selection is the
process by which some individuals are more reproductively successful than others and hence
disproportionally pass on their characteristics into the next generation.
In 1859 I published my book Origin of species by means of natural selection, or the preservation of
favoured races in the struggle for life, otherwise known as The Origin of Species. I felt that it wasn’t
quite finished, but Alfred Wallace had come to the same conclusions as I and I felt the pressure to
publish my findings extensively.From my observations on the Beagle trip as well as studies made in
1
England on the breeding of pigeons, my book virtually became an explanation for life on Earth. I was
very defensive in my arguments. Predicting a backlash I tried to find scientific evidence for any
counter argument that may be proposed post publication. I argued that if natural selection acted upon
a species long enough, that species could actually become a new species.
I made 4 observations on which I based the Theory of Natural selection.
1.
2.
3.
4.
Even though when writing The Origin of Species I took great care to provide a surplus of examples for
evolution by Natural Selection, there was still a great deal of backlash from the scientific community.
Many still thought each species was created separately, or independently, rather than evolving slowly
over time due to each organism being selected for by nature with regards to their natural variety.
Many were even aware that farmers ‘select’ (as nature does) the better qualities of their stock in
order to improve it. I was mocked in public yet was too ill to defend myself.Why did everyone wish to
believe we evolved from monkeys, rather than my proposal that we evolved, like the monkey, from a
common ancestor?
As I predicted, over the years and long after my death, scientists have used the fossil record to
accumulate a great deal of evidence in support of evolution by natural selection. In my day very little
was understood regarding genetics, which has also provided evidence in support of my theory. The
theory of evolution is now generally accepted even though there is still some gaps in the fossil
record.In 1885 my good friend Thomas Huxley (who publicly defended evolution on my behalf) unveiled
my statue at the Natural History Museum in London.
Evolution and the Physical Environment
Evolution by natural selection can be influenced by the physical environment in which the species lives.
Changes in the physical conditions and factors in the environment such as ____________________,
__________________, wind _____________ and direction, amount of _________________ can
determine the evolution of plants and animals. The change in physical conditions can be ___________.
For example, the movement of Australia north after the breakup of __________________ changed
weather conditions. Organisms had to adapt to a drier climate or face extinction. The Australian
desert hoping mouse Notomys alexis has adapted to living in arid conditions in many ways. It conserves
water by producing ______________________ urine, metabolizes much of its own ____________,
has a low metabolic rate, is inactive during the day and ________________ during the day. Similar
animals living in non-arid conditions have developed non of these adaptations. The change in physical
conditions can also be sudden. Organisms living in a changing habitat must be able to adapt in order to
survive there.
Evolution and the Chemical Environment
Evolution by natural selection can be influenced by the chemical environment in which the species lives.
Chemical conditions, such as _______________, iron concentration, ________________ and food
______________________ content can vary greatly from one environment to another and organisms
have adapted to live in such places. Example 1 - when rabbits became a pest across Australia, the
myxomatosis virus was introduced in order to kill them off. Some rabbits had an immunity to the virus
2
and survived to reproduce and produce more resistant rabbits. The species hence survived a sudden
dramatic chemical change. Example 2 - plants adapt to salty environments by using a multitude of
processes. They can block the uptake of ions, or use active transport to pump ions out.
Evolution and Competition
Competition for resources occurs between species living within an ecosystem. Darwin was aware that
population _________________ played an important role in survival for species competing for
limited resources such as _______________, _______________ or _______________. Two or
more species in constant competition may result in one or more of the species either being eliminated
or forced to occupy a different ____________________. As a result of a species changing habitat
it has to evolve with similar but slightly different resources. Native Australian honey bees and feral
honey bees have existed together in Australia for abut 150 years. They are in constant competition
for nesting sites and flowers from which to take nectar. In order to adapt to the competition they
have had to forage further a field.
