THE BIG BANG
Let’s pretend, “in the beginning there was no planet called earth…” According to biblical scholars, Genesis falls into two unequal parts. One deals with the primordial history, which introduces the believers to the story of salvation, and they search back into the origin of the world and survey the entire human race as seen through the eyes of the bible. They tell of the creation of the universe and they tell of the great flood which destroyed all God had built except two of every living thing. The repopulation of the earth thus begins with Noah, the prototype ancestor of Israel but this is oxymoronic if you breathe the scientific view which says Noah sprang from an African.
“In the beginning God created the heavens and the earth. Now the earth was a formless void, and there was darkness over the void, there was darkness over the deep, and God’s spirit hovered over the water.” That’s cool…but science takes a different view… it says that earth wasn’t the first planet in the universe and actually did not exist until some 13.5 billion years ago when matter, energy, time and space came into being as a result of what science calls, “The Big Bang,” and the story of these fundamental features of our universe is called physics…not Genesis!
About 300,000 years after this experience and the newly formed planet Earth came to be as a shecht in the vast universe, nature began to coalesce into complex structures causing matter and energy to form atoms which then combined into molecules. These combinations and their interaction in science is called chemistry. Now, things are really jiving out there dude…left along for ten billion years, about 3.8 billion years ago, on this planet we call Earth certain molecules combined to form particularly large and intricate structures (get ready for this) called organisms and this process we label as biology! Think of that…WOW, physics, and biology, not Genesis!
But there is more as you might think skip forward 70,000 years ago these large structures, these organisms belonging to the species Homo sapiens began to form even more elaborate structures called cultures. The subsequent development of these human cultures is known in our world as history. And…there have been three important revolutions which have shaped the course of history: This is heavy dude…follow me now! Cognitive Revolution 70,000 years ago began the modern human. The point at which it is believed that man began to reason within a developing brain. Next up…Agricultural Revolution, next up some 12,000 years ago, and, finally the Scientific Revolution which got under way some 500 years ago which nearly didn’t happen because those creatures of Genesis would not believe God would create a world for them which was round! As a matter of fact, these “wise men” did not believe much of any thing which did not contain some element of voodoo.
God willing, the book I hope to write and share with you will follow the history of how these three revolutions have impacted humans and their fellow organisms in the 21st century.
Let us remember, according to the best science, there were humans before recorded history. But since it is the belief that animals first appeared about 2.5 million years ago, and Homo sapiens 70,000 years ago there is a question in this scribe’s mind about any connection between humans and chimps? It just doesn’t make sense to me that it would have taken that much time to interject the possibility that man transcended from an ape. Moreover, it is known that for countless generations animals did not stand out from the myriad other organisms with which they shared their habitats. I do not believe they shared their beds!
Long before the modern man’s lust for the safari…back some two million years ago you might well have encountered a familiar cast of characters: Mothers fretting about this and that…wondering about where she would scrounge enough food for the evening meal. Dirty children playing among the filth and old folks swatting flies as they attempted to catch a never-ending nap below a monster shade tree dripping monkey waste. No doubt young men flexing muscle in sight of some babe he hoped to lure into the bush as mother’s watched, knowing the babes would go since they themselves had done it all. Experience does not learn nor teach when there is little else to entertain.
These archaic humans lived life as we do, fussing, fighting, working, stressing, loving forming close bonds and fought for status and power. Just as the animals did, and in point of fact, before wisdom came there was nothing which set the human apart from the chimp. Not a single human at that time could conceive of man walking on the moon, split the atom to create devastation capable of ending all of life on earth and perhaps beyond. The most essential element to remember about prehistoric humans is that they were as insignificant as animals with no more impact on their environment as a jellyfish.
Biologists classify organisms into species. Animals they say belong to the same species if they tend to mate with each other, giving birth to fertile offspring. But sometimes things go haywire…let us take a look at horses and donkeys as an example: They have a recent ancestor in common and share many physical traits, but they show little sexual interest in each other. They will mate if induced but the offspring, called mules…will be sterile! Mutations in donkey DNA may never crossover to horses or to the donkey. The two types of animals are consequently considered two distinct species, moving along separate evolutionary paths. Could this be true in humans as well. Are there human species who can mate if induced but producing nurtured or biologically incapable of production or perhaps even worse, producing offspring capable of reproduction but passing a deadly gene?
Is this the reason the bible admonishes, “Stay in your father’s house?”
Species which evolved from a common ancestor are bunched together under the heading ‘genus’. Thus, lions, tigers, leopards, and jaguars are different species within the genus Panthera. Biologists label organisms with a two-part Latin name, genus followed by species. Therefore, my guess is that everyone reading this intellectual treaty is a Homo sapiens- the species sapiens (wise) of the genus Homo (man).
Homo sapiens belong to a family. This fact used to be one of history’s most closely held secrets. Homo sapiens long preferred to view itself as set apart from animals, not belonging to anyone, even lacking siblings or parents. But as we all know this just didn’t fit. Like it or not we must all “buy into” being members of a large family. Now, here is where the rubber hits the road and we get down to the rim of it…according to legend, six million years ago, Jane, a female ape was impregnated by someone or something and she had twin females. One became the ancestor of all chimpanzees…and the other is our grandmother?
