My Favorite Enzyme, Part 2

My favorite enzyme (see previous post about enzymes in general, and why I have a favorite) has a very specific job, as all enzymes do. But my enzyme, Aminoacyl tRNA Synthetase (or Syase for convenience) has a job that is both extremely difficult and absolutely crucial to all life.

The job is to link up two chemicals that otherwise would have no chance of getting together. The sad fact is that most chemical molecules are very unreactive, and only very few sets of molecules will react with each other to form new compounds or even a complex from the two joining together. In this case, one of the molecules is an amino acid, and the other is an interesting RNA molecule called transfer RNA or tRNA. Because of the very different chemical nature of these molecules, (they belong to very different chemical families) spontaneous, uncatalyzed combination of the two would simply never happen.

As you know (or you should), there are 20 amino acids, and about 60 tRNAs, so this is an impossible job to get right for one enzyme. Luckily, it turns out my favorite enzyme is not one enzyme but a collection of 20, one for each amino acid.

To explain why there are 60 tRNAs and not 20, we need a small diversion to discuss the genetic code (and yes, it is a code!). The genetic code works  much like written language, a code we know well, does. In English, for example, meaning is assigned to words, and there are 26 letters to construct these words (which can be of any length). A word is a collection of the letter symbols in the correct order that means something different from its physical nature (which is simply a collection of shapes).

DNA operates the same way, with some important differences. First, there are only four “letters,” which are actually molecular entities, but they function as symbols. Since their importance is in their symbolism, we generally designate them by the first letter of their names, A (for adenine), C (for cytosine), G (for guanine), and T for (thymidine). The word length is constant: three letters are a code word. For example, ACC is a code word for threonine, and CAA means glutamine.

So, why three, and not four or two? Well, two-letter words would allow for 16 permutations, not enough for the 20 amino acids. Four letters would give far more possibilities than needed and would cause confusion and chaos. So three letters, which gives 64 possible arrangements, is what we have. What this means is that there are synonyms, more than one word (or codon in Biologese) for each amino acid. Thus ACA, ACG and ACT also mean threonine, and CAG also codes for glutamine. Some amino acids have as many as 6 synonyms.

I am not going to discuss the details of how the proteins are built on the ribosome (see Figure 1 and online videos), but I need to tell you that the key step in making the right protein (meaning having the right amino acids in the right order) is for each tRNA/amino acid complex to bind to the codon copied from the DNA onto a long RNA strand called messenger RNA (mRNA). Now, if you read the post on how to be a molecular biologist, you will remember that the secret is that A always and only binds to T, and C only and always to G (even though this not actually true, but see the post if you forgot why).

Syase 1

Figure 1.

The point is that the tRNA for each amino acid contains a three-letter sequence designed to perfectly bind to the codon. That sequence is the complementary sequence of the codon, called the anticodon. So for the codon ACC, the anticodon is UGG. And for CAA, the anticodon is GUU. (One little detail, in RNA we use U instead of T. Doesn’t matter why.)

Now, since there are anywhere from 1 to 6 different codons for each amino acid, there are from 1 to 6 different tRNAs for each amino acid, each with its own anticodon. And each of the 20 Sysases must be able to attach its specific amino acid to each of the different (up to 6) tRNAs that have the correct anticodon.

I should apologize for oversimplifying this whole thing. The reality is far more complicated, and you will notice that I haven’t even gotten to describe what it is that my favorite enzyme actually does. But I thought it was important to set the stage, as it were, and explain what the task it must do entails. Now that we have that all straight, I should (hopefully) get to how Syzase does its job (and if you think this is hard for you to understand, imagine how a poor senseless molecule feels!) in the very next post. I promise (sort of).

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My Favorite Enzyme

All enzymes are great. So by saying I have a favorite, I don’t mean to denigrate the others in any way. All enzymes are just great at what they do, and most of them simply couldn’t possibly do their jobs better than they are doing them.

Having said that, I do indeed have a favorite, and I will explain why. But first, you might be asking: what is an enzyme? Enzymes are proteins, meaning they are strings of amino acids linked in long chains. More specifically, enzymes are proteins that function as catalysts. And you know what a catalyst is, right? A catalyst is a chemical that makes a chemical reaction go faster than it would go otherwise but isn’t part of the reaction itself, so it doesn’t get used up.