Evolutionary Divergence
The gradual formation of a number of different species (or varieties) from a common ancestor that
have adapted to a different ecological niche is known as _______________ ________________ or
_________________ ______________. One species gives rise to other organisms that are
different because they have somehow become _________________ from the original population and
have needed to adapt to a new/different environment through evolution. Organisms can become
different due to:
•geographical isolation (sea levels rise and separate landmasses, continents drift apart)
•competition for resources (population might increase so much that some individuals change
their niche ie nectar feeding birds become insect eaters and develop shorter/tougher beaks)
Classic example of evolutionary divergence: Darwin’s finches – :
•Darwin thought that the original variety of finch that arrived on the Galapagos Islands were so well
adapted that they flourished in number. Due to the large numbers, pressure on the birds forced them
to expand their niche’s. Some became seed eaters with strong beaks, some had curved beaks for
reaching into flowers for the nectar, and others formed long slender beaks for catching insects.
Darwin believed the 13 species of finch’s found on the Islands were derived from one common
ancestor.
•Another example: the fossil record suggests the first primitive placental mammal appears 58 million
years ago. Among these was the Credodonta that diverged into a number of carnivores including
marine mammals such as the whales and dolphins.
Evolutionary Convergence
•When species that are not necessarily closely related share a similar physical environment, they can
acquire adaptations that help them survive better in that particular environment. This is called
___________________ ___________________. An example is the development of wings in
vertebrates and insects that occurred separately by two different lines of organisms who sought to
adapt to life in the air (note the bat and bird are not examples of convergence as they both formed
from the same ancestor with 5 digit fingers).
3
Support for Evolution
Palaeontology
Palaeontologists have been studying fossils for many years and have noted that preserved remains of
some organisms are not only similar in structure to ones currently living, but similar to other
________________ organisms found in the fossil record. The fossil record provides a _________
___________ of evolution due to the oldest fossils being found in rocks ___________ in rock layers
with the youngest fossils found in the _______________ layers. Due to changes in geography over
time, it is not always possible to compare different sites, but scientists can compare fossils within the
same site. Fossils that can be compared to others in an attempt to indicate the evolutionary
development of one group of organisms to another, or from a variety of groups of organisms to a
common ancestor are called _______________ __________ or ____________ ______________.
One of the most famous transitional fossils is the Archaeopteryx. It has features of
_____________ such as _______________ and a solid ____________, as well as features of
___________ such as a ______________ and _______________. This provides evidence of an
evolutionary path from _______________ to ______________.
Biogeopgraphy
The study of the distribution of living things is called biogeography. We know that certain types of
organisms are only found in certain areas and not in others – Australia is classic example as it harbours
many unique species, many of which have become national symbols. The unique flora and fauna on the
Australian continent is thought to be due to the long term isolation of the land mass after the
breakup of Gondwana. Alfred Wallace attempted to draw lines on maps (the Wallace lines) to show the
distribution of different organisms. With the patterns of distribution of an organism today, as well as
its fossil distribution in the past, scientists are able to reconstruct its evolutionary history. Example:
the fossil evidence indicates that ____________________ originated in South America as well as
Australia when the countires were once connected. The ___________________ can also be found in
South America and Australia. This supports the theory that these organisms evolved from an
ancestral species within a particular geographical region.
Comparative Embryology
The study of the differences and similarities in embryonic development between different organisms
is called comparative embryology. Many species of __________, ____________, ____________,
______________ and ________________ show greater similarity as ______________ than they
do as fully formed adults. By comparing embryos, scientist can link ______________ species and
assist the search for a common ancestor. Example: all vertebrates have gill slits (or gill _________,
as they are not really slits) when they are embryos but they only develop through to adulthood in fish.
This indicates a fundamental stage in the early development of _______________________ that
represents the proposal of a common ancestor.
Comparative Anatomy
The study of the _______________ and _________________ in _______________ between
different organisms is called comparative anatomy. Vertebrates can often be more easily grouped
together by comparing their anatomy than by comparing their outer structure due to ____________
caused by body covering and shape and function of various body parts. ___________, ___________,
__________ and _____________ in birds, bats, mammals, reptiles and amphibians are limbs that
consist of similar basic ______________ ____________ ____________________ that have been
adapted for different functions. They are therefore known as __________________
________________. The whale and snake have skeletal _________________ of back limbs that
are buried under their skin which are the remains of hind legs. Vestiges are remodeled structures
that have reduced or no current function. Can you think of some human vestiges?