This of course flies in the face of earlier testimony that Homo sapiens came to be 70,000 years ago, not six million years ago. I suggest here, at the risk of being ostersized from all scientific luncheons at the Harvard Club, that Jane was impregnated by a deformity, delivered twin females, one an ape and the other became known as a chimp, todays modern negro!
This isn’t the only disturbing secret. Not only do we have a basement filled with troubled cousins, once upon a time we had an abundance of inbred brothers and sisters of mixed parentage. We are quite adept at thinking we are exclusively purely driven at copulation and that we are the only humans, because in fact for the last 10,000 years we have been the only species hitting the ball out of the park. Yet, the real meaning of the word human is an ‘animal belonging to the genus Homo and as I have cited there used to be many other species of the genus besides Homo sapiens. Prediction, just as nature found its door to Homo sapiens within Earth, it is entirely possible with all the universe exploration we may very well, once again, have to contend with the reality of non-sapiens humans here and on other planets yet to be discovered! (Welby Thomas Cox, Jr. October 15, 2020).
Though there is conjecture over the evolution of human, it is the majority of scientists who believe it took place in East Africa. The more daring suggest that the modern human evolved after the great flood in the Caspian Sea or ‘Ponto Caspian’ or Eurasian continental interior. Once again ‘scientific consensus’ does not yet recognize there was a flood. Yet there are whispers near Azerbaijan that human bones have been discovered in a deep hole which may be ‘the modern man.’
THE WORLD ACCORDING TO CARL SAGAN
Please permit me to digress on this Sunday morning as I watch the sun rise at 6:39 am. I would like to share a few thoughts about one of the worlds great thinkers, Carl Sagan.
We live in Carl Sagan’s universe–awesomely vast, deeply humbling. It’s a universe that, as Sagan reminded us again and again, isn’t about us. We’re a granular element. Our presence may even be ephemeral—a flash of luminescence in a great dark ocean. Or perhaps we are here to stay, somehow finding a way to transcend our worst instincts and ancient hatreds, and eventually become a galactic species. We could even find others out there, the inhabitants of distant, highly advanced civilizations—the Old Ones, as Sagan might put it.
No one has ever explained space, in all its bewildering glory, as well as Carl Sagan did. He’s been gone now for nearly two decades, but people old enough to remember him will easily be able to summon his voice, his fondness for the word “billions” and his boyish enthusiasm for understanding the universe we’re so lucky to live in.
He led a feverish existence, with multiple careers tumbling over one another, as if he knew he wouldn’t live to an old age. Among other things, he served as an astronomy professor at Cornell, wrote more than a dozen books, worked on NASA robotic missions, edited the scientific journal Icarus and somehow found time to park himself, repeatedly, arguably compulsively, in front of TV cameras. He was the house astronomer, basically, on Johnny Carson’s “Tonight Show.” Then, in an astonishing burst of energy in his mid-40s, he co-created and hosted a 13-part PBS television series, “Cosmos.” It aired in the fall of 1980 and ultimately reached hundreds of millions of people worldwide. Sagan was the most famous scientist in America—the face of science itself.
Now “Cosmos” is back, thanks largely to Seth MacFarlane, creator of TV’s “Family Guy” and a space buff since he was a kid, and Ann Druyan, Sagan’s widow. They’re collaborating on a new version premiering on the Fox Network on Sunday March 9. MacFarlane believes that much of what is on television, even on fact-based channels purporting to discuss science, is “fluff.” He says, “That is a symptom of the bizarre fear of science that’s taken hold.” The astronomer Neil deGrasse Tyson, of the American Museum of Natural History in New York City, serves as narrator this time, giving him a chance to make the case that he’s the Sagan of our generation. “‘Cosmos’ is more than Carl Sagan,” Tyson told me. “Our capacity to decode and interpret the cosmos is a gift of the method and tools of science. And that’s what’s being handed down from generation to generation. If I tried to fill his shoes I would just fail. But I can fill my own shoes really well.”
It’s an audacious move, trying to reinvent “Cosmos”; although the original series ran in a single fall season—and on public television! —it had an outsize cultural impact. It was the highest-rated series in PBS history until Ken Burns took on the Civil War a decade later. Druyan loves to tell the story of a porter at Union Station in Washington, D.C. who refused to let Sagan pay him for handling luggage, saying, “You gave me the universe.”
The revival of “Cosmos” roughly coincides with another Sagan milestone: The availability of all his papers at the Library of Congress, which bought the Sagan archive from Druyan with money from MacFarlane. (Officially it’s the Seth MacFarlane Collection of the Carl Sagan and Ann Druyan Archive.) The files arrived at the library loading dock in 798 boxes—Sagan, it seems, was a pack rat—and after 17 months of curatorial preparation the archive opened to researchers last November.
The Sagan archive gives us a close-up of the celebrity scientist’s frenetic existence and, more important, a documentary record of how Americans thought about science in the second half of the 20th century. We hear the voices of ordinary people in the constant stream of mail coming to Sagan’s office at Cornell. They saw Sagan as the gatekeeper of scientific credibility. They shared their big ideas and fringe theories. They told him about their dreams. They begged him to listen. They needed truth; he was the oracle.
