![]() Likewise, the recently discovered Tiktaalik, a fossilised amphibian-like fish with lungs, connects the fish with land vertebrates. Our 3.5 million-year-old ancestor Lucy ( Australopithecus afarensis) is one of a string of "missing links" that took us from common ape ancestor to human. We now know it is around 4.6 billion years old - much more time for transitional forms than even he imagined. ![]() Darwin conjectured that the Earth was perhaps millions of years old. He also expresses a hunch that vastly more species exist or have existed than we know - including many transitional forms crucial to his theory. His challenge: if you accept that natural traits are variable, that variation is heritable and that there is a struggle for existence, evolution by natural selection must follow. ![]() ![]() The final rehearsal of Darwin's "one long argument". ![]()
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