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INTRODUCTION
Biological
evolution is a population-level process guided by selection and, in small
populations, also by different random processes. In the biological world selection
is targeted at individuals and based on the differences of their genes. In the
latter half of the 19th century Charles Darwin, the father of the
theory of evolution, described two types of selection. The first type of
selection is natural selection [1]. It is based on the differential survival
and reproductive capacity of the individuals. The second type of selection is
sexual selection [2]. Sexual selection means that individuals tend to select
their reproductive partners so that the offspring receive the most favorable
genes possible regarding both natural and sexual selection.
In the theory of evolution, the concept of
‘fitness’ is central. ‘Fitness’ is the relative capacity of the individual to
produce fertile offspring; in other words, to have its genes represented in the
gene pool of the next generation. It must be stressed that fitness is a
relative concept; the individual in question is compared to the other
individuals of the population, and, more-over, fitness is dependent on the
environmental circumstances in which the individual is living. A given
individual which has a good fitness in a given environment can have poor
fitness in some other environment.
In general, fitness is constituted of two
components, the survival component and the reproduction component. To be fit,
an organism must survive until reproductive age and then reproduce. In addition
to this, many animals, notably several birds and all mammals possess a third
component of fitness which may be called a ‘fostering’ or ‘nursing’ component.
By this, it is meant that these animals, to be fit, must foster their offspring
until they reach their reproductive age. In man this third component of fitness
is very significant – apparently more significant than in all other mammals.
As, by
definition, individuals with good fitness, reproduce most, the mean fitness of
the population increases. In other words, the frequencies of alleles, which
offer the best fitness, increase.
The universal
principles of biological evolution, as for man as well, thus regarding also
man, are the following three: the principle of variation, the principle of
inheritance and the principle of selection. These principles comprise all the
necessary conditions for biological evolution of all species, including man. Thus,
together they also constitute a sufficient condition for biological evolution
[3,4]. If these principles are in force, biological evolution necessarily
follows.
Cultural
evolution, or the development of cultures, can be defined as the change of the
behavior of individuals through learning from one individual by another.
A parallel can
very well be drawn from cultural evolution to biological microevolution –
though less so to biological macroevolution. Researchers of the topic are
rather united regarding the hypothesis that cultural evolution in general
mainly obeys the same regularities as biological evolution, even though
considerable differences exist.
For example, it
is worthwhile to emphasize that while the conditions for biological evolution
are universal, the conditions for cultural evolution are species-specific – in
this case specific for man.
It is quite
clear that the necessary conditions for the development of culture also include
the principle of variation, the principle of inheritance and the principle of
selection. However, these are not all the necessary conditions for cultural evolution, and thus, conversely to
biological evolution, they, as a group, do not constitute a sufficient
condition for human cultural evolution. It seems that all the necessary
conditions are not even known yet, but
Organisms are adapted to the environmental
circumstances where they live. This means that they can produce so much
offspring that the relative number of fertile individuals in the population
does not decrease. In other words, the mean fitness of the population remains
constant or increases. In the biological evolution fitness is a simple index
which measures the reproductive success of individuals. The question arises
regarding whether a corresponding success index appears in cultural evolution.
The concept of ‘cultural fitness’ has been
proposed for such an index by WH Durham, the American biological anthropologist
[5]. Cultural fitness is defined as a function of time. The longer the period
of time that a cultural character is preserved and transmitted from one
individual to another in the population, the better it’s cultural fitness.
This formulation of the concept of cultural
fitness must, however, be regarded as too simple due to the fact that the
preservation of a cultural trait is dependent on the number of learning chances
an individual has to adopt the trait. At the same time, it has been proposed
that the course of cultural evolution can be predicted precisely on the basis
of the number of repeats of the learning event in the population [6].
The main significance of the foregoing
reasoning is, however, that while the progress of biological evolution can be
expressed in numbers of individuals; the progress of cultural evolution can be
expressed by measuring the length of time that a given cultural trait or
character is preserved and transmitted in the population.
Considering cultural evolution, it is
self-evident that biological evolution must have produced the conditions for
its existence. In other words, cultural evolution is a product of biological
evolution. On the other hand, cultural evolution has changed and continuously
changes our behavior in such a way that it affects our biological evolution. An
illustrative example is the evolution of erect walking on two feet, where behavioral
changes associated with it affect anatomical and physiological changes and vice
versa. Many other examples of this kind of evolutionary feedback loops have
been described demonstrating the fact that biological and cultural evolution of
man proceed in concert.
1. Darwin
C (1968) The origin of species by means of natural selection or the
preservation of favoured races in the struggle for life. A reprint of the sixth
edition. Oxford University Press, London.
2. Darwin
C (1913) The descent of man and selection in relation to sex. A reprint of the
second edition. John Murray, London.
3. Lewontin
R (1970) The units of selection. Annu Rev Ecol Syst 1: 1-18.
4. Lewontin
R (1982) Human diversity. Scientific American Books, New York.
5. Durham
WH (1982) Interactions of genetic and cultural evolution: Models and examples.
Hum Ecol 10: 289-323.
6. Strimling
P, Enquist M, Eriksson K (2009) Repeated learning makes cultural evolution
unique. Proc Natl Acad Sci U S A 106: 13870-13874.
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