WEIT: The Meaning of Life

At last we've arrived at the final chapter of Why Evolution Is True, and it's a short but sweet one. Coyne devotes these last few pages to a discussion on evolutionary theory's impact on society, and some of the common misconceptions that often arise from it.

We have plenty of evidence for evolution, plenty of fulfilled predictions, and no pieces of evidence (e.g. Precambrian rabbits) that would have disconfirmed it. Scientists disagree on minor points, like the importance of genetic drift or the precise cause of the Cambrian explosion, but there's no controversy on the big ones. So why is it that people find evolution so hard to accept? Most of the opposition comes from religion. Creationists create fear of evolution by claiming that it robs us of purpose, causes us to behave "like animals," and sanctions the killing of those who are weaker than us.

None of this is true. Evolution is a description of how life changes over time; it says nothing about whether such change is good or bad. It tells us how things are, not how they should be. It's not somehow "wrong" to defy natural selection by caring for the weak—that would be like saying that it's wrong to defy gravity by jumping or firing rockets into space.

Burn the heretics of our holy prophet Newton!

The idea that support for evolution would make us behave "like animals" is a non-starter. Animals exhibit an endless variety of behaviors, many of them altruistic. Perhaps creationists think that evolution would cause us to act like rhesus monkeys, who will starve themselves before allowing one of their companions to experience an electric shock?

Of course, it's true that humans have behaviors that are hard-wired as a result of natural selection: that's the realm of evolutionary psychology. Coyne criticizes this field for venturing too far into speculation, but he suggests eating, sleeping, sex, parenting and the favoring of relatives as uncontroversially inherited instincts. Another such instinct, the relative promiscuity of men compared to women, might seem to validate creationist concerns. But this behavior exists whether we accept evolution or not—and humans have higher mental faculties to override these urges and societies that can shame the cheaters.

What about purpose, then? How can we go on living without the notion that we were created by a loving God? Simple: we make our own meaning. We can love our friends and family, enjoy art, food and sport, and revel in the wonders of our universe. While evolution says nothing about meaning, it does grant us a vast appreciation for the extraordinary journey our species has taken to get to this point.

I think it would be appropriate to bring this series to a close with the quote from Richard Dawkins that begins this chapter:

"After sleeping through a hundred million centuries we have finally opened our eyes on a sumptuous planet, sparkling with color, bountiful with life. Within decades we must close our eyes again. Isn't it a noble, an enlightened way of spending our brief time in the sun, to work at understanding the universe and how we have come to wake up in it? This is how I answer when I am asked—as I am surprisingly often—why I bother to get up in the mornings."

WEIT: The Naked Ape

This is why the "no transitional fossils"
canard just makes me laugh.

Coyne begins WEIT's penultimate chapter by expressing the cultural and religious importance of human evolution. Even many religious people and institutions that otherwise except evolution (the Catholic church, for example) still reject the notion that humans could have evolved from other primates. Incredibly, John Scopes was convicted of the crime of teaching such facts less than a century ago, in 1925. Because of the potential public outcry, Darwin barely mentioned the issue in the Origin, and another scientist reburied the bones of a Homo erectus specimen for 30 years.

Thankfully, though, we have a decent understanding of our lineage today. Our evidence includes things like homology and genetic data, but fossils are the focus of Coyne's chapter. Here's what we should expect if humans evolved:

"Around five to seven million years ago [based on molecular evidence], we expect to find fossil ancestors having traits shared by chimpanzees, orangutans, and gorillas, but with some human features too. As the fossils become more and more recent, we should see brains getting relatively larger, canine teeth becoming smaller, the tooth row becoming less rectangular and more curved, and the posture becoming more erect. And this is exactly what we see."

To summarize (and ignore over a dozen other important finds): First comes the 6 to 7 million year old Sahelanthropus tchadensis, possibly our last common ancestor with chimps, which has a long skull and small brain like apes, but a flat face, small teeth and brow ridges like later species in our lineage. Then there's Australopithecus afarensis, of which Lucy is one. We know they were bipedal because their femurs angle inward from the hips, making upright walking far more efficient. They may even be responsible for the 3.6 million year old Laetoli footprints.

At this point, brain sizes begin growing steadily. Homo habilis, from about 2.5 mya, still have some apelike characteristics, but also have larger (though not human-sized) brains and have been found with carved stone tools that would be used for things like butchering. Homo erectus "still had a flattened, chinless face," but used even more complex tools, along with fire for cooking. Finally, just a couple of hundred thousand years ago, we have Homo neanderthalensis, distinct from but extremely similar to modern Homo sapiens. We most likely wiped out the Neanderthals either by outcompeting them or killing them.

While these fossils finds are more likely to come from close evolutionary cousins than our direct ancestors, they still tell us an enormous amount about our history. Anyone who looks honestly at the fossil evidence (let alone things like DNA and vestigial organs) would conclude, as modern science has, that we have a common ancestor with the other great apes. Coyne drives this home with one particularly amusing yet compelling point. Creationists who look at the evidence must classify all fossils as either apes or humans. If we really are a distinct creation of God, this ought to be a simple matter, but here's what happens when they try:

Via TalkOrigins

They can't even agree amongst themselves.

