The Case for a Creator: Meet Your Ancestors
The Case for a Creator, Chapter 3
In the final section of chapter 3, Strobel and Wells turn to the evidence that creationists loathe above all else: the fossil hominids that make up the human family tree. Human ancestors are not only a clear, obvious transition that even a layperson can understand, they directly demonstrate that we ourselves are a product of evolution, thus striking at the desire to be separate, special creations that almost certainly motivates nearly all creationists.
I strongly suspect that creationism as a movement would never have arisen if scientists hadn't insisted on encompassing the human species in evolution's family tree. Whatever the creationists say, they don't really care about turtles or oak trees or earthworms. If scientists were willing to grant that human beings were special, unrelated to the rest of Earthlife, creationists would probably have been happy to concede that every other species came about from a process of mindless natural selection. But the evidence doesn't support a separate origin for humanity, and the idea that we might be one of those animals - a relative of slime molds and toadstools, of centipedes and cyanobacteria - enrages creationists, who can't bear to believe in a universe in which they are not the central and most important figure. In their quest to reclaim that sense of specialness, they would gladly obliterate the best theory ever devised to explain the true origins and diversity of life as we now see it.
And this leads us to the last section of Strobel's interview with Jonathan Wells. We begin with Java Man, who, according to his discoverer Eugene Dubois as quoted by Strobel, "represents a stage in the development of modern man from a smaller-brained ancestor" [p.61]. Strobel points out - for once, correctly - that the find consisted of a skullcap, a femur and some teeth, but that the femur and the teeth are now believed to belong to different species.
Nevertheless, Strobel writes as though Java Man is an isolated find, a single fossil fragment drifting in a void of uncertainty. As usual, the creationists have ignored the abundant corroboratory evidence. Java Man is just one specimen of a well-known hominid species, Homo erectus, that is known from many other specimens - including Sangiran 17, a far more complete skull that was also found on Java - and even more spectacularly, the Turkana Boy, a nearly complete skeleton of an approximately 12-year-old erectus boy found near Lake Turkana in Kenya. All these specimens, including Java Man, share the characteristics that make them unlike modern humans: a sloping forehead, heavy brow ridges, large jaw with no chin, and a braincase much smaller than ours (between 750 and 1100 cc, depending on age, while most modern sapiens have brains about 1350 cc).
What do the creationists think Homo erectus is? We never find out Strobel's viewpoint, since neither he nor Wells ever mentions these fossils. The closest he ever comes is asserting that Java Man is a "true member of the human family" [p.62]. That's actually correct, although it doesn't mean what Strobel thinks it does.
Aside from this brief discussion of Java Man, we hear nothing more about any specific fossil. Wells spends the rest of this brief section complaining about how artistic reconstruction of fossils is a speculative field [p.62] and quote-mining science writers who point out that we cannot reconstruct exact lines of descent from fossils - which is true, but Wells acts as if this means that every theory ever devised about human evolution is worthless. The lesson he takes away is not that we must be careful to only propose testable hypotheses supported by the evidence, but that "Darwinists assume the story of human life is an evolutionary one, and then they plug the fossils into a preexisting narrative where they seem to fit" [p.63], as if the fossils themselves had no meaning and could be used to support any conceivable hypothesis equally well.
I also want to highlight one particularly obnoxious bit of dishonesty. Here's Wells quoting science writer Henry McGee:
"In fact, he said that all the fossil evidence for human evolution 'between ten and five million years ago - several thousand generations of living creatures - can be fitted into a small box.'" [p.63]
It's true that the oldest fossil evidence of human evolution - the species nearest the branch point of humans and other apes - is fragmentary. But by definition, those species would be the least humanlike. What Wells neglects to mention is that all the most important fossil evidence showing how humans became human is younger than five million years! Australopithecus afarensis, and the other australopithecines, are between 4 and 3 million years old. Homo habilis is between 2.5 and 1.5 million years old. Homo erectus is between 2 million and half a million years old. We have multiple fossils for most of these species and others, far more than would fit in a "small box". Wells' sleazy tactics would be like a defense attorney getting a witness to admit that he saw nothing unusual between 5 and 6 PM, and triumphantly concluding his client was innocent - even though the crime took place at 7.
Again, what stands out about this section is how little time Strobel and Wells spend on discussing the actual fossils of human ancestors. We never hear about Turkana Boy. We never hear about Lucy or Homo habilis. What were these creatures? How does the intelligent-design worldview explain them? This is a question Wells steers well clear of, other than repeating postmodernist claims that any explanation is just as good as any other.
Now I'll do something that Strobel and Wells never do: show you the fossils so you can see them for yourself. Here's a table, with pictures, which lists some of the most important hominid specimens and shows what creationists think about each of them.
As you can see from the table, although all the creationists are adamant that every fossil is either fully human or fully ape, they can't agree which is which. (Java Man in particular is an almost even split, especially if you include Strobel and Wells' claiming that it's human.) This, of course, is exactly what we would expect if these fossils were genuinely transitional: being intermediate between two groups, they would resist unambiguous classification as one or the other. Ironically, the creationists themselves provide the best testimony of that.
Other posts in this series:
The Case for a Creator: Ancient Wings
The Case for a Creator, Chapter 3
Up until now, Jonathan Wells' critiques of evolution, although misguided, have been fairly sophisticated, touching on topics such as abiogenesis, the Cambrian explosion, and embryology. That's about to change. In this section, Wells and Strobel haul out the most breathtaking, shameless lie bandied about by creationists: that there are no such things as transitional fossils. This opening quote foreshadows the direction they're going:
I was under the impression that [Archaeopteryx] was featured in my books on evolution because it is just one example of many transitional links that have been found. But I was wrong. [p.56]
Strobel then quotes this jaw-dropping passage from Michael Denton:
[T]he universal experience of paleontology... [is that] while the rocks have continually yielded new and exciting and even bizarre forms of life... what they have never yielded is any of Darwin's myriads of transitional forms... The intermediates have remained as elusive as ever and their absence remains, a century later, one of the most striking characteristics of the fossil record. [p.56]
Even by creationist standards, this is a bald-faced and brazen lie. Not only do transitional fossil series exist, we have a strikingly large number of them, bridging most of the major evolutionary changes in life's history. But don't take my word for it, see the evidence for yourself.
