Allopatric & Sympatric Speciation | A-level Biology | OCR, AQA, Edexcel

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The key points covered of this video include:

1. Speciation
2. Allopatric Speciation
3. Sympatric Speciation

Speciation

When two populations become too genetically distinct they are said to have speciated. Speciation is the evolution of two different species from an existing one. Populations are said to be reproductively isolated if there is no mixing of genes between them. If two populations are reproductively isolated for several generations, then genetic differences between them begin to accumulate. Eventually the populations are genetically distinct enough to be unable to breed and produce fertile offspring.

Allopatric Speciation

Reproductive isolation of two populations is often caused by physical barriers - this form of isolation leads to allopatric speciation. Allopatric speciation is the formation of two species from an original one due to geographical isolation. Common barriers to gene flow in allopatric speciation include rivers, mountain ranges and deserts. Species that are less able to disperse effectively will be more likely to speciate allopatrically.

Sympatric Speciation

Speciation can still occur without a geographic barrier - this type of speciation is called sympatric speciation. Sympatric speciation is the formation of two species from one original species due to reproductive isolation whilst occupying the same geographical location. Reproductive isolation in sympatric speciation can be created in several ways including: Temporal variation, Behavioural variation, Gametic variation.

Summary

Speciation is the evolution is the evolution of two new species from an original species due to reproductive isolation between populations
Allopatric speciation occurs when a geographical barrier isolates two populations for a significant period of time
Sympatric speciation occurs when there is no geographical barrier between populations
Reproductive isolation can arise in several, non-geographic, ways:
a. Temporal isolation - two populations breed at different times
b. Behavioural isolation - two populations have different courtship displays
c. Gametic isolation - gametes from two populations are genetically incompatible or unrecognisable

[inktothedarkness]

This video is done very well. Im going to recommend it to my class this week because it explains everything we will need for the exam in just a short amount of time. Thank you for making this video!

[AlevelStudent-cy]

For sympatric speciation, there isn’t any geographic barrier between the 2 populations so wouldn’t they experience the same selection pressures?

[NephilimFree]

What evolutionists refer to as speciation is not evolutionary change. It does not develop new anatomical features and therefore does not move an organism towards become a different kind of organism. It amounts to mere variation, often produced by phenotypic plasticity. It is not a pro0dfuict of mutation. It is a product of gene expression. Speciation is the opposite of evolutionary change in that it causes a continuous loss of genetic information by making genes recessive and eventually turned off permanently, unable to be expressed. Evolution, if it could have been true, would require the opposite - a continuous input of new information, which mutation is incapable of producing.

There are over 50, 000 varieties of spiders in the world. All of them are spiders.
There are an estimated 4, 300 species of horse and deer flies in the world. All of them are flies.
There are about 17, 500 varieties of butterflies in the world. All of them are butterflies.
There are over six thousand varieties of lizards in the world and come in a variety of sizes. All of them are lizards.
There are over 100 varieties of deer in the world. All of them are deer.
There are over 100 varieties of chicken in the world. All of them are chickens.
There are over hundreds varieties of cat in the world including Lion, Tiger, Cheetah, Lynx, Bobcat, Jaguar, Puma, Leopard, African Wildcat, etc. All of them are cats.
The list goes on and on.





"The species problem is the set of questions that arises when biologists attempt to define what a species is. Such a definition is called a species concept; there are at least 26 recognized species concepts."


"What are species? Perhaps no other issue in comparative or evolutionary biology has produced quite so much disparate opinion as this simple question" - Steve Jones, leading geneticist

"What are species? Perhaps no other issue in comparative or evolutionary biology has produced quite so much disparate opinion as this simple question" - Niles Eldredge, nobel Prize winning scientist, evolutionist

“When we descend to details, we cannot prove that a single species has changed; nor can we prove that the supposed changes are beneficial, which is the groundwork of the theory [of evolution].” Charles Darwin, The Life and Letters of Charles Darwin, Vol. 1, p. 210.

"Within the period of human history we do not know of a single instance of the transformation of one species into another one... It may be claimed that the theory of descent is lacking therefore in the most essential feature that it needs to place the theory on a scientific basis. This must be admitted." - T H Morgan, evolutionist, Evolution and Adaptation, Quoted in Why I Believe, 57

"And let us dispose of a common misconception. The complete transmutation of even one animal species into a different species has never been directly observed either in the laboratory or in the field.” - Dean H. Kenyon, Professor of Biology, San Francisco State University, affidavit presented to the U.S. Supreme Court, No. 85–1513, Brief of Appellants, prepared under the direction of William J. Guste Jr., Attorney General of the State of Louisiana, October 1985, p. A-16. Kenyon has repudiated his earlier book advocating evolution.

“... no human has ever seen a new species form in nature.” Steven M. Stanley, The New Evolutionary Timetable (New York: Basic Books, Inc., 1981), p. 73.

"My attempts to demonstrate Evolution by an experiment carried on for more than 40 years have completely failed." - Bacteriologist Dr. Nils Heribert-Nilsson


“Although the vast majority of research in evolutionary biology is focused on adaption, a general theory for the population-genetic mechanisms by which complex adaptations are acquired remains to be developed.” Proceedings of the National Academy of Sciences of the U.S., “Scaling expectations for the time to establishment of complex adaptations”, September 7, 2010, doi:10.1073/pnas.1010836107

“Dr Eric Bapteste, an evolutionary biologist at the Pierre and Marie Curie University in Paris, said: 'For a long time the holy grail was to build a tree of life. We have no evidence at all that the tree of life is a reality.' Dr Rose said: 'The tree of life is being politely buried – we all know that. What's less accepted is our whole fundamental view of biology needs to change.'”



“The fact that all the individual species must be stationed at the extreme periphery of such logic [evolutionary] trees merely emphasized the fact that the order of nature betrays no hint of natural evolutionary sequential arrangements, revealing species to be related as sisters or cousins but never as ancestors and descendants as is required by evolution.” [emphasis in original] - Denton, p. 132.