1.There are certain lower group animals which live as host on higher group animals.eg.PLATYHELMINTHES(T.solium,T.saginata on humans,dog,cows as parasites),lices on humans etc.
But evolutionally these have developed before higher forms,then how were they surviving when higher forms were not developed?
2.Diff hosts like definitive & alternative hosts eg humans,dogs,sheep,pigsetc.have developed at diff times also,then how were they maintaining their life cycles?
I wonder whether these parasites lived on other forms of life prior to their present hosts. For example, did sabre-toothed tigers have parasites that "jumped" to other hosts when their hosts died out? This would have been adaptive behavior that ultimately evolved into a greater suitability for the hosts they have now. Isn't this what virus and bacteria do all the time? If the polar bear, for example, were to become extinct, would not its parasites find somewhere else to go and then evolve to accommodate the new situation?
I agree with answer #4. As I understand it, scientists believe in the idea of coevolution. They say that parasites and their hosts evolved together so that the parasite would not kill its host. I also do not think that it is true that parasites evolved in their current form before the hosts did -- do you have evidence that they did?
For one thing, these parasites have evolved along with their hosts; that is, the lice/fungus/whatever did not always exist in exactly the same form as they do now. As higher organisms developed, the parasites evolved and changed, too. Think of the example of species developing resistance to pesticides. The ones that are already resistant survive to produce offspring. As host species change, the parasites that are able to survive are the ones that leave offspring. The main point is that *all* the species are continually evolving and changing, so yes, there were no mites that specifically live on dogs before there were dogs.
Wow. I’m not a biology major, (I hope that would be the correct science to which I need to refer.) but I would predict that they were meeting their needs in some less efficient way before dogs, cows, humans, and etc. evolved. After these species evolved, perhaps the parasites evolved in order to function more efficiently with their hosts.
If you are talking about evolution, you are talking a constantly changing environment. One does not have to think much to know that the forms might have existed in other forms before. Not only do lower forms change but higher forms as well.
The evolution of parasites is not independent of the evolution of their hosts, who defend themselves. Generally, parasites have an advantage in this arms race due to their shorter generation time and greater numbers. Co-evolution leads to extensive local adaptation. That is, parasites in a particular area infect hosts from that area more efficiently than they infect hosts from another geographically distinct population.
It is quite true that a parasite could not have evolved before the evolution of a host for the parasite. But this does not mean that the current host of the parasite should have evolved before the parasite. The parasite could have depended on some other variety of host that developed before the parasite. When we accept this view of relationship between development of a parasite and its host, it is not difficult to imagine a situation i which the parasite and host have developed in parallel rather than one after another.
sorry!mistakenly i wrote host instead of PARASITES>