As a questioning creationist investigating the evidence for evolution, the image above blew my mind. Self-proclaimed creationist experts like the infamous Duane Gish confidently asserted that there are no human transitional fossils. Yet ironically, their classifications of various fossils follow a gradient from "apelike" to "humanlike" that beautifully confirms the evolutionary paradigm. Some individuals can't even decide whether a given fossil is ape or human, while others have changed their minds. Their willful blindness to the obvious conclusion is, frankly, fascinating.

Coyne goes on to address a few other interesting topics, including a thorough debunking of evolutionary racism: we diverged only about 80,000 years ago—not enough time for any major disparities to develop—and most differences between races are physical, the result of differing climates and sexual selection. Most of the rest isn't relevant to this blog, though, so instead I'll sign off with an informative chart of growth in hominid cranial capacity over time:

How anyone can group these into "ape" and "human"
with a straight face is beyond me.

Why Creationists Should Drop the Issue

Just fill in the quote marks around
"museum" using your imagination.

As a child of about ten, I enthusiastically embraced young earth creationism because at the time I thought it gave me concrete support for what I believed. A few years ago I became curious about what evolution supporters had to say about various issues, and I was blown away at how much sense it all made. It took a long time for me to eventually deconvert from Christianity, but the evolution/creation issue was one of the major factors that caused me to start questioning my faith.

Here's the deal: creationism is obviously wrong, and that should be enough reason to stop promoting it. But for creationists themselves, who can't see the evidence staring them right in the face, there's a more pragmatic reason not to try and press this issue. Nearly all creationists in the West are also fundamentalist Christians, and thus presumably consider saving souls to be more important than promoting what they think is the correct view of our origins. Evangelism is paramount; creationism is an important but still peripheral side issue.

I think that such creationists are doing more harm than good, even from their own perspective. There are many others like me, former creationists whose discovery of the real science behind our origins led us to wonder what else we had been lied to about. Unfortunately much of my evidence is anecdotal—I've heard and read a great many stories about people like these—but based on one informal poll, "science-based reasoning" was the number-one factor that led to people to leave the faith.

By promoting creationism as the only valid interpretation of the Bible and demonizing evolution as "atheistic," creationists are creating what many (especially theistic evolutionists) see as a false dichotomy. This leads people who reject creationism to reject their religion wholesale rather than adopting a more liberal form of it. Personally, I have my own reasons for finding theistic evolution unsatisfactory, but who knows? Maybe I'm wrong. Maybe millions of people are marching straight into hell because they switched quickly from conservative Christianity to atheism, with creationists unwittingly holding open the gates.

So from their own point of view, creationists should probably stop pushing so hard. And from mine? It's true that I find their alternate narrative irritatingly immune to reality and hate to see people taken in by it. However, I do appreciate them helping to create a fast track from fundamentalism to unbelief, allowing millions to neatly avoid the vague and wishy-washy quagmire that is liberal religion. Even if creationists refuse to drop the issue, though, I think it will slowly fade away whether they like it or not. Although public opinion is moving at a snail's pace, science is gradually prevailing.

Endogenous Retroviruses

If I were asked to present the single line of evidence that best supports common descent, endogenous retroviruses (ERVs) would probably be my choice. They attest not only to evolution in general, but to human evolution specifically and even to the age of the earth—and they present a potential point of falsifiability.

Retroviruses reproduce by inserting their genetic code into a cell's DNA. In rare cases, they happen to do this to one of the host organism's germ line cells (which become sperm or egg cells). When that organism reproduces, the retrovirus' genetic code is passed down to future generations. The retrovirus is now an ERV, which then lies dormant in the genome, slowly accumulating mutations just as the rest of the DNA sequence does. ERVs are essentially genetic fossils, remnants buried not in the ground, but deep within every cell of the body.

We know ERVs are actual remnants of viruses—and not just because they look exactly like viruses, although that should be evidence enough. In 2006, a team of French scientists actually revived an ERV from the human genome, which they dubbed "Phoenix." When introduced to a cluster of human cells, Phoenix was able to infect them—which would of course be impossible if Phoenix wasn't a real virus that actually infected one of our distant ancestors.

Even if ERVs didn't demonstrate our common ancestry with other animals (I'll get to that in a minute), they'd still be completely incompatible with a 6,000 year old earth. They make up almost 8 percent of the human genome in the form of 98,000 fragments from 30,000 retroviruses—and everyone's ERVs are more or less the same, give or take a few mutations. For that many viruses to insert themselves into just the right sperm or egg cells and spread evenly throughout the entire population would take several orders of magnitude longer than the young-earth paradigm allows.

So why are ERVs important evidence for evolution? Simple: they're arranged in patterns called nested hierarchies, and there's no reason to expect to such patterns unless common descent is true. If an ERV shows up in one species, which later splits in two, it will show up in both "daughter" species. For example, in the graph below, some specific ERVs are found in gibbons, orangutans, gorillas, chimps, and humans, because the virus infected the common ancestor of all five. Some ERVs are found in just the latter four, some in just the latter three, and so on. What's more, we find them in the exact same location in the genome of each species, meaning that the virus didn't happen to somehow infect them independently.

From Lebedev et al 2000. Time goes left to right.
Arrows represent ERV insertion at specific points in the genome,
which carry over to all subsequent species in that lineage.

At no point should we ever expect the same ERV in the same location in, say, humans and gibbons but not chimps—and we don't. The same goes for any two species that don't share a direct common ancestor, and the pattern holds each and every time. Let no one ever tell you that evolution is unfalsifiable; if the above examples turned to be true for some ERV, it would be completely unexplainable by common descent. However, the nested hierarchies we do find beautifully match the ones formed by other types of evidence.

