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Originally Posted by Klox
I have wondered about this for a long time. How does the evolutionary theory explain these questions:
How does a whole new species come about? Is it the offspring that is a new species? If so, does it just mate with the old species and its offspring advances the evolutionary species and that keeps escalating until you get a significant population? Do muliple offspring evolutionize in the same timeframe to mate with each other?
Thanks for any replies/answers.
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One divides different speciation modes according to where and how they occur
Allopatric speciation - speciation can occur when a geographic barrier separates two populations of a species, so that there is limited to no gene-flow between the population
Parapatric speciation - speciation can occur on the border between two species - in the hybrid zone
Sympatric speciation - speciation can occur without any separation of ancestral populations in different geographic areas.
In these three models of speciation, which are not mutually exclusive, as one species may have evolved by one route, and another may have evolved via the other route, there are various mechanisms at work on a smaller scale. Earlier there were great controversies within between evolutionists whether the allopatric mode of speciation was the only one, or whether speciation could take place parapatrically or sympatrically as well. With the many examples of parapatric and sympatric speciation in plants, this controversy should be put to rest, although there is still some controversy on whether or how often parapatric and sympatric speciation occurs in animals.
In the
allopatric model of speciation, it is thought that the geographic barrier is the first step in evolving reproductive isolation. As the populations are separated in space, natural selection, as well as genetic drift will act on each of the population. Different mutations will accumulate in the two populations over time. If there is a great environmental difference between the two geographic areas this may cause natural selection to act faster on evolving one of the populations to become more adapted to the environment. One example of this: beetle species of several genera, when blown out to an isolated island, rapidly evolve wingless conditions, because those individuals that fly, tend to leave the island
At some point in time after the geographic separation, it will be a separation even if the two populations meet each other. This might be due to pre-zygotic reasons or post-zygotic reasons.
Pre-zygotic reasons can for example be:
- ecological or habitat isolation (if the two populations mate on different species of plants for example, they will not meet each other, even if present in the same geographic area)
- seasonal or temporal isolation: if the two populations occur as sexual individuals in two different seasons of the year (or even during one day, as in night active and day active organisms)
- mechanical isolation: sex organs do not match
- gametic isolation: female and male gametes may not be attracted to each other, or male gamets of one species may not be viable in the sexual ducts of the other species.
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Postzygotic mechanisms can be:
- hybrid inviability - hybrid zygotes have reduced viability or are inviable
- hybrid sterility - hybrids are viable, but fails to produce functional gametes
- hybrid breakdown - hybrids are viable, and produce functional gametes, but hybrid offspring have reduced viability or fertility.
The parapatric model of speciation is very common in plants, where speciation may occur by hybdridization. If the hybrids have reduced ability to pollinate the parents, but increased ability to pollinate other hybrids, there will be a reinforcement by natural selection to select for hybrids that reproduce well. This mode of speciation by hybridization is not thought to be very common in animals, but there are other forms of speciation by hybridization that might occur more frequently, for example if the viable and fertile hybrids of the two species occupy another host than the parental species. This might then act as an isolating barrier.
Sympatric speciation: This mode of speciation can take many forms. In plants, new species may evolve in an instant by polyploidy and self-fertilization. This can happen within the parent population
In animals, one way to get a new species sympatrically is when a species develops stable polymorphic traits in camoflage, and these traits are linked to habitat/host preference Such a polymorphism can develop via divergent natural selection. Once a stable polymorphism exists, assorted mating would be favored, as intermediates between the two morphs would not be camoflaged well in either habitat. Assortative mating may be caused by difference in breeding time, or differences in mating behaviour (such as different courtship songs).
To answer your questions:
Is it the offspring that is a new species?
Generally not, the exception seems to be speciation by polyploidy in species able to do self-replication. Most often, there is a gradual change in two populations, as they get more and more reproductively isolated, until they no longer can reproduce with individuals of the other population (by prezygotic or postzygotic mechanisms)
