The Tangled Tree | David Quammen

Summary of: The Tangled Tree: A Radical New History of Life
By: David Quammen

Introduction

Welcome to the fascinating world of ‘The Tangled Tree: A Radical New History of Life’ by David Quammen. In this book summary, you will discover the concepts behind the tree of life, the history of evolution, and the groundbreaking work of Charles Darwin. Delve into the mysteries of cell development through symbiosis and the controversial theories of Constantin Merezhkowsky and Ivan E. Wallin. Uncover the discoveries in the field of molecular phylogenetics, Carl Woese’s work in determining the ‘Big Tree’, and the realization that horizontal gene transfer is largely responsible for the tangled tree of life. As you embark on this journey, brace yourself to be enlightened about the complexity of life and how it continuously evolves.

Evolutionary Tree Diagrams

The evolution of the tree of life diagram, from Aristotle’s ladder of ascent to Ernst Haeckel’s precise lineage illustrations, is a story of progress, exploration, and knowledge sharing. The tree of life remains a useful tool for categorizing biological information and understanding the evolutionary relationships between living organisms.

The tree of life diagram is a familiar image to many, representing the evolution of one type of life from a primordial amoeba to various animals and plants. This tool can be traced back to Aristotle, who wrote about the progressional development of animals in his book History of Animals, using a ladder of ascent model where living organisms gradually evolve into humans and heavenly beings. By 1745, Enlightenment-era thinkers started using tree-like models, as explorers saw more of the world, scholars needed a way to categorize all the diverse new plants and animals.

In 1801, French botanist Augustin Augier wrote, “an illustrated tree appears to be the most proper way to grasp the order and gradation” of plant life. However, it was Ernst Haeckel’s illustrations that brought the tree of life to its apex. Haeckel drew evolutionary trees that illustrated the precise lineage of living things, including vertebrates, mollusks, plants, and mammals. His work was an extension of Charles Darwin’s ideas.

Despite its history, the tree of life remains a useful tool for understanding the evolutionary relationships between living organisms and categorizing biological information. The evolution of the tree of life diagram is a story of progress, exploration, and knowledge sharing.

Darwin, Wallace and the Theory of Evolution

In 1831, Charles Darwin set sail on HMS Beagle, embarking on a journey that would profoundly shape his understanding of the natural world. His observations led to the development of his groundbreaking theory of evolution, which he largely sorted out shortly after his return. At the core of his theory was “natural selection,” which he believed to be the driving force behind adaptation and the inheritance of traits. However, Darwin delayed announcing his ideas publicly until a man named Alfred Russel Wallace pushed him to do so. In 1858, Wallace’s publication on evolutionary adaptation and inheritance caught Darwin’s attention, leading them to jointly present their ideas at the Linnean Society. Unfortunately, the presentation failed to make an impact, and Darwin only gained widespread recognition after publishing his book On the Origin of Species a year and a half later. Nevertheless, his ideas eventually changed the course of scientific exploration forever.

Evolutionary Symbiosis

The book recounts notable discoveries by Russian zoologist Constantin Merezhkowsky and American biologist Ivan E. Wallin on symbiosis, an idea that posits the combining of organisms to form new ones. Merezhkowsky gained notoriety in science circles after suggesting that plant cells developed chloroplasts by merging with photosynthetic bacteria. He called this new way of life “symbiogenesis”. Wallin saw another example of symbiosis under the microscope, this time with mitochondria, which provide energy to cells. Wallin suggested that the symbiotic relationship between bacteria and organisms was responsible for major developments in life on Earth. The story concludes with the revelation that advances in molecular biology later confirmed Merezhkowsky’s and Wallin’s ideas, marking a significant discovery in the history of science.

Evolutionary Origins Unveiled

Scientists prove the symbiotic origins of eukaryotic cells through molecular phylogenetics. Francis Crick’s discovery about the information contained within proteins and Carl Woese’s study of cell “internal fossil records” led to groundbreaking revelations about the evolution of life on Earth. The popular opinion that organisms didn’t incorporate other organisms was overturned, and it was shown that all eukaryotic cells are the result of symbiosis with bacteria.

Woese’s Revelations

This book section explores how the work of microbiologist Carl Woese and his team in sequencing the RNA of microorganisms challenged the prevailing belief that organisms do not merge with other branches once a species branches off. Woese’s “fingerprinting” methods unveiled that peculiar organisms, known as methanogens, could not be classified as either proks or euks, paving the way for the discovery of archaea. Further research by Woese’s team confirmed that chloroplasts and mitochondria had once been bacteria, absorbed by another organism through symbiosis, suggesting horizontal gene transfer. These groundbreaking revelations challenged mainstream views, revealing how genetic information had been routinely absorbed from one species by another, no reproduction needed.

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