The Sagan files remind us how exploratory the 1960s and ’70s were, how defiant of official wisdom and mainstream authority, and Sagan was in the middle of the intellectual foment. He was a nuanced referee. He knew UFOs weren’t alien spaceships, for example, but he didn’t want to silence the people who believed they were, and so he helped organize a big UFO symposium in 1969, letting all sides have their say.
Space itself seemed different then. When Sagan came of age, all things concerning space had a tail wind: There was no boundary on our outer-space aspirations. Through telescopes, robotic probes and Apollo astronauts, the universe was revealing itself at an explosive, fireworks-finale pace.
Things haven’t quite worked out as expected. “Space Age” is now an antiquated phrase. The United States can’t even launch astronauts at the moment. The universe continues to tantalize us, but the notion that we’re about to contact other civilizations seems increasingly like stoner talk.
MacFarlane, Tyson, Druyan and other members of Sagan’s family showed up at the Library of Congress in November for the official opening of the Sagan archive. The event was, as you’d expect, highly reverential, bordering on the hagiographic. One moment reminded everyone of Sagan’s astonishing powers of communication: After the speakers finished their presentations, the organizers gave Sagan the last word, playing a tape of him reading from his book Pale Blue Dot.
Recall that in the early 1990s, as Voyager I was heading toward the outer reaches of the solar system, Sagan was among those who persuaded NASA to aim the spacecraft’s camera back toward Earth, by then billions of miles away. In that image, Earth is just a fuzzy dot amid a streak of sunlight. Here’s Sagan, filling the auditorium with his baritone, lingering luxuriantly on his consonants as always:
“That’s here. That’s home. That’s us. On it, everyone you love, everyone you know, everyone you have ever heard of, every human being who ever was, lived out their lives...[E]very king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every revered teacher of morals, every corrupt politician, every superstar, every supreme leader, every saint and sinner in the history of our species lived there–on a mote of dust suspended in a sunbeam.”
He started young. In the Sagan papers, there’s an undated, handwritten piece of text—is it a story? an essay?—from the early 1950s in which Sagan, then an undergraduate at the University of Chicago, sounds very much like the famous scientist-essayist he would come to be:
There is a wide yawning black infinity. In every direction the extension is endless, the sensation of depth is overwhelming. And the darkness is immortal. Where light exists, it is pure, blazing, fierce; but light exists almost nowhere, and the blackness itself is also pure and blazing and fierce. But most of all, there is very nearly nothing in the dark; except for little bits here and there, often associated with the light, this infinite receptacle is empty.
This picture is strangely frightening. It should be familiar. It is our universe.
Even these stars, which seem so numerous, are, as sand, as dust, or less than dust, in the enormity of the space in which there is nothing. Nothing! We are not without empathetic terror when we open Pascal’s Pensées and read, “I am the great silent spaces between worlds.”
Carl Edward Sagan was born in 1934 in Brooklyn, the son of a worshipful, overbearing mother, Rachel, and a hard-working garment industry manager, Samuel, a Ukrainian immigrant. As he entered adolescence, he became an avid reader of science fiction, and gobbled up the Edgar Rice Burroughs novels about John Carter of Mars. His family moved to New Jersey, and he distinguished himself as the “Class Brain” of Rahway High School. In his papers we find a 1953 questionnaire in which Sagan rated his character traits, giving himself low marks for vigorousness (meaning, liking to play sports), an average rating for emotional stability and the highest ratings for being “dominant” and “reflective.”
The adult Sagan always sounded like the smartest person in the room, but in the papers we encounter this interesting note in a 1981 file, right after “Cosmos” hit it big: “I think I’m able to explain things because understanding wasn’t entirely easy for me. Some things that the most brilliant students were able to see instantly I had to work to understand. I can remember what I had to do to figure it out. The very brilliant ones figure it out so fast they never see the mechanics of understanding.”
After earning his doctorate Sagan began teaching at Harvard, and as a young scientist, he earned notice for research indicating that Venus endured a greenhouse effect that roasted the surface—hardly a place congenial for life. Later he would make strides in linking the changing surface features on Mars to planetary dust storms—dashing any hope that the markings were linked to seasonal changes in vegetation. It’s an obvious irony of his career that two of his major hard-science achievements showed the universe less hospitable to life, not more.
His speculative nature—freely discussing the possibility of life beneath the surface of the moon, for example—disturbed some of his colleagues. He seemed a bit reckless and had a knack for getting quoted in newspaper and magazine articles. He published in the popular press—including writing the “life” entry for Encyclopedia Britannica. His own calculations in the early 1960s showed that there could be about one million technological, communicative civilizations in our galaxy alone. And yet he thought UFOs a case of mass misapprehension. Among his papers is a November 1967 lecture Sagan gave in Washington as part of the Smithsonian Associates program. The very first question from an audience member was: “What do you think of UFOs? Do they exist?”
Though a skeptic about UFOs, Sagan had a tendency to be squishy in his comments about flying saucers, and at first he equivocated, saying there’s no evidence that these objects are alien spacecraft but leaving open the possibility that some “small fraction might be space vehicles from other planets.” But then he launched on a protracted riff about all the ways people get fooled.
“Bright stars. The planet Venus. The aurora borealis. Flights of birds. Lenticular clouds, which are shaped like lenses. An overcast [night], a hill, a car going up the hill, and the two headlights of the car reflect on the clouds—two flying saucers moving at great velocity in parallel! Balloons. Unconventional aircraft. Conventional aircraft with unconventional lighting patterns, like Strategic Air Command refueling operations. The list is enormous.”
