text: Ahead of his time is putting it
  moderately for Charles Darwin. The father of evolution had conjectures that were only proved, or
  greatly substantiated, decades after his death in 1882, in some cases not until
  recently. Today, evidence that unequivocally supports his theory of evolution
  by natural selection, as well as other surmises he had, comes from an array of
  scientific disciplines, including paleontology, geology, biochemistry,
  genetics, molecular biology, and, most recently, evolutionary developmental
  biology, or "evo devo." "The notion that all these lines of
  evidence could converge and give a common answer to the question of where we
  came from is truly powerful," says Brown University biologist Kenneth
  Miller. "This is the reason why scientific support for the theory of
  evolution is so overwhelming." Here, bone up on Darwin's most
  prophetic ideas.—Peter Tyson
  Darwin wasn't the first to
  suggest the theory of evolution—that all living things originate from
  ancestral forms and that their distinguishable differences are due to
  modifications in successive generations. But no one gave it more thought, or
  provided more evidence for it, or more deeply ingrained the theory into our
  collective consciousness than Charles Darwin. Today, researchers using the
  genetic techniques of "evo devo" can trace the evolution of the
  various kinds of organisms that Darwin fit into his "tree of life"
  (here, from an 1837 notebook, his first such tree). As the geneticist Theodosius
  Dobzhansky once wrote, "Nothing in biology makes sense except in the
  light of evolution."
  Evolution happens through natural
  Darwin was not content to say that
  organisms evolve. The theory of evolution, he wrote, "even if well
  founded, would be unsatisfactory until it could be shown how the innumerable species inhabiting this world have
  been modified so as to acquire that perfection of structure and coadaptation
  that most justly excites our admiration" [italics added]. In what has
  been called "the greatest idea anyone ever had," Darwin theorized
  how those modifications occurred—through a process he called natural selection,
  which holds that individuals within a species that are best suited to their
  environment will survive and reproduce more than those less suited, thereby
  passing on their more useful traits and genetic qualities to successive
  generations. "Nothing that we have learned in the intervening 175
  years," writes paleontologist Niles Eldredge of the time since Darwin
  first started formulating his theory, "has contravened Darwin's
  basic description of how natural selection works."
  Evolution happens through
  natural selection. (continued)
  Suitably, one of the most striking
  examples of natural selection in action concerns the very Galapagos finches
  that Darwin made famous. Since 1973, biologists Peter and Rosemary Grant,
  working on the tiny island of Daphne Major in the Galapagos, have studied a
  species of finch called Geospiza fortis
  (upper right in illustration, which appeared in Darwin's 1839 book about
  his five-year journey aboard the Beagle). After a drought in 1977 devastated plants bearing small seeds, more
  than 1,000 of the 1,200 G. fortis
  finches on the island died. The Grants discovered that larger G.
  fortis, which could break open larger seeds
  than smaller G. fortis could,
  survived better. The survivors mated in 1978, and, on average, their offspring
  had beaks 4 percent larger than those of the previous generation. Following
  another drought in 2003, G. fortis
  with smaller beaks survived better, in part because of stiff competition for
  bigger seeds after a larger finch species, G. magnirostris, settled the island. Between 2003 and 2005, the
  Grants found, G. fortis beaks
  shrank by 5 percent.
  Evolution by natural selection
  must have a mechanism.
  Darwin knew in his heart that
  evolution by natural selection happened, but he didn't know how. In fact, he proposed a mechanism of heredity that
  proved to be dead wrong, something he called pangenesis. Ironically, the actual
  mechanism of heredity—genetics—was revealed in Darwin's
  lifetime, though he never knew it. Working with pea plants, the Austrian priest
  Gregor Mendel discovered the fundamental laws of genetics in 1865. But
  Mendel's work was neglected until 1900, and it wasn't until the
  1940s that scientists identified DNA as the genetic material (here, Francis
  Crick's first sketch of DNA's double helix structure). Today, the
  clear focus of the revolutions now under way in genetics, medicine, and other
  fields is on the genomes of living organisms.
  The mechanism—whatever it
  is—is natural, not supernatural.