There's the tetrapod transitional series - fossils documenting the evolutionary change from fish to four-legged land animals - whose crown jewel is Tiktaalik roseae. There's the therapsids, the fossils documenting the evolution of mammals from reptiles, which preserve in exquisite detail the evolution of the jaw. There's the well-known horse transitional series. We know much detail about the evolution of whales, including Ambulocetus, the so-called walking whale. And of course, there's the evidence creationists hate the most - fossil human ancestors - which we'll get to in due time.
But this section focuses on Archaeopteryx, a particularly striking example of evolutionary transition. This feathered dinosaur is far too well-known even for creationists to deny it exists, but Wells tries to fog the evidence by implying that it's not really transitional:
"Besides, we see strange animals around today, like the duck-billed platypus, which nobody considers transitional but which has characteristics of different classes." [p.57]
This is another example of the things Wells should already know. In fact, the platypus is transitional - albeit a kind of living transition.
The platypus belongs to a very rare group of mammals called monotremes. Although these animals have fur, give milk and show other mammalian traits, they have others that are more primitive, most notably the fact that they lay eggs. They also lack the well-developed nipples of mammals that their young can suck on; their milk oozes from glands on their chest, and the babies lick it up. But they also have advanced adaptations not shared by other mammals, like venomous spurs or the platypus' famous "bill" - which has nothing in common with the bills of ducks, but is actually an electrosensitive organ of exquisite sensitivity.
Living monotremes are found only in Australia and New Guinea, and this separation is a clue to their evolutionary history. The most likely explanation is that, during the Mesozoic era, the animals that would ultimately become mammals split into several branches. One branch became the placental mammals, which includes us. Another branch became the monotremes. Both groups inherited proto-mammalian features such as fur and milk from their common ancestor, while others, such as the bearing of live young, evolved in placentals after the branch point, while monotremes retained the ancestral egg-laying state. In this sense, and discounting its own unique adaptations, the platypus is a sort of living example of what our common ancestor might have looked like.
But, back to Archaeopteryx. As I said, even Wells can't deny it exists, but he does resort to lying about the nature of the species:
"But the archaeopteryx is a half-bird, half-reptile, right?"
"No, not even close," he insisted. "It's a bird with modern feathers... not part bird and part reptile." [p.57]
Wells makes no attempt to justify this assertion, because it is patently false. Other than its feathers and a few other subtle characteristics, Archaeopteryx is actually much more like a dinosaur than it is like a bird. The Talk.Origins Archive's All About Archaeopteryx FAQ lists its reptilian features, which far outnumber the avian characteristics. (See also.)
And even besides this, what about the many other feathered dinosaurs, such as Sinornithosaurus and Microraptor? Over twenty genera of feathered theropods are known, most from China. Wells steers well clear of these, other than to mutter an accusation that they're probably all fakes [p.59]. We do, however, get a sermon on Archaeoraptor, which serves the same purpose as Haeckel's embryos - a convenient whipping boy for creationists which they use to distract attention from the real facts that support evolution.
Archaeoraptor was a chimera - a composite of bones from several different animals - most likely created by unscrupulous amateur fossil hunters. The fraud was detected almost immediately, within a matter of weeks, and was never published in peer-reviewed papers (source). In fact, the Archaeoraptor saga is an excellent example of how science is supposed to work. The only reason we're hearing anything about it is because one popular, non-peer-reviewed publication, National Geographic, exercised insufficient caution and ran with the story before scientists had authenticated it.
After lying about the existence of well-known scientific evidence and accusing paleontologists of mass fraud, Wells has one final card to play:
"...reptiles that are more bird-like in their skeletal structure... they find them millions of years after archaeopteryx! So here we have archaeopteryx, which is undeniably a bird, and yet the fossils that look most like the reptilian ancestors of birds occur tens of millions of years later in the fossil record." [p.57]
As I said earlier, Wells has an education in biology and should know better than to make these obviously deceptive claims. A real scientist would have known the explanation for this immediately and would not have tried to mislead readers by implying that this is unexpected or a problem for evolution.
Evolution rarely, if ever, works in a single, smooth trajectory of change - species A changes into species B, which changes into species C, and so on. Instead, what we usually see is a path of descent more like a densely branching bush: species A radiates into species B1, B2, B3... and so on. Most of these go extinct, but B2, say, speciates into C1, C2, and C3, and again, some of the daughter species go extinct and others diverge in their own ways. But species don't have fixed lifespans, and there's nothing to dictate how long a particular species will survive before it goes extinct. There may still be living species from the A or B generation existing side-by-side with far more advanced descendants. (Readers are referred, again, to the platypus for an example of how this can turn out.)
In the case of Archaeopteryx, that's just what happened. In the bird family tree, feathers were an early innovation, one that arose before most of the other features typical of modern birds, and Archaeopteryx was one of the earlier species to have them. (Remember, again, that it has far more reptilian than birdlike characteristics.) But other feathered reptiles, other lines of descent in the same family tree, spun off descendants of their own, and some of these had more of the features that, in retrospect, we classify as diagnostic of birds. In short, Archaeopteryx wasn't a direct ancestor of modern birds: it was an aunt or an uncle. But even if it's not on the direct line of descent, it's still a powerful and compelling example of transition in progress, one twig on the branching tree of life's history.
Other posts in this series:
The Case for a Creator: The More Things Change
The Case for a Creator, Chapter 3
Strobel's discussion of embryonic similarities with Jonathan Wells leads into a broader discussion of homology, which deserves its own post.
I've been harder on Wells than I otherwise would because he, unlike the vast majority of creationists, has a legitimate degree in biology. It's impossible that he doesn't understand some of the things he claims not to understand, or that he doesn't know the actual scientific explanations for the questions he poses. That being the case, there's no explanation for many of the confusions or patently false claims he makes, other than that he's deliberately attempting to deceive lay readers. This post will point out some examples of that.
To get our definitions straight, homology is a detailed similarity of organization that is functionally unnecessary. The streamlined shapes of fish and dolphins are not homologous, because they can be explained by similar adaptive pressures acting on both species to increase their swimming speed. But the fact that both humans and dolphins have five finger bones (in dolphins, buried in their fins) is an example of homology, because no adaptive necessity that we know of would compel such a similarity of structure. In fact, nearly all mammals show this striking pattern, even though their limbs have been radically modified to serve purposes as different as swimming, burrowing and flying:
Below: Examples of homology in vertebrate limbs: Bats, moles, and dugongs all have five fingers. From Carl Zimmer, At the Water's Edge, p.58.
