Whenever I give a talk on evolution for the public, I always get this question:  “Are we still evolving?”  People want to know if our species is changing.  Are we getting smarter or better-looking?  Or are we degenerating as medicine keeps alive many of us who would have been ruthlessly culled on the savanna?

My answer usually goes like this:  “Yes, many of the genes that would have been eliminated now persist.  I am myopic, and wouldn’t have been a good hunter. Genes for nearsightedness are undoubtedly accumulating in our species. So in some respects we are genetically degenerating. But so long as there are sources of mortality — and the genetic variation to resist them — we will continue to evolve.  In Africa, for instance, thousands of children die yearly from infectious diseases. It’s highly likely that genes for resistance to those diseases are becoming more numerous.”

Now this answer is speculative, based on evolutionary theory.  There’s not a lot of evidence about whether and how fast the human species is changing.  But a new paper in The Proceedings of the National Academy of Sciences goes one step further: it not only demonstrates genetic variation for sources of mortality, but shows that that variation is correlated with reproductive output.  If both of these hold, then we must be evolving.  The paper goes on to predict how much genetic change for several traits that Homo sapiens will experience over the next ten generations.

The paper is by Byers et al. (see reference below), and should be online this week. (Thanks to Steve Stearns for letting me see a galley proof.)  There has already been a flurry of publicity — one example is here — and there will be more.

The sample population included about 5,000 women from the famous “Framingham heart study,” a survey begun in 1948, with the individuals sampled every four years for a variety of physical and traits (weight, height, age at first reproduction, blood pressure, serum cholesterol, etc.).  Since the individuals measured are now on the senior side, the original sample population (now past reproduction) has produced their allotment of children.

This gives us a basis for detecting natural selection.  The underlying rationale is that we look for a correlation between an individual’s traits and the number of children she produced.  If we find one, and there is genetic variation for the trait, we can reasonably assume that natural selection is acting on it, and we can see what type of natural selection by seeing how variation in the trait is associated with variation in offspring number.  If, for example, higher cholesterol is associated with lower reproductive output (as it might be if cholesterol is associated with heart disease that strikes before reproduction is finished), then we can assume that there is natural selection against higher cholesterol. If we know how much variation in people’s cholesterol is based on variation in their genes (a proportion called heritability, which ranges between zero and one), we can then calculate how we expect the trait to change in the future.  That is, we can see if we’re evolving, and predict how much.

The underlying method, developed by quantitative geneticists such as my old mate Russell Lande, involves looking at several traits, any or all of which may be subject to selection.  These traits may have some “genetic correlation,” that is, genes affecting one trait might affect another. (For example, genes for higher weight might raise blood pressure as a byproduct).   These correlations can be measured using data on the observed variation in the traits and the degree to which this variation is passed from one generation to the next (the heritability of the traits).

If you calculate all these correlations and then multiply them by the amount of selection that appears to act on each trait (this has to be discounted using the correlations), you can estimate the degree of genetically based change you expect each generation: that is, the amount that each trait will change over one generation by natural selection.

What they found.

Several traits did indeed appear to be undergoing selection.  From the amount of this selection, we can predict the percentage change in the trait that we expect to see after ten more generation of reproduction (roughly 300 years from now).

Total cholesterol: going down.  Projected to drop 3.6% in ten generations

Weight:  going up a tad, projected to increase 1.4% in ten generations

Height:  we’re getting shorter projecting a drop of 1.3% (2.1 cm) in ten generations.

Systolic blood pressure:  Going down, as predicted. Projected to drop 1.9% in ten generations.

Age at menopause:  Going up; projected to rise 1.6% (0.8 years) in ten generations.

Age at first reproduction: Going down. Projected to drop 1.7% (from 26.18 to 25.74 years).

So women, at least, are getting shorter,  stouter, and reproducing earlier and over a longer period of time.   This is evolutionary change.  Based on this study, we can tentatively say, with more assurance than I used to, that yes, our species is still evolving.

But there are two important caveats to this study, both of which were recognized by the authors.

1.  The “inheritance” of the trait includes not just genetic inheritance, but cultural inheritance.  Humans pass not only their genes to their offspring, but aspects of culture that may mimic a genetic inheritance.  For example, parents who eat a lot may induce their kids to eat a lot, and some of the correlation of weight between parents and their kids may be due not to shared genes, but to shared food.  Parents who for cultural reasons have their kids early may induce their own kids to produce grandchildren early.  As the authors say, “We are not able to differentiate the effects of genes and culture with these data.”

This is a bit of a problem, because the evolutionary projections are based on assuming that all of inheritance is genetic.   It’s hard to get around, since distinguishing genetic from cultural inheritance involves difficult work using data from adopted children or twins raised together versus apart.  Nevertheless, we can probably assume that some selection is acting on these traits, discounted by the degree to which parent/offspring resemblance reflects cultural similarity.

2.  The predictions may be hard to verify, because they assume that the environments of our species — that is, the environments that are relevant to each trait — will remain constant over the next few generations. Cholesterol is predicted to drop from 224 to 216 mg/100 ml blood over the next ten generations, but this assumes that diet is constant.  If people stop eating fatty foods, the drop may be even steeper because of this dietary change.  Conversely, if people flock even more frequently to fast-food joints,  the predicted drop may be negated by an increased intake of burgers and fries.

