Extinction is a factor that you have to take into account for any reconstruction of the evolution of a group. Climate change (aridification of Africa in the past 20 MYA) is the main factor of recent missing links, both for my plants and your animals. The problem is, you cannot reconstruct a true phylogeny of old groups because the deeper you dig, probabilities of extinction increase.

Extinction is a factor that you have to take into account for any reconstruction of the evolution of a group. Climate change (aridification of Africa in the past 20 MYA) is the main factor of recent missing links, both for my plants and your animals. The problem is, you cannot reconstruct a true phylogeny of old groups because the deeper you dig, probabilities of extinction increase.

I think that the main problem here, regarding fossils in chimp's evolutionary lineage, is the problem with fossilization in Africa. Generally, the conditions for fossilization are not so good there. The fossils of hominids are present because they seem to be very abundant all over Africa. Chimps and their ancestors probably were presented with small populations and in areas with even worse conditions for fossilization. That's my opinion...

Dear Alfonso I work on microorganisms. It is even more difficult to determine their presence or extinction.

Extinction is an intrinsic factor of evolution. I agree and it is also difficult to get fossils of all the links. But another question arises. Is evolution always slow and steady with all the possible intermediates and links or it can be abrupt also? Many animals or plants are on the verge of extinction. For example tiger is on the verge of extinction. Does it mean the lineage of tiger will end with its extinction? I think only fossils can not provide answers.

Fossils are not the answer indeed for your microorganisms. Speciation is not always slow and uniform; bursts of speciation are more plausible, usually triggered by climate changes or by the acquisition of a novel trait. All this is very dynamic and fast-moving, and lineages appear and become extinct (e.g., neanderthals). 

Dear Naveen,

                 I work on microfossils specifically on pollen and spores. Extinction and speciation are the two lineages of evolution. There are two types of competitions amongst the organisms, one is inter and other is intra-competition. The inter and intra- species competition and surrounding environment regulate the life processes of every organism. Those who adapt themselves lead to speciation and those who can not are out-competed by others and get extinct. Evolutionary processes are generally slow and steady but they can be spontaneous too (favourable mutations). Every extinction is the past were natural, man has no play in it as we have not evolved then. But now, when we talk about Tigers, the cause of their extinction is entirely dependent on us. Loss of their habitats, ruthless killing and afforestation took this species to the verge of extinction. The changes in their surrounding is so spontaneous that they can't adapt and this may lead to their extinction.  

          As far as the evaluation of extinction events on the basis of fossils records is concerned, their presence must give us the clues of the life that existed once. But, their absence doesn't mean that there was no life at that instance of time. Fossilisation of any organism is regulated by taphonomic processes. Only 1 percent of organisms get preserved as fossils. We may not find the complete leneage of any genus preserved as fossils. So, fossil presence give us the clue of past life but no fossil doesn't reffer to no life at that time and area.

          I hope my answer is helpful for you.

Dear Shreya

What can you think or propose to be the possible reasons that can lead to extinction of humans from earth (of course apart from some catastrophe). 

Oh, a tricky question. Well, humans are the smartest species on earth. So, I think we will make some way out to live in the plastic (artificial) environments prior to our extinctions. But, I think the surrounding would not remain same as green and fresh as they are today.

Oh that is a different debate altogether. Are humans the smartest species or the prokaryotes (which were before us and I think will remain here even after us) or the reptiles and similar examples in Kingdom Plantae.

Yes, no doubt that prokaryotes evolved much before and are consistently invading the Earth from that then. But, maybe we were also counted amongst them in the times to come.

I think Dinosaurs were the most powerful and dominant organism on the Earth till date. But, they have also faced an extreme devastation that led to their extinction. Mammals were small and few in number at that instance of time. Extinction of Dinosaurs provided room for the mammals to flourish. So, I think in the days to come we may face the same circumstances but its not certain. Nature is far beyond our predictions and imaginations.

Hi Naveen,

I think it'll be helpful if you could elaborate on what you mean by 'species in between humans and chimps.' or 'missing links'. Chimpanzees and Bonobos are the closest extant relatives of humans, but that doesn't mean we need to have half-human-half- bonobo organisms. All it means is that humans, chimps, and bonobos share common ancestors. If you mean fossils of those common ancestors by species-in-between, I think we believe we have rich fossil data. "the fossil record of extinct humans is now incredibly rich, so there are more 'discovered links' than there are 'missing' links" (Prothero 2007: p. 126;). 

As to why some species live and why some species go extinct, that's a really complex question. It might be partly due to chance, and partly due to lots of other environmental/genetic reasons.

Let me know what you think,

Charu