So there we have it: ERVs point powerfully to an old earth, human evolution, and common descent in general. Naturally, creationists have tried to undermine this evidence, and as usual they fail miserably. I've already answered one objection (that they were never viruses at all), but these two blog posts by a graduate student specializing in ERVs offer a better response than I ever could. It saddens me that so many people—40% in America—believe in strict creationism, when most of them have never so much as glanced at the extraordinary evidence available.

WEIT: What Makes a Species

The seventh chapter of Why Evolution Is True delves deeply into the nuances of the biological species concept, or BSC. This idea is fundamental to evolutionary biology, and was defined by Ernst Mayr in 1942 as follows:

"A group of interbreeding natural populations that are reproductively isolated from other such groups."

By "reproductively isolated," we mean that individuals in two different species do not generally produce viable offspring. Coyne points out that there's no obvious reason that life should be divided into discrete species—instead it could have all blurred together, so that every point between, say, "cat" and "dog" was equally represented. While "God did it" would be equally compatible with these or any set of circumstances, evolution explains our specific observations perfectly.

In order for geographic speciation (the most common speciation process) to occur, a reproductive barrier such as a mountain range or a body of water must come between two groups of the same species. Once the groups are separated, genes cannot flow between them, so they start to become genetically distinct. This occurs largely due to natural selection as the groups adapt to differing environments, although the "random walk" produced by genetic drift can play a role as well. When the groups diverge far enough, the genomes of one group will be incompatible with the genomes of the other, so they remain distinct species even if the reproductive barrier vanishes.

We can use the principles in the above paragraph to make predictions that we can then go out and test. Lo and behold, what we find matches up precisely with what evolution predicts. First, we should be able to create reproductive barriers in the laboratory. And we do: groups of flies placed in different environments lose the ability to interbreed with other groups, sometimes in a year or less. One of Coyne's own experiments also showed that the more the DNA of two existing fly species differ, the more mating discrimination they exhibit and more likely their offspring are to be sterile.

The second prediction comes from biogeography: species that have similar genes should be found relatively close to one another, but separated by a geographical barrier. And they are: there are seven corresponding species of snapping shrimp on each side of the Isthmus of Panama (which arose to divide the Pacific and Atlantic 3 million years ago). The same holds true for islands: we don't usually find similar species on the same small island because there's not enough isolation, but we do find them on nearby islands in an archipelago. We see this in flightless crickets, Drosophila flies, and lobelia plants. Coyne points out that this pattern is also evidence against creationism:

"After all, there's no obvious reason why a creator would produce similar species of birds or lizards on continents but not on isolated islands."

Third, we should be able to observe reproductive barriers forming and speciation occurring in the wild, albeit very slowly. The example Coyne gives is the orchid Satyrium hallackii, which for now is classified as one species. In northern South Africa they have long nectar tubes that allow only hawkmoths and long-tongued flies to pollinate them, while they have short nectar tubes on the coast, where bees are the only available pollinators. The two groups are genetically isolated, and would probably remain so even if they lived in the same area.

Satyrium carneum, a close relative of the orchid Coyne mentions

Coyne ends by covering two more complex types of speciation, allopolyploidy and autopolyploidy, which involve the accidental duplication of chromosomes. Unlike normal speciation, these processes occur mostly in plants and can result in new species in just two generations. Polyploid speciation allows us to directly observe entire speciation events in the wild, which normally take too long for this to be feasible (although a certain mosquito species is a notable exception).

What we've seen here is a powerful illustration of evolution's explanatory power and scope. The biological species concept as applied to evolution allows us to make predictions with stunning accuracy. In contrast, the creationist concept of "kinds" or "baramins" is poorly defined and grants us no useful insights into the natural world. This is what we mean when we say that evolution is science, while creationism is nothing more than Bible-based wishful thinking.

Quotable Me

Previously I posted some memorable quotes from various thinkers on religion, atheism, skepticism and other topics that I'd previously posted on Twitter. Now I've compiled the tweets containing my own thoughts on those subjects. Some of these ideas are mine, but many of them are distillations of what I've learned from reading and listening to others.

Here are some bite-sized thoughts on Christianity:

• Even if Christianity somehow turned out to be true, 99% of Christians would still believe in it for terrible reasons.
• To most Christians, the Bible consists of the NT and a few OT bits like Genesis and Psalms. Books like Leviticus and Deuteronomy don't even exist.
• Why didn't God (a perfect communicator) convey criteria for salvation (the most vital topic possible) so Christians would all agree on them?
• Early Christian sects like the Marcionists and Gnostics often viewed the OT god as a wicked tyrant. I kind of wish they'd won the doctrine wars.
• We can't fully comprehend eternity, so no one can ever grasp just how awful hell would be, and how unjust it would be as punishment.
• Christians ask if you think you're "good" to begin their evangelism spiel. But of course they really mean "perfect," so why not just say so up front?
• Every believer in the resurrection should believe in UFOs: they're also BS, but at least they're based on extensive modern testimony and not an ancient book.
• It's remarkable that the Old Testament contains so much violence and yet manages to remain mind-crushingly dull.
• Funny how Harold Camping's explanation of May 21—a spiritual beginning of judgment—looks identical to nothing having happened at all.

