More than ever before, the future is in our hands. We are shaping not just our own destiny but also the destinies of much of life on this planet. That is the take-home message of the final essay, On the Origin of Tomorrow, in Science's Origins series.
As Carl Zimmer points out in this essay, Charles Darwin gave a nod to the future, finishing On the Origin of Species with a paragraph that talked about continuity: "... endless forms most beautiful and most wonderful have been, and are being, evolved.” He recognized that as long as the ingredients for the evolutionary process still exist, life has the potential to change. He didn’t believe it was possible to forecast evolution’s course, but he did expect humans would have a big effect—they had demonstrated this power already by domesticating plants and animals and driving some species to extinction. Darwin also expected that our own species would change.
As the world celebrates the 150th anniversary of the publication of On the Origin of Species this year, scientists continue to think deeply about what lies ahead. Some feel a new sense of urgency about understanding what might happen. Since Darwin’s day, humans have gained an unprecedented influence over our own evolution. At the same time, our actions, be it causing climate change, modifying the genomes of other organisms, or introducing invasive species, are creating new sources of natural selection on the flora and fauna around us. “The decisions we and our children make are going to have much more influence over the shape of evolution in the foreseeable future than physical events,” says Andrew Knoll, a paleontologist at Harvard University.
In this essay, Zimmer examines Darwin's perspective on the future and discusses how humans have helped to alter the course of their own evolution. He describes the ways humans have shaped the world around them—through global change, for example—and thereby affected the futures of countless other organisms and ecosystems. Finally, he ends with the question of whether humans will ultimately be smart enough to prolong the life of the planet.
The National Science Foundation has released an online special report on the influence of Charles Darwin on many walks of science. Evolution of Evolution: 150 Years of Darwin's On the Origin of Species features essays, videos, and podcasts from prominent researchers, as well as a timeline of advances in evolution, all beautifully crafted to enchant anyone curious about the history of life. Special topics cover anthropology, biology, astronomy, polar sciences, and geosciences, as well as Darwin.
“Ardi,” the oldest known skeleton of a hominin, or member of the human family, has grabbed headlines around the world since her unveiling in Science Thursday. Not surprisingly, the press coverage of the 4.4-million-year-old Ardipithecus ramidus has sometimes been sensational—and, in some cases, completely wrong. Some newspapers and broadcasters have misinterpreted the authors’ finding that Ardi did not look like a chimpanzee or gorilla. Based on this anatomy, the authors proposed that Ardi shows that humans did not evolve from a “chimpanzee-like ape.” By that, they meant that Ardi evolved from an ancient ape that didn’t look like a chimpanzee or gorilla does today and that humans have retained some of those primitive traits.
But the word “chimpanzee-like” sometimes got lost in translation. Even the first version of a press release from Kent State University, where co-author C. Owen Lovejoy is on the faculty, said “Man Did Not Evolve From Apes.” And some media were clearly confused. The Torstar News Service in Canada wrote: “Man didn’t descend from apes. What is closer to the truth is that our knuckle-dragging cousins descended from us.”
A radio announcer in Baltimore, Maryland, asked me in an interview Monday if it was true that we were not apes—or even primates—and that we had our own, separate lineage that was more ancient. The same question came up in a Facebook chat with me and my editor at Science, Elizabeth Culotta, and has popped up in other media.
Most disconcerting to the authors was the reporting on Ardi by the Arabic news network Al Jazeera, based in Doha, Qatar. A translation of the article written in Arabic starts with a headline that reads “Ardi Refutes Darwin’s Theory,” and the first sentence reads “American scientists have presented evidence that Darwin’s theory of evolution was wrong.” The article states that Ardi’s discovery “refutes the long-standing assumption that humans evolved from monkeys.”
Dr. Zaghloul El-Naggar, a professor of geology in several Arab universities (the article does not specify which ones), exclaims in the story that Westerners were beginning to “come to their senses after they used to deal with the origins of man from a materialistic perspective and by denying religions.” He goes on to claim that the age of Earth does not exceed 400,000 years, and that Ardi’s age of 4.4 million years is an exaggeration.