Enzymes are the best catalysts known. Lots of metals can act as catalysts for chemical reactions used to make stuff, and cars have a catalytic converter that helps eliminate air pollution. But enzymes are thousands of times more efficient and more specific than any other kind of catalyst. Life could not exist at all without enzymes (or some kind of catalyst), because the chemical reactions that make life work must go on very rapidly, and without catalysis, those reactions could take hours or weeks.

Enzymes work so well as catalysts because they are large molecules that are perfectly shaped to bind to the molecules that need to react, and then they encourage, simulate, and… well, catalyze the reactions by moving the reactants closer together; by using some of the chemical properties of their amino acids; by providing energy to some reactions; and by making sure only the exactly correct chemicals react with each other (and not some closely similar chemicals).

Enzymes are so close to being perfect at their job because it’s the enzymes (mostly) that are the targets of natural selection and evolution, so after a couple of billion years of trial and error, most enzymes have become really good at what they do.

And that brings me to my favorite enzyme. My favorite enzyme has a terrible name, so let’s call it Syzase, as a nickname. Its real name is Aminoacyl tRNA Synthetase, so you see why I prefer Syzase.

Syzase is the most important enzyme in the most important biological process in evolution – and in life in general. The process is called protein synthesis or translation, and it’s the way that proteins (including all the enzymes, including Syzase itself) are synthesized. You might have already learned that the exact sequence of the amino acids in a protein (which is the critical feature that allows them to act as very specific catalysts for specific reactions) is determined by the sequence of the nucleotide bases in a gene made of DNA.

So the DNA sequence determines the amino acid sequence. That seems fine, unless you happen to know some chemistry. Because, chemically, there is no way that the nucleotides in DNA can interact with amino acids to produce a protein with a specific sequence. Amino acid chemistry and nucleic acid chemistry just don’t go together.

So how does it happen? The answer is why I love Syase. The code in the DNA sequence needs to be translated into amino acid chemistry. Translation is in fact the name of the process, and it’s probably the most complex chemical process in the universe. And my favorite enzyme, Aminoacyl tRNA Synthetase, is at the very center of the process and might even be considered the actual translator, the chemical entity that speaks two languages, nucleotidese and amino acidese, and can translate each into the other.

But this post is getting too long, so I will post the amazing details of how my beautiful, favorite enzyme does its job so spectacularly well in the next post (coming very soon, I promise).

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Replication (Part 2)

In a recent post I said that the replication of cells is required for evolution and the origin of modern life as we know it. While it’s true that the daughter cells of a parent dividing cell end up containing all the elements and features of the parent (assuming replication accuracy is very high, as it is in all life forms), the fact is that cells don’t actually replicate all of their components. In other words, each protein doesn’t produce a faithful copy of itself, and neither do membranes, filaments, flagella, or ribosomes. There is only one component of living cells that is replicated with high accuracy, and that is the DNA molecule. The reason that works is that DNA is not only capable of being copied almost exactly, it is also the part of the cell that is responsible for guiding the production of all the other components of the cell – all the proteins, enzymes, membranes, and cell organelles. (One exception is the energy-producing mitochondria in eukaryotes, but we won’t go there now). This means that if the DNA of the parent cell is faithfully copied, then the entire cell will be faithfully copied in the two daughter cells.

There is a scientific consensus that the modern life system of DNA replication and DNA control of the synthesis of all subsequent cellular components is so complex that it could not have been present in very early life forms. The idea that earlier life forms might have used RNA (similar to DNA) as the original replicating molecule has become known as RNA world. This RNA world is proposed to have predated our current DNA world (along with LUCA, the last universal common ancestor of all life today).

RNA can probably be copied (although the details of how this happens are not yet completely worked out. See previous post). In addition, RNA can act as a catalyst, so all the protein enzymes present in modern cells might not be needed. How RNA world turned into DNA world is a question that has not yet even been addressed.

Aside from the existence of some kind of replicator molecule like DNA or RNA (there are one or two other possible candidates), there is no known possible mechanism for a cell to replicate itself into two daughter cells that are just like the parent. This is the reason that replicator-first proponents insist that cells that have plenty of metabolism but no replicators could never evolve to produce anything like the life we know.

But even if primitive early cells had replicators that were able to manage the production of an accurate copy of the parent cell phenotype (meaning all the components and characteristics of the cell), there is a potential problem that has only rarely been addressed. That problem can be stated simply: How did the accuracy of replication become so high?

