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DDT was used during second world war to control malaria among the troops and the civilians. Later, it was used as pesticide in agricultural and household practices. Due to its excessive use it entered into the food chain and its amount in the food crossed the permissible level. So, it was banned by United States.
Two Types of Coevolution
Coevolution is common among organisms participating in a mutual interaction. In mutualism, both the organisms benefit from each other. When coevolution occurs among mutually benefiting species, it is called mutualistic coevolution.
When coevolution is found among species that have negative effects on each other, it is called competitive coevolution. There are two kinds of interactions between species that can lead to competitive coevolution:
<span><span>Predation is when one organism kills and eats another organism. The prey is the species that gets eaten by the predator, which is of course the species that eats the prey.</span><span>Parasitism is when one organism benefits by damaging, but not killing, another organism. The parasitespecies benefits from this relationship, while the host species is negatively affected.</span></span>
These two frog species separate by reduced hybrid viability. In reduced hybrid viability gene of different parent species may interact and impair the hybrid's development while in a reduced hybrid fertility a viable individual is sterile often due to the inability to produce normal gametes in meiosis. Hybrid breakdown; the first generation are viable and fertile, but when they mate the offspring are feeble and sterile.
