In the chapter The Origin of Species, Coyne describes how the majority of species that form the diversity of the biosphere we live in. The predominant pro-evolution theory is that different species were caused by a single population being separated geographically and evolving in a different manner from its distanced kin until a point where if the two populations were reintroduced, they would be unable to reproduce with each other and therefore recombine their genes. However, can we really expect that of the millions (and perhaps billions depending on the classification system) of species in the world that they all were separated by a landmass forming across the sea or a mountain chain rising amidst a forest? Granted that the earth has been around for a long time and that the planet has changed a lot since life first inhabited it but what other possible ways could a population evolve separately from another population of the same species to the point where it can no longer share genes and becomes a different species? Dr. Coyne also gives the example of flowers adapting to different pollinators and therefore not being able to recombine their genes so obviously this one is exempt.
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As Jerry Coyne mentions in his book, evolutionary adaptation can occur not only because of selective environmental pressures, but also because of genetic drift. Two species that live in almost identical environments, but are separated, could develop many different features. Genetic drift is "the change in the relative frequency in which a gene variant (allele) occurs in a population due to random sampling and chance" (Wikipedia). Very often evolution is misinterpreted to only occur when selective pressures are put onto a species, but simply isolation and genetic drift can cause one species to split into two. An example of this would be the different blood types of Native Americans and Asians, Caucasians, Africans, etc. There are no selective pressures that effect blood TYPE, yet there are distinct differences. How is this possible? This can easily be explained if groups of nomads who originally traveled over the Bering Strait had just a slightly higher amount of say, B+ type blood, and then as time passed on, it would be more likely for their offspring to have b+ type blood. Then, as long periods of time passed on, even without environmentally selective pressures, the differences between the two groups would be noticeable. While this is merely touching the topic, since there aren't multiple species of humans, it its touching it on a smaller scale. Another example of genetic drift would be bacteria, there are many types of bacteria (due to high reproductive speed), that have shown genetic drift during laboratory tests even with the same outside pressures. Once again, there are many factors that contribute to evolution and also speciation, but genetic drift works alongside natural selection to provide a multitude of new species.
ReplyDeleteSources:
Why evolution is true
Biology book
http://en.wikipedia.org/wiki/Genetic_drift
http://www.scientificblogging.com/tropical_ecology_notes/blog/where_does_species_diversity_come
http://www.ucl.ac.uk/~ucbhdjm/courses/b242/InbrDrift/InbrDrift.html
Well the example given of when one species is separated into two populations in different locations and adapt and evolve into different species is called speciation. Speciation is only one type of evolution. There is also adaptaion, co-evolution and cooperation. Adaptation is the process where an organism becomes better fit to live in its habitat which can be caused by a sudden change in environment so the organism must adapt or die. Co-evolution is when the evolution of one species causes an adaptation in another prey or competitor species which causes an adaptation in the original species creating a cycle of evolution. Cooperation is where cooperatoin of two species benefits both groups, so the evolution of one may benefit both. So there are many ways that species can evolve, whether it be one species evolving into two separate, one species adapting to its habitat and creating a single new species, or two species causing adaptations and evolution in the other.
ReplyDeleteSources:
http://en.wikipedia.org/wiki/Evolution
pbs.org/evolution
Reproductive isolation is one way that a species can diverge into two different species without being geographically isolated. This is when barriers to breeding among a population occur until the population has reproduced enough times that the offspring have selected different genes many times so that they are so genetically different that they can no longer reproduce with each other. This starts because of disruptive selection, when two extremas of a specific trait in a population are selected for in reproduction differentiating the two organisms. For example, the wood frog and the leopard frog separated from the same species. The disruptive selection that occurred was their chosen time to breed even though they were not geographically separated one group of frogs chose to breed in early april and the other in mid april eventually separating into the wood frog and the leopard frog because of the continued genetic differences that occurred once they stopped breeding together due to their varied breeding times. Interestingly enough when put in captivity these frogs have been seen to learn to breed with each other again. Another way that species can diverge into separate species is when a predator is especially active or extinct in an area. Even if the species is not geographically separated by a mountain or ocean or some landmass a predator can be especially abundant in a specific area. This would affect the way that the species in that small area that is being attacked evolves because natural selection would be choosing different traits than in an area where the predator is extinct so the species does not need to adapt to it. This can create two different species as well.
ReplyDeletehttp://bioweb.cs.earlham.edu/browse/formation/index.html
http://en.wikipedia.org/wiki/Disruptive_selection
Well Coyne points out we see certain animals in these places that look very similar, and have adapted to their surroundings (92). This would be called speciation. This is the evolutionary side to the argument. Creationists would argue that these creatures are different.
ReplyDeleteThough there is one way in which a species could separate besides a physical land mass or ocean, and this would be through animal behaviors. For instance let's say that a species is inhabiting a piece of land. This specie ate only mouse, but now on this source of land, the mice are completely gone. What would happen is that the some of the creature would move across to other parts of the land in search of food. Some of the species would remain, and these species decided to get a different source of food off the food chain. They would have to develop certain adaptations in order to capture their food. Along with these adaptation could be that they might develop stronger legs in order to move faster so they can catch their food, or that they develop a different set of teeth to help chew different food. They might also get specific enzymes, etc. The species that move in search of the same food being the mouse, would also have to develop adaptation, but not in eating of catching their food, but to the environment that they are in. They need to develop certain key characteristics that enable them to live in this environment so that they don't die. Natural selection plays a major role in this because it needs to choose the creatures that develop those adaptations that enable it to survive in the conditions it is presented. So we can see that these creatures that were once one, now became two different species because of its behaviors that it choose in order to deal with the food problem that they were facing. Through the conditions that they encountered, they now have different adaptations to cope with their conditions. Throughout time, they would eventually start evolving, and they would not share the same genes any more.
I would agree with Tianyu that blood type would be a factor that helps separate us humans. It is weird to think though how we are still able to have children if our blood types are not the same.
Sources:
Coyne: Why Evolution is true
Tianyu's comment
http://en.wikipedia.org/wiki/Speciation
http://evolution.berkeley.edu/evosite/evo101/VBDefiningSpeciation.shtml
The last source is great animation for speciation.