Why darwin was wrong about dating
By the mid-1980s there was great optimism that molecular techniques would finally reveal the universal tree of life in all its glory. The problems began in the early 1990s when it became possible to sequence actual bacterial and archaeal genes rather than just RNA.Everybody expected these DNA sequences to confirm the RNA tree, and sometimes they did but, crucially, sometimes they did not."We have no evidence at all that the tree of life is a reality," says Bapteste. The discovery of the structure of DNA in 1953 opened up new vistas for evolutionary biology.That bombshell has even persuaded some that our fundamental view of biology needs to change. Here, at last, was the very stuff of inheritance into which was surely written the history of life, if only we knew how to decode it.The tree is thus a record of how every species that ever lived is related to all others right back to the origin of life.For much of the past 150 years, biology has largely concerned itself with filling in the details of the tree.It was to prove a fruitful idea: by the time he published 22 years later, Darwin's spindly tree had grown into a mighty oak.The book contains numerous references to the tree and its only diagram is of a branching structure showing how one species can evolve into many.
At its base is LUCA, the Last Universal Common Ancestor of all living things, and out of LUCA grows a trunk, which splits again and again to create a vast, bifurcating tree.
As early as 1993, some were proposing that for bacteria and archaea the tree of life was more like a web.
In 1999, Doolittle made the provocative claim that "the history of life cannot properly be represented as a tree" (, vol 284, p 2124).
But today the project lies in tatters, torn to pieces by an onslaught of negative evidence.
Many biologists now argue that the tree concept is obsolete and needs to be discarded.