Sagan was denied tenure at Harvard in 1968 but was quickly scooped up by Cornell. When not teaching and writing, he helped create plaques for the space probes Pioneer 10 and Pioneer 11. The plaques notoriously depicted a naked man and woman, with some graphical descriptions of the position of the Earth in the solar system and other scientific information—just in case the spacecraft bumped into alien scientists out there somewhere.
To go a step further, It seems appropriate to use this a moment in the history of science when we are awakening to the other forms of consciousness on this planet, the ways of being alive and of understanding the environment on the part of other life forms here on earth..
Inevitably, if you’re interested in astrobiology and you’re interested in the question of intelligent life elsewhere, it requires a certain degree of self-consciousness about the lives we share on this planet. So, let us explore what is called exoplanets, and, imagining the deepest human future possible. Of course, inevitably, it’s also examining the shadow on that future which many informed people feel.
It seems to this lonely scribe that the flaming question to middle planet Earth should be… “are we ever going to be able to take the revelations of science to heart in the way that we take art to heart, the way that art affects us? Will we ever be able to really feel those things and awaken from our stupor and act”? That’s the big question, I think, of our moment in history. Is there anything that can make us value the things we need to live — our air, our climate, our water — more than we value money? That’s the big challenge. Is there anything that can make us think in the timescales of science, not the timescale of the balance sheet? We must live with our descendants in mind, and this includes a responsible piece of legislation on our combined use of the environment. This legislation must be fostered by a committee of the whole to include scientist, biologist, accountants, lawyers, and regular folk to clean up and protect the world in which we live and are now systematically destroying.
In the 70’s Carl Sagan, collaborated with fellow astrophysicist Ed Salpeter, to design life forms with plausible evolutionary histories for long term survival in the rolling clouds of Jupiter. Among them were ‘floaters,’ vast hydrogen blimps pumping helium and heavier gases out of their interior to retain only the lightest gas, hydrogen.
It was always in Sagan’s long-term plan in collaboration with Dr. Steven Soter of doing a series called Ethos. Each of them would have been, in their own way, kind of a season of Cosmos. But that was, tragically, not to be. After Sagan’s death, some wanted to do another season of Cosmos. Steve Soter Neil deGrasse Tyson joined Sagan’s widow to create an outline for a new season of Cosmos, and for several years, they went from network to network, three in all. I think much to the horror of Steve and Neil and our other colleague, Mitchell Cannold, every network wanted to do Cosmos, but none of them would give complete creative control to Sagan’s widow, nor would they give her the money necessary to create the kind of cinematic, transporting experience that she felt very strongly Cosmos had to be.
Since she was representing the deceased, and was not a scientist, she was driving these guys crazy by refusing to step aside and let the pros have the control. So, it didn’t happen for several years, until she met Seth MacFarlane. Who promised her he would send the concept to the stars, that he would bring in Peter Rice, who was then the head of the Fox television network? Seth kept every single one of those promises. He was passionate in his desire to see Cosmos. Not just that Cosmos would be a new season, that Cosmos would be produced, but that it would be on Fox, which was such an irony.
When Carl Sagan was alive, he didn’t write for the scientific publications alone. He wrote as well for Parade magazine, which is a Sunday supplement that reached 70 million ordinary people. He wrote about climate change, and a piece called “The Warming of the World.” This goes back to the ’80s. Disappointing to think how this great mind, this courageous individual would take the time to warn of a coming environmental disaster and how other scientists have been warning about the greenhouse effect of the building-up of carbon dioxide and methane in the atmosphere, only to be ignored by the political machine protecting the pockets of those who endow them through corruption.
Peter Rice had missed the first run of the original series and was kind enough to say he would watch the DVD. He watched it with his kids, who were horrified that they were going to be forced to watch what was then something like a 30-year-old science documentary.
But the thing that really turned Peter around was his kids, after some chuckles at the beginning about Carl’s sideburns or whatever, they became obsessed with the show. They would call him at work and say, “Daddy, when are you going to come home? Can we watch another Cosmos?” That immediately persuaded him that it was time to do it.
EVIDENCE SUPPORTING BIOLOGICAL EVOLUTION.
A long path leads from the origins of primitive "life," which existed at least 3.5 billion years ago, to the profusion and diversity of life that exists today. This path is best understood as a product of evolution.
Contrary to popular opinion, neither the term nor the idea of biological evolution began with Charles Darwin and his foremost work, On the Origin of Species by Means of Natural Selection (1859). Many scholars from the ancient Greek philosophers on had inferred that similar species were descended from a common ancestor. The word "evolution" first appeared in the English language in 1647 in a nonbiological connection, and it became widely used in English for all sorts of progressions from simpler beginnings. The term Darwin most often used to refer to biological evolution was "descent with modification," which remains a good brief definition of the process today.
Darwin proposed that evolution could be explained by the differential survival of organisms following their naturally occurring variation—a process he termed "natural selection." According to this view, the offspring of organisms differ from one another and from their parents in ways that are heritable—that is, they can pass on the differences genetically to their own offspring. Furthermore, organisms in nature typically produce more offspring than can survive and reproduce given the constraints of food, space, and other environmental resources. If a particular offspring has traits that give it an advantage in a particular environment, that organism will be more likely to survive and pass on those traits. As differences accumulate over generations, populations of organisms diverge from their ancestors.