"Actually, these homologies were described and named by Darwin's predecessors - and they were not evolutionists." [p.52]
From the emphasis Wells puts on this statement, it seems we're meant to find it shocking. I don't know why he thinks we should be surprised that scientists who predated Darwin were not evolutionists. Is the argument here that if something was first noticed by non-evolutionists, it can't be used to support evolution? That would be a ridiculous distortion of how science works.
As with the similarities in vertebrate embryos, the homology among living creatures is an observation. Evolution is an explanation for that observation, and many others as well, which shows how a wide variety of observed facts can spring from the root of a single unifying principle. That's how science is meant to work. No one scientist "owns" an observation, nor are they the final judge of what theories it can be used to support, even if they're the one that discovered it.
Wells goes on to claim that homology can't be used as evidence for evolution unless we understand how it arises. This is a fair point, but the explanation is obvious, though he tries very hard to make it seem incomprehensible:
"A more common explanation nowadays is that the homologies come from similar genes. In other words, the reason two features are homologous in two different animals would be that they're programmed by similar genes in the embryo. But it turns out this doesn't work very well...
There's a gene that's similar in mice, octopuses, and fruit flies. If you look at a mouse eye and an octopus eye, there's a superficial similarity, which is odd because nobody thinks their common ancestor had an eye like that. What's more striking is if you look at a fruit fly's eye - a compound eye with multiple facets - it's totally different. Yet all three of these eyes depend on the same or very similar gene.
In fact, it's so similar that you can put the mouse gene into a fruit fly that's missing that gene and you can get the fruit fly to develop its eyes as it normally would." [p.53]
Wells claims that this is a deep mystery and an insurmountable difficulty for explaining homology, but it's neither.
In addition to creating proteins which do the hard work of building body parts, genes can also turn other genes on or off. Genes like the one Wells mentioned (its actual name is eyeless, because of the effect on development when it's knocked out) are master control switches. When activated, they set in motion an entire cascade of other genes. It's differences in those downstream genes that create the differences between mouse, octopus, and fly eyes, but the initial genetic switch that kicks off this program is very similar across species - so similar that, as Wells notes, the mouse eyeless gene can trigger the development of eyes in fruit flies.
This is the explanation for homology that Wells claims not to understand. When we see these homologies, what we're seeing is alterations of a developmental program. All mammals have inherited a toolbox of genes from their common ancestor which they use to do things common to all mammals, such as building limbs. In every mammal species, the same master control switches are there; the same genes building the same body parts are there. But the program has been altered by selective pressure - turning some genes on for longer, or suppressing others sooner - to change the limbs in ways that are adaptive for various different niches.
This leads into Wells' next distortion, about the genetic similarities between humans and apes:
"If you assume, as neo-Darwinism does, that we are products of our genes, then you're saying that the dramatic differences between us and chimpanzees are due to two percent of our genes... The problem is that the so-called body-building genes are in the ninety-eight percent. The two percent of genes that are different are really rather trivial genes that have little to do with anatomy. So the supposed similarity of human and chimpanzee DNA is a problem for neo-Darwinism right there." [p.54]
This passage implies that Wells rejects not only evolution, but genetics itself, which would put him well on the way to rejecting every discovery in biology in the last several hundred years. What explanation is he proposing for the differences between humans and chimps if he doesn't think it's due to genes? Do tiny angels with hammer and chisel reshape human embryos in the womb?
That aside, the evolutionary explanation neatly accounts for this supposed difficulty. Humans and chimps, after all, have the same body parts in the same basic arrangement. Our "body-building" genes don't need to be much different. What is different is the genetic master switches, the developmental program, which has been altered to emphasize certain features and reduce others. Indeed, it's widely understood that many of the differences between human and chimp stem from a developmental principle called neoteny: the retention of juvenile features into adulthood. To put it another way, humans look a lot like larger versions of baby chimps. This is most apparent if you look at our skulls:
Top row: A fetal, infant, and adult chimpanzee skull. Bottom row: Fetal and adult human skull. Note how the adult human strongly resembles the infant chimp.
The final card Wells has to play is the one that creationists always use to explain away homology, the "common design" argument.
"A designer might very well decide to use common building materials to create different organisms, just as builders use the same materials - steel girders, rivets, and so forth - to build different bridges that end up looking very dissimilar from one another." [p.55]
The flaw in this argument is that, although it can explain isolated similarities on an ad hoc basis, it cannot explain the overall pattern of similarities we see in living things. Designers, particularly omnipotent ones, are not constrained by past history in their work. They are not limited to variations or elaborations on designs they've already produced. They can borrow useful designs from anywhere and incorporate them into their plans.
But when we observe life on Earth, we don't see this kind of mix-and-match planning. We don't see dolphins with gills, bats with feathers, and so on. Instead, what we see are organisms whose adaptations apparently are constrained by past history. The mammal five-finger pattern is a clear example: it has no obvious explanation under common design (how would "common building materials" explain why a designer chose to repeat a pattern with no apparent purpose?). But it's just what we'd expect if mammals were all descended from a common ancestor with five fingers.
As the old saying goes, the more things change, the more they stay the same. That slogan excellently summarizes the principle of homology. Even though the bodies of living creatures have changed dramatically to adapt to different environments, they still retain the deep similarities that point to their common descent from ancient ancestors.
Other posts in this series:
The Case for a Creator: Beating a Dead Haeckel
The Case for a Creator, Chapter 3
Ernst Haeckel died
a hundred and fifty almost a hundred years ago [fixed - thanks, Alex!], but the creationists won't let him rest in peace. In this section, Wells again exhumes these old bones and takes a few kicks at them, and imagines that by doing so he's brought the entire edifice of modern evolutionary biology crashing down.
If you're not familiar with Haeckel, here's a bit of background. Ernst Haeckel was a nineteenth-century biologist, one who lived at about the same time as Charles Darwin. He's best remembered for his dictum "ontogeny recapitulates phylogeny", meaning that a developing embryo retraces the evolutionary history of its ancestors - i.e., a human fetus first passes through a fish-like stage, then an amphibian-like stage, then a reptile-like stage, and so on. Haeckel is also infamous for defending this claim by using his own drawings of developing embryos, which turned out to be faked to exaggerate the stages he claimed were there.
What makes this more than a hundred-year-old cautionary tale is that creationists claim that Haeckel's drawings are still presented in textbooks as evidence for evolution. Here's how Wells puts it:
"They're still being used, even in upper-division textbooks on evolutionary biology. In fact, I analyzed and graded ten recent textbooks on how accurately they dealt with this topic. I had to give eight of them an F. Two others did only slightly better; I gave them a D." [p.48]
Strobel chimes in, declaring that he too remembers being taught about these drawings as evidence for evolution, and that "anger was brewing inside of me" [p.48] as he realized that he had been duped.