These problems mean that one has to be a bit careful about not only predicting the degree of selection, but also testing those predictions in the future. Yesterday Stearns was on NPR’s Science Friday, discussing how the authors deal with the conflation of culture/environment and genes, and why the prediction of increasingly plump women may not be what it seems.

But regardless of the caveats, the study of Byars et al. is based on a good idea, and makes a reasonable case that selection is indeed acting in our species.  One would, of course, like confirmation from other datasets, but since the Framingham study is unique, this may be hard to do.

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h/t: Steve Stearns (who reviewed this post for accuracy).

Byars, S. G., D. Ewbank, D. R. Govindaraju, and S. C. Stearns. 2009.  Natural selection in a contemporary human population.  Proc. Nat. Acad. Sci. USA: in press.

Cats are thin on the ground in Guatemala, but I did find a few.  First up is Sammy, the resident cat at Nim P’ot, a textile/weaving store in Antigua (their webpage is a virtual museum of local styles of weaving).  Sammy, who’s now 13, was deliberately shot by someone when he was three.  As a result, one of his front paws is deformed, so he walks with difficulty.  He spends his day sleeping on the piles of hupiles, but, I’m told, has no problem limping to his food bowl and litterbox.

Next up is Oreo, who lives on the coffee-and-tea farm and biological reserve of Los Andes, on the side of the volcano Atitlán.  Oreo is one of the few cats in Guatemala who has his own bed, but he prefers to lie on a lap, or bask before the traditional wood stove while the cook makes tortillas.

And what would Guatemala Caturday be without a felid weaving?  Here’s a cat-themed huipil (I suspect it’s a jaguar):

Once again the mysterious Jesus and Mo artist proves him/herself a diligent reader of the atheistic blogosphere. Earlier this week the ever-slippery Karen Armstrong, whose continued writing career proves that you can fool some of the people all of the time, published a musheaded defense of religion. (For a decisive takedown of this piece, see P.Z.’s post on Pharyngula).

You can read Armstrong’s piece to see the breathless hauteur with which she claims to know exactly what God is.  Like Robert Wright, she deliberately uses the word “God” when she means “the idea of God,” so that her readers can move seamlessly from the notion of God to the reality of The Bearded One himself:

But it is only since Sept. 11, 2001, that God has proven to be alive and well beyond all question — at least as far as the global public debate is concerned. With jihadists attacking America, an increasingly radicalized Middle East, and a born-again Christian in the White House for eight years, you’ll have a hard time finding anyone who disagrees. Even The Economist’s editor in chief recently co-authored a book called God Is Back. While many still question the relevance of God in our private lives, there’s a different debate on the global stage today: Is God a force for good in the world? . . .

Homo sapiens is also Homo religiosus. As soon as we became recognizably human, men and women started to create religions. We are meaning-seeking creatures. While dogs, as far as we know, do not worry about the canine condition or agonize about their mortality, humans fall very easily into despair if we don’t find some significance in our lives. Theological ideas come and go, but the quest for meaning continues. So God isn’t going anywhere.

But Armstrong didn’t fool the J&M artist:

Alert reader Cathy Newman forwarded this photograph, taken by her friend last week in Huntsville, Alabama.

Over at Rationally Speaking, Massimo Pigliucci discusses “the scope of skeptical inquiry,” and asserts that atheism is not a scientific position but a philosophical one.  Here’s part of what he says:

First, let me define what I mean by skeptical inquiry, atheism and political philosophy. Skeptical inquiry, in the classic sense, pertains to the critical examination of evidential claims of the para- or super-normal. This means not just ghosts, telepathy, clairvoyance, UFOs and the like, but also — for instance — the creationist idea that the world is 6,000 years old. All these claims are, at least in principle, amenable to scientific inquiry because they refer to things that we can observe, measure and perhaps even repeat experimentally. Notice, of course, that (some) religious claims do therefore fall squarely within the domain of scientific skepticism. Also in this area we find pseudohistorical claims, such as Holocaust denial, and pseudoscientific ones like fear of vaccines and denial of global warming. Which means of course that some politically charged issues — like the latter two — can also pertain properly to skeptical inquiry.

So far, so good.  But then he goes on to assert that the atheist position is not one that derives from “skeptical inquiry”:

Second, let us turn to atheism. Once again: it is a philosophical, not a scientific position. Now, I have argued of course that any intelligent philosopher ought to allow her ideas to be informed by science, but philosophical inquiry is broader than science because it includes non-evidence based approaches, such as logic or more broadly reason-based arguments. This is both the strength and the weakness of philosophy when compared to science: it is both broader and yet of course less prone to incremental discovery and precise answers. When someone, therefore, wants to make a scientific argument in favor of atheism — like Dawkins and Jerry Coyne seem to do — he is stepping outside of the epistemological boundaries of science, thereby doing a disservice both to science and to intellectual inquiry. Consider again the example of a creationist who maintains in the face of evidence that the universe really is 6,000 years old, and that it only looks older because god arranged things in a way to test our faith. There is absolutely no empirical evidence that could contradict that sort of statement, but a philosopher can easily point out why it is unreasonable, and that furthermore it creates very serious theological quandaries.