Charles Darwin arrived at many of his insights into evolution by studying the variations among species on the Galápagos Islands off the coast of Ecuador.
Darwin's original hypothesis has undergone extensive modification and expansion, but the central concepts stand firm. Studies in genetics and molecular biology—fields unknown in Darwin's time—have explained the occurrence of the hereditary variations that are essential to natural selection. Genetic variations result from changes, or mutations, in the nucleotide sequence of DNA, the molecule that genes are made from. Such changes in DNA now can be detected and described with great precision.
Genetic mutations arise by chance. They may or may not equip the organism with better means for surviving in its environment. But if a gene variant improves adaptation to the environment (for example, by allowing an organism to make better use of an available nutrient, or to escape predators more effectively—such as through stronger legs or disguising coloration), the organisms carrying that gene are more likely to survive and reproduce than those without it. Over time, their descendants will tend to increase, changing the average characteristics of the population. Although the genetic variation on which natural selection works is based on random or chance elements, natural selection itself produces "adaptive" change—the very opposite of chance.
Scientists also have gained an understanding of the processes by which new species originate. A new species is one in which the individuals cannot mate and produce viable descendants with individuals of a preexisting species. The split of one species into two often starts because a group of individuals becomes geographically separated from the rest. This is particularly apparent in distant remote islands, such as the Galápagos and the Hawaiian archipelago, whose great distance from the Americas and Asia means that arriving colonizers will have little or no opportunity to mate with individuals remaining on those continents. Mountains, rivers, lakes, and other natural barriers also account for geographic separation between populations that once belonged to the same species.
Once isolated, geographically separated groups of individuals become genetically differentiated as a consequence of mutation and other processes, including natural selection. The origin of a species is often a gradual process, so that at first the reproductive isolation between separated groups of organisms is only partial, but it eventually becomes complete. Scientists pay special attention to these intermediate situations because they help to reconstruct the details of the process and to identify particular genes or sets of genes that account for the reproductive isolation between species.
A particularly compelling example of speciation involves the 13 species of finches studied by Darwin on the Galápagos Islands, now known as Darwin's finches. The ancestors of these finches appear to have immigrated from the South American mainland to the Galápagos. Today the different species of finches on the island have distinct habitats, diets, and behaviors, but the mechanisms involved in speciation continue to operate. A research group led by Peter and Rosemary Grant of Princeton University has shown that a single year of drought on the islands can drive evolutionary changes in the finches. Drought diminishes supplies of easily cracked nuts but permits the survival of plants that produce larger, tougher nuts. Droughts thus favor birds with strong, wide beaks that can break these tougher seeds, producing populations of birds with these traits. The Grants have estimated that if droughts occur about once every 10 years on the islands, a new species of finch might arise in only about 200 years.
The different species of finches on the Galápagos Islands, now known as Darwin's finches, have different-sized beaks that have evolved to take advantage of distinct food sources.
The following sections consider several aspects of biological evolution in greater detail, looking at paleontology, comparative anatomy, biogeography, embryology, and molecular biology for further evidence supporting evolution.
The Fossil Record
Although it was Darwin, above all others, who first marshaled convincing evidence for biological evolution, earlier scholars had recognized that organisms on Earth had changed systematically over long periods of time. For example, in 1799 an engineer named William Smith reported that, in undisrupted layers of rock, fossils occurred in a definite sequential order, with more modern-appearing ones closer to the top. Because bottom layers of rock logically were laid down earlier and thus are older than top layers, the sequence of fossils also could be given a chronology from oldest to youngest. His findings were confirmed and extended in the 1830s by the paleontologist William Lonsdale, who recognized that fossil remains of organisms from lower strata were more primitive than the ones above. Today, many thousands of ancient rock deposits have been identified that show corresponding successions of fossil organisms.
Thus, the general sequence of fossils had already been recognized before Darwin conceived of descent with modification. But the paleontologists and geologists before Darwin used the sequence of fossils in rocks not as proof of biological evolution, but as a basis for working out the original sequence of rock strata that had been structurally disturbed by earthquakes and other forces.
In Darwin's time, paleontology was still a rudimentary science. Large parts of the geological succession of stratified rocks were unknown or inadequately studied.
Weathering has exposed layers of sedimentary rock near the Praia River in Utah
Darwin, therefore, worried about the rarity of intermediate forms between some major groups of organisms.