  Darwin held off on publishing his
  theory for 20 years, until forced to by fellow naturalist Alfred Russel
  Wallace, who had independently come up with the same idea. One of the reasons
  for Darwin's delay was he knew what a shock his theory would represent to
  Christians, including his beloved wife Emma, who believed that God had created
  all living things, whole and independent of all others. Darwin didn't
  hold this view. His friend, the biologist T. H. Huxley, agreed. "As a
  natural process of the same character as the development of a tree from its
  seed, or of a fowl from its egg," Huxley wrote, "evolution excludes
  creation and all other kinds of supernatural intervention." Of course,
  many people around the world still believe in a divine instrument of creation.
  Embryology is "the
  strongest single class of facts in favor of change of forms."
  Darwin considered the process that
  a fertilized egg goes through on the way to becoming a multibillion-celled adult
  as crucial to understanding how basic anatomical parts of both animals and
  plants change over evolutionary time. The new science of evolutionary
  developmental biology, "evo devo," is revealing the truth behind
  Darwin's assertion quoted above. Until recently, scientists could say
  that forms do change, but they couldn't say exactly how, because they didn't know which genes were
  essential for the development of any organism. They now know that, remarkable
  as it may seem, all organisms on Earth, from microbes to man (a human embryo is
  seen here), share a common "tool kit" of so-called master genes,
  which govern how bodies and body parts form. When and which of these genes are
  turned "on" or "off" during the embryonic stage
  determines how each organism is built.
  Sexual selection also drives
  The peacock posed an enigma to
  Darwin. How could its extravagant tail feathers have come about? How do they
  aid in the "survival of the fittest" (a phrase coined by the
  philosopher Herbert Spencer)? Darwin proposed an answer in his book Descent
  of Man, in which he introduced a novel
  concept—sexual selection, the critical role that the opposite sex plays
  in the evolution of traits. Over time, Darwin believed, peahen choices about
  which peacocks constituted the finest mates could have led to the males'
  absurdly ostentatious tails. In the 1990s, biologist Marion Petrie of the
  University of Newcastle-upon-Tyne showed Darwin's hunch to be true. On
  average, peacocks have 150 "eyes" on their tails. By clipping off
  just a few of those eyes, Petrie found he could significantly reduce a
  male's chances of mating; males with fewer than 130 eyes rarely mated at
  all. Petrie reasoned that the healthier a peacock was, the more he could invest
  in the production of eyes—something that peahens clearly saw for
  All animals, including humans,
  descend from a common ancestor.
  Darwin knew the idea that man was
  just another animal would go over like a lead balloon in Victorian society. But
  in the Origin of Species, he was
  unequivocal on this notion, writing that "I should infer from analogy
  that probably all the organic beings which have ever lived on this earth have
  descended from one primordial form, into which life was first breathed."
  Evidence supporting this view has accumulated ever since, with arguably the
  strongest support coming from evo devo. Scientists comparing the genomes of
  members of the three domains of life—archaea, bacteria, and the eukaryotes
  (animals, plants, fungi, and protists)—have discovered about 500 genes
  that all living things share. These "immortal" genes have survived
  essentially unchanged for over two billion years (including the portion of a
  protein's sequence seen here, with shared amino acids indicated by shading). Says
  Brown's Ken Miller: "Despite the extraordinary diversity of life,
  all living organisms share a nearly identical set of essential genes,
  reflecting their evolutionary development from a common ancestor."
  Humans evolved from an ape-like
  Fearing that many of his contemporaries would be deeply offended if he suggested that humans and apes share
  a common ancestor, Darwin barely touched on human evolution in the 1859 Origin
  of Species. But by the 1871 Descent
  of Man, he was ready, stating baldly that
  "man is descended from a hairy, tailed quadruped, probably arboreal in
  its habits." He also maintained that the difference between the mind of
  man and that of a chimpanzee or gorilla is a matter of degree, not of kind.
  Summing up, Darwin wrote, "We must … acknowledge, as it seems to
  me, that man with all his noble qualities … still bears in his bodily
  frame the indelible stamp of his lowly origin." Today, many a schoolchild
  can cite the figure perhaps most often called forth in support of this
  view—namely, that we share almost 99 percent of our DNA with our closest
  living relative, the chimpanzee. (The illustration shown here appeared in T. H.