For the record, all of this is plain wrong. Ardi is a primate descended from more ancient apes, as are all humans and human ancestors. Apes in turn are descended from monkeys. Chimpanzees are our closest living relatives— we share 96% of our DNA with them, and our lineages shared an ancestor sometime between 6 million and 8 million years ago, possibly earlier. The authors’ point is that the last common ancestor we shared with chimpanzees didn’t look like a chimp—which means that chimpanzees also have been evolving since the two lineages diverged. Finally, Ardi confirms rather than refutes Darwin’s prediction in 1871 that our progenitors lived on the African continent, as well as providing another link in the evolutionary chain from primitive apes to humans.
In late January, New York-based internet consultant Phil Terry made a pitch on Facebook for members to post a Happy Birthday Darwin message. By 12 February, more than 200,000 members had signed on, far exceeding his expectations, he said. Since then, he's been shooting to make an even bigger splash. The goal is to have 1 million Facebook members by 24 November celebrating the 150th anniversary of the publication of Darwin's seminal book, On the Origin of Species.
Within a week of setting up the Facebook campaign, Terry started a Web site, Darwin150, complete with Tweets. Self-described as a "grassroots and scrappy" initiative "with a sense of humor," the project is run by volunteers with no funding other than in-kind contributions from organizations such as National Geographic. Yet it has set up a lecture series that will be webcast live. The series begins 16 September and runs through 24 November, with speakers that include Harvard University's E.O. Wilson and other biology luminaries.
"This series is unique in both the medium and the audience," says evolutionary biologist and author Sean Carroll of the University of Wisconsin, Madison, who has been active in Darwin celebrations across the globe and is involved in making a TV documentary on evolution. "It will be interesting to see its reach and the make-up of the audience."
Right now, the Facebook campaign is 750,000 members short. But, says So Young Park, head of the volunteer marketing team, "We are confident that we'll make our goal" and are expecting exponential growth in the days leading up to the anniversary. Go here to join.
Cooperation has created a conundrum for generations of evolutionary scientists. If natural selection among individuals favors the survival of the fittest, why would one individual help another at a cost to itself? And yet cooperation and sacrifice are rampant in nature. Humans working together have transformed the planet to meet the needs of billions of people. Countless examples of cooperation between species exist as well. In this month's Origins essay, I examine our current understanding of this conundrum.
Cooperation has played a key role in evolutionary transitions, helping to create integrated systems. Worker ants have no offspring of their own and feed their queen’s offspring instead in colonies often considered “superorganisms” many thousands of individuals strong. Cells managed to specialize and stay together, giving rise to multicellular organisms. In both cases, formerly independent reproductive units become integrated into a single reproductive unit that became the target of selection.
The challenge of cooperation is to explain how self-interest is overcome, given the way natural selection works. Darwin suggested that selection might favor families whose members were cooperative, and researchers today agree that kinship helps explain cooperation. But cheaters—those who benefit without making sacrifices—are likely to evolve because they will have an edge over individuals that spend energy on helping others, thus threatening the stability of any cooperative venture. That puzzle has inspired biologists, mathematicians, even economists to come up with ways to explain how cooperation can arise and thrive. The essay examines how researchers have spent countless hours observing social organisms ranging from man to microbes. Humans are a particularly interesting case, as they cooperate with strangers, forgoing the genetic benefit derived from helping relatives. Yet even single-cell organisms have sophisticated means of working together. The study of both is helping to clarify the origin of this particularly important behavior.
Charles Darwin’s book On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life contained his first thoughts on evolution. Now, 150 years later, computer scientist Greg McInerny is turning the idea on its head, drawing diagrams showing the “evolution” of the book as new editions were published. In the editing process, certain sections became “extinct,” that is, did not make it to the next edition. Other, stronger sections avoided the editor’s chopping block to make it into the final sixth edition—a kind of survival of the sentences—and in some cases, entirely new sections of text were added.