On religion, God and atheism:

• If you wouldn't accept something as evidence for another religion, don't accept it as evidence for yours.
• Even some atheists think religion automatically deserves respect. Why shouldn't it be held to the same standard as other beliefs?
• Vague "God hypotheses" yield no useful predictions; specific ones are easily falsified.
• Religion offers you a cure to a disease you don't have.
• Not only is "no atheists in foxholes" false, it'd be worthless even if true, because people are less rational in dangerous situations.
• When people say God works in mysterious ways, they mean he works exactly as if he wasn't working at all.
• It still amazes me that most just accept the existence of a parallel reality that overlays and interacts with the physical world.
• I wonder how long it'd take for religion to die out with zero child indoctrination? My guess: 80% gone within 50 years, 95% gone in 100.
• Isn't derisively declaring "I don't have enough faith to be an atheist" a tacit admission that faith is a bad thing?
• "You're just rebelling against God!" Um... to the extent that I "rebel" against any other fictional villain, I guess.
• I think maybe half of all religious belief would evaporate if everyone on earth had to learn about the actual psychology of said beliefs.

On evolution:

• Creationists: if evolution violated the Second Law of Thermodynamics, then so would prenatal development.
• I only believe in microdevelopment. Macrodevelopment from a zygote to an adult human is just a ridiculous theory!
• "Evolution isn't science, it's not observable and repeatable!" Oh, okay. I guess we'll be throwing out forensics and archaeology too, then?
• It would take a lot to falsify evolution—and that's fine, just as you wouldn't simply assume the theory of gravity was false if something fell up one day.

And on skepticism:

• Possibly the most difficult mental feat is to calmly and impartially correct cherished beliefs in the face of evidence.
• You can be biased and wrong or biased and right. Unbiased? There's no such thing.
• Deciding if a treatment works based only on your experience is like testing it with no controls, no blinds, and a sample size of one.
• Absolutely everyone is biased in how they take in new information. Those who don't acknowledge this can't even begin to counteract it.
• Certainty and correctness have virtually no correlation. What's important is how you arrive at your conclusions.
• The brain deludes itself constantly. For example: most people go their entire lives not realizing they can't see color in the periphery of their vision.
• Confirmation bias acts like a semi-permeable membrane: it lets information supporting your conclusion into your mind, and keeps contrary information out.
• On avoiding bias. Step 1: Gather all evidence. Step 2: Consider all evidence. Step 3: Draw conclusion. (Note: #3 comes last, not first.)
• Don't think of dissenting arguments as obstacles to your conclusions; think of them as tools you can use to clarify your thinking.
• Coincidences are deceptively common. In a group of 7 people, the chances that 2 will have birthdays within a week of each other is over 50%.
• Asking empirical questions about supernatural phenomena is the quickest way to reveal their absurdity.
• Correcting your mistakes is a greater virtue than being right the first time around.

While some people find tweeting to be a shallow form of communication, I think it's potentially very useful. It's not well-suited to fleshing out your ideas, but it forces you to take what you want to say and express it with efficiency and clarity. In the marketplace of ideas, the advantage often goes to those concepts that are can be quickly absorbed and understood. Since many people are averse to atheism and skepticism, this may help us get our ideas across before they close their minds.

Christianity as a Meme

"Yo dawg, I herd you like DNA, so I
put DNA in your DNA so you can
replicate while you replicate."
OK, no more internet memes now.

Any idea or fact can be thought of as a meme: a unit of information that can be transferred from one mind to another. Like living organisms, memes can self-replicate (by transferring to other minds), mutate (by modifying the idea), and undergo natural selection (since memes that self-replicate well survive, while others die out). Memes are often compared to viruses, but this doesn't imply that they're false or in any way bad. However, a well-adapted meme will spread easily through a population regardless of whether or not it's true.

Religions often have many of the traits associated with extremely powerful memes, and Christianity is no exception. Below I'll explain what these traits are, and provide Bible references to show how they're encouraged within Christianity. I'll start with "vertical" meme transmission—from parent to child. Memes will of course spread better if parents produce more offspring for those memes to transfer to. And here's what Genesis 1:28 says:

"And God said to them [Adam and Eve], 'Be fruitful and multiply; fill the earth and subdue it."

Many Christians have taken this to heart and produced more offspring than they would have otherwise. An extreme example is the Quiverfull movement, in which having many children is strongly encouraged. Then there's the ability of parents to pass memes on to their children. Christianity is as good at this as any religion out there. Here's Proverbs 22:6:

"Train up a child in the way he should go, and when he is old he will not depart from it."

There's nothing wrong with this sentiment per se, but within Christianity, "the way he should go" is always going to be Christianity. In fact, this was my school's Bible verse of the year in sixth grade. And it's almost always true that children "will not depart from" the religion they've been taught; I'm the exception rather than the rule.

Next up are the "horizontal" aspects of meme transmission—that is, from person to person outside of parent-child relationships. Proselytizing is an integral part of many branches of Christianity. Here's Jesus' Great Commission in Matthew 28:19-20:

"Go therefore and make disciples of all the nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all things that I have commanded you."

The Great Commission encapsulates horizontal meme transmission perfectly, and it takes a salient position at the end of both Matthew and Mark. And because it's such a prominent part of the worldview, missionaries are compelled to travel all over the world converting people to Christianity. Even my sister recently shared the gospel with strangers in our area as part of a school project.

