Sunday, April 11, 2010
The origin of species
In the beginning of the chapter The origin of species, Mr. Coyne states that the thing that defines a species is that organisms of that species can't mate with some one outside that species. Organisms have certain characteristics that make them undesirable towards different species for mating. Explain the advantages of not being able to mate outside your species and explain how it relates to evolution. Provide an organism that helps you explain the concept.
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The purpose of having sex and reproducing is to keep an organism's gene pool alive to spread its genes. Sex between different species often results in nonviable or sterile offspring. For example,the mule which is the offspring a female horse and a male donkey is sterile and can't reproduce. There is no evolutionary advantage to sterile offspring because the "hybrids certainly can't exchange genes"(173), so the species' gene pool is not being preserved.
ReplyDeleteAlso, sex also uses much energy which is best conserved to keep alive an organisms genes. Wasting energy generating gametes (or for females, housing the "parasite" embryo) to produce an offspring that cannot survive or cannot produce offspring of its own is not a selective advantage. Not only is the fitness of the parent decreased, but the purpose of sex is not met in that the organism's gene pool is not being kept alive.
Knowing that inter-species sex may be a selective disadvantage, species use many methods to limit interspecies breeding.
Some species use chemical methods such as pheromones which may not be attractive to other species. For example, females of [i]Drosophilia[/i] have "chemicals on their abdomens" (173) that discourage males of other species.
Other species may use reproductive barriers such as time to prevent inter-species breeding. Plants may have "flowering seasons [that] don't overlap" (172) with the flowering seasons of other nearby plants.
This connects to the theme of evolution because preventing inter-species breeding is a selective advantage. When two species start interbreeding, less viable and less reproductive compatible offspring start appearing. The organisms who could not prevent interspecies breeding did not produce offspring that could spread their genes, so their gene pool dried up. When an organisms was able to avoid interspecies sex, they were able to produce viable and non-sterile offspring to prolong their gene pool.
I agree with Frank that there are so many disadvantages to mate with other species such as wasted energy for a sterile offspring or one that is not even living, but I would like to address more of the advantages in species mating with their own species.
ReplyDeleteIn most species that have been able to survive to modern time, the reason they are able to survive is because they express genes that are capable of surviving in a certain environment and the consequences of living there such as predators, temperature, etc. Some of these genes would lost through inter-species breeding since only half of the chromosomes come from a parent. To be able to reproduce offspring that have nearly all the genes that are found in a specific species that may complement with each other will create an offspring that will have a higher chance of surviving and reproducing in an environment that the specie's predecessor could survive and reproduce in.
This concept relates to the theme interdependence in nature in that the genes expressed to let an organism survive in a certain environment does depend on the nature. That is why it is essential for intra-species mating because of the fact that the species must have the genes in order to be able to survive in an environment in which it most likely has its realized niche.
I disagree with Andrew because though sometimes a better and strong organism comes out of interbreeding, weaker animals too can be a result.
ReplyDeleteI totally agree with Frank. The use of a lot of energy to create an offspring is not worth it if they cannot survive and reproduce.
Suppose interbreeding was legal and different species could mate with each other, then I feel that there won't be a balance. It would lead to destruction. More and more new "species" would be created. SOme stronger and some weaker. The population of organisms on Earth would grow exponentially. There would not be enought space to accomodate every organism. The weaker species will soon become extinct and the stronger species will rule the planet. There would be no sense of competition and Predation. There would be no limit. Campbell says, "biotic and abiotic factors influence the density, distribution, size and age structure of populations" (Campbell 1174). The limitless breeding would create havoc. Evolution wouldn't exist. COyne said that the modern theory of evolution comprises of "six components: evolution, gradualism, speciation, common ancestry, natural selection and nonselective mechanisms of evolutionary change" (3). Gradualism would be eradicated as the change will take place in a generation. Natural selection would not exist as inbreeding would lead to stronger animals which would get rid of the smaller ones. Speciation would not exist as inbreeding would create a new species everytime. Common ancestry would be more difficult to trace. Nonselective mechanisms of evolutionary change like "random changes in the proportion of genes" would not happen. Since the above components would not take place, evolution won't exist.
A theme addressed is interdependence in nature. The organisms need predation and competition and evolution to maintain balance on earth so as to reduce exponential growth and the elimination of weaker species.
I disagree with Andrew because even though interbreeding creates stronger species, it creates weaker species as well which would not be provided with an advantage.
ReplyDeleteI agree with Frank that it is not worth it if the organisms have to use a lot of energy in order to create infertile organisms.
Suppose interbreeding was legal and species can mate with other species, there won’t be diversity. The stronger organisms will defeat the weaker organisms and the weaker organisms will become extinct. The populations will grow exponentially and exceed the carry capacity of Earth. Predation and competition would not exist. There would be no limit. Campbell says, “…biotic and abiotic factors influence the density, distribution, size and age structure of populations” (Campbell 1174). The limitless population will keep on growing with nothing stopping it. Evolution would mostly likely not exist. Coyne says that the theory of evolution is made up of “six components: evolution, gradualism, speciation, common ancestry, natural selection and nonselective mechanisms of evolutionary change” (Coyne 3). Gradualism would not exist as a drastic change would take pace within one generation. Speciation would not be even known as “species” would be created every generation. Common ancestry would not exist as we wouldn’t be able to trace common ancestors. Natural selection would not occur as interbreeding would cause change. Nonselective mechanisms of evolutionary change would not lead to “random changes in the proportion of genes” (Coyne 13) as the gene populations would change entirely as completely new genes would be present. Since the other five components won’t exist, neither would evolution.
A theme addressed would be interdependence in nature as predation, competition and evolution need to occur to create a balance in nature.