Charles Darwin: Natural Selection
Through his books 'Origin of Species by Means of Natural Selection (1859)' and 'The Descent of Man (1871)', Darwin created what was effectively a new paradigm that was to eventually change the way that many people viewed the world. Today, Darwin's paradigm is considered nature's model for the evolution of the species. However, this was not always the case and little over a hundred years ago, most people would have believed that all species had existed since the moment of their creation, which according to some biblical references was around 6000 years ago. Therefore, Darwin's idea of natural evolution was a very recent and profound paradigm shift based on the following principles:
- Biological species do not have a fixed, static existence rather
they are in a permanent state of change.
- All biological life struggles for existence and to produce the
greatest number of offspring.
- The struggle for existence culls out those organisms less well
adapted to any particular ecology and allows those better adapted
to flourish via a process called 'Natural Selection'.
- Natural selection and evolution require enormously long periods
of time. So much so that that process is barely perceptible in terms
of human history.
- The genetic variations that ultimately produce increased survivability
are random and not caused by God or by the organisms own striving
Of course, many people may still dispute the implication within the last bullet, i.e. that God is not involved in evolution; either by rejecting the very suggestion or by the argument that God was the architect of the very mechanisms by which natural selection works. However, putting aside the religious debate for now, the idea of natural selection has become the predominant principle of evolution. Subsequently, through the process of evolution, science has tried to provide an ever-growing rational explanation for the diversity we see. As such, there is a need to estimate when all the observed diversity took place. Common sense might tell us that the more two species are related, the more recently they diverged. Originally, taxonomy used this approach, albeit expressed in slightly more scientific jargon, i.e. the degree of phenotype similarity is reflective of a similar genotype similarity. However, with the growing knowledge of DNA sequencing, it has become possible to estimate when genetic diversity started to take place. For the rate of genetic change to be quantified, this change needs to be measured against some sort of clock; assuming the rate of mutation is fairly constant. To verify the potential of this method, its results need to be aligned to other methods, such as geology, which provide the base timeline of life on Earth. The oldest known fossils indicate that life began at some 3.8 billion years ago.
Alternative Evolutionary Ideas
The principle idea behind creationism is that the origin of all life, and presumably every species of life that has ever lived, is a supernatural deity, i.e. some deity that corresponds to one of the 250 major religions worldwide, ignoring all other creation myths. By way of example, according to Judo-Christian scriptures, written some 2000 years ago, the land, sky, plants and animals were all created by a supernatural being called Yahweh or God in 7 days, although the concept of time might be a debated issue. However,in order to align to accepted scriptures, some believe that creation has to have happened within the last 6000 years, which flies in the face of all geological and archaeological evidence. Of course, with 30,000+ branches of just the Christian church, there many variants of the basic idea, e.g. some believe that plants and animal species are unchanging, while others believe that different species can arise from existing species, as long as the 'original' species was created by God.
Inheritance of Acquired Traits
Jean-Baptiste Lamarck (1744-1829) is usually remembered today mainly in connection with a theory of heredity called the 'inheritance of acquired traits', although his theory was never fully accepted. Lamarck's ideas about evolution were based on the premise that individuals adapt during their own lifetime and transmit the traits they 'acquire' to their offspring. Offspring then adapt from where the parents left off, enabling evolution to advance. As a mechanism for adaptation, Lamarck proposed that individuals developed specific capabilities by exercising them, while losing others through disuse. While this concept of evolution did not originate wholly with Lamarck, he has come to personify both pre & post-Darwinian ideas about evolution, now called Lamarckism. While natural selection contradicts the scope of Lamarckism in the 'natural' world of evolution, the concept is not precluded when evolution is driven by design - see Artificial Life