  Huxley's 1863 book Man's Place in Nature. All skeletons are to scale except the gibbon, which is shown
  twice natural size.)
  Modern humans arose in Africa.
  In Darwin's day, virtually no
  fossils of early humans were known—one of the few was Neanderthal Man, discovered
  in Germany's Neander Valley in 1856—nor could anyone date them
  reliably. But noticing our close anatomical relationship to chimps and
  gorillas, Darwin surmised that Homo sapiens had evolved in Africa. In his customary careful way, he wrote,
  "It is somewhat more probable that our early progenitors lived on the
  African continent than elsewhere." Today, the fossil known as Lucy is
  only the most famous of numerous fossils of human and human-like species whose
  age and other particulars confirm the notion that modern humans first came into existence in Africa. Here, a
  1999 evolutionary tree based on DNA shows how the five great apes, including us, arose from a
  common ancestor. Branch length indicates how far the genes of each population
  have diverged from those of near relatives.
  The Earth is at least several
  hundred million years old.
  In 1658, based on his reading of
  the Bible and on historical records, the Irish clergyman James Ussher declared
  that God had created the Earth on October 22, 4004 B.C. Geologists of
  Darwin's day begged to differ, arguing for a far older Earth. Darwin,
  knowing that evolution required vastly more time than just six millennia,
  concurred. In the first edition of the Origin of Species, he estimated our planet to be at least several
  hundred million years old. In fact, as is well known today, it is far more
  primeval. In the 1900s, after Marie and Pierre Curie discovered radioactivity,
  physicists learned how to use the half-life of uranium and other radioactive
  elements to estimate the age of rocks. The oldest minerals found on Earth are
  about 4.1 to 4.2 billion years old, indicating our planet is at least that old.
  But meteorites, which scientists believe formed at the same time as the planets
  and which, unlike the Earth, are not geologically active and therefore retain
  evidence of their formation, date even further back. Using several different
  dating methods on dozens of different kinds of meteorites, scientists have, in
  instance after instance, come up with an age of roughly 4.5 billion years—the
  current widely accepted estimate of our planet's age.
  Gaps in the fossil record will
  be filled in with key transitional fossils.
  In his notebooks, Darwin worried
  about the many gaps in the fossil record that then existed, "like pages
  torn from a book." Perhaps the most glaring was the complete lack of
  fossils before the Cambrian Period (544-510 million years ago). "To the
  question why do we not find rich fossiliferous deposits belonging to these assumed
  earliest periods before the Cambrian system, I can give no satisfactory
  answer," he wrote. If his theory of evolution was right, he knew such
  gaps would eventually be filled in. Only in the past half century have
  paleontologists unearthed fossils from the Precambrian, and it's a huge
  and ever-growing trove, with the oldest fossils dating to about 3.5 billion
  years ago. Moreover, they continue to unearth key fossils that bridge those
  gaps Darwin bemoaned, including Archaeopteryx, shown here. To see a range of such transitional fossils, go to
  An insect with a foot-long
  tongue must exist to pollinate this orchid.
  Not all of Darwin's
  conjectures were so broad in scope or so earth-shaking; some were simple
  predictions. Take the case of this species of orchid, Angraecum
  sesquipedale, from Madagascar. When Darwin
  saw this orchid in 1862, he, like anyone who saw it, was astonished by the
  length of its spur, which can reach over a foot in length. (See long, slim tube in photo.)
  "Astounding," he wrote. "What insect could suck it?"
  For some as-yet unknown insect must, he insisted, and it had to have a
  foot-long tongue to get at the plant's nectar, which pools at the very
  base of the spur. Entomologists of his day were skeptical, for no such creature
  had ever turned up. But several decades after Darwin's death in 1882,
  scientists discovered a giant hawk moth in Madagascar, and it lapped the
  orchid's nectar with, yes, a foot-long tongue. The moth was named Xanthopan
  morganii praedicta in honor of his
  prediction. Once again, Darwin was right.
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