Creatures either adapt to their environment or become extinct. So called 'ancient' types of animal have been doing this successfully for as long as the 'modern' ones.
There are very many misconceptions about what most biologists understand by evolution. By definition any possible ancestor must be long dead, and describing any animal as ‘primitive’ is not the same as saying that it has not undergone the same amount of adaptive change as everything else. Coelacanths are certainly very much like some fossils, but that does not mean that they have stopped evolving. In much the same way modern crocodiles are very similar to fossil crocodiles. In both cases we can see that these animals are supremely adapted to their environments, but these environments have not changed recently and so nor have the animals.
Mantis Shrimps, as a group of animals, are twice as old as the dinosaurs. The dinosaurs’ environment changed too rapidly for them to adapt (maybe literally overnight if asteroid-impact theories are correct ), but the Mantis Shrimps have obviously been able to cope with changes. Everything alive today is equally ‘modern’, and when biologists describe a creature as ‘primitive’ they mean simply that it does not appear to have changed much recently. Fossils only give information about the harder parts of animals that existed in the past. Nothing about the physiology or behaviour of deceased animals is preserved in the rocks.
‘Survival of the fittest’ is a concept that is often misunderstood. It does not imply any ‘quality judgment’. In fact it is not even what Darwin said, his version was ‘survival of the best fitted’ … to their environment. The evolution of a species does not always lead to a more complicated version either - look at the barnacle parasites of crabs! These creatures evolved from shrimp-like ancestors to become parasites that look rather like blobs of jelly.
There appear to have been several periods in the earth’s history when the environment changed too rapidly for most animals to adapt. These events are known as ‘mass extinctions’, and it seems that we are presiding over one at the moment. Humans are causing much of the earth to change at a rate that is too fast for many species to cope with, and those species that are affected will probably join all those that are already extinct.
Evolution implies that all species alive today will either adapt to their changing environments or become extinct.
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