Together with London-based visual artist Stefanie Posavec, McInerny has devised the (En)tangled Word Bank, which shows the construction and evolution of the book. In some cases, the editions varied quite a bit, says McInerny, who is based at Microsoft Research in Cambridge in the United Kingdom. “For the second edition, Charles Darwin wanted a more popular and available version,” he says, so Darwin inserted references to a creator who may have been behind the initial creation of life. In the sixth edition, he added a whole new chapter discussing the support and criticism that had surrounded the book.
The diagram (left) represents the fifth edition. In it, the rim consists of four layers. The outer ring represents sentences; the next ring in signifies paragraphs, then subchapters and chapters follow. The central branching design represents the same divisions, with chapters at the base and sentences at the tips. The green “leaflets” show sentences that have “survived” multiple editions, and orange “leaflets” represent those that are “dying” and will be absent from the next edition. The darker the green or orange, the longer that sentence has survived through multiple editions.
(En)tangled Word Bank is an example of a “literary organism,” a structure devised by Posavec to show visually how books are constructed from their basic units. Her first such work was based on Jack Kerouac’s novel On the Road.
The nervous systems of modern animals are amazingly diverse. A few hundred nerve cells are all a lowly nematode needs to find food and a mate. With about 100,000 neurons, a fruit fly can perform aerial acrobatics, dance to woo a mate, and throw kicks and punches to repel a rival. The sperm whale’s 8-kilogram brain, the largest on the planet, is the navigation system for cross-ocean travel and 1000-meter dives and enables these highly social creatures to communicate. The human brain—one-sixth that size—is the wellspring of art, literature, and scientific inquiry.
In this month's Origins essay, Greg Miller takes a look at how nervous systems got started. He investigates what the first neurons might have looked like and what advantages they conferred on the animals that possessed them. These were questions the father of evolution, Charles Darwin, was ill-equipped to address. Only around the time Darwin died in 1882 were scientists beginning to develop stains to label individual cells for detailed postmortem neuroanatomical studies. Methods for investigating the electrical properties of individual neurons in living brain tissue were still decades away, to say nothing of techniques for investigating genes and genomes. Using such modern tools, scientists have recently begun to gain some tantalizing clues about the evolutionary origins of nervous systems. By looking down the tree of life, they are concluding that assembling these components into a cell a modern neuroscientist would recognize as a neuron probably happened very early in animal evolution, more than 600 million years ago. Most scientists agree that circuits of interconnected neurons probably arose soon thereafter, first as diffuse webs and later as a centralized brain and nerves. But the resolution on this picture is fuzzy. The order in which early branches split off the animal tree of life is controversial. And Miller takes a look at the different story lines implied by these different arrangements.
Charles Darwin’s theory of evolution certainly transformed the way we view life on Earth. Brian Regal (left) thinks it also had an impact on mythical creatures. Regal, a science historian at Kean University in Union, New Jersey, says that with the publication ofOn the Origin of Species, canine-man hybrids went out of fashion, making way for new beasts that embodied Darwin’s thinking: ape-men such as Bigfoot (a.k.a. Sasquatch) and the Yeti (a.k.a the Abominable Snowman). I spoke to Regal about how his study of the history of evolutionary theory led him to monsters and eventually to monster hunting.
Q: How did Darwin kill the werewolves? B.R.: There were already writers in learned circles questioning the concept of the werewolf in the late 1500s. From an evolutionary point of view, the werewolf makes no sense. A half-human half-wolf/dog composite doesn’t work. An ape-man, however, a Bigfoot, makes sense because the ape-man idea is [at] the heart of human evolution. If you look at all the “wild man” stories in various cultures around the world, none of them mentions apes prior to the mid-19th century and the public debate brought on by Darwin's On the Origin of Species (1859) and T. H. Huxley's Man's Place in Nature (1863). This was the key to my idea. The “wild man” and the “ape” did not join forces to become the ape-man until after Darwin.
