#43: Five Big Additions to Darwin's Theory of Evolution

He had the main idea right, but in the past 150 years, scientists have filled out a lot more of the picture.

By Jessica Marshall|Tuesday, January 26, 2010

Charles Darwin would have turned 200 in 2009, the same year his book On the Origin of Species celebrated its 150th anniversary. Today, with the perspective of time, Darwin’s theory of evolution by natural selection looks as impressive as ever. In fact, the double anniversary year saw progress on fronts that Darwin could never have anticipated, bringing new insights into the origin of life—a topic that contributed to his panic attacks, heart palpitations, and, as he wrote, “for 25 years extreme spasmodic daily and nightly flatulence.” One can only dream of what riches await in the biology textbooks of 2159.

1. Evolution happens on the inside, too. The battle for survival is waged not just between the big dogs but within the dog itself, as individual genes jockey for prominence. From the moment of conception, a father’s genes favor offspring that are large, strong, and aggressive (the better to court the ladies), while the mother’s genes incline toward smaller progeny that will be less of a burden, making it easier for her to live on and procreate. Genome-versus-genome warfare produces kids that are somewhere in between.

Not all genetic conflicts are resolved so neatly. In flour beetles, babies that do not inherit the selfish genetic element known as Medea succumb to a toxin while developing in the egg. Some unborn mice suffer the same fate. Such spiteful genes have become widespread not by helping flour beetles and mice survive but by eliminating individuals that do not carry the killer’s code. “There are two ways of winning a race,” says Caltech biologist Bruce Hay. “Either you can be better than everyone else, or you can whack the other guys on the legs.”

Hay is trying to harness the power of such genetic cheaters, enlisting them in the fight against malaria. He created a Medea-like DNA element that spreads through experimental fruit flies like wildfire, permeating an entire population within 10 generations. This year he and his team have been working on encoding immune-system boosters into those Medea genes, which could then be inserted into male mosquitoes. If it works, the modified mosquitoes should quickly replace competitors who do not carry the new genes; the enhanced immune systems of the new mosquitoes, in turn, would resist the spread of the malaria parasite.

2. Identity is not written just in the genes. According to modern evolutionary theory, there is no way that what we eat, do, and encounter can override the basic rules of inheritance: What is in the genes stays in the genes. That single rule secured Darwin’s place in the science books. But now biologists are finding that nature can break those rules. This year Eva Jablonka, a theoretical biologist at Tel Aviv University, published a compendium of more than 100 hereditary changes that are not carried in the DNA sequence. This “epigenetic” inheritance spans bacteria, fungi, plants, and animals.

For example, rats exposed to certain fungicides during pregnancy give birth to male progeny with lower sperm counts and an increased chance of developing diabetes and cancer. In each generation that follows, none of which were exposed to fungicides directly, the male offspring continue to suffer the same fate. Jablonka argues that environmental exposures—toxic substances, diet, and even stress—can affect the genome. In extremely high-stress cases, they could possibly rearrange it enough to create new species. Eventually, she says, “evolution will have to yield.”

3. Mutations reveal surprising branches on the tree of life. Darwin would have been dumbfounded to find that our genes are littered with changes that have no effect on our form or function. Mutations give rise to new genes, but only some of those produce discernible changes that improve (or reduce) fitness. Many of them do nothing much at all. Those do-nothing mutations are a major force for discovery today, because they accumulate at a measurable rate. Generally, the more silent mutations two species have in common, the more closely related they are. If you could just sequence all the genes in all the organisms in the world, in principle you could uncover the complete tree of life.

That is what evolutionary biologist Casey Dunn of Brown University is trying to do, and his initial findings are confounding expectations. Dunn compared the genomes of 71 animal species and found that the common ancestor of all the animals on the planet may not have been as simple as a sponge, as previously thought. Instead, Dunn identified the more complex comb jellyfish—a carnivorous ocean drifter—as the earliest to diverge from the animal family tree. The idea that the simplest organism may not have come first upends the popular notion of an evolutionary march toward complexity. This past year Dunn has been busy expanding his revamped family tree, starting with Acoelomorpha, a flatworm that was long considered one of the most difficult animals to put in its evolutionary place. With the help of a supercomputer, Dunn’s team showed that the worm is a product of the first split among bilateral animals more than half a billion years ago—a discovery that will help biologists understand the origins of the digestive and nervous systems.

4. The “missing link” is not missing. In October paleontologists unveiled the earliest known skeleton of a potential human ancestor, the 4.4-million-year-old Ardipithecus ramidus, known as Ardi, and it was not what anyone was expecting. Behaving more like modern monkeys than like chimps, Ardi walked on two feet with opposable toes and scampered through the branches on all fours. This find suggests that what made us human was the social switch from aggressive male to attentive mate, says C. Owen Lovejoy, an anatomist at Kent State University. By the time Ardi appeared, our ancestors had stopped fighting over mates—as suggested by the small canines and woodland diet of the male Ardipithecus—and started providing for their females and offspring instead. Walking upright, according to Lovejoy, is an adaptation to carrying food through the forest as gifts for potential mates.

Not everyone agrees. “The whole profession of paleoanthropology is undergoing a big bout of indigestion right now because they’ve had a lot of material dropped on them,” says Ian Tattersall, an anthropologist at the American Museum of Natural History.

5. We are closing in on how life began. Gerald Joyce is not saying that he reproduced the origin of life, but by some definitions that is exactly what he has done. In 2009 he and his graduate student Tracey Lincoln at the Scripps Research Institute in La Jolla, California, engineered a system of molecules that can sustainably replicate themselves and undergo Darwinian evolution in a test tube. Now Joyce wants to see “if we can get the molecules to invent novel function for themselves,” he says.

So where would the first life on earth have picked up RNA, the simple hereditary molecule that is notoriously hard to synthesize? Two papers published in 2009 propose plausible chemical routes. In Science a July report discusses a “helper molecule” to RNA, which the author was able to construct in his lab, that shows the basic properties necessary for evolution. And a separate experiment, published in Nature in May, showed that it is possible for the building blocks of RNA to emerge spontaneously from simple molecules thought to have been present on the early earth. John Sutherland and his colleagues at the University of Manchester in England argue that the precursors came together in a warm-water solution, reminiscent of Charles Darwin’s notion that life began in some “warm little pond.” In the meantime, 2009 Nobel laureate Jack Szostak of Harvard Medical School has been packaging prebiotic chemistry into simple membranes to see how protocells could have self-assembled out of fatty acids.

The huge strides from the past year significantly clarify how life could arise from the laws of chemistry. “If Darwin were around now,” Sutherland says, “maybe he would have been an organic chemist.”

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