I'll give Strobel the benefit of the doubt and assume he's confabulating memories. Wells, however, I don't intend to treat so charitably: again, he is lying, making statements which he must know are false. P.Z. Myers quotes one of the books which Wells disparages by claiming that it is "resurrecting Haeckel", Campbell's Biology:
The theory of recapitulation is an overstatement. Although vertebrates share many features of embryonic development, it is not as though a mammal first goes through a 'fish stage', then an 'amphibian stage', and so on. Ontogeny can provide clues to phylogeny, but it is important to remember that all stages of development may become modified over the course of evolution.
Myers also cites a post listing a large number of other college textbooks that point out the problems with Haeckel's hypothesis. Out of 15 books reviewed, only one presents recapitulation uncritically - and that one is from 1937!
All of Wells' indignation is a smokescreen, intended to cover up an uncomfortable point: namely, vertebrate embryos do pass through a stage, called the phylotypic stage or the pharyngula, in which they all look very similar. Haeckel's biogenetic law was a hypothesis intended to explain that observation. By criticizing one particular faulty hypothesis, Wells hopes to cast doubt on the observation itself.
Wells repeatedly attacks textbooks for making claims such as "the early embryos of most vertebrates closely resemble one another" [p.50], implying that this is an endorsement of Haeckel. In fact, this is a completely true statement, referring to the phylotypic stage. These patterns of embryological development are real, and they do not disappear just because one particular explanation of their origin is falsified.
To take the measure of Wells' mendacity, realize that when he gives "grades" to textbooks, he lowers the grade if the book contains actual photos of embryos. He considers this a "misleading" tactic when it comes to making the case for evolution. Why, we wouldn't want to show people what embryos actually look like, do we? It might give them the wrong idea!
This fact explains Wells' great annoyance over the term "gill slits", a lay term for branchial arches, which are a structure common to embryos at the phylotypic stage. Wells insists, despite the name, that these are not gills [p.51]. This is true, but unfortunately for him, he then goes on to undermine his own argument:
"In humans, the ridges become one thing; in fish, they become gills." [p.51]
It's correct to say that human embryos do not have gills. (That would be Haeckel's biogenetic law.) But the more important point is one that Wells, unintentionally I'm sure, has illustrated: vertebrate embryos pass through a stage where they are very similar, and the same structures that exist in the embryonic forms of many species develop into completely different adaptations in the adult forms of those species. This is a phenomenon that evolution provides a good explanation for. How, or whether, ID can explain it is a question never raised in this book.
Other posts in this series:
The Case for a Creator: Small Twigs
The Case for a Creator, Chapter 3
Jonathan Wells' second "icon" is Darwin's tree of life, which he says is a "dismal failure" [p.43] as an illustration of the fossil record.
With a lead-in like that, you'd expect a typical creationist jeremiad against transitional fossils. In fact, that's not what we get. The focus of Wells' complaint is about the Cambrian explosion, 550 million years ago. No transitional series more recent is treated here: not the origin of tetrapods, not the therapsids which illustrate the evolution of reptiles into mammals, not the beautiful and compelling whale transitional series, and certainly not the emergence of the human species. Wells never even mentions these compelling, and indisputably relevant, examples of evolutionary transition preserved in the fossil record. Instead, the source of his ire dates all the way back to the origins of modern phyla:
"Darwin knew the fossil record failed to support his tree. He acknowledged that major groups of animals - he calls them divisions, now they're called phyla - appear suddenly in the fossil record. That's not what his theory predicts." [p.43]
This is a lie. For the record, Darwin was well aware of the imperfection of the fossil record, and devoted an entire chapter of his book to explaining why we should not expect to see clear transitions preserved. If anything, he was too pessimistic, and our paleontological surveys have surpassed his expectations.
"Then at the beginning of the Cambrian - boom! - all of a sudden, we see representatives of the arthropods, modern representatives of which are insects, crabs, and the like; echinoderms, which include modern starfish and sea urchins; chordates, which include modern vertebrates; and so forth. Mammals came later, but the chordates - the major group to which they belong - were right there at the beginning of the Cambrian.
This is absolutely contrary to Darwin's Tree of Life. These animals, which are so fundamentally different in their body plans, appear fully developed, all of a sudden..." [p.44]
Wells' argument is that the various phyla are so different in their body plans, they could not possibly have all diverged from a common ancestor in such a brief period of time. The best answer to this is a clever analogy originally proposed by Richard Dawkins to clear up just this sort of confusion:
Suppose you have a great oak tree with huge limbs at the base and smaller and smaller branches toward the outer layers where finally there are just lots and lots of little twigs. Obviously the little tiny twigs appeared most recently. The larger boughs appeared a long time ago and when they did appear, they were little twigs. What would you think if a gardener said, "Isn't it funny that no major boughs have appeared on this tree in recent years, only small twigs?"
Strobel and Wells would like their readers to believe that the various phyla were already radically different from each other at the time of the Cambrian explosion. This is not the case.
The phyla are like the twigs on Dawkins' tree. Originally, far back in the Cambrian, they were very similar to each other. But over great spans of geological time, they have diverged farther and farther, and what were originally slight differences became accentuated by evolution to fit the varying lifestyles to which they adapted. Today, the living representatives of these groups have major differences from each other, and looking all the way back, we can see how those differences developed from what were originally slight distinctions. In that sense, it's fair to say that the "fundamental body plans" first appeared in the Cambrian. But that's not the same thing as saying that the earliest members of these groups were radically different when they lived side by side.
When Wells speaks of "major groups", he subtly misleads the reader. Based on his examples, a lay reader might erroneously conclude that starfish, crabs, reptiles, insects, and the like all just suddenly appeared during the Cambrian. In fact, as already stated, most species of the Cambrian explosion were relatively similar, and none of them looked much at all like the modern groups that are thought to have descended from them. Here are several Cambrian animals that Wells claims represent "major groups" that are "fundamentally different in their body plans". Can you tell which one is the ancestor of what modern group?
(All images from the Smithsonian's Burgess Shale Fossil Specimens page.)