Today, many of the gaps in the paleontological record have been filled by the research of paleontologists. Hundreds of thousands of fossil organisms, found in well-dated rock sequences, represent successions of forms through time and manifest many evolutionary transitions. As mentioned earlier, microbial life of the simplest type was already in existence 3.5 billion years ago. The oldest evidence of more complex organisms (that is, eucaryotic cells, which are more complex than bacteria) has been discovered in fossils sealed in rocks approximately 2 billion years old. Multicellular organisms, which are the familiar fungi, plants, and animals, have been found only in younger geological strata. The following list presents the order in which increasingly complex forms of life appeared:
Millions of Years Since First Known Appearance (Approximate)
Microbial (procaryotic cells): 3,500
Complex (eucaryotic cells): 2,000
First multicellular animals: 670
Shell-bearing animals: 540
Vertebrates (simple fishes): 490
Nonhuman primates: 60
Earliest apes: 25
Australopithecine ancestors of humans: 5
Modern humans: 0.15 (150,000 years)
So many intermediate forms have been discovered between fish and amphibians, between amphibians and reptiles, between reptiles and mammals, and along the primate lines of descent that it often is difficult to identify categorically when the transition occurs from one to another particular species. Actually, nearly all fossils can be regarded as intermediates in some sense; they are life forms that come between the forms that preceded them and those that followed.
The fossil record thus provides consistent evidence of systematic change through time—of descent with modification. From this huge body of evidence, it can be predicted that no reversals will be found in future paleontological studies. That is, amphibians will not appear before fishes, nor mammals before reptiles, and no complex life will occur in the geological record before the oldest eucaryotic cells. This prediction has been upheld by the evidence that has accumulated until now: no reversals have been found.
Inferences about common descent derived from paleontology are reinforced by comparative anatomy. For example, the skeletons of humans, mice, and bats are strikingly similar, despite the different ways of life of these animals and the diversity of environments in which they flourish. The correspondence of these animals, bone by bone, can be observed in every part of the body, including the limbs; yet a person writes, a mouse runs, and a bat flies with structures built of bones that are different in detail but similar in general structure and relation to each other.
Scientists call such structures homologies and have concluded that they are best explained by common descent. Comparative anatomists investigate such homologies, not only in bone structure but also in other parts of the body, working out relationships from degrees of similarity. Their conclusions provide important inferences about the details of evolutionary history, inferences that can be tested by comparisons with the sequence of ancestral forms in the paleontological record.
A bat wing, a mouse forelimb, and a human arm serve very different purposes, but they have the same basic components. The similarities arise because all three species share a common four-limbed vertebrate ancestor
The mammalian ear and jaw are instances in which paleontology and comparative anatomy combine to show common ancestry through transitional stages. The lower jaws of mammals contain only one bone, whereas those of reptiles have several. The other bones in the reptile jaw are homologous with bones now found in the mammalian ear. Paleontologists have discovered intermediate forms of mammal-like reptiles (Therapsida) with a double jaw joint—one composed of the bones that persist in mammalian jaws, the other consisting of bones that eventually became the hammer and anvil of the mammalian ear.
The Distribution of Species
Biogeography also has contributed evidence for descent from common ancestors. The diversity of life is stupendous. Approximately 250,000 species of living plants, 100,000 species of fungi, and one million species of animals have been described and named, each occupying its own peculiar ecological setting or niche; and the census is far from complete. Some species, such as human beings and our companion the dog, can live under a wide range of environments. Others are amazingly specialized. One species of a fungus (Laboulbenia) grows exclusively on the rear portion of the covering wings of a single species of beetle (Aphaenops cronei) found only in some caves of southern France. The larvae of the fly Drosophila carcinophila can develop only in specialized grooves beneath the flaps of the third pair of oral appendages of a land crab that is found only on certain Caribbean islands.
How can we make intelligible the colossal diversity of living beings and the existence of such extraordinary, seemingly whimsical creatures as the fungus, beetle, and fly described above? And why are island groups like the Galápagos so often inhabited by forms similar to those on the nearest mainland but belonging to different species? Evolutionary theory explains that biological diversity results from the descendants of local or migrant predecessors becoming adapted to their diverse environments. This explanation can be tested by examining present species and local fossils to see whether they have similar structures, which would indicate how one is derived from the other. Also, there should be evidence that species without an established local ancestry had migrated into the locality.
Wherever such tests have been carried out, these conditions have been confirmed. A good example is provided by the mammalian populations of North and South America, where strikingly different native organisms evolved in isolation until the emergence of the isthmus of Panama approximately 3 million years ago. Thereafter, the armadillo, porcupine, and opossum—mammals of South American origin—migrated north, along with many other species of plants and animals, while the mountain lion and other North American species made their way across the isthmus to the south.
The evidence that Darwin found for the influence of geographical distribution on the evolution of organisms has become stronger with advancing knowledge. For example, approximately 2,000 species of flies belonging to the genus Drosophila are now found throughout the world. About one-quarter of them live only in Hawaii.
Until about 3 million years ago, North and South America were separated by a wide expanse of water, so mammals on the two continents evolved separately. After the isthmus of Panama formed, armadillos and opossums migrated north, and mountain lions migrated.
More than a thousand species of snails and other land mollusks also are found only in Hawaii. The biological explanation for the multiplicity of related species in remote localities is that such great diversity is a consequence of their evolution from a few common ancestors that colonized an isolated environment. The Hawaiian Islands are far from any mainland or other islands, and on the basis of geological evidence they never have been attached to other lands. Thus, the few colonizers that reached the Hawaiian Islands found many available ecological niches, where they could, over numerous generations, undergo evolutionary change and diversification. No mammals other than one bat species lived in the Hawaiian Islands when the first human settlers arrived; similarly, many other kinds of plants and animals were absent.