Q: How do you think Darwin viewed werewolves, centaurs, and other half-man, half-animal creatures? B.R.: I have checked Darwin’s correspondence and published works, and I have not found him [to] make any direct reference to werewolves. In a letter from Darwin to the naturalist G. R. Waterhouse, dated 3 or 17 December 1843, he does mention that he did not believe there can be half of one thing and half of another. He also called animal monsters "a nasty, curious subject” when addressing a new book he had read by the French naturalist Saint-Hilaire.
Q: We often hear about people who have claimed to have seen Bigfoot, or the Yeti, or Sasquatch. Could they exist today? B.R.:Peter Byrne, one of the grand old men of Bigfoot hunting, said it well. He said the way we will probably find out these creatures are real is when one of those giant 18-wheel logging trucks from the Pacific Northwest pulls into a roadside diner with a Bigfoot splattered all over the front grill. All my Bigfoot friends will get mad at this, but I think in the end they probably do not exist.
Q: You say that Darwin’s theory has caused us to shift our focus to ape-man hybrids. But recently in pop culture, creatures like Bigfoot seem to be replaced by the werewolf. For example, Harry Potterand Twilight, both blockbuster books and movies, have werewolves as major characters. Why do you think that is? B.R.: We have to remember that monsters are deeply emotional creations. We tend not to react to them in a rational way, so there are many reasons for believing or not believing in them. While evolutionary theory helped do away with the werewolf [right] as a biological reality, it helped create Bigfoot as one. However, Bigfoot is, in some people's eyes, more real. It has a certain amount of scientific support for its existence where the werewolf does not. It's also less threatening.
Q: Well, it is a very intriguing idea. What sort of feedback have you received so far? B.R.: It has run the gamut, from "That's an interesting idea" to "How can you say Darwin killed the werewolves? I just saw Twilight, and they show werewolves!” So far, no one has called me crazy, though.
Q: How are you going to present your argument? B.R.: I am using pictures of werewolves, apes, and Bigfoot to trace the visual transformation of the werewolf into Bigfoot. They come mostly from science books and medieval manuscripts. If you look at early drawings of apes, and then cavemen, they look disturbingly like werewolves. I also have an illustration from a Boston almanac from 1785. It’s the first illustration [left] of a primate in North America (based on the work of Edward Tyson), but it is astonishing as to how much it looks like a happy, smiling Sasquatch carrying a walking stick.
Q: If there's someone who believes that the whole Darwin-werewolf-Bigfoot connection has no proof, what would you tell them? B.R.: I would tell them that as a professional scholar, I looked at the evidence of the written record, saw patterns, made analogies, and came up with a hypothesis that I think is also supported by the visual record. Others might look at the exact same materials I did and come to a different conclusion or find something more interesting in it. That's how the historical method works.
When I sit down to read a scientific paper, I usually brace myself for the worst. I prepare to slog through esoteric, murky language—to have to dig deep to find the buried beauty of science.
But every now and then, you sit down and read a paper that starts like this:
"Picture a pile of freshly cut weeds at the sunny edge of a tropical forest. Metallic green flies dart and circle over it, chasing one another in short dashes. Your eye is caught when a chase ends as one fly grasps another in midair and the pair immediately lands on the pile of weeds. Their genitalia are already coupled, and the male immediately turns to face away from the female. After a few seconds, paradoxically (because he is already securely attached), he begins to court, rhythmically waving his colorful hind legs and tapping the female's abdomen. The courtship continues for a few minutes as the pair remains coupled, and then the flies separate. The female walks down into the pile where she lays eggs (her larvae will feed on the rotting vegetation), while the male rejoins the frenetic chases above the pile."
Why would a male fly wait to court a female until after he has already achieved his evolutionary objective of copulating with her?
The paper is titled Postcopulatory sexual selection: Darwin's omission and its consequences. It was written by William G. Eberhard, an evolutionary biologist at the Smithsonian Tropical Research Institute in Panama, and was just posted online at the Proceedings of the National Academy of Sciences Web site. It offers some wonderfully bizarre examples of the extremes to which evolution reached once sex emerged a couple billion years ago.
