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40 41 its imPossiBLe how does nature do it Opponents of evolutionary theory sometimes point to features that seem to deny the possibility of their having been through an evolutionary progression. Examples are the carnivorous leaf of the Venus flytrap and the mammalian eye. The argument is that they either work or they dont, there can be no halfway development. But imagine evolution in reverse. The mammalian eye is a lens held in front of a retina by a sac of fluid. Imagine that sac of fluid getting progressively smaller, so the lens eventually sits on the retina. The lens and retina then fuse and the number of photosensitive cells reduces down to one. The result is a simple eye, common to many different organisms. It can still detect a movement around it, for instance an advancing predator blocking out the light. In the case of the flytrap leaf lower opposite, imagine the trigger mechanism removed. It may still trap the occasional tired old fly, but what if the leaf now exuded a glue to hold its prey while its lobes very slowly closed Going back further, the fingerlike appendages reduce and the lobe hinge disappears, so that the leaf can only fold itself by rolling. Earlier still, the surface area of the gluey substance may be optimised by forming droplets on hairlike protrusions. The result is the leaf of a sundew below. Above The long evolution of man from apes seems to have had some key factors driving it. The use of tools and division of labor between the sexes led to individuals becoming specialised to an extent unknown outside our species. The basically monogomous nature of mankind also ensures that a large proportion of males and females get to breed, further encouraging specialization. Left The Venus fly trap. An example of the kind of organism used to oppose evolutionary theory. How could it have come about Answer Small refinements and improvements over a very large number of generations, with occasional larger mutations, each conferring advantage to its descendants, while the failures remain hidden by history.
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