If you've given up, the first of these animals is called Aysheaia, and is thought to be an ancestor of the velvet worms (phylum Onychophora), segmented worm-like animals with rows of clawed feet. The second is Canadia, believed to be an ancestor of annelids (phylum Annelida), whose modern representatives include earthworms and leeches. And the last is Pikaia, believed, with some dissenters, to be an ancestor of the phylum Chordata - us. All modern animals with dorsal nerve cords - fish, amphibians, reptiles, birds, mammals - all of them were represented in the Cambrian by this tiny, one-inch-long free-swimming creature.
These supposedly vast phylum-level differences, in the beginning, were trifling things. It's only time and evolution that have turned these small twigs into great branches spreading far and wide.
Other posts in this series:
The Case for a Creator: Bubble, Bubble, Toil and Trouble
The Case for a Creator, Chapter 3
Having established Jonathan Wells' bona fides, let's get down to business. The first of his "icons" is the Miller-Urey experiment, a landmark study proving that the chemical building blocks of life could emerge relatively easily under conditions similar to those of the early Earth.
This is not, strictly speaking, an "icon of evolution" at all. Miller-Urey was an experiment about abiogenesis, the question of how life first arose from nonliving precursors. This is an entirely separate question from evolution, which is concerned only with how life adapted and diversified once it existed. The lines of evidence for each of those theories are parallel, but distinct. If an Intelligent Designer had zapped the first cell into existence in a puff of smoke, evolution could have taken over normally from there; and even if Miller-Urey was found to be false, misleading, or irrelevant, that would not in the least affect the abundant evidence cited by scientists in support of evolution.
Still, we press on. The Miller-Urey experiment is a famous result in which a chamber filled with methane and ammonia - called "reducing" compounds because they tend to take electrons from other molecules, giving themselves a more negative electric charge - produces large quantities of amino acids, the building blocks of proteins, when exposed to an electric current. Through Strobel, Wells claims that this experiment was unrealistic:
"Well, nobody knows for sure what the early atmosphere was like, but the consensus is that the atmosphere was not at all like the one Miller used... The atmosphere probably consisted of carbon dioxide, nitrogen, and water vapor" [p.37].
In fact, the consensus among geologists is that the early atmosphere was not as strongly reducing as in the Miller-Urey experiment, but even weakly reducing atmospheres still produce significant quantities of amino acids. In addition, Wells completely neglects an obvious alternative: the origin of life may not have been in the open air at all. There were other sources of reducing compounds on the early Earth, most notably hydrothermal vents - the "black smokers" of the ocean bottom - and some researchers believe that life did indeed begin there.
Wells also omits another important point, which is that we have direct evidence that amino acid synthesis was occurring at the right time. Amino acids have been found in comets and meteorites, which contain pristine material dating back to the origin of the solar system; they have also been found in interstellar molecular clouds. This is more than just indirect evidence that amino acid synthesis was going on in the early solar system: it's possible that a comet or meteorite impact actually delivered the amino acids to Earth that became involved in the first life.
Wells goes on to assert that, even if the Miller-Urey experiment was a success, we'd be left with the problem of what happened next:
"You would have to get the right number of the right kinds of amino acids to link up to create a protein molecule - and that would still be a long way from a living cell. Then you'd need dozens of protein molecules, again in the right sequence, to create a living cell. The odds against this are astonishing" [p.39].
Again, Wells obfuscates the point at issue via his constant references to a "living cell". Cells as they exist today are enormously complex and unlikely to form from any simple chemical process, but cells today have had billions of years of evolution to increase in complexity. The first living thing would have been nothing at all like a modern cell, but merely a molecule (or a series of molecules - called a hypercycle) with the ability to make copies of itself. Such a creature would have been far, far simpler than the complex and specialized cells that exist in living things today.
Strobel does raise this obvious objection, but Wells brushes it aside, insisting that the odds of abiogenetic assembly of even a simple self-replicator are "simply insurmountable" [p.39]. Obviously, Wells has no knowledge of the total catalogue of self-replicating molecules or all the pathways by which each one of them can form. His argument here is pure assertion, unbacked by any conceivable evidence.
Of course, the origin of life is by no means a solved problem. There are still many important unanswered questions, and even if we found a plausible route from simple organic molecules to true self-replicators, we would probably never be able to prove that it was the route by which life came into existence. But Strobel and Wells are not merely sounding this note of caution; they are counseling surrender. They assert that they personally can't see any way to solve these problems, so we should give up and declare it a miracle.
"And if you try to invoke another explanation - for instance, intelligent design - then the evolutionists claim you're not a scientist." [p.41]
Let me be generous for a moment to Lee Strobel and Jonathan Wells: intelligent design is not, in principle, an unscientific hypothesis. The idea that life was created by an intelligent agent is an idea that could theoretically be put to the test; after all, we routinely consider the possibility of intelligent agents in other fields of science, such as forensics. (Was the death a result of natural causes, or was it artificial?) The problem lies with ID advocates, who refuse to do the work!
Testing any sort of hypothesis about an intelligent origin for life would require speculating about the nature, motivations, and capabilities of the designer, speculations which we can then use to make predictions about what life created by such a designer would look like. Then we would go out and test those predictions against the real world to see if they hold up. A hypothesis which was used in this way, to derive and then confirm some startling piece of knowledge about how life works, would be a revolutionary scientific advance that would win its discoverer tremendous honors.
But Wells and the other ID advocates have no interest in doing any sort of work like this. They don't do research, they don't make predictions, they don't write papers, they don't discover new things. Instead, they sit on the sidelines and complain about how scientists are being unfair by not accepting their beliefs uncritically. If they are not accepted as scientists, they have only themselves to blame.
Other posts in this series:
To those who are following the continuing genocide in Darfur, every day brings grim headlines:
Fighting has prompted thousands of people in the southern part of Sudan's Darfur region to seek security and shelter at a refugee camp in the northern part of the war-torn area, according to the United Nations.
...An estimated 300,000 people in the western Sudanese region have been killed through combat, disease or malnutrition, according to the United Nations. An additional 2.7 million people have been forced to flee their homes because of fighting among rebels, government forces and the violent Janjaweed militias.
Though its plight has attracted the most attention, Darfur is far from the only troubled region of Africa. There's the failed state of Somalia, now a haven for terrorism and piracy, and the outbreaks of famine and cholera brought on by the near-total collapse of Zimbabwe in the face of dictator Robert Mugabe's refusal to surrender power, to name just the two most prominent examples from recent headlines. How did we let this happen?
Africa was the human race's first home. It is our birthplace, our cradle. The continent should be a sacred place to all of us, a living temple of memory reminding us of our origins. Instead, it's poverty-stricken, politically fractured, still laboring under corrupt autocracies and mired in backwardness and superstition. The picture is not all bleak - there are success stories, and notable bright spots - but even so, Africa as a whole lags behind the rest of the world, and still struggles with the legacy of imperialism and the unbridged chasms of its own political divides.