Earlier this month, I wrote in Science about the origin of sex. Despite the disadvantages of reproducing with both males and females, sex dominates the animal kingdom and is common among our fellow eukaryotes (plants, fungi, and protozoans). Studies point to several possible benefits that outweigh the cost of sex. Sex may speed up the evolution of adaptations, cleanse our genomes of harmful mutations, or let us fight against parasites more effectively. However sex evolved, it created a new arena in which the evolutionary process could take place. Now reproductive success was not just a matter of surviving and finding enough food. Now it also depended on whether organisms could find a mate.
Darwin recognized this distinctive kind of selection, which he dubbed sexual selection. In his 1871 book, Descent of Man, he argued that males competed with each other for the opportunity to mate with females, and as a result, males had evolved claws, horns, and other weaponry. Darwin also argued that females were attracted to certain males over others, and this preference drove the evolution of gorgeous courtship displays such as the extravagant plumage on some birds.
Over the past 138 years, scientists have discovered a wealth of evidence demonstrating that sexual selection is indeed a powerful force. But it drives evolution in ways that Darwin did not anticipate. In many species, females actually mate with lots of males. And those multiple matings open up yet another arena for evolution. Along with the courtship and battling that goes on before mating, there's an opportunity for lots of strategies for boosting reproductive success after mating.
The underlying logic of postcopulatory sexual selection is simple: Once a male has inserted his sperm in a female, he has not sealed the deal. A female may have the sperm from several males inside of her. There are many strategies that appear to have evolved because they boost a male's reproductive success, from fast-swimming sperm to male genitals that explode after mating, to prevent other males from adding their own sperm.
One of the most intriguing strategies biologists have discovered is when a male courts after the copulation has started. In the case of the flies that Eberhard describes at the start of his paper, it appears that males engage in this after-the-fact courtship so that females will lay eggs immediately after their courtship. If scientists prevent the males from courting during copulation, the female flies fly away without laying any eggs.
Scientists are only starting to test hypotheses about postcopulatory sexual selection, but its effects could turn out to be huge. In fact, it may have bearing on our food supply. Some studies indicate that plants can choose between the pollen of other plants that land on them in order to fertilize their seeds. Plants may even abort fruits that don't come from suitable mates. Such are the unexpected directions in which Darwin's initial ideas have traveled.
Tracing the origin of flowering plants has long been a challenge for evolutionary researchers, as discussed in this month's Origins essay. Paleobotanist David Dilcher thinks part of the reason is that researchers in his field misidentified fossil plants as members of modern groups. Back in 1979, he and a colleague reanalyzed fossil leaves collected from 45-million-year-old clay pits in Tennessee. Careful cleaning revealed previously unnoticed stipules, small outgrowths from the base of the leaves, calling into question the fossils’ supposed identity as modern corkwood. A close examination of the venation pattern and the cuticle of the leaves convinced Dilcher that these leaves were an extinct group belonging to the coffee family. Dilcher, now at the Florida Museum of Natural History in Gainesville, talks about the impact of this and subsequent work by others on understanding flowering plants.
Often the phrase “the origin of the flowering plants is an abominable mystery” can be read in popular and scientific literature. This phrase is credited to Darwin and comes from a letter that Darwin wrote to J. D. Hooker on 22 July 1879 (Darwin, 1905). It represents Darwin’s frustration with the paleobotanical record of his time. The literature available to Darwin in the 1870s shows that when flowering plants are first found in the fossil record, they are nearly all given names of extant genera. At the time of Darwin, there was no evolution that could be demonstrated from the fossil record of flowering plants. This record was based almost entirely upon impressions and compressions of fossil leaves, and paleobotanists of the 19th and first half of the 20th centuries looked for “matches” or similar leaf types with the leaves of living flowering plant genera. This ”leaf matching” can be done if one does not look closely at detailed characters of fossil and living leaves. When characters such as fine venation, epidermal cell patterns, trichome types, and stomatal complexes are examined carefully (Dilcher, 1974), a different view of early flowering plants emerges.
