<p>Darwin's theory of evolution was for more than a century dogged by a major problem: the evidence proving the connections between the main groups of organisms was nowhere to be found.<br><br>By the 1970s this absence of 'transitional fossils' was hotly debated; some palaeontologists wondered if these 'missing links' had been so quick that no trace of them was left. However, during the past three decades fossils of walking whales from Pakistan, ...