And yet, there was a time when all humans were Africans. Though we've spread all over the world in successive waves of migration, our genes have not forgotten the past. Whether you're European or Asian, from the Arctic or from Polynesia, your heritage can be traced back to families that lived in Africa millions of years ago. If you care to categorize on the basis of something as superficial as skin color, then you can know to a certainty that the blood of black men and women flows in your veins.
It was Charles Darwin who ventured the bold guess that the human race evolved in Africa, and the evidence has vindicated him. It's in Africa that we find the bones of our earliest known ancestors and our close cousins in the human family tree: species like Lucy's, Australopithecus afarensis, small hominids who had the heavy brows and brain size of chimpanzees but stood and walked upright like us. It's in Africa, in Laetoli, that we find the oldest trace evidence of human bipedalism: two trails of footprints frozen in stone, four million years old, where three people - perhaps a family of man, woman and child - walked together across a field of new-fallen volcanic ash. It's in Africa, in Tanzania's Olduvai Gorge, that we find the earliest stone tools. And more controversially, it's in Africa, at sites like Kenya's Koobi Fora, that we find possibly the earliest evidence for the domestication of fire.
In short, it's in Africa that we learned to be human. It was under the shade of Africa's trees that we first descended to the ground, and on African savannas that we stood upright and walked for the first time. The songs of our childhood were first sung beneath an African dawn; the stories that echo in your bones were first told around African campfires.
Of course, we did not stay in our birthplace forever. As the population grew and wanderlust took the human spirit, we flowed out in successive waves of settlement and conquest. We spread north into the fertile crescent of the Middle East, where we first domesticated animals and plants and built the world's oldest cities, and into Ice Age Europe, where we eradicated our brothers - the stocky, heavy-browed Neanderthals, who had lived and thrived in the frozen landscape for tens of thousands of years until we arrived. We walked across the Bering Strait into the Americas and fanned out across the Pacific by raft and canoe. We spread over the face of the earth, building mighty civilizations and forging empires in battle and conquest. And, in due time, the conquerors returned - to their own birthplace, had they but known it - and put it under their heel as well.
It took centuries for Africa to throw off that yoke, and the injuries that it suffered still are not fully healed. Its people still grapple with endemic disease, with political corruption and with their own tribalisms, all of which are exacerbated by poverty and international neglect. But still and all, Africa is a noble continent, not in the condescending caricature of the "noble savage", but nobility in the true sense of the word: those whose blood is purest, whose lineage traces back longest. It is still the home of the most deeply rooted branches of the human family tree: as Richard Dawkins writes in The Ancestor's Tale, the disappearance of everyone outside Africa would decrease human genetic diversity only slightly, while the disappearance of everyone in that continent would mean the loss of most of our species' gene pool. Compared to Africa, all the rest of humanity is a prodigal son, descended from a relatively small number of restless wanderers who left a great and ancient family to seek their fortunes in the world.
In the slow ascent of human progress, we have many milestones left to reach. There are ancient trouble spots throughout the world, and we can count ourselves more advanced as we overcome each of them. But the turmoil of Africa is our species' greatest shame. I can imagine an Earth where Africa takes its rightful place among the pantheon of peoples; an Africa where the archaeological sites of humanity's origin are sites of pilgrimage, sacred places preserved for all to see and walk in the footsteps of our ancestors. I can imagine an Africa that's peaceful and prosperous, where gleaming cities exist alongside the simple beauty and grandeur of the savannahs and rainforests that were our childhood home. We may, perhaps, have no right to call ourselves truly advanced until that world is a reality.
Bands of Iron
On a wintry day late last year, I visited the Museum of Natural History in New York City. While touring the geology wing, I came across this boulder-sized chunk of a rock formation:
A banded iron formation from the geology exhibit of the Museum of Natural History. Photo credit to Erich Vieth.
It was out in the open with no ropes or glass around it, inviting visitors to touch it. I brushed a hand across its polished surface, which was as smooth and cool as a sheet of glass. Nothing about that touch hinted at the stone's age or history; yet it had traveled down immense vistas of time to come here, to our era, so that I could see and touch it on that day. And in the moment of that touch, I knew, I as a modern Homo sapien was briefly reunited with predecessors ancient beyond imagining, perhaps some that date back almost to the origin of life on Earth itself.
The curious, gorgeously colored strata of this stone are called banded iron formations. The dark bands are layers of metallic iron oxide compounds such as magnetite and hematite, while the reddish layers are silica-rich quartz minerals like chert, jasper and flint. Banded iron formations occur almost exclusively in very ancient rocks, and are common in strata dating to between 2.5 billion and 1.8 billion years ago. This is the period commonly called the Precambrian, although its more technical name is the Proterozoic Eon.
True multicellular life first appears in the fossil record at the very end of the Proterozoic, in the form of the bizarre and famous Ediacaran biota that would become the precursors of the Cambrian explosion. But for most of the Proterozoic, the most common fossils are stromatolites: puffy accretions of sedimentary rock laid down by vast colonies of bacteria.
The Earth in this eon was a different place. Most notably, from chemical and geological evidence, we know that its atmosphere had no oxygen. The only life was colonies of purple bacteria, making a living using the chain of chemical reactions called photosystem I, which converts light, carbon dioxide and hydrogen sulfide into sugar and releases sulfur as a byproduct. But the Proterozoic was when this began to change: this was the time when evolution invented photosystem II, the more advanced version of photosynthesis that uses water and carbon dioxide to make sugar, liberating oxygen as a byproduct. This is the very same set of reactions that sustains all green plants, and ultimately all animal life, today, two and a half billion years later.
At first, oxygen was an annoyance to Proterozoic life, but it soon became a menace. Unlike today, there were no oxygen-breathing animals to expire carbon dioxide and close the cycle, and so it quickly built up in the atmosphere as photosynthetic bacteria spread and thrived. To us, it's the breath of life, but to these bacteria, it was a deadly toxin.
At the same time, another process was taking place. Weathering of the Earth's primordial rocks had been releasing iron, most of which washed down to the sea and ended up as iron ions dissolved in the oceans. Until then, that iron had had nothing to react with, but when it encountered oxygen, the two chemically combined into iron oxides like magnetite and hematite. These compounds are insoluble, and when they formed, they precipitated out and sank to the ocean bottom, gradually building up those dark silver layers.
