Speciation

Speciation

“Both in space and time, we seem to be brought somewhat near to that great fact --that mystery of mysteries--the first appearance of new beings on earth.” -Darwin  Speciation is the development of new species through evolutionary processes. This concept, although valid is not expansive enough to explain the evolution of adaptations in a population. There are many ways that speciation can come to exist, one being ecological opportunity. This is the case when there are essentially no predators or competitors within an environment. This was shown with the finches that Darwin found during his time on The Beagle. Another way for speciation to occur is through geographic isolation, within this example finches would have been isolated physically and that would have limited interbreeding. Evolutionary change is also a large part of speciation. This process involves natural selection, genetic drift and the founder effect. In some cases, evolutionary change will only produce subspecies which are organisms with differences that are still able to breed. Although this is possible, even a small change in just a couple of loci can create a complete new species. Reunion is a significant way to determine whether speciation has taken place. If the original species and new species are reunited and successfully interbreed the changes have not been significant enough to create a new species, just a subspecies. Only if the new species and original species are unable to breed has speciation occurred.

Microevolution and macroevolution, despite the small change in pronunciation, are very different concepts. Microevolution is a gradual change in gene frequency. This would be the case in a population of flowers that the first year it was observed had 80% white flowers and 20% purple flowers and the second year had 60% white flowers and 40% purple flowers. This change can be due to a couple of different factors, one being mutation. Some purple genes just mutated to white genes. Another can be the case of migration, where pollen from white flowers was transported from another population by migrating bugs. Genetic drift is also a form of microevolution, where by random luck alleles became more prevalent. Natural selection is also a form of microevolution, in this case white flowers were more fit for the environment than purple flowers. Maybe because predatory bugs are more attracted to white flowers than purple flowers or pollinating bugs more attracted to purple flowers than white. In comparison, macroevolution is major evolutionary change, it is what we see when we look at the large picture of the tree of life. Macroevolution will show the origin of mammals and the radiation of flowers. Although looking at this large picture seems overwhelming, it is the small changes that take place over hundreds of years that result in this large scale evolution. These are the same changes as that of microevolution; mutation, gene flow, genetic drift, and natural selection. These little evolutionary changes are responsible for the vast difference between lizards and grizzly bears. There are four distinct patterns of macroevolution: status, character change, linear splitting and extinction. Status is lineage that does not change over time, organisms in this pattern are called living fossils. Character change can result from adding or losing sections resulting in acceleration or reversed change. Lineage split is much like speciation, it is the uncommonly frequent changes of an organism. Extinction is a huge change to the environment and although this pattern can be rare, it also has the ability to affect a large population quickly and vastly. Over 99% of species that have lived on Earth are now extinct.



There are two different forms of lineage evolution, anagenesis and cladogenesis. These terms deal with the evolutionary change of the genetic lineage. Anagenesis is also referred to as phyletic evolution, which is lineage where the new organism does not branch off from the original organism even though a completely new species is created. Anagenesis results in the extinction of the old organism. Cladogenesis is also referred to as branching evolution, this is evolution that branches from original lineage to create a new species. This process is more common and allows for diversity as it is the branching of one original species into more new species. The original species does not become extinct which allows for a larger population. Although these are presented as two different ideas, there is some speculation that anagenesis is just another form of cladogenesis.



The only way to determine whether or not speciation has occurred is through interbreeding, it is not something that can be determined by appearance. Organisms can look alike but not be the same species, such as rabbits and cats, although they share many characteristics they cannot interbreed. Organisms can also be the same species but look different, such as a lion and a house cat, despite their differences, could interbreed if given the chance. Speciation is best tested by determining whether or not interbreeding is possible.

There are two main ways that speciation can occur, allopatric and sympatric speciation. Allopatric speciation is when a new species is produced because a population becomes separated. There are three steps to this: 1. A population is separated geographically. 2. New species are created due to environmental factors. 3. The original species and the new species produced by separation are too different to interbreed. Sympatric speciation is when two populations do not breed due to other factors. A common reason for this to occur is off timing during breeding season as some organisms are only fertile for a short time. Factors such as this prevent interbreeding.



The tempo of speciation, also called speed of speciation, occur in two levels; gradualism and punctuated equilibrium. Gradualism is the process of species evolving slowly over a period of time such as with natural selection. Small changes over a long period of time are gradual and produce incremental changes which can then be seen in fossils. This is the case with humans or the finches that Darwin discovered on his voyage. Punctuated equilibrium is when speciation occurs sporadically. There is a rapid change in the genetic make up of a population and then it remains exactly the same for many years. Fossils of the organism bryozoan show that the species was developed 140 million years ago and remained unchanged for 40 million years. The rate of change is just as important to the evolutionary process as change itself.

