I was led to this book by my friend who sent me a link to a New York Times excerpt from this book. I am grateful to her. Sitting in India, my opportunities are very limited to get access to books like this. There is no Barnes and Noble ( I cannot forget their huge store in New York). Unlike New York Times, or Washington Post, or The Guardian, newspapers in India do not carry a section on books. So when I read the excerpt, I ordered the book through Amazon.
The Tangled Tree, very properly, is about Carl Woese, who showed that archaea are a separate class of organisms.
The book starts with a tree traced by Charles Darwin. This is the Tree of Life. Above it he writes, I think.
The branches of this tree represent various organisms. Some of the limbs wither because they do not evolve and therefore, are unable to survive. Life originated from a single point because the microorganisms were ignored. The single point represent all the eukaryotes- plants and animals.
But the micrororganisms exist and very soon it is realized that they are different from eukaryotes. So the Tree of Life is modified. There were two points of origin- One that evolved into bacteria and the other that eventually led to us.
It is here that Carl Woese makes an entry. He wants to trace the origin of life. And he uses a technique that we still use today. He sequences a molecule called 16S rRNA and shows that there is third branch. These are organisms that live in extreme conditions- hot springs, extreme cold conditions etc. He names them as archaeabacteria though we now call it archaea. These are peculiar organisms, closer to us than to bacteria. The tree of Life, Carl Woese proposes, has three independent origins.
But it turns out that it is not still the complete story. Mitochondria, that I talked about in last post, are really bacteria engulfed by an ancient cell and this engulfment led to the evolution of eukaryotes and eventually us. This process is known as Endosymbiosis. This was proposed by many and popularized by Lynn Margulis (one of the few female scientists that the book acknowledges though there are unnecessary details about her personal life. Such details were not provided for the male scientists). The hypothesis was later proved true by using the same technique that Carl Woese had perfected. So here is where we diverge from Darwin's theory. It is just not a question of survival of the fittest.
And then it turns out that this is also not the complete story. Genes move horizontally, not just vertically. So it is not that we just pass our genes to our progeny but also that we can acquire genes from viruses and bacteria. This process is known as Horizontal Gene Transfer (HGT). This is how antibiotic resistance spreads. HGT is extremely common in bacteria. So common, in fact, that it is difficult to create a tree for them. Branches cross over and the tree looks like a web.
It is at this point, I think, David Quammen over reaches for he proposes that HGT occurs as commonly in higher organisms as it does in bacteria and therefore, the tree of life as proposed by Charles Darwin can not be created. I do not buy this argument. Yes, HGT is common in bacteria but it is not as common in higher organisms as he claims. We are still closer to apes than to bacteria.
The Tangled Tree, very properly, is about Carl Woese, who showed that archaea are a separate class of organisms.
The book starts with a tree traced by Charles Darwin. This is the Tree of Life. Above it he writes, I think.
The branches of this tree represent various organisms. Some of the limbs wither because they do not evolve and therefore, are unable to survive. Life originated from a single point because the microorganisms were ignored. The single point represent all the eukaryotes- plants and animals.
But the micrororganisms exist and very soon it is realized that they are different from eukaryotes. So the Tree of Life is modified. There were two points of origin- One that evolved into bacteria and the other that eventually led to us.
It is here that Carl Woese makes an entry. He wants to trace the origin of life. And he uses a technique that we still use today. He sequences a molecule called 16S rRNA and shows that there is third branch. These are organisms that live in extreme conditions- hot springs, extreme cold conditions etc. He names them as archaeabacteria though we now call it archaea. These are peculiar organisms, closer to us than to bacteria. The tree of Life, Carl Woese proposes, has three independent origins.
But it turns out that it is not still the complete story. Mitochondria, that I talked about in last post, are really bacteria engulfed by an ancient cell and this engulfment led to the evolution of eukaryotes and eventually us. This process is known as Endosymbiosis. This was proposed by many and popularized by Lynn Margulis (one of the few female scientists that the book acknowledges though there are unnecessary details about her personal life. Such details were not provided for the male scientists). The hypothesis was later proved true by using the same technique that Carl Woese had perfected. So here is where we diverge from Darwin's theory. It is just not a question of survival of the fittest.
And then it turns out that this is also not the complete story. Genes move horizontally, not just vertically. So it is not that we just pass our genes to our progeny but also that we can acquire genes from viruses and bacteria. This process is known as Horizontal Gene Transfer (HGT). This is how antibiotic resistance spreads. HGT is extremely common in bacteria. So common, in fact, that it is difficult to create a tree for them. Branches cross over and the tree looks like a web.
It is at this point, I think, David Quammen over reaches for he proposes that HGT occurs as commonly in higher organisms as it does in bacteria and therefore, the tree of life as proposed by Charles Darwin can not be created. I do not buy this argument. Yes, HGT is common in bacteria but it is not as common in higher organisms as he claims. We are still closer to apes than to bacteria.
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