The Hawaiian Islands are not less hospitable than other parts of the world for the absent species. For example, pigs and goats have multiplied in the wild in Hawaii, and other domestic animals also thrive there. The scientific explanation for the absence of many kinds of organisms, and the great multiplication of a few kinds, is that many sorts of organisms never reached the islands, because of their geographic isolation. Those that did reach the islands diversified over time because of the absence of related organisms that would compete for resources.
Similarities During Development
Embryology, the study of biological development from the time of conception, is another source of independent evidence for common descent. Barnacles, for instance, are sedentary crustaceans with little apparent similarity to such other crustaceans as lobsters, shrimps, or copepods. Yet barnacles pass through a free-swimming larval stage in which they look like other crustacean larvae. The similarity of larval stages supports the conclusion that all crustaceans have homologous parts and a common ancestry.
Similarly, a wide variety of organisms from fruit flies to worms to mice to humans have very similar sequences of genes that are active early in development. These genes influence body segmentation or orientation in all these diverse groups. The presence of such similar genes doing similar things across such a wide range of organisms is best explained by there having been present in a very early common ancestor of all of these groups.
New Evidence from Molecular Biology
The unifying principle of common descent that emerges from all the foregoing lines of evidence is being reinforced by the discoveries of modern biochemistry and molecular biology.
The code used to translate nucleotide sequences into amino acid sequences is essentially the same in all organisms. Moreover, proteins in all organisms are invariably composed of the same set of 20 amino acids. This unity of composition and function is a powerful argument in favor of the common descent of the most diverse organisms.
In 1959, scientists at Cambridge University in the United Kingdom determined the three-dimensional structures of two proteins that are found in almost every multicellular animal: hemoglobin and myoglobin. Hemoglobin is the protein that carries oxygen in the blood. Myoglobin receives oxygen from hemoglobin and stores it in the tissues until needed. These were the first three-dimensional protein structures to be solved, and they yielded some key insights. Myoglobin has a single chain of 153 amino acids wrapped around a group of iron and other atoms (called "heme") to which oxygen binds. Hemoglobin, in contrast, is made of up four chains: two identical chains consisting of 141 amino acids, and two other identical chains consisting of 146 amino acids. However, each chain has a heme exactly like that of myoglobin, and each of the four chains in the hemoglobin molecule is folded exactly like myoglobin. It was immediately obvious in 1959 that the two molecules are very closely related.
During the next two decades, myoglobin and hemoglobin sequences were determined for dozens of mammals, birds, reptiles, amphibians, fish, worms, and mollusks. All of these sequences were so obviously related that they could be compared with confidence with the three-dimensional structures of two selected standards—whale myoglobin and horse hemoglobin. Even more significantly, the differences between sequences from different organisms could be used to construct a family tree of hemoglobin and myoglobin variation among organisms. This tree agreed completely with observations derived from paleontology and anatomy about the common descent of the corresponding organisms.
Myoglobin, which stores oxygen in muscles, consists of a chain of 153 amino acids wrapped around an oxygen-binding molecule. The sequence of amino acids in myoglobin vanes from species to species, revealing the evolutionary relationships among organisms.
Similar family histories have been obtained from the three-dimensional structures and amino acid sequences of other proteins, such as cytochrome c (a protein engaged in energy transfer) and the digestive proteins trypsin and chymotrypsin. The examination of molecular structure offers a new and extremely powerful tool for studying evolutionary relationships. The quantity of information is potentially huge—as large as the thousands of different proteins contained in living organisms and limited only by the time and resources of molecular biologists.
As the ability to sequence the nucleotides making up DNA has improved, it also has become possible to use genes to reconstruct the evolutionary history of organisms. Because of mutations, the sequence of nucleotides in a gene gradually changes over time. The more closely related two organisms are, the less different their DNA will be. Because there are tens of thousands of genes in humans and other organisms, DNA contains a tremendous amount of information about the evolutionary history of each organism.
Genes evolve at different rates because, although mutation is a random event, some proteins are much more tolerant of changes in their amino acid sequence than are other proteins. For this reason, the genes that encode these more tolerant, less constrained proteins evolve faster. The average rate at which a particular kind of gene or protein evolves gives rise to the concept of a "molecular clock." Molecular clocks run rapidly for less constrained proteins and slowly for more constrained proteins, though they all time the same evolutionary events.
The figure on this page compares three molecular clocks: for cytochrome c proteins, which interact intimately with other macromolecules and are quite constrained in their amino acid sequences; for the less rigidly constrained hemoglobin’s, which interact mainly with oxygen and other small molecules; and for fibrinopeptides, which are protein fragments that are cut from larger proteins (fibrinogens) when blood clots. The clock for fibrinopeptides runs rapidly; 1 percent of the amino acids change in a little longer than 1 million years. At the other extreme, the molecular clock runs slowly for cytochrome c; a 1 percent change in amino acid sequence requires 20 million years. The hemoglobin clock is intermediate.
The concept of a molecular clock is useful for two purposes. It determines evolutionary relationships among organisms, and it indicates the time in the past when species started to diverge from one another. Once the clock for a particular gene or protein has been calibrated by reference to some event whose time is known, the actual chronological time when all other events occurred can be determined by examining the protein or gene tree.
Species that diverged longer ago have more differences in their corresponding proteins, reflecting changes in the amino acids over time. Proteins evolve at different rates depending on the constraints imposed by their functions.
