Download Evolution Charles Darwin

Evolution
Darwin’s theory of evolution explains how species of living things have changed over geological time.
The theory is supported by evidence from fossils, and by the rapid changes that can be seen to occur in
microorganisms such as antibiotic-resistant bacteria. Many species have become extinct in the past and
the extinction of species continues to happen.
Charles Darwin
Charles Darwin was an English naturalist. He studied variation in plants and animals
during a five-year voyage around the world in the 19th century. He explained his
ideas about evolution in a book called On the Origin of Species, which was
published in 1859.
Darwin’s ideas caused a lot of controversy, and this continues to this day, because
the ideas can be seen as conflicting with religious views about the creation of the
world and creatures in it.
Charles Darwin (1809 - 1882)
Darwin’s finches
Darwin studied the wildlife on the Galápagos Islands - a group of islands on the equator almost 1,000
kilometres west of Ecuador. He noticed that the finches - songbirds - on the different islands there
were fundamentally similar to each other, but showed wide variations in their size, beaks and claws
from island to island. For example, their beaks were different depending on the local food source.
Darwin concluded that, because the islands are so distant from the mainland, the finches that had
arrived there in the past had changed over time.
Darwin’s drawings of the different heads and beaks he found among the finches on the Galápagos Islands
Darwin studied hundreds more animal and plant species. After nearly 30 years of research, in 1858 he
proposed his theory of evolution by natural selection.
Darwin's theory of evolution
The basic idea behind the theory of evolution is that all the different species have evolved from simple
life forms. These simple life forms first developed more than three billion years ago - the Earth is
about 4.5 billion years old. The timeline below shows some of the key events in the evolution of life
forms on Earth, from the first bacteria to the first modern humans.
******* SEE FLASH ANIMATION TIMELINE ON THE WEBSITE *******
Natural selection
The theory of evolution states that evolution happens by natural selection. Here are the key points:
Individuals in a species show a wide range of variation.
This variation is because of differences in genes.
Individuals with characteristics most suited to the environment are more likely to survive
and reproduce.
The genes that allowed the individuals to be successful are passed to the offspring in the
next generation.
Individuals that are poorly adapted to their environment are less likely to survive and reproduce. This
means that their genes are less likely to be passed to the next generation. Given enough time, a species
will gradually evolve.
Evidence for evolution - fossils
Most of the evidence for evolution comes from the fossil record.
Fossils show how much, or how little, organisms have changed over
time. One of the problems with the fossil record is that it contains
gaps. Not all organisms fossilise well, and there will be many fossils
that have been destroyed by the movements of the Earth, or simply not
yet been discovered.
Fossils of ammonites - sea creatures that
became extinct about 65 million years ago
The horse
One of the few animals for which we have a fairly complete evolutionary record is the horse because
all the main stages of the evolution of the horse have been preserved in fossil form. Over 60 million
years, the horse evolved from a dog-sized creature that lived in rainforests into an animal adapted to
living on the plains and standing up to 2 metres high.
The evolution of the horse
time period
height
1 million years ago
1.6 metres
10 million years ago
1.0 metres
30 million years ago
1.0 metres
40 million years ago
0.6 metres
60 million years ago
0.4 metres
Modern horse
Pliohippus
Merychippus
Mesohippus
Eohippus
In the process its multi-toed feet, that were adapted for walking across the forest floor, evolved into
single-toed hooves more suited for running over open country.
******* SEE VIDEO ABOUT THE FIRST FISH ON THE WEBSITE *******
Evidence for evolution - rapid changes
Evolution is difficult to observe because it usually takes many years to happen. This is one reason why
the theory of evolution is still a theory, not a law. Since no-one was around millions of years ago to
make observations, take notes and carry out experiments, evolution cannot be proved in the usual
scientific sense. However, rapid changes in species have been observed that support the theory.
Peppered moths
Before the industrial revolution in Britain, most peppered moths were of the pale variety. This meant
that they were camouflaged against the pale birch trees that they rest on. Moths with a mutant black
colouring were easily spotted and eaten by birds. This gave the white variety an advantage, and they
were more likely to survive to reproduce.
Airborne pollution in industrial
mutant black moths were now
predators. This gave the black
reproduce. Over time, the black
pale variety.
areas blackened the birch tree bark with soot. This meant that the
camouflaged, while the white variety became more vulnerable to
variety an advantage, and they were more likely to survive and
peppered moths became far more numerous in urban areas than the
The pale peppered moths camouflage well against the pale birch tree
The darker mutant peppered moths camouflage well against the
blackened birch tree
Antibiotic-resistant bacteria
Microorganisms such as bacteria and viruses reproduce very
rapidly and can evolve in a relatively short time. One example
is the bacterium E. coli. Its DNA can be damaged or changed
during replication, and most of the time this causes the death of
the cell. But occasionally, the mutation is beneficial - for the
bacteria. For example, it may allow resistance to an antibiotic.
When that antibiotic is present, the resistant bacteria have an
advantage over the bacteria that are not resistant. Antibioticresistant strains of bacteria are an increasing problem in
hospitals.
E. coli bacteria (Photo from Rocky Mountain
Laboratories, NIAID, NIH)
Extinction
Individuals that are poorly adapted to their environment are less likely to survive and reproduce than
those that are well adapted. Similarly, it is possible that a species that is poorly adapted to its
environment will not survive and will become extinct.
Here are some of the factors that can cause a species to become extinct:
changes to the environment, such as a change in climate
new diseases
new predators
new competitors
The fossil record shows that many species have become extinct since life on Earth began.
Extinction is still happening and a lot of it occurs because of human activities. We compete with other
living things for space, food and water, and we are very successful predators.
The dodo
The dodo was a large flightless bird that lived on Mauritius, an
island in the Indian Ocean. The island was uninhabited and the
dodo had no natural predators. Then Mauritius was colonised
by the Dutch in 1638. Dodos were hunted for food and easy
to catch because they were not afraid of people. New
competitors were brought onto the island, including pigs, cats
and rats, which ate the dodos' eggs and their young. Within 80
years, the dodo was extinct.
Engraving of the extinct dodo
Useful Vocab
genes: The basic units of genetic materials inherited from our parents. A gene is a section of DNA
which controls part of a cell’s chemistry – particularly protein production.
DNA: The material inside the nucleus of cells, carrying genetic information. NDA stands for
Deoxyribonucleic Acid.
Questions
1. According to Darwin, how do new species evolve?
2. Which individuals are most likely to survive to reproduce?
3. What is likely to happen to an individual that is poorly suited to its environment?
4. What sort of variation is inherited? Environmental? Genetic? Both? None?
5. Why do we have a good evolutionary record of the horse?
6. Why are white peppered moths likely to be more common than black ones in country areas?
7. Which of the following is not likely to cause a species to become extinct? A new disease? A new
predator? A new food source?