Earth Science: Evolutionary Factors – the Evolution Of New Species
New species evolve when groups of individual organisms of a species are isolated from each other due to barriers that prevent sexual reproduction. There are two types of speciation due to isolation: allopatric and sympatric speciation.
Allopatric speciation happens when a new species evolves due to geographic isolation over a long period of time. Geographic isolation may be the result of populations migrating onto an island, structural construction work by humans, or climate change and associated consequences (such as the glaciation of an area). Isolated populations continue the evolutionary process separately whereby new races or subspecies may evolve due to mutations.
Initially, individuals of different subspecies are still able to reproduce. However, over time the gene pool (the total gene variation within a population) may not be able to mix anymore due to so-called isolation mechanisms, even if the previously separate populations repopulate a common area. If the individual organisms from different gene pools cannot reproduce anymore, they are, by definition, considered separate species.
There are various isolation mechanisms: isolation due to behavioral differences (such as changes in mating behavior), seasonal isolation (such as plants flowering at different times), mechanical isolation (such as anatomically altered sex organs), ecological isolation (such as population of different ecological niches as observed in Darwin’s finches) and genetic isolation (such as polyploidic plants whose genetic material is made up of more than one chromosome set).
Sympatric speciation
This type of speciation does not involve a previous geographic isolation but is due to the genetic isolation of individual organisms occupying a common area. The genome changes in such a way that a gene exchange with other individuals of a population becomes impossible.
A mechanism that can lead to sympatric speciation is a doubling of the chromosome set (polyploidy). This happens especially in plants that may, for example, self-fertilize or inbreed. A tetraploid plant (with four chromosome sets) and a diploid plant (with two chromosome sets) are unable to produce any fertile offspring.
JOURNEY TO THE GALAPAGOS ISLANDS
The English naturalist Charles Robert Darwin (1809- 1881) is considered the founder of modern evolutionary theory. He stated that a visit to the Galapagos Islands inspired his hypotheses about the origin of the species which he compiled and illustrated in his chief work The Origin of Species by Means of Natural Selection.
Conditions for speciation are unique on the Galapagos Islands as they are not only relatively far away from the mainland but the islands themselves are also more isolated from each other than other groups of islands. For this reason.
Darwin observed the same plants and animals on the individual islands, but they often showed substantial variations. The most well-known example is the 14 finch species he collected on the Galapagos Islands.
BASICS
BIOLOGICAL SPECIES TERMINOLOGY The term species is one of the fundamental categories of biological classification. There are, however, very different definitions of what a species is. As a result, various definitions also lead to a range of different classification systems.
One of the most commonly used definitions is: a species includes all individual organisms that are capable of naturally producing fertile offspring.