One would expect lots of errors in primitive replication systems, no matter what chemical composition they had. It’s likely that replication became more accurate over time thanks to the only biological process we know that makes things better over time – evolution. But wait, if accurate replication is required for evolution, and evolution is required for accurate replication…? We have a problem.

And that is the problem I have been working on. I will present some preliminary results in Part 3. Stay tuned.

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How to Be a Molecular Biologist

It’s easy. All you need to know about molecular biology is that it’s all about DNA. And you don’t need to know what that stands for, or anything else about DNA except this. It’s a really long molecule, like a chain with millions of links. Actually make that a double chain. And there are 4 different kinds of links that go by 4 different letters. Those letters are A, C, G, and T, and it doesn’t matter where they come from either. And now here is the secret to all of molecular biology: the A link on one chain always pairs up with a T link on the other chain. Always. You will not find an A opposite another A, or a C or G. Only T. Got that? You can remember it if you just think of the most important symbol these days: @. Which of course stands for “at” or in Molecular Biologese AT.

Now you might ask if A and T are always so bound up with each other, what about C and G? What do you think they are doing? Take a guess. YES, they have a thing going also, what else would they be doing? So, since A and T are always matched, so are C and G. And that, boy and girls, is all there is to molecular biology. Let’s review:

1.The A on one strand (chain) of  DNA always and only bonds to a T on the other strand.

2 The C on one strand of DNA always and only bonds to a G on the other strand.

That’s it. The rest is details. Once you know the two statements above, its easy to understand how DNA replicates, what a gene is and how it works, how genes make proteins, what a mutation is, how evolution works, and why identical twins are clones, but everybody else is genetically unique. Pretty simple, eh?

Of course, we know where the Devil lives, right? Right. Those pesky details. And there are lots of them. The peskiest of all the details in biology, the thing that drives biology grad students insane, is this: biology (and that includes molecular biology) is full of lies.

That isn’t a value judgement, or an expression of hostility – it’s the truth. Almost every statement in biology is a lie. Or more precisely, it isn’t true. This is not the case in physics or chemistry. We can say that force is equal to mass times acceleration and that is true all the time, everywhere. The volume of a gas depends on its volume and  temperature. Fact. No wiggle room.

In biology there are no such statements. Nothing you can say in biology is always true. Not even what I just told you about A and T always pairing up is true. Sometime A will form a bond with a G or a C, or even (gasp) another A. Yes, it happens, and so when I said always and only, I lied. I am after all a biologist, and we all lie all the time. (Actually, that isn’t true either.)

So how could I dare to say something that isn’t true? How can I say that A only bonds with T, when in fact sometimes it doesn’t? Shameful, I admit. So let’s rephrase. Under the vast majority of normal circumstances, A does only pair with T. But sometimes circumstances in biology are not normal. And mistakes are made. When that happens, and an A matches up with a G, or a T finds itself opposite a C, we have something called a mutation. In fact that is the definition of one kind of mutation. (In biology there are always several different kinds of everything).

Are mutations good or bad? Ha ha, what a question. Clearly if you asked that, you are not a biologist. Nothing is good or bad in biology = everything depends on something else. Mutations can be very bad; they  can lead to diseases like cancer or genetic diseases like cystic fibrosis or to increased susceptibility to a host of diseases. A mutation can make you stupider or shorter or uglier than you would otherwise be. Of course, it could also make you smarter, taller or prettier. Mutations are also essential for evolution – if there were no mutations we would still be very primitive bacteria and wouldn’t be having this conversation.

Speaking of evolution, some people sometimes ask why evolution is still a theory and not a law. A law is a statement of a scientific truth in mathematical terms. Laws can have exceptions, sometimes, but laws don’t do well in biology (there are a total of maybe three biological laws), because the number of exceptions to anything we might say about how biology works are too many to be dealt with. Too many lies, in other words. So, while a lot of people have come up with a lot (thousands, actually) of mathematical laws of evolution, none of these are all-encompassing, because none of them fit all of the various and diverse situations that apply to evolution.

Getting back to molecular biology, let’s take a look at how the basic fact of AT and GC base pairing (I might not have mentioned this. but those links named A, C, G, and T are actually called “bases”) works. When a cell is ready to divide into two cells, the DNA double strand (which is  wound around into a helix) separates into two individual strands. And then each A on one strand attracts a T, each C attracts a G, and a new strand  is built up with all the correct matching bases. Since this happens to both of the original strands, what we end up with is two double strands, each of which is identical to the original double strand. Pretty neat, eh?

