Another difference: After being dogged by privacy advocates, Google now anonymizes search results -- making them difficult, if not impossible, to trace back to an individual user -- after nine months.

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Many Israelis trace their roots back to Arabic-speaking countries, and this fusion is reflected in their creative cuisine.

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Friday's significance can trace its roots back to mid-April.

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After analysing the genes of modern people, though, Dr Quintana-Murci reckons that most Indians, at least, trace their roots back to a parallel spread by sea, via southern Arabia.

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"Because mutations start occurring at regular intervals in these genes as soon as a new species evolves - like the ticking of a clock - we can use them to trace the evolutionary history of a species back to its time of origin, " said Dr Hedges.

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The authorities are now looking for anything that might have been part of the explosive devices - bits of metal or sharp objects that they might be able to trace back to its owner or owners.

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The typical Viennese coffee house -- an elegant institution with high ceilings, marble-top tables and a stack of newspapers to make one linger over an impeccable black brew with a customary glass of water -- may be more famously known than its Ukrainian cousin, but to trace back the origin of the communal coffee space, you have to go to Lviv, a Medieval city in western Ukraine.

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Fiercely anti-immigrant, the Freedom Party (PVV), claims to trace its ideological roots back to the ideas of the Enlightenment and to defend them against culturally different newcomers.

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Then they sat back and watched, using a kind of glow-in-the-dark technique that allowed them to trace the fate of the cells.

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