With iron reactions steadily removing oxygen from the atmosphere, anaerobic bacteria thrived for a time. But eventually, there was no more free iron. Once that point was reached, oxygen started to build up in the atmosphere. Heedless, the bacteria kept churning it out - until a toxic tipping point was reached, and the Earth's atmosphere was changed to such an extent that it became poisonous to Earth's life. The consequence was mass death among the planet's abundant bacterial colonies - an oxygen holocaust that knocked life back down to nearly nothing. Only a few anaerobes survived, in isolated nooks and crannies where the deadly gas did not reach.
After this catastrophe, the planet would have seen several million years of relative quiet. In this life-poor era, layers of silica minerals were deposited on the ocean floor. But in the meanwhile, erosion continued to free up iron atoms, which slowly scrubbed the atmosphere and oceans of oxygen. Eventually, the world was cleansed, and life bounced back, spreading from its refuges to once again cover the planet. Of course, this exuberance contained the seeds of its own downfall - bacteria still spewed out the waste oxygen that they could not abide - and the cycle repeated, not just once but many times. Each time, a layer of iron oxides was deposited, followed by a layer of iron-poor silicates in the aftermath. And that leads me back to the Natural History Museum, on that cold winter day where I stood and brushed a hand across a banded iron formation.
Looking at this stone, you get some idea of the dizzying vistas of geological time, as well as the turmoil that life has endured to reach the present day. Each of those colorful red and silver layers represents what was, in its own era, a disaster beyond imagining, one that reset life to its starting point. Each of those layers, as well, is a silent testament to life's tenacity in the face of overwhelming odds. Of course, the cycles of growth and destruction did not last forever. Eventually, evolution found a way, as evolution nearly always does, and oxygen was tamed to become a power source in an entirely new metabolic cycle. The oxygen-breathers arose, the remaining anaerobes retreated to the deep crevices of rocks and the sea, and life found a new equilibrium, with the balance of the atmosphere permanently changed. All the oxygen we breathe today is biologically produced, a tangible proof of life's power to reshape its own world.
As well, these banded iron formations may be a metaphor for our own foolhardiness. In our time, we too are changing the composition of the planet's atmosphere, this time through the release of greenhouse gases. In the process, we are becoming the first species since the ancient photosynthetic bacteria to have such a global effect. The danger we face may not be as severe - but it is severe enough. Those bands of iron are not only a record: they are a warning of what happens when life reshapes its own environment without thought for the consequences.
The Age of Wonder
If you search the internet, it's not hard to find New Agers and others who think that the dawning of the age of reason was a mistake. They envision a more "holistic" approach, one that properly pays heed to the mystery and complexity of existence, and castigate science for being cold, unfeeling, heartless in its probing, reductionist scrutiny of the natural world. For example:
The reason things are advancing so slowly... is that science has neglected the (spiritual) indications necessary for its efficient performance - "with all your heart and all your soul...." -- indications that govern higher creativity and exist for the specific purpose of breaking the cosmic bank. The upshot is that science has become excessively expensive, bureaucratic and materialistic. The integration we need, external and internal, requires an incomparably more intense confrontation between the spirit of the researcher and the natural phenomena he is contemplating than what is currently practiced by even the most zealous of researchers.
And yet, the age of reason is also an age of wonder. The devotees of superstition and pseudoscience do not know what they are missing. In grasping after fool's gold, they have missed the true vein. The universe is a grander, more majestic and more beautiful place than any human being has ever imagined, or can imagine. The unsubstantiated and anthrocentric claims and inventions of people can never compare to the wonder and mystery held by reality as it truly is, and now that we truly have begun to understand how the cosmos works, we are at last getting a glimpse of that awe and wonder.
Consider what we witness when we peer into the cosmos with our telescopic eyes. We see light born billions of years ago in the crucible of dying stars, shining out across the cosmos and becoming ever more diffused, until at last our telescopes captured the lonely few photons that arrive bearing news of stupendous, ancient catastrophes. We see colliding galaxies, matter swirling into the abyss of black holes, and stars exploding with titanic force, sending out jets of energy visible across the known universe.
Our astronomy bears witness to births as well as deaths. We sift invisible light and see the ripples in the faint microwave glow that bathes all of space, distant echoes of the incomprehensible cauldron of heat and density in which the universe itself was born. We see dense nebulae where new stars are being born, burning away the dusty cradles of their formation like sunrise through fog. We see young planets circling their parent stars, their gravity cutting clear swaths through the veils of gas surrounding them. Most of the planets we have detected are hot Jupiters, but perhaps in some of these systems lurk embryonic Earths, awaiting their chance to cool and condense and one day become cradles of life of their own.
Turning closer to home, our emissaries have explored the solar system and brought back news of the other shores that await us. We have seen the shadows of the setting Sun creep across the mountains of the satellites of Jupiter, and we have seen the Earth rise in the night sky from the surface of the Moon. We have traveled the surface of Mars with our robot rovers, and sent landers parachuting down to the methane seas of Titan. Our age, for the first time ever in our planet's history, has sent ambassadors voyaging so far beyond our own shores that they could look back and see the Earth itself, our one and only home, as a pale blue point of light drifting in infinite dark.
Closer still, we have turned our gaze back upon ourselves, exploring our world in all its complexity. We have learned of the web of evolutionary kinship that connects all life on Earth. Everything - from human beings to redwood trees, from the lowliest cyanobacterium to the fluorescent tube worms on the ocean bottom - is a branch of the same family tree, every living creature a cousin, however distant, to every other.
We have delved down to the molecular roots of life itself, glimpsing the intricate choreography that turns inanimate molecules into living, growing cells, and the equally intricate assemblage that builds living cells into living beings. We have begun an effort to survey the tree of life, discerning the family relationships among countless species living and dead, and mapping the vast, frozen structure branching multidimensionally through those sections of design space that evolution has so far explored.
Traveling down into Earth's history, we have learned to read the record of the rocks and the chronicles they tell. We have retraced the multimillion-year drifting of the continents and learned of the planetary convulsions that wiped out whole branches of the tree of life and ushered in new ones in their place. We have glimpsed primordial eras long before humanity and envisioned the strange landscapes that once existed where we now place our feet.
All these findings far exceed the most fantastic imaginings of ancient mythology or modern pseudoscience, not least because they are true. In what other age of human history has anyone been able to look on a shooting star or a volcano and know what it really is? In what other age have we known the true age of the planet or understood the power source of the sun? These wonders and countless others, most of which are familiar and mundane to us, would have made people of past ages gasp in awe.