When James Watson and Francis Crick solved the puzzle of the DNA structure in 1953, they realized right away that the obligatory base pairing and the double helix solved the biochemical mystery of how DNA replicates to form two perfect copies of itself. Thus the basis of inheritance was discovered.

There is more. (A lot more, actually.) The genetic code, which is the way the genes (DNA) make all the characteristics of the cell, called the phenotype (the proteins), also relies on base pairing. But that is a very long and complex story that we should save for later. For now, just practice saying AT… AT… AT. And maybe also practice a little bit of lying, if it doesn’t already come naturally. And you will be on your way to becoming a real  molecular biologist.

 

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Replication (Part 1)

In the transition from chemistry to biology, many new features had to emerge from an increasingly complex chemical system. Examples include some form of membranous enclosure to allow for appropriate concentration of reactants, thus defining the borders of a living cell; the inclusion of catalysts to allow for rapid reactions; the ability to derive energy from molecular reactions and to synthesize useful chemical end products and structural components; and many more. Most of these features, while remarkable can undoubtedly arise spontaneously given a sufficiently large pool of soluble chemicals and time.

Membrane enclosed vesicles containing rapid and complex chemical reactions that will allow for such vesicles to survive for long periods (days or longer) could be considered to be living cells. This assumes we define life in the most elementary way – an enclosed cell in which chemical reactions allow for the cell to grow to a size at which it spontaneously divides in two.

But that is not the kind of life we know. All living forms on earth are indeed composed of cells that carry out extremely complex catalyzed chemical reactions, and such cells do grow and divide. But living terrestrial cells, going all the way back to the first cell from which all modern life evolved, the Last Universal Common Ancestor (LUCA), do more than that – they evolve.

The primitive protocells that I described above cannot evolve, and they will eventually die out. The reason is that the simple division of cells, whereby a cell splits in two, is not what life does. Living cells, since before LUCA, don’t just divide – they replicate. And it’s cell replication, not cell division, that allows for evolution.

Cells replicate themselves by making close to identical copies of themselves when they divide. When one cell becomes two cells, the new cells (usually called daughter cells) are close to identical to each other and to the original (parent) cell. The new cells contain the same ingredients, catalysts, subcellular systems, and all features of the original cell. Simple division of a cell into two parts cannot do this, since there is no copying mechanism to make sure that every feature of the original cell is shared by both daughter cells. With replication, however, everything within the cell is duplicated and then equally distributed in the two new daughter cells after division.

Nothing else outside of life does this. Crystals grow in ways that replicate the starting structure, but crystals do not make copies of themselves. Neither do stars or storms, galaxies or glaciers, mountains or molecules (outside of life). Nothing does.

The ability for a single cell to make a perfect or near-perfect copy of itself is the actual beginning of life as we know it. Non-replicating cells might appear to be alive, but they cannot last beyond a short time span. To become truly alive in the sense that cells can survive and reproduce for years or millennia, evolution is essential. Evolution allows primitive cells to become more stable, more fit, more able to do what they need to do in order to survive. And evolution requires actual replication, not simply division.

To see why that is true, imagine a cell that by lucky chance has incorporated a catalyst that allows it to perform a very useful chemical reaction – say, one that generates energy. The cell now has a higher fitness (defined as the probability of survival until division). When this lucky, very fit cell does divide, the chemical catalyst it found goes into one of the daughter cells, but not the other. So one of the new cells has inherited the higher fitness of the parent, but the other has not. It isn’t hard to see that as time goes by, the more fit cell becomes more and more of a minority, and while its probability of survival might be higher than its relatives’, it’s still not very high, so eventually one of the descendants of the original lucky cell containing the new catalyst will die and that’s the end of that. No evolution has taken place.

On the other hand, if the original cell had replicated the new catalyst so that both daughter cells had inherited it, then a new population of cells with higher fitness would have developed and survived to continue to improve its fitness, leading to evolution of a strong population of living cells.

So the central question of the origin of life becomes clear:
how did accurate cell replication originate?

There are some fascinating theoretical offshoots of this question, and I have started working on them using statistical modeling. There are strong implications for the origin of life, and I will explore some of them in future posts.