An interesting additional line of evidence supporting evolution involves sequences of DNA known as "pseudogenes." Pseudogenes are remnants of genes that no longer function but continue to be carried along in DNA as excess baggage. Pseudogenes also change through time, as they are passed on from ancestors to descendants, and they offer an especially useful way of reconstructing evolutionary relationships.
With functioning genes, one possible explanation for the relative similarity between genes from different organisms is that their ways of life are similar—for example, the genes from a horse and a zebra could be more similar because of their similar habitats and behaviors than the genes from a horse and a tiger. But this possible explanation does not work for pseudogenes since they perform no function. Rather, the degree of similarity between pseudogenes must simply reflect their evolutionary relatedness. The more remote the last common ancestor of two organisms, the more dissimilar their pseudogenes will be.
The evidence for evolution from molecular biology is overwhelming and is growing quickly. In some cases, this molecular evidence makes it possible to go beyond the paleontological evidence. For example, it has long been postulated that whales descended from land mammals that had returned to the sea. From anatomical and paleontological evidence, the whales' closest living land relatives seemed to be the even-toed hoofed mammals (modem cattle, sheep, camels, goats, etc.).
Recent comparisons of some milk protein genes (beta-casein and kappa-casein) have confirmed this relationship and have suggested that the closest land-bound living relative of whales may be the hippopotamus. In this case, molecular biology has augmented the fossil record.
Creationism and the Evidence for Evolution
Some creationists cite what they say is an incomplete fossil record as evidence for the failure of evolutionary theory. The fossil record was incomplete in Darwin's time, but many of the important gaps that existed then have been filled by subsequent paleontological research. Perhaps the most persuasive fossil evidence for evolution is the consistency of the sequence of fossils from early to recent. Nowhere on Earth do we find, for example, mammals in Devonian (the age of fishes) strata, or human fossils coexisting with dinosaur remains. Undisturbed strata with simple unicellular organisms predate those with multicellular organisms, and invertebrates precede vertebrates; nowhere has this sequence been found inverted. Fossils from adjacent strata are more similar than fossils from temporally distant strata. The most reasonable scientific conclusion that can be drawn from the fossil record is that descent with modification has taken place as stated in evolutionary theory.
Special creationists argue that "no one has seen evolution occur." This misses the point about how science tests hypotheses. We don't see Earth going around the sun or the atoms that make up matter. We "see" their consequences. Scientists infer that atoms exist, and Earth revolves because they have tested predictions derived from these concepts by extensive observation and experimentation.
Furthermore, on a minor scale, we "experience" evolution occurring every day. The annual changes in influenza viruses and the emergence of antibiotic-resistant bacteria are both products of evolutionary forces. Indeed, the rapidity with which organisms with short generation times, such as bacteria and viruses, can evolve under the influence of their environments is of great medical significance. Many laboratory experiments have shown that, because of mutation and natural selection, such microorganisms can change in specific ways from those of immediately preceding generations.
On a larger scale, the evolution of mosquitoes resistant to insecticides is another example of the tenacity and adaptability of organisms under environmental stress. Similarly, malaria parasites have become resistant to the drugs that were used extensively to combat them for many years. As a consequence, malaria is on the increase, with more than 300 million clinical cases of malaria occurring every year.
Molecular evolutionary data counter a recent proposition called "intelligent design theory." Proponents of this idea argue that structural complexity is proof of the direct hand of God in specially creating organisms as they are today. These arguments echo those of the 18th century cleric William Paley who held that the vertebrate eye, because of its intricate organization, had been specially designed in its present form by an omnipotent Creator. Modem-day intelligent design proponents argue that molecular structures such as DNA, or molecular processes such as the many steps that blood goes through when it clots, are so irreducibly complex that they can function only if all the components are operative at once. Thus, proponents of intelligent design say that these structures and processes could not have evolved in the stepwise mode characteristic of natural selection.
However, structures and processes that are claimed to be "irreducibly" complex typically are not on closer inspection. For example, it is incorrect to assume that a complex structure or biochemical process can function only if all its components are present and functioning as we see them today. Complex biochemical systems can be built up from simpler systems through natural selection. Thus, the "history" of a protein can be traced through simpler organisms. Jawless fish have a simpler hemoglobin than do jawed fish, which in turn have a simpler hemoglobin than mammals.
The evolution of complex molecular systems can occur in several ways. Natural selection can bring together parts of a system for one function at one time and then, at a later time, recombine those parts with other systems of components to produce a system that has a different function. Genes can be duplicated, altered, and then amplified through natural selection. The complex biochemical cascade resulting in blood clotting has been explained in this fashion.
Similarly, evolutionary mechanisms are capable of explaining the origin of highly complex anatomical structures. For example, eyes may have evolved independently many times during the history of life on Earth. The steps proceed from a simple eye spot made up of light-sensitive reticula cells (as is now found in the flatworm), to formation of individual photosensitive units (ommatidia) in insects with light focusing lenses, to the eventual formation of an eye with a single lens focusing images onto a retina. In humans and other vertebrates, the retina consists not only of photoreceptor cells but also of several types of neurons that begin to analyze the visual image. Through such gradual steps, very different kinds of eyes have evolved, from simple light-sensing organs to highly complex systems for vision.