I’m baffled.  But let’s be clear about what atheism is.  I’ll call “weak sense atheism” the position that, I think, most atheists hold.  It is this:  “There is no convincing evidence for God, so I withhold belief.”  This can be further refined, as Dawkins does in The God Delusion, into the statement, “There could be lots of evidence for God, but none has appeared. Therefore I think it improbable that God exists.”  This is the stand that informs the atheist bus posters that read, in part, “There probably is no God.”

The second form of disbelief, which I call “strong sense atheism,” is the flat assertion, “I know there is is no God.”  Note that this elides a bit into the “probably-no-God” position, depending on how strong you think the evidence is.  The existence of suffering in the world, for example, convinces many, but not all, that there is not a beneficent God.

Now I don’t know anyone who is a strong-sense atheist.  Even Dawkins, as I recall, is a “70% probability” man — he thinks it pretty improbable that God exists, but adds that he can’t disprove the existence of some kinds of gods. I’m pretty much on board with him.   You’d be a fool to say that you know absolutely that there is no being up there at all, including one that doesn’t interfere in the workings of the universe.

So let’s take weak-sense atheism (WSA) as the default stance.  In its very weakest, “no-evidence-for-God” sense, WSA is absolutely scientific.  After all, what is science but the claim that one needs empirical evidence before accepting something as a reality? When one says, “I see no evidence for a god, and therefore refuse to accept his/her/its reality,” one is saying nothing different from, “I see no evidence for the view that plants have feelings, and therefore I don’t accept the idea that they do.”

What about the “probabilistic” form of WSA?  That’s equally scientific.  If there could be evidence for a phenomenon, but repeated investigations fail to give that evidence, one becomes less willing to accept that phenomenon. In this sense, being a WSA is no different from making a perfectly scientific claim like this: “I think it pretty improbable that the Loch Ness monster exists.” After all, if there were a giant reptile trapped in the Loch, presumably you could find it.  And people have tried. They’ve looked underwater with cameras, hung around the lake trying to photograph it, and conducted sonar and satellite investigations.  Nothing has turned up.  In all probability, the Monster is a myth.

Based on these searches, is it then a “philosophical position” to say that it’s highly unlikely that Nessie exists? I don’t think so.  It’s an evidence-based position — in other words, a scientific one.  Similarly, the god that many people believe in, who is said to be beneficent, answer prayers, heal the sick, come back from the dead, and the like, is contradicted by evidence: the failure of prayer and spiritual healing, the existence of inexplicable evil, and so on.  There are a million ways that a theistic god could have shown itself to us Earthlings, but it hasn’t happened.  There is no more evidence for a world-touching God than for the Loch Ness Monster.

Now of course we can’t refute, or find any evidence for or against, the existence of a purely deistic, hands-off God.  In this sense, saying that “God certainly does not exist” is a philosophical position.  But that’s not the most common form of atheism.

I’m not a philosopher, so maybe Massimo’s argument is more subtle than I perceive.  But I see my own non-acceptance of a deity as a purely scientific stance.  I believe it was Bertrand Russell who was asked, “But what if you’re wrong about your atheism? What if you die and find yourself before God, who asks you why you didn’t believe?” Russell’s reply was, “Not enough evidence, Lord; not enough evidence.”

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UPDATE:  Over at Sentient Developments, Russell Blackford, who is a philosopher, has a long and trenchant critique of Pigliucci’s post.

Unnecessary quotation marks are my bête noire, but these seem appropriate:

See more examples here.

In case you don’t read Salon, today’s issue has both a print and a video interview with Dawkins about his latest book, The Greatest Show on Earth.  Of course the reviewer can’t stay away from Dawkins’s atheism:

In the past few years, especially with “The God Delusion,” you’ve become sort of an evangelist for the atheist movement. How have you dealt with becoming a more polarizing figure over the past few years?

I don’t quite know why it should be polarizing. I like to think “The God Delusion” is a humorous book. I think actually it’s full of laughs. And people who describe it as a polarizing book or as an aggressive book, it’s just that very often they haven’t read it. They’ve read other people reacting to it. It is true that religious people do react to any kind of criticism as almost a personal insult, it’s almost as if you’re saying their face is ugly or something, and so that has put out the idea that “The God Delusion” is an aggressive book. You’ve heard words like strident and shrill, as well. I’d like to suggest that actually it’s quite a funny book.

Do you regret having that kind of reputation? Do you feel like it’s handicapping you in the future — that you’ll always be seen as having a certain kind of agenda in mind?

Yes, I think it’s unfortunate. I think it comes from people who haven’t actually read the book, or who haven’t actually met me personally, and so I’m described as a very aggressive, strident person, which I’m not.

And he isn’t.

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Oh, curiously enough, the Socialist Party of the UK has published a joint review of The Greatest Show on Earth and Why Evolution is True.  Let a hundred evolution books blossom!