 

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A Goldfish Sings a Tentative Psalm

Today’s guest post is a poem by my wife (and collaborator), Aniko Albert. There is a story behind this poem related to our relationship. After reading it, you might want to take a look at an earlier post on this blog called Tank God (dated 11/19/2015). I had first posted that piece in December 2011 on a now defunct chat site called Gather.com, where I met Aniko in 2010. Aniko had written this poem a couple of months before I posted my piece, and when she saw it, she sent me the poem. We were both struck by the coincidences in the two pieces (although my piece is more snarky, and hers is more poetic, which is sort of typical of both of us). I told her that we must be cosmically connected (yes I was already very interested in her, although at that point we hadn’t met or spoken). In the following two years we became closer, exchanging emails and texts, Skyping, and to make a long story short, at the beginning of 2014 Aniko moved across the country to live with me, and we were married that summer. The best thing that ever happened to me. So besides the beauty of the poem in its own right, I have very special feelings about it, since I have always thought it was an important part of my success in finally finding the love of my life.  

A Goldfish Sings a Tentative Psalm

By Aniko Albert

 

The perfection of the universe is written around me:

bounded yet infinite space.

Light bounces back and forth

reflecting and refracting

in every direction

defining its liquid geometry.

I sway with the perfect cadence of its smooth substance,

I dance with the caressing currents of its fine-tuned laws,

I’m one with its still, self-enclosed beauty.

I lack nothing: colorful manna falls in its appointed time,

Brine shrimp and worms in their seasons.

Down I go to bury my nose in sand,

to lay in cool green glades of leaves.

Up I glide to the shining flat boundary,

where the gate to nothingness is open,

a soft, rippling surface my fin can break without effort.

I play at jumping into it, just for the thrill,

to shudder at the feel of vacuum on my skin,

to feel the sting of emptiness in my gills.

I draw a circle up there, and laugh on my way down

as the nature of things pulls me back where I belong.

On other days, when I feel like it,

I race along the curved boundary,

brushing its closed hard brilliance with my tail,

thinking about its mysteries.

Some say those images on it are illusions,

tricks of the light as its rays hit our eyes,

paradoxes we can expect at the edges of reality.

Some propose that they are our dreams,

perverse projections from our minds,

things to write poems in the sand about but not take too seriously.

But there are those who think the shadows are real:

that there’s a world on the other side,

like ours, but different,

where strange misshapen beings

with clumsy columns for fins and tails

lumber along their illogically curved paths,

obeying a force unknown to us.

Eli the Black stops me on some days

as I make my rounds,

taps an antenna against the boundary,

curls the others into a frown of gravity

and tells me his theory.

The clumsy shadow creatures, he says, are

no myth

or mirage,

but the very reason we’re here.

They’re the creators of our world,

the designers of its beauty,

the refreshers of its substance.

They provide the flakes and the worms,

they remove what’s dirty and bad

and restore goodness.

I like the story. Some days I almost believe it.

But remember the source: Eli is a Shelled One.

They are half strange themselves, aren’t they?

They spend much of their time stuck to the boundary,

Not knowing the beauties the rest of us share in.

They eat dirt,

and crawl around ungracefully

with those heavy burdens on their backs

whenever they’re not hiding those devilish faces they have.

No wonder they like to make up stories.

I smile at Eli,

the light,

the coolness,

and keep swimming.

 

 

 

 

 

 

 

 

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The Right Thing

People talk about morality a lot. Some say there are moral facts, others that moral codes are subjective and depend on culture. I have read the argument that human moral instincts are the product of evolution, or simply the collective experience of what works. Others claim that morality is of divine origin and part of the imago Dei, the image of God, in which humans were created.

This is a tough subject, almost as tough as the question of evil. And it’s primarily a problem in philosophy, although some folks have tried to make it all about science. (Of course, these are the same folks who make everything all about science.) Because it’s so hard to figure anything out about the nature of good and evil, I generally stay away from the subject. But I do have some ideas on the matter, and while probably naïve and way under the standard for philosophical discourse (I am, after all, only a mere scientist), I thought this blog would be a great place to express them – since, well, why not?

So what is my view of morality? In a nutshell, I believe that all of the statements in the first paragraph above are correct. There are moral facts and morality also depends on culture. Evolution plays a role in how people behave, and we do learn to do better on practical, empirical experience. And morality is a central aspect of our God-given human nature. The idea that any of these statements are mutually exclusive with any of the others is an example of the kind of philosophical absolutism that has become (or maybe has always been) so popular: if human nature derives from genes, then culture has no role, and vice versa. The truth, of course, is that both play a role. Another example of modern absolutism is the idea that since science tells us a lot about the world, only science can tell us anything true about everything.