Such was the case for Paleorubiaceophyllum eocenicum (far left), which was once classified as Leitneria floridana (near left) but which really represents an extinct group of plants.
Darwin’s “abominable mystery of the origin of the angiosperms” can be understood when careful observations of characters are made. With the study of detailed leaf venation and leaf epidermal cell characters, it is clear that many of the earliest flowering plants represent extinct species, extinct genera, extinct families, and perhaps even extinct orders (Dilcher 1974, 2000). This paradigm change has caused a revolution in the study of fossil flowering plants which only in the past 40 years has begun to present a realistic record of extinct flowering plants.
It seems to be human nature that when a fossil leaf is found, the first question asked is what is its living counterpart. When fossil leaves are examined only as hand specimens, using gross form, it is easy to find leaves of trees living today that “match” the fossils. The success of early paleobotanists depended upon making such matches. It has taken a philosophical shift in angiosperm paleobotany in order for researchers today to strive to understand relationships between fossil and living plants, based upon detailed characters, rather than feeling the need to find a living genus to which they can name a fossil. Using character analyses, we now have an emerging new fossil record of flowering plants with many extinct taxa that would have delighted Darwin. This new record is one he could have understood because it demonstrates the evolution of flowering plants, a major group of organisms on Earth. We do not yet know all the details, but there is no longer any “abominable mystery” to the origin of flowering plants.
Darwin, F. (Ed.). More letters of Charles Darwin. Vol. 2. (Murray, London, 1905).
Dilcher, D. Approaches to the identification of Angiosperm leaf remains. The Botanical Review, 40:1, 1 (1974).
Dilcher, D. "Toward a new synthesis: Major evolutionary trends in the Angiosperm fossil record. pages." Variation and Evolution in Plants and Microorganisms: toward a new synthesis 50 years after Stebbins. F. J. Ayala, W. M. Fitch, and M. T. Clegg, Eds. (National Academy Press, Washington, D.C., 2000), pp 255-270.
Credits: Paleorubiaceophyllum eocenicum: H. Wang and D. L. Dilcher; Leitneria floridana: J. S. Peterson, USDA NRCS NPDC. Missouri Botanical Garden.
The publication of Charles Darwin’s On the Origin of Species in 1859, the 150th anniversary of which we celebrate this year, was a landmark event in the history of biology and widely noted at the time. But when, 7 years later, Gregor Mendel published his findings on the laws of inheritance, they were widely ignored. Not until the 20th century did scientists realize that the two theories were entirely compatible and put them together in what we now call the modern evolutionary synthesis.
In a fascinating paper published online this week in the Journal of Biology, geneticist Jonathan Howard of the University of Cologne ponders why Darwin, who took it as a given that natural selection acted on traits that were passed from generation to generation, didn’t scoop Mendel when he had the chance. The answer, Howard suggests, is that Darwin was focused on very small, often infinitesimal variations in plants and animals, which he saw as the raw material on which natural selection could work. Yet, as Mendel brilliantly demonstrated, inheritance is actually based on the passing on of discrete units—what today we call genes—from one generation to another.
Howard points out that Darwin had many chances to understand inheritance, but his mind was focused elsewhere. For example, Howard writes, in The Different Forms of Flowers on Plants of the Same Species, published in 1877, “Darwin wrote an entire book on a perfect Mendelian character” with “numerically precise and well-established behavior, yet he failed to extract Mendelian insights from his work.”
This week in Science, Carl Zimmer writes about the origin of life on Earth in the first of a monthly essay series about key moments in the evolution of life and human culture. Although Charles Darwin considered it impossible to reconstruct how life began, researchers today are making headway in coming up with molecules and cells akin to what existed in those earliest days. See what Zimmer has to say, and share your own thoughts with us here on the Origins blog.