4
Biochemistry
1. Comparing Amino Acid Sequence: •Comparing particular ______________________ across
species provides further evidence of relatedness and common ancestry. Before the use of
biotechnology, molecular comparison of organisms was not possible. Now, biochemical evidence
continues to expand and support the theory of evolution and common ancestry. ___________
_________ and _____________ (nucleotide) sequences can be compared across species. The
___________ related species have the __________ sequences matching. __________________
______ molecules are _____________ that are involved in cellular respiration – something that
takes place in all living things. By comparing the nucleotide sequence of cytochrome C scientists can
quantify the number of differences between living things. ____________ closely related have less
_______________. For the organisms that possess it, the protein haemoglobin is relatively well
preserved across species so its sequence of amino acids can be used to compare species that are
already known to be quite closely related. This is a more sensitive method than using a protein common
to all living things. For example humans and rhesus monkeys have only 8 amino acids from about 300
sequences different compared to humans and lampreys - 125. Other proteins such as hormones can
also be compared, as well as base pair sequences in RNA.
2. Comparing Blood Plasma: •By comparing the compatibility of blood plasma of different animals
when mixed together, scientists can also identify how similar they are. Mixing the blood shows the
compatibility of the antigen-antibody reaction. If there is a small reaction, ie the blood samples don’t
recognize each other as totally foreign, then the animals are more closely related.
3. Comparing Base Pair Sequence in DNA: •Scientists can use a technique called DNA
_____________________ to compare similarities between DNA molecules from different species.
This is how; DNA from species A & species B is isolated from the nucleus and placed in a test tube.
The DNA is ______________ so that the two strands break apart. This is called _______________
and occurs when the hydrogen bonds that form the ‘rungs’ of the DNA ‘ladder’ break. After
denaturation four single strands of DNA are mixed up in the test tube – two species A strands & two
species B strands. Slowly ______________ the DNA and its bases will ________/_____________
- the hydrogen bonds reform so that the ‘rungs’ of the DNA return it to its ‘ladder’ appearance. Some
of the single DNA from species A will randomly pair with species A again (as it was originally), but
some will also ____________________ pair with species B. If species B is _____________ to
species A, many of the bases will pair showing _____________ compatibility of the DNA. If species
A and species B are not closely related then less of the bases will pair showing ____________
compatibility of the DNA.
Punctuated Equilibrium
In 1972 the idea of ________________ __________________ was put forward by Eldridge and
Gould who noted in the fossil record that some species remained the ____________ for millions of
years and others seemed to ____________ or ________________ relatively rapidly. They proposed
that there were long periods of time where some species remained relatively unchanged while others
underwent relatively rapid change. These short bursts of change that were interspersed amongst the
long periods with little change is known as punctuated equilibrium. Punctuated equilibrium was in
contrast to Darwin’s ‘_________________’ that states evolutionary change was gradual. This is a
current debate that exists due to the lack of _______________ still occurring from the fossil
record. The only organisms that can be studied are those with hard parts! An example of punctuated
equilibrium is the rapid evolution of mammals (~100 families in 30 million years) compared to bivalves
(~100 families in 500 million years)
5
Stage 6 HSC syllabus dot-points covered
Linked to part 1 – Evidence of evolution suggests that the mechanism of inheritance, accompanied by
selection, allow change over many generations:



outline the impact on the evolution of plants and animals of:
o Changes in the physical environment
o Changes in the chemical conditions in the environment
o Competition for resources
describe, using specific examples, how the theory of evolution is supported by the following areas of
study:
o Palaeontology, including fossils that have been considered as transitional forms
o Biogeography
o Comparative embryology
o Comparative anatomy
o Biochemistry
explain how Darwin/Wallace’s theory of evolution by natural selection and isolation accounts for
divergent evolution and convergent evolution
Linked to part 4 – The structure of DNA can be changed and such changes may be reflected in the
phenotype of the affected organism:


explain how an understanding of the source of variation in organisms has provided support for Darwin’s
theory of evolution by natural selection
describe the concept of punctuated equilibrium in evolution and how it differs from the gradual process
proposed by Darwin.
6