Another horizontal trait is the ability to suppress other competing memes. There are plenty of extreme examples in the Old Testament in which the Israelites massacred unbelieving nations. Deuteronomy 20:17-18 provides a good summary:

"You shall utterly destroy them: the Hittite and the Amorite and the Canaanite and the Perizzite and the Hivite and the Jebusite, just as the Lord your God has commanded you, lest they teach you to do according to all their abominations which they have done for their gods, and you sin against the Lord your God."

Of course Christians don't perform similar slaughters in modern times, but there are plenty of other historical examples, such as the Crusades and the Inquisition. And in Galatians 1:8, Paul expresses a highly diluted version of the same general sentiment:

"But even if we, or an angel from heaven, preach any other gospel to you than what we have preached to you, let him be accursed."

Here Paul takes the groupthink, us-versus-them mentality to incredible extremes: absolutely any idea that doesn't fit with established dogma is to be shunned, and even the most trustworthy sources become "accursed."

An effective meme should also give people strong motivations for adopting the beliefs in question. And what motivations could possibly be more powerful than the promise of eternal salvation and the threat of eternal damnation? This is Romans 6:23, a verse that Christians regularly use when trying to convert people:

"For the wages of sin is death [i.e. hell], but the gift of God is eternal life in Christ Jesus our Lord."

It's hard to pass up a gift like that. Christianity is so deeply imbued with incentives that even I, as an atheist, occasionally feel drawn to it. Even though I know full well how unlikely it is that Christianity is true, the speck of possibility that I could be tortured forever is enough to send a chill down my spine and make me think, "Maybe I should look at this one more time, just to be sure." The pure, raw psychological power this meme wields is downright unfair; it games the system by playing with infinities.

Going hand in hand with this is the characteristic of giving the meme carriers a desire to continue holding that meme as long as possible. The Bible continually emphasizes perseverance in belief as a great virtue. Here are Proverbs 3:5-6 and 1 Corinthians 15:58:

"Trust in the Lord with all your heart, and lean not on your own understanding; in all your ways acknowledge Him, and He shall direct your paths."

"Therefore, my beloved brethren, be steadfast, immovable, always abounding in the work of the Lord, knowing that your labor is not in vain in the Lord."

With a mentality like that, how could a sincere believer possibly be persuaded away from their position? The only way to even begin questioning the Christian worldview is to "lean on your own understanding." By cordoning off rational inquiry, the meme's fate is completely secure.

Finally, there's the one trait I don't have a verse for: cultural pervasiveness. While this didn't apply to early Christianity in the Roman Empire, it certainly applies to modern-day America. About 78% of Americans are Christians. Countless biblical phrases crop up in everyday language: "Pearls before swine," "my cross to bear," "an eye for an eye," "faith can move mountains." Even many of our names come from the Bible: My first and middle names are Timothy Joseph, and there are even people named Jesus and Christian. But most importantly, the Christian message of redemption and salvation is ubiquitous in western culture (the Christ figure character trope is a good example). Thus, the meme makes more sense to us and can keep its stranglehold far better than if we were being presented with it anew.

I should emphasize again that Christianity's extraordinary capacity for self-replication does not in itself imply that Christianity is false. However, it does offer a perfectly adequate explanation for why so many people believe in it, even in the face of strong evidence. In contrast, all religious people can offer as to why atheists don't believe are unsupported accusations of denial and rebellion against God. The belief we observe in the world makes sense whether or not those beliefs are true. But for the unbelief we see, the best explanation is that despite all the protests to the contrary, we really don't have sufficient evidence for God.

WEIT: The Peacock's Tail

Coyne spends an entire chapter of Why Evolution Is True explaining the role of sex in evolution. I'll start with the question of why sexual reproduction evolved in the first place. Asexual reproduction is simpler and results in twice as many offspring on average as sexual reproduction; this is called the two-fold cost of sex. However, sexual reproduction allows for beneficial genes to spread rapidly throughout a population. It also allows for increased genetic diversity, meaning that a population can adapt to the onslaught of diseases and parasites. In contrast, a more homogenous group might be quickly wiped out.

If we assume that life on earth popped into existence at God's whim, there's no reason to expect the massive emphasis on sex that we observe in the natural world—especially if he's so persnickety about how humans perform the act. But sex lies at the very core of evolution, and its implications echo through every aspect of animal behavior. Males in most species have almost no investment in their offspring, so they're programmed for promiscuity. Creating offspring is a huge investment for females, so they're hard-wired for choosiness.

This tension between male and female behavior results in the phenomenon of sexual selection. Males are forced to compete for mating opportunities. Sometimes this manifests through direct battle: "the clashing antlers of deer, the stabbing horns of the stag beetle." In other cases the competition can even occur after sex. Coyne describes several clever and even devious strategies, including male millipedes that ride females for days to block the access of other males and damselflies that use spines on their penises to scoop out the semen of previous suitors. By religious standards, God's supposed creation is both ruthless and sexually depraved.

Sexual selection also provides an answer to one apparent problem for evolution: the males of some species possess traits called sexual dimorphisms, which in many cases are oddly cumbersome. For example, the feathers of the male peacocks are heavy and easily noticeable to predators, thus greatly reducing their apparent fitness. Why would they have evolved?

Whoa.

