The word evolution means an unfolding, gradual development, and it is a word that has become closely linked with the origin of animal and plant species as they exist today.
Scientists now believe that through millions of years of the earth’s life, simple organisms have developed into more complex ones. each better adapted to prevailing conditions than its predecessor. It is generally accepted that the ultimate survival of a new form is determined by an effect known as natural selection or the survival of the fittest theory intimately associated with the name of Charles Darwin( 1809-82).
Ideas about the origin of species
Darwin published his theory of evolution in 1859 in a book whose full title is On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, but which was popularly abbreviated to The Origin of Species.
He suggested that the development of species is a continual process, and implied that man himself must have evolved from an ape-like stock. This was considered by many to be a heretical proposal at the time.
After much critical examination by scientists. and a great deal of public scorn and derision concerning man’s supposed origins in apes, the theory of natural selection was assimilated and has remained ever since the central pillar of our ideas on evolution.
The modern conception of species as such began with John Ray (1627—1705) in the seventeenth century and was established fully by Carl Linnaeus (1707—78) in the following century. It was the Linnaean classification system that really emphasized the relationship between similar species, the variations on a theme that so impressed Darwin in his observations.
One theory about the origin of species that held sway for a long time, and encompassed the Christian view on the creation of man, suggested that species were created spontaneously, perhaps sequentially, after a series of disasters.
But the obvious relationships between species that emerged from studying Linnaeus’s classification of organisms forced people to look for the origin of species in a process of gradual change.
It was Georges Buffon (1707—88) who first seriously suggested that the environment had an important effect on the evolution of species. This idea was developed by Jean Baptiste Lamarck (1744—1829). and it is his name that is attached to the suggestion that species inherited characteristics that were adaptations to the environment.
The basis of Lamarck’s theory
Basically, Lamarckism is simple and attractive. It proposes that changes in external conditions create new needs in the species living there.
These new demands lead to new patterns of behavior that may involve modifying the use of existing organs, thereby altering their structure. It is these altered structures that the offspring are thought to inherit.
For instance, the Lamarckian theory proposes that giraffes have developed long necks as a result of their repeated attempts to reach food in high trees. Lamarckism attracted a lot of support, some of it after Darwin’s natural selection theory was published, and it is easy to see why.
But in fact, the laws of inheritance simply do not allow Lamarckian inheritance to operate. As we now know from modern genetics, characters are passed from parent to offspring by means of the genes in the germ cells (the ones that form gametes), and structural changes in distant parts of the body do not modify the genetic constitution of the germ cells or indeed of any cells.
It was against the background of Lamarckism that Darwin produced his theory of natural selection. He set sail in HMS Beagle as the expedition’s naturalist and returned five years later a confirmed evolutionist, the transformation has taken place on the Galapagos Islands.
The fruits of Darwin’s voyage
In all his explorations during the five-year voyage, Darwin was impressed by the subtle variation between species, particularly among the finches on the Galapagos Islands.
Darwin noticed that in almost all organisms there is a massive production of potential offspring (whether eggs or spores) and that only a few survive. Life, then, was a struggle for existence. The next important step in the development of Darwin’s ideas was his recognition of the great individual variation within populations.
The combination of these two points produced a third: those variants that survived to adulthood in the struggle for life were, presumably, the ones most fit to do so. Darwin supposed that individual variation could be inherited by offspring from their parents. He, therefore, saw evolution operating through the natural selection of inheritable variations.
Darwin first developed this theory as early as 1838 but felt unable to publish it, perhaps because it went so much against his father’s beliefs.
Eventually, he was virtually forced into publishing when Alfred Russel Wallace (1823—1913) sent Darwin a short paper on his theory of evolution, a theory that matched Darwin’s own exactly. The two men presented a joint paper to the Linnean Society in 1858, and Darwin published The Origin of Species a year later.