Darwin's Theory of Evolution
Charles Darwin is renowned in many countries across the globe as the
man who developed the Theory of Evolution. His theory sets about explaining
the progressive changes that occur within species down the generations,
as well as the formation of new species, when environmental pressures
have differential effects on the reproductive success of all individuals.
Darwin's theory has two aspects to it, namely Natural Selection and
Adaptation, that work together to shape the inheritance of alleles (forms
of a gene) within a given population. Darwin made the following five
fundamental observations, from which three inferences can be drawn.
- All species have such great potential fertility that their population
size would increase exponentially if all individuals that are born
go on to reproduce successfully.
- Populations tend to remain stable in size, except for seasonal fluctuations.
- Environmental resources for things such as food and shelter are
- Individuals of a population vary extensively in their characteristics
(to the extent that no two individuals are exactly alike) which impacts
upon their own ability to survive and reproduce.
- Much of this variation is genetic and is therefore heritable.
Inferences drawn from observations
- Due to the limited resources, there is a struggle for existence
among individuals - often with only a fraction of offspring surviving
through each generation to reproduce successfully.
- It is not a random process that determines which individuals will
reproduce and which will not, as it depends in part on the genetic
/ hereditary constitution of those surviving individuals. Those individuals
whose inherited characteristics best suit them to that environment
in which they live are likely to have more offspring than those that
are not so well adapted to the environment. This, by definition, is
- The unequal ability between individuals to survive and reproduce will lead to
gradual evolution of the population, with favourable characteristics
accumulating over the generations through natural selection.
Natural selection shapes adaptations and differentiates between the
reproductive success of individuals. Adaptations are anatomical structures,
physiological processes, or patterns of behaviour that contribute to
ancestral survival through the unique suitability of those traits /
characteristics (Crawford, 1998). There are three key conclusions to
be drawn from the theory of evolution:
- Natural selection is differential success in reproduction.
- Natural selection occurs through an interaction between the environment
and the variability inherent among the individual organisms making
up a population.
- The product of natural selection in the adaptation of populations
of organisms to their environments.
Things to remember about evolution
This information is taken from the lecture notes for
175.202 students at Massey University written by Professor Andy Lock.
Click here if you want to be taken to the site where a fuller account
- Evolution is not progressive - Evolution is not designed
to produce the best quality products, it only seeks to design adaptations
'that will do the job' most efficiently and economically. Therefore,
evolution used the 'mammal template' throughout the development of
all mammal species - eg. pentadactyl limbs, mammary glands, spinal
curvature, pelvis structure - and made the necessary modifications
to suit the niche that species lived in.
- Evolution is not an argument for the status quo - Evolution
does not dictate why things are the way they are. It must be remembered
that some of an animals features may be trade-offs or by-products
of the evolution of an unrelated adaptation.
- Evolution provides constraints - What has gone before sets
physical limits on what we can do now. This is seen in the fact that
we learn some things much more readily than others. In this sense
evolution has also constrained what things we are able to perceive
and attend to.
- Evolution provides complexity from simplicity - Species that
depend on each other for food (predator - prey relationships) often
enter into 'arms races', as they try to outdo each other.
Click here for a link to Darwin's 'Origin of Species'
Environment of Evolutionary Adaptation
The social function of intelligence
References and Bibliography
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