Out of the entire span of human history, these breathtaking discoveries have been made only in the last few hundred years, when we began to think and explore rationally. It was not crystals or prayer or Tarot cards that brought us these things. It was not superstition that was responsible, nor mysticism, nor credulous acceptance of extraordinary and unverified claims. It is the scientific method – institutionalized skepticism, rigorously and comprehensively applied – that has given rise to these wonders of understanding and accomplishment. As long as we human beings were willing to blindly accept the claims of others, to be meek and easily led, to believe without questioning, we remained frightened, brutish, short-lived and ignorant. There are some today who would gladly have us return to that state. Worse, there are some whose methods would inadvertently lead us back to that state, even as they hypocritically seek to take credit for the fruits and innovations of science while rejecting its rules.
But as for me, I remain a skeptic. I am proud to call myself a rationalist. And I will always fight against the proponents of darkness and unreason, because I believe that humanity has barely begun to tap its potential, and that if we continue the path of science, we may some day create wonders we currently lack the ability even to dream of.
We Are Myriad
Do I contradict myself?
Very well then I contradict myself,
(I am large, I contain multitudes.)
—Walt Whitman, "Song of Myself"
Creationists who think themselves clever sometimes ask why, if evolution is true, we don't see bacteria re-evolving into multicellular organisms. But, as is often true of creationists, this taunt gets the situation completely backwards. Evolution is not a teleological march of progress but a blind algorithm, concerned exclusively with reproductive success. Looked at in this light, a far better question is why multicellular life ever evolved at all. In the metrics of success that evolution is concerned with, bacteria are our undisputed superiors. They far outnumber us; they thrive in environments we could never survive in; and, if they were ever to disappear, all of the so-called higher life on this planet would swiftly follow them into extinction.
Bifidobacterium, one of the first species to colonize a newborn's intestinal tract (usually introduced through the mother's breast milk). Image credit: MicrobeWiki.
To drive this point home, consider this mind-boggling statistic: in the body of every healthy human being, there are ten times as many bacterial cells as there are human cells. If this seems impossible, realize that bacteria are prokaryotes, lacking the complex internal structure of, and therefore much smaller than, our own eukaryotic cells. Most of the bacteria in the human body live in the intestines, and the 15 trillion or so bacteria in a healthy gut would just about fill a ten-ounce soup can.
Our gut flora are not invaders or pathogens, but an important part of the body's normal functioning. Far from being mere passengers, they live in an intimate symbiosis with the cells of the digestive tract. They play a vital role in extracting nutrients from food: mice raised in absolutely sterile environments need to eat 30% more to stay at the same weight as normal mice. (This partnership is more prominent in herbivores like cows or termites, whose resident bacteria enable them to digest the woody plant tissues that no animal could otherwise eat - but our natural bacteria do the same for us, helping break down complex carbohydrates and proteins that the body cannot digest on its own.) In fact, it's believed that the gut flora are a vital barrier against disease: by occupying all the niches within the body, they leave less room for genuinely pathogenic species to get a toehold.
Jessica Snyder Sachs, in her book Good Germs, Bad Germs, quotes an unforgettable portrait of the microbial jungle that lives just in the human mouth alone:
...I was able in my mind's eye to zero in on the little fleshy crevices around Tom's and Jenny's teeth as they ate their meal and to see the turmoil of microbic life there, the spirochetes and vibratos in furious movement, the thicker corkscrew-like spirilla and vibrios gliding back and forth and the more sluggish or quiet chains and clusters and colonies of bacilli and cocci, massed around or boiling between detached epithelial scales and the fibers and debris of cells and food particles. Like the great and beautiful animals in whose mouths they live, these too are organisms, living things; and I could imagine them, quite like Tom and Jenny, making the most of the sudden accession of nourishment after a long fast. (p.36)
Staphylococcus epidermidis, a common skin bacterium. The average human being has three to sixteen of these living on the surface of every skin cell. Image credit: NIAID.
But our relationship with bacteria is more intimate still. Other species of them do not just live within our bodies, but within our cells, and it is only because of them that life like ours is possible. Richard Dawkins puts it succinctly in The Ancestor's Tale:
All our cells are... stuffed with bacteria which have become so transformed by generations of co-operation with the host cell that their bacterial origins are almost lost to sight... [They] have become so intimately enmeshed in the life of the eukaryotic cell that it was a major scientific triumph to detect that they were there at all. (p.537)
Each of our cells contains organelles called mitochondria. Colorfully speaking, they are the cell's power factories - the reason we breathe oxygen is so the mitochondria can use it in the production of ATP, an energy-carrying organic molecule that's used as a common currency for many of the cell's chemical reactions. Mitochondria also have their own DNA - not the complexly packaged chromosomes of our own nuclei, but simple circular chromosomes similar to those of bacteria - and are capable of self-replication, dividing autonomously within the cell.
Above: The famous
Escherichia coli, one of the most common gut bacteria. Most strains are harmless. Image credit: NIAID.
The evolutionary biologist Lynn Margulis is famed for discovering the origin of mitochondria: as their separate DNA hints, they were once free-living bacteria. Long ago in the mists of evolutionary history, these bacteria merged with the cells that would ultimately become our ancestors. Both cells benefited from this symbiotic partnership, and so it persisted and thrived. Over long stretches of time, the mitochondria lost most of their DNA, as it was no longer needed in their new environment. Though they have become so intertwined with us that they are no longer capable of independent existence, they remain as traces of the ancient eukaryotic union that was the first flowering of life recognizably like ours. Incredibly, even today, we can guess at the identities of those species involved in this historic partnership. From Richard Dawkins again:
...molecular comparison tells us the particular group of bacteria from which mitochondria are drawn. Mitochondria sprang from the so-called alpha-proteo bacteria and they are therefore related to the rickettsias that cause typhus and other nasty diseases. (p.539)
Though their wild relatives cause us grief, the tame mitochondria are essential to life as we know it. And not just our life, either: chloroplasts, the organelles that give green plants their color and make photosynthesis possible, are, like mitochondria, the remnants of an ancient symbiosis. For both plants and animals, the seen depends on the unseen: each of us is not a single organism but a myriad, a kind of ecosystem made up of hundreds of different species. If it were not for our microbial partners, our kind of life could not exist. This insight, and the humility it brings, are worth remembering whenever we Homo sapiens are tempted to imagine ourselves the crowning glory of life on Earth.