The Evolution of Evolution

In the past 200 years evolution has developed to become the dominant theory in all of biology, which owes to the work of many important scientists.

Where do good ideas originate? Some evidence suggests that they are inevitable. New innovations and discoveries might have multiple patriarchs who converged on similar thoughts at the same point in history simply by following the next logical step. This is one of the dominant lessons of Where Good Ideas Come From, a recent book by Steven Johnson, and the same principle can be applied to the theory of evolution through natural selection, which had been pursued independently by Charles Darwin and Alfred Russel Wallace at concurrent moments in time. And yet some scientists are so incisive that they revolutionize their field beyond the mere introduction of new facts and theories.

Darwin in 1881, a year before his death. - Wikimedia Commons

The Origin of Species

Both Darwin and Wallace had initially drawn inspiration from an essay by Thomas Malthus entitled "An Essay on the Principles of Population" which was first published in 1798. Its central tenet was that some individuals of a population would fail to survive long enough to reproduce. Though Malthus primarily focused on humans, from this insight both Darwin and Wallace conceived of the idea of selection: variation within the population allows certain individuals to survive better than others. The image of a great battleground in nature began to take hold.

Darwin, fearing that decades of careful work had been rendered obsolete by Wallace, was reticent to proceed, but he nevertheless published his seminal book "On the Origin of Species" in 1859. This fastidious tome had presciently answered all objections to evolution and proved almost irrefutable. Much of his evidence is still applicable today. Wallace, meanwhile, had evanesced and quickly moved onto other work.

Both Darwin and Wallace had intended to make a joint presentation at the Linnean Society of London, the world’s oldest society for the study of natural history, but Darwin had to demure due to the death of his son. Although the theory was greeted rather surreptitiously at first—the society’s president Thomas Bell noted in his journal that nothing of importance had taken place that year—it has since revolutionized the field of biology. Evolutionary geneticist Theodosius Dobzhansky once famously said, “Nothing in biology makes sense, except in the light of evolution.”

There are two primary meanings to the word evolution: descent with modification, meaning the change of species over time, and the actual mechanisms that allow it to occur (Darwin actually favored the term descent with modification, and the word evolution only appeared in later editions of his book). Many biologists of the 19th century had already accepted evolution as an inexorable fact.

The order of the fossil layer revealed by modern geology suggested that species had descended from each other over the course of millions of years, forming a contiguous line that made up a great “tree of life”. But for a long time the actual mechanism was unknown. Many different explanations were proposed to fill the void. The French naturalist Lamarck had theorized that the use of an organ may develop or change depending upon its use in the environment. One common example of Lamarck’s hypothesis is of a giraffe stretching its neck to reach leaves.

Genetics

Darwin’s theory had garnered greater acceptance and prospered into the 20th century, and the eventual emergence of genetics vindicated natural selection once and for all. The “father of modern genetics” is a man by the name of Gregor Mendel. He observed that plants predictably inherited dominant and recessive traits from their parents. Though formulated near the same time as natural selection, there is little proof that Darwin knew much about Mendel. His work remained mostly obscure until the year 1900, when three different European botanists had simultaneously helped resurrect his laws. At this time more powerful technology had allowed scientists to hone in on the genetic carrier in the cells.

The existence of DNA had actually been known since the 19th century, but its role in heredity was not confirmed until 1952. The following year, James D. Watson and Francis Crick discovered the double helix structure of DNA. The model was based on a single X-ray diffraction image taken by Rosalind Franklin and Raymond Gosling in May of 1952. Watson, Crick, and Maurice Wilkins, who had also contributed to the discovery of the DNA structure, all won Nobel Prizes for their efforts.

Modern Synthesis and Beyond

Around the same time the modern evolutionary synthesis was born. It demonstrated that Mendelian genetics was consistent with natural selection and gradual evolution. New mechanisms such as genetic drift were being proposed too. The term was originally invented in 1942 by Julian Huxley, but the major founders of the modern synthesis also included Ernst Mayr, Sewall Wright, JBS Haldane, and many others. Together they helped unite many disparate fields such as morphology, ecology, paleontology, and genetics into one cohesive theory.

The major innovation since the birth of the modern synthesis has been the ability to sequence DNA, which has allowed us to understand how organisms evolve on a molecular level. Normally genes are used to encode proteins, but scientists have also discovered that proteins regulate genes by switching them on and off systematically during the development of an organism.

According to a article by Carl Zimmer in the "New York Times", genes actually cooperate in clusters to produce a trait. Sometimes these clusters can get rewired, which gives rise to new evolutionary innovations. For example, 13 human genes that help encode the neural network in the brain are also found in single-celled organisms, which obviously lack neurons. Darwin used homology as proof of evolution, arguing that a bat wing was similar in characteristics to the morphology of a human hand, but modern scientists have also begun to find homologies between genes. The PBS show NOVA produced a special titled “What Darwin Never Knew”, which demonstrates the remarkable progress made since the publication of his book, and yet most of his work has stood the test of time. Evolution has developed beyond—but never quite outgrown—Darwin’s principle insights. Like life, it seems, our understanding of biology is always being evolved.

Reference:

The Search for Genes Leads to Unexpected Places - NY Times