In effect, these traits tell females that the male is capable of survival in spite of these handicaps. In the case of peacocks, the longer and more numerous the vibrant feathers, the more fit the male is, and the more attractive he is to the female. In one experiment, scientists painstakingly clipped eyespots from some peacock tails and even glued them to other peacocks. The result: more eyespots meant dramatically more mating opportunities. Another experiment showed that "males with more eyespots produce young that not only grow faster but also survive better."

The rule holds for other species as well. Female house finches also prefer bright red males because their coloring indicates a healthy diet of pigment-filled seeds. Female gray tree frogs prefer males with longer calls—which, it turns out, produce tadpoles that grow faster and larger. Thus, the major elements comprising sexual selection have been confirmed through repeated experiment and observation.

The power of natural sexual selection as a theory is that it makes testable predictions. First, if one gender displays more flamboyant physical traits or behavior, that gender is the one that will be competing for the opportunity to mate. Second, we should observe that species that tend to be more monogomous (like penguins or geese) will show less sexual dimorphism, since sexual competition and selection play less of a role. Both of these predictions have been widely confirmed—and there's no reason for this to be the case unless evolution is true.

Where Morality Comes From

Theists tell us that morality comes from God, and some even go so far as to say that atheists can't explain why humans are moral. If we are solely the product of evolutionary processes, why is it that we often care deeply about those around us? Shouldn't we be selfish, concerned only with passing on our genes as efficiently as possible? As it turns out, no. Below I'll cover several intriguing phenomena that, when taken together, explain surprisingly well why we act the way we do.

The easiest concept to understand from an evolutionary perspective is parental investment. Fitness is defined as the ability to produce viable offspring, but this entails more than just surviving long enough to procreate. Once the offspring are born, they must in most cases be protected by one or both parents: for example, a father may go off to hunt while the mother protects her young. If the parents fail to do this, their offspring will die and their genes won't be passed on. Thus, natural selection molds the behavior of many species to form a powerful parent-child bond.

What about cases where the genetic relationship is less pronounced? For example, why would a worker bee care about building the hive if it doesn't get to procreate? Why would a prairie dog sound an alarm to warn its siblings of an approaching predator if this could cause it to be eaten? Kin selection provides the answer. Suppose animal A has a gene that causes it to help related animal B, even if doing so reduces A's reproductive fitness. Because B's genes are similar to A's, B is also likely to have the gene that caused A to do this. Since A has made B more likely to survive and reproduce, A's gene is more likely to be passed on indirectly through B.

Awww.

The first two concepts I've mentioned depend on the genetic relatedness of individuals, but many others do not. For example, there's reciprocal altruism, which is perhaps best summarized by the phrase "I'll scratch your back, you scratch mine." When animal C does a favor for unrelated animal D, then D is expected to do a favor for C. If D does not oblige, then he is punished by C and the other members of the community. In this way, the two are motivated to help one another because their pact is mutually beneficial. In more advanced species, this idea works even with long time intervals and a wide range of "social currencies." For example, if C grooms D, then D might look out for predators on C's behalf several weeks down the line.

Among those species capable of complex cognition, a wide range of cooperative group behaviors are possible. For example, social predators hunt in packs: bottlenose dolphins will surround a school of fish, force it toward the surface, and take turns eating from it. Some dolphin groups off the coast of Africa even form alliances with fishermen, driving fish into the nets onshore in exchange for part of the catch. Sperm whales will defend themselves by creating a flower formation: vulnerable juveniles are protected in the center, surrounded by a circle of adults who face inward to create a barrier of powerful tails along the perimeter. And perhaps most touchingly, when one odontocete is near death, the others in its group will lift it to the surface to breathe.

We're already well on our way to explaining the moral sense we all share today. One additional idea to consider is that sufficiently advanced social creatures eventually form a culture. Individuals in such societies—and humans especially—are taught to hold certain values and beliefs. We learn them from our parents, from our friends, from our government and media, and even from complete strangers. These cultural values are so heavily reinforced that they become a part of us; this is known as enculturation. This idea may sound a little ominous, but in itself it's neither good nor bad: enculturation simply is.

Along with other values, cultures have a strong tendency to promote moral systems, because they help maintain order and are generally beneficial to society as a whole. These moral systems build upon our hard-wired altruistic and cooperative tendencies. Religion is one common source of moral values, but morality need not be so formal and ritualized. For example, the people of Scandinavia are largely nonreligious, but they seem by any measure to be just as moral as people in religious countries.

These phenomena give us a reasonably detailed understanding of the origin of morality in humans and other animals. However, it's important to realize that by explaining the evolutionary and cultural origins of morality, I'm not trying to derive an ought from an is. While these concepts tell us why we are moral, they say nothing in themselves about why we should be moral, or what moral truth is from an objective standpoint (if such a thing exists). These questions are better suited to philosophers, and I hope to examine them in depth—but that's for another day.

(Aside: I learned much of this information from a course I took on animal cognition. Book learnin' really can come in handy!)

WEIT: A Force to Be Reckoned With

Chapter 5 of WEIT is an overview of the force that has shaped all of life on earth: natural selection. When the less savvy creationists say they don't think we could have evolved purely by chance, they reveal a fundamental misunderstanding. Evolution contains an element of randomness (mutations), but natural selection is not random—and in fact, that's the very reason evolution works. (Coyne also briefly discusses genetic drift, a process that occurs more noticeably in small populations, which is in fact random.)