But let’s get back to morality. Most humans agree with and generally follow certain moral principles, such as “it’s wrong to harm children,” and “it’s wrong to cause death or pain to another human being.” But for many other issues of moral behavior –and, in fact, for even these basic ones – different cultures can have different codes. By different cultures, I mean both different parts of the world and the same part of the world at different time periods. Causing the death of human beings used to be far more tolerated in most cultures than it is today. The death penalty was accepted as a just punishment for murder, theft, vandalism, some forms of sexual misconduct, etc. in cultures from Asia to the Middle East to Western Europe a mere 500 years ago. Slavery, a practice we all find repugnant today, was wide-spread in the ancient world and deemed not only acceptable but necessary for a functioning society. The abolition of slavery in the Mediterranean world would have been as impossible to conceive of as the enforcement of a fully vegan diet in the Western US (although no doubt some people feel the two are morally equivalent).

Did we get our moral standards from the evolution of the human brain? Or have moral values simply kept pace with the growing recognition that certain ways of acting make our lives better? As I said above, both are true to some extent. Like other primates, we are social, and genetically based instincts that act in ways that do not disrupt but reinforce group success are likely inherited from our primate forebears. And yes, it’s probably true that people have come to see that some ways of behaving toward our fellow creatures don’t really work that well. Early historical moral codes like the ten commandments are probably based on such experiences in agrarian, civilized societies.

But none of these things tell the whole story about morality and the role it plays in human interactions.  The concept of right and wrong is uniquely human. As C.S. Lewis so eloquently pointed out, arguments between people are almost always about whether somebody did or said something “wrong.” This assumes that there exists a right and a wrong. When accused of being “bad,” only a psychopath would say, “yeah, so what?” Everyone else will answer either “No, I didn’t do that,” or “Well, I did that, but I had a good excuse.” Some might argue “I did it, but it isn’t wrong to do that”. But in every case, there is tacit agreement that there is such a thing as “wrong.”

Where did humans get this idea that something exists that is morally right or not? Not from evolution. While other animals do good things or bad things, they are not aware of the existence of good or evil. They simply do what they do. They can be trained, of course, but that is a function of human definitions of good and evil, not theirs. The fact that many mammals care for their young, protect their mates, and do other things that we consider to be morally right is not relevant to the question of right and wrong.

Animals don’t do these things from a learned moral code, or because they were born with a human-like understanding of the concept of good and evil. All the individuals of a species will exhibit the same behavior, a sure sign that this is a built in, programmed result of an evolutionary based instinct or biologically determined response. The fact that human morality is largely culturally based, and not universal in time or across cultures argues strongly against a biological evolutionary mechanism. Of course, kindness toward kin and care of offspring, are not only considered moral, but are also likely originated from evolution. But how to care for one’s offspring, is not.

So where did that come from? And when did that start? We don’t know, but human beings as a species are about 250,000 years old, and there is no evidence that the human brain includes any particular genetic polymorphism linked to a concept of right and wrong. In fact, one would be hard pressed to imagine what sort of protein (which is the product of genes, after all) might have as its function making us recognize that it’s possible to be bad or good. Perhaps the answer is that morality, like so many amazingly complex non-material thought processes from mathematics and humor to sexual proclivities and literary creativity, arises from the billions of neural interactions in that incredibly complex organ, the human brain. Maybe. But that isn’t really an answer, is it? It’s a confession of ignorance.

Francis Collins tells us that one of the most compelling arguments that led him to accept Christianity was what he called the moral law. By this he means not just that people have a sense of morality, but that sometimes that moral sense can take such radical forms, as in extreme cases of self-sacrifice or altruism, that it defies logic, common sense, and a host of biological imperatives. The moral law says that we know what is right and what is wrong, and we often do the latter, for which we feel another uniquely human trait: guilt.

As a Christian, I agree with Lewis and Collins, and I see the concept of morality as something given to human beings by our Creator. The Bible presents the creation of Adam as God’s breath bringing to life of a creature made of clay.  But the moment when Adam and Eve became fully human, as we are today, was when they learned of good and evil, and in that moment also knew they had sinned.

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