Opponents of evolution and natural selection are fond of quoting the eye as an example of irreducible complexity which they imagine will wash away all objections to their creeds: “How could anything so complex have evolved without a very clever chap like God being behind it?” they ask, “and why would it have evolved as it only works when it’s completed?” Aside from the logical error which astute readers will have spotted at once, the story of how eyes evolved not only demonstrates how it happened, but answers so many other questions,that it’s actually rather more interesting than the stories offered as an alternative. Read this beautifully explained article in the Conversation by George Kafetzis and Dan Nillson [1] for a full exposition. Our humble summary appears below.
About 620 million years ago there lived an animal that was ancestral to all animals that would ever have two sides and move forward. It needed to steer as it swam: so it had two light sensitive areas symmetrically up front on either side. Another patch on top told light from dark, and which way up it was. And there it might have ended except for two things One group of these animals went to live in the mud as filter feeders. Having no need to swim they lost the steering eyes. Of course they kept the middle eye as it as still important to know if the Sun was shining. But when some of their descendants in turn started swimming again they needed to steer. Slowly the sides of the top eye moved apart, developed lenses and became eyes. These were the vertebrates. And this is why the eyes of all vertebrates-fish, lizards, birds and humans are so very very different from all other animals :invertebrates, such as scorpions, flies, octopuses and so on . Never giving up moving, their ancestors needed those original bilateral side eyes which slowly became more and more complex. Look at a fly if you don’t believe us. For the record the vertebrates kept the third top eye, its just that in mammals it has shrunk to the internal pineal gland where it still controls lots of light-related things like sleep and melatonin release
Its funny to think of eyes starting simple, evolving, un-evolving in some groups, and then evolving again, all according to the needs of those animals at the time. Its refreshing to find our basic LSS beliefs confirmed. Truth, or knowledge worth knowing, is complex and requires a lot of patient exposition to tease out. And it shows that simple, this-explains-it -all tales only end up obfuscating any real understanding.l. Nice to think that what happened 600 million years ago still has lessons for us today.
#evolution #natural selection #eye #cambrian #vertebrates #invertebrates #paleonto;ogy #biology
Learning, Science and Society 