Coyne first lists the three components required for natural selection to take place: a trait must vary across individuals, it must be heritable, and it must affect the probability of reproduction. We can also make predictions based on this idea. As a general rule, natural selection predicts that a trait will:

1. Evolve only by step-by-step processes.
2. Raise the fitness of its possessor at each step.
3. Increase reproductive output, but not necessarily survival.
4. Never solely benefit members of a different species.
5. Raise the fitness of the individual, but not necessarily some larger group.
6. Be well-designed, but not necessarily optimally designed.
7. Evolve regardless of any resulting suffering, however extreme.

We see these predictions fulfilled at every turn. Take #4, for instance: Coyne says that at first glance, the hollow thorns and nectar of certain acacia trees appear perfectly designed to house and feed ant colonies without benefit to the trees themselves. Could it be that nature isn't so impartial and pragmatic after all? Not so: having the ants around is useful because they attack animals that eat the trees' leaves and cut down rival seedlings.

Note also that most of these predictions (particularly the last two) are not necessarily what we would expect from a good and competent God. One example Coyne gives of cruelty in nature are the Asian giant hornets, which will invade a hive of bees and bite off their heads by the thousands. Japanese honeybees will respond by mobbing the hornets and cooking them alive through vibration. However, European honeybees are defenseless against them, having only been recently introduced.

Next Coyne moves on to observed evidence of natural selection and speciation, starting with bacteria and viruses. In Richard Lenski's famous experiment, E. coli mutated to grow 70% faster in conditions with varying amounts of available nutrients and gained the ability to eat citrate. In another experiment, E. coli evolved a new biochemical system for breaking down lactose in a series of three separate mutations. In a third, the bacteria strain Pseudomonas fluorescens formed two additional new species within just ten days. He also mentions drug resistance: for instance, after just 70 years, "more than 95 percent of staph strains are resistant to penicillin."

Finally, he goes over some examples of natural selection observed in plants and animals. A study of Galapagos finches found that during a drought which produced mainly hard-to-crack seeds, average beak size increased by 10 percent—astonishingly, all in a single generation. The length of the soapberry bug's proboscis (needed to penetrate fruit skins) changed by 25 percent within a few decades of colonizing three new plant species. And the wild mustard plant began blooming one week earlier in response to a five-year drought.

Coyne has a section on irreducible complexity as well, but I plan to cover that topic in more detail sometime in the future. Next up is a full chapter on sexual selection.

WEIT: Island Evolution

Last time I covered Coyne's evidence from the geographical distribution of fossils and current life on the world's continents. The rest of the chapter is based on the distinction between types of islands. Oceanic islands are land masses that rose up from beneath the sea—for example, the Hawaiian and Galapagos islands. In contrast, continental islands such as Japan (at right) and Madagascar began as part of the nearby continent but later broke off and drifted away.

When we study the life on these islands, here are the trends we find:

• Continental islands generally have every major type of animal just as the mainland does: insects, birds, amphibians, mammals, and so on.
• In contrast, oceanic islands often have native birds, plants and insects, but generally lack amphibians, reptiles, mammals and freshwater fish.
• There tend to be a huge number of bird, plant and insect species on oceanic islands, which are related to one another, but fill different niches.
• The species existing on oceanic islands tend to be the most similar to species that live on the closest mainland continent.

And now for the big question: why exactly do we see this unusual pattern? If you're a creationist... well, no real reason. God just felt like it, maybe. But even leaving aside the fact that this explanation lacks any evidence, it could be used to explain literally any pattern we happened to see. It is completely devoid of what scientists call explanatory power. A good explanation is detailed, non-arbitrary, makes testable predictions, and can be falsified. "God did it" has none of these traits.

The real answer is much more interesting. Unsurprisingly, the ecosystems of continental islands look normal because they were once part of the mainland. But what about oceanic islands? Their species are most similar to the nearest mainland species—for example, species from the Galapagos Islands (at right) resemble those from South America—because that's where they originated. And why do we see only certain forms of life on oceanic islands? Because there are practical limits to crossing large bodies of water. Birds can fly, while plant seeds and insects can attach to their feathers or be carried in droppings. Some seeds and bugs are even light enough to drift on the wind, and other seeds can survive for long periods floating in salty oceans. In contrast, amphibians and freshwater fish can't handle the saltwater, while reptiles and mammals can't swim far enough. Mammals like seals and bats are the lone exceptions and are found on oceanic islands, elegantly confirming this trend.

Finally, in the absence of competition, the species that are found on oceanic islands undergo rapid speciation to play a wide variety of roles. Coyne gives several examples. Of the 28 bird species in the Galapagos, half are finches—all descended from one ancestor. He says:

"[D]ifferent species specializ[e] on foods as different as insects, seeds, and the eggs of other species. The "woodpecker finch" is one of those rare species that uses tools—in this case a cactus spine or twig to pry insects from trees. ...And there's even a "vampire finch" that pecks wounds on the rear ends of seabirds and then laps up the blood."

There are also about 60 species of honeycreepers (with diverse feeding habits and beak shapes) and almost a thousand species of Drosophila fruit flies have been discovered on the Hawaiian islands. And on the South Atlantic island of St. Helena, members of the daisy and sunflower family have evolved into "small woody trees."

