Wednesday, October 1, 2014

Animal Varieties Seen By Darwin

Darwin spent 3 1/4 years, (over 2/3 of his 4.8 Beagle voyage years), exploring on land, (18 months at sea).  He decided early that he could write a book about geology, and he showed a gift for theorising.  Darwin collected and made detailed observations of plants and animals, with some results disturbing his educated belief that species were stable fixed life forms.  Back in England, that provided the basis for ideas which came to him, leading to his good theory of evolution by natural selection.
More than half of Darwin's carefully organised zoology notes were about marine invertebrates.  They show closely reasoned interpretations of what he found about their complex internal anatomy while dissecting specimens under his microscope, or from his little experiments on their responses to stimulation.  His onshore observations of creatures had included intense analytical comments on possible reasons for their behaviour, distribution, and relation to the environment.

1837 Jan. 4 Charles Darwin had presented to the Geological Society of London his mammal and bird specimens.  Ornithologist John Gould soon announced that the Galapagos birds which Darwin had thought were a mix of blackbirds, "gros-beaks", and finches, were in fact 12 separate species of finches.  Also what Darwin had thought was a wren was in the finch group.  All that had then led Darwin to ponder: how could such variety have developed for finches?  What could have accomplished such food eating beak specializations good for using different kinds of plants on different islands?

Also at Punta Alta in Patagonia, Darwin had found fossil bones of huge extinct mammals in cliffs beside modern seashells, indicating gradual quiet rises in some near-ocean lands, not extinctions with any signs of change in climate or bad catastrophe.  This had also made him puzzle over how so much change in life forms could have slowly occurred over lengthy ancient times.

Later in England Darwin had puzzled over other features of life.  Why do human early embryos show at the neck the tiny beginning of fish like gill slits, which would develop into bones of the inner ear?  It was as if land animals start life developing partly like fish!  How could this have happened?  Also a snake embryo temporarily showed the beginnings of legs.  Why?  Darwin also studied how people bred different kinds of dogs, effectively nicely achieving slight evolution in mammals.  He noted how farmers chose for their future farms the best stocks for improved farm breeding from past natural evolved varieties.

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