Download THE HISTORY OF EVOLUTIONARY THEORY

THE HISTORY OF EVOLUTIONARY THEORY
Darwinian Evolution
Darwin was not the first person to explain the process of evolution. Many had done so before him.
Darwin’s unique contribution was that he proposed a systematic mechanism for evolution – a set of
rules which evolution played by.
His famous book was called On the Origin of Species by Means of Natural Selection. Darwin provided
really detailed evidence to support his ideas – much of this came from his collections from the
Galapagos Islands. The book is therefore quite complex. This is surprising because the things Darwin
was saying were very simple. His main ideas were:
(a) Living things tend to produce too many offspring.
They produce more offspring than could possibly survive. Only a small percentage of the
offspring survive because resources such as food, shelters, mates etc. are limited.
(b) These offspring will not be identical for the most part
The offspring will vary, even if only slightly. Nowdays we know this is due to random mutations
or combinations of genes due to sexual reproduction. You are different to your parents and
siblings.
(c) Some of the variations (traits) in the offspring will allow them to be better adapted to their
environment.
Some offspring are better able to find food, shelters, and mates. These offspring are the
“fittest” and will survive and produce the next generation of offspring.
(d) Variation (traits) in organisms is inherited
The offspring of the ‘fittest’ and most successful organisms will inherit the new successful trait
(e) Eventually, a population will be made up mainly of individuals with the new trait
The species has adapted to be more successful in their environment. Evolution has occurred.
Natural Selection is the term used by scientists to describe Darwin’s theory.
1.
Describe how Scientists would use Darwin’s’ theory of natural Selection (outlined above)
to explain the following observations.
(a)
In some species of birds, the parent birds do not give food to each chick (baby bird). The chicks
have to fight for the food brought back to the nest by the parents.
(b)
In the past rabbits had much smaller ears compared to modern day rabbits.
(c)
On a forest floor there are many seedlings of eucalyptus trees. Those that are the tallest appear
to be the healthiest.
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Lamarckian Evolution
At about the same time as Darwin was trying to gain acceptance for his idea of Natural Selection, a
man called Lamarck had similar yet different ideas about evolution.
Lamarck believed in almost all the same points that Darwin proposed. The key difference was in point
(b) in Darwin’s theory. Lamarck believed that animals acquired traits because they were responding to
the pressure of their environment. If the organism changed during its lifetime, Lamarck believed this
physical change would be passed onto the offspring.
For example, Lamarck believed that giraffes developed longer necks by gradually stretching them as
they tried to reach higher leaves. The next generation of giraffes had longer necks because their
parents had been stretching their necks their whole life. Darwin on the other hand viewed the changes
(such as longer necks in giraffes) as arising by chance (a mutation or new combination of genes) in
an offspring. Because that offspring had a longer neck it was more successful (better adapted or
“fitter”) and was more likely to survive and pass this trait on to the offspring by inheritance.
2.
Read each of the following explanations of an example of evolution. In the right column
list which theory (Darwin or Lamarck) is being used to make the explanation.
DARWIN or LAMARCK?
Waterfowl originally did not have webbed feet. As they moved to the
water to obtain food, they had to stretch their toes to stand in the mud.
This stretched the skin between the toes in this way, waterfowl evolved
to have webbed feet.
In the evolution of the human races, dark-skinned people living away
from the equator were not absorbing enough sunlight to synthesise
Vitamin D. Those born by chance with lighter skin could synthesise this
important vitamin more easily and so survive better. The “lighter skin”
gene was passed onto their offspring and so eventually the people in
these areas evolved to have lighter skin.
When ostriches kneel down to sleep or eat, the skin on their legs rubs.
During the life of an ostrich, calluses on the skin build up. This
characteristic is passed onto their offspring so that ostriches are now
born with calluses.
3.
Darwin’s theory was accepted by the scientific community over Lamark’s theory. (a) What
do the two theories have in common, and (b) what is their main difference(s)?
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