These examples are powerful displays of evolution's ability to mold both behavior and physical traits to suit the environment. Again, creationism is at a loss to explain these phenomena. Why did God make it so that there are nearly 1,000 species of Drosophila on one island group, and 14 finch species that variously feed on seeds, insects, fruit, eggs, nectar and blood on another? Well, now we know: he didn't.

WEIT: The Layout of Life

Chapter 4 of WEIT is dedicated to the evidence for evolution gleaned from biogeography, the study of the geographical distribution of life. The case Coyne makes is based on a few basic patterns of life that we consistently find across the globe.

Coyne first covers an interesting observation about continents: not only do they often have similar habitats—deserts, forests, jungles and so forth—but they have species that appear similar, yet are fundamentally different. He illustrates this by comparing and contrasting Australia and the Americas: anteater, mole, and flying squirrel-type creatures can be found in both habitats. But the Australian versions are marsupial mammals (which have pouches and prematurely-born young), while the species in the Americas are ordinary placental mammals. Coyne rightly asks:

"If animals were specially created, why would the creator produce on different continents fundamentally different animals that nevertheless look and act so much alike?"

Perhaps the habitats are subtly different, such that the marsupials couldn't have survived in the Americas (and vice versa)? Unfortunately for the creationists, no. Various plant and animal species often thrive when introduced onto a new continent. In truth, the pattern we see is explained quite well through a combination of speciation and convergent evolution. Coyne explains that we find the earliest fossil marsupials (80 million years ago) in North America. They then migrated down into South America (40 mya) and eventually found their way to Australia (30 mya). From there, convergent evolution kicked in: traits that are extremely useful in certain habitats will tend to evolve independently. This explains, for example, why gliding flaps can be found in both flying squirrels and the marsupial sugar glider.

The marsupials' "jump" from South America to Australia was possible possible because both continents were once part of the supercontinent Gondwana. So was Antarctica—and marsupial fossils from 35–40 mya have also been found there, just as scientists predicted. Trying to make sense of this trend in young earth creationist terms would be futile: why would the flood bury them in this precise configuration, and why do the fossil dates line up so perfectly?

Continental drift also explains the bizarre distribution of Glossopteris tree fossils. They can be found scattered haphazardly across all the southern continents—but as the map below illustrates, this pattern makes perfect sense:

1: South America; 2: Africa; 3: Madagascar; 4: India; 5: Antarctica; 6: Australia

Some of the less savvy YECs probably deny continental drift altogether, but with evidence like this, the facts are hard to ignore. As I mentioned here, the accelerated young-earth version of this drift is both arbitrary and completely impossible. In contrast, both the biogeographical patterns and continental drift are beautifully consistent with (and even strengthen) evolutionary theory.

I had hoped to cover this whole chapter in one shot, but there's so much material that I'll have to split it in two. I'll summarize the biogeographical evidence from islands in the next installment.

WEIT: Other Vestigiality & Atavisms

I have a lot of ground to cover this time around. Last time I covered WEIT's description of vestigiality and atavisms in humans, and now I'll do so for other animals.

There are many examples of birds with vestigial wings: ostriches and penguins use them for a different purpose, while kiwis' wings (see below) are stubby and basically useless. Other species have vestigial eyes that are malformed and covered by skin or scales, including the eastern Mediterranean blind mole rat and certain varieties of fish, salamanders and snakes. Why might this loss of function occur? Because both wings and eyes are costly to create and maintain. Notably, kiwis live in New Zealand, where a lack of large predators makes their inability to fly less of a disadvantage. And loss of eye function occurs only in species that live underground or in caves, and thus have little use for vision.

Cetaceans are some of the best cases of these phenomena. Whales have several vestiges, such as the pelvises embedded deep within their bodies. Embryology reveals yet more examples: hindlimb buds are initially visible but vanish after about seven weeks, a thin coat of hair is grown (and quickly lost), toothless baleen whales "develop embryonic teeth that disappear before birth." And remarkably, in rare cases whales are born with atavistic legs—sometimes even fully formed ones. These features point to their common ancestry with furry, four-legged, toothed land mammals.

Other examples of atavisms: Chicken embryos develop teeth if provided with a certain protein, revealing their reptilian ancestry. And splint bones in horses sometimes form into extra toes, showing how they "descend from smaller, five-toed ancestors."

Next up are genetic vestiges. 50 percent of the 800 olfactory receptor (OR) genes present in humans and other primates are inactivated, probably because we're so visually oriented that we don't need them. Dolphins—which "don't need to detect volatile odors in the air...and have a completely different set of genes for detecting waterborne chemicals"—still have OR genes, although 80 percent are inactivated. Genes for synthesizing vitamin C are also inactive in primates, fruit bats and guinea pigs. And genetic vestiges are sometimes directly connected to physical ones: for example, most mammals have a vestigial yolk sac, but mutations have inactivated the genes for producing the nutritious protein that once filled it.

The most amazing thing about these genetic vestiges is that "the sequences of the dead gene exactly mirror the pattern of resemblance predicted from the known ancestry of these species." That is, if a gene-inactivating mutation occurs, it generally occurs at the same place in all species, and the more closely related two species are, the more similar the genetic sequence will be. This phenomenon perfectly matches the hierarchical structure of the tree of life.

There's so much more I could cover from this chapter—at some point in the future I'll take an in-depth look at endogenous retroviruses and poor design—but I want to move on to some of the other completely different lines of evidence. Up next: biogeography.