Wish­ful Sci­ence

A de­bate about the ivory-billed wood­pecker demon­strates yet again that even among sci­en­tists, ev­i­dence is of­ten a mat­ter of bias and be­lief

Canadian Wildlife - - WILD THINGS - By Jay Ingram Il­lus­tra­tion by Min Gyo Chung

One of the many things that the fol­low­ers of Don­ald Trump have brought to our at­ten­tion is the fact that peo­ple can wil­fully ig­nore ev­i­dence in favour of be­lief. In re­sponse, there has been a cry for “ev­i­dence-based” think­ing and ac­tions. But “ev­i­dence” is very much in the eye of the be­liever.

When some­one wants some­thing to be true, de­ci­sions of what con­sti­tutes sup­port­ing ev­i­dence are in­flu­enced by a set of un­con­scious psy­cho­log­i­cal mech­a­nisms: con­fir­ma­tion bias, the band­wagon ef­fect, se­lec­tive per­cep­tion — there are many. In a con­tro­versy, it might be im­pos­si­ble to choose ev­i­dence that both sides agree is ac­cept­able. This is true in pol­i­tics, but also in sci­ence.

Take the case of the ivory-billed wood­pecker. A mag­nif­i­cent, but ex­tinct, wood­pecker (so revered for its splen­dour and size it was called the “Lord God bird”), it was last of­fi­cially sighted in North Amer­ica in the mid-1940s (with a relict pop­u­la­tion last­ing longer in Cuba). But then in 2004, a wave of ex­cite­ment rolled over bird­ers with the re­lease of a video show­ing what could be an ivory-bill in the swampy woods of Arkansas.

But was it? The ivory-billed and the rel­a­tively com­mon pileated wood­pecker are sim­i­lar, and any claim of an ivory-billed sight­ing has to elim­i­nate the pos­si­bil­ity of con­fu­sion be­tween the two. And that turned out to be ex­tremely dif­fi­cult.

The video did in­deed show a large white and black wood­pecker, first a glimpse of part of the bird on the other side of a tree trunk (of course!), then a few wing­beats as it fled the cam­era into the woods.

One of the key di­ag­nos­tics that would sep­a­rate the two birds is the amount of white on the up­per sur­face of the wings. Pileated wood­peck­ers have lit­tle; ivory-billed, a lot. You’d think that video of the bird fly­ing away from the cam­era would set­tle the ques­tion, but it did not.

The con­tro­versy reached the pages of the pre-em­i­nent jour­nal Sci­ence: first an ar­ti­cle de­tail­ing the var­i­ous bits of ev­i­dence from the video, then a re­tort by bird artist and field guide writer David Si­b­ley, claim­ing a host of er­rors and un­jus­ti­fied con­clu­sions. Si­b­ley is a re­spected char­ac­ter in the bird­ing world, but his op­po­nents, those claim­ing the sight­ing was real, weren’t in­signif­i­cant ei­ther: Cor­nell Univer­sity, the Na­ture Con­ser­vancy and even the U.S. gov­ern­ment.

What was fas­ci­nat­ing about the back-and-forth was the in­cred­i­ble de­tail mined from the video by its pro­po­nents. Ac­cord­ing to them, one par­tic­u­lar frame, a bit of un­fo­cused white just be­hind a tree, shows the up­per sur­face of the wing be­fore the bird has ac­tu­ally taken flight. Up­per sur­face white equals ivory-bill. To Si­b­ley and his col­leagues, the same frame of white is ac­tu­ally the un­der­side of the wing as the bird launches it­self, there­fore un­der­side white equals pileated. Un­for­tu­nately, the video it­self can­not re­solve that dis­pute.

Then there is the view of the bird in re­treat, wings flap­ping, flashes of black and white. Here the two sides couldn’t agree on which side of the wing re­vealed a flash of white. It’s as­ton­ish­ing to me that no anal­y­sis of this video, flawed and indis­tinct as it is, has been able to re­solve that fun­da­men­tal ques­tion.

Even the mak­ing of wooden mod­els of the two birds with wings that flapped when a cord was pulled, and then recording videos of those mod­els un­der con­di­tions de­signed to repli­cate the orig­i­nal dis­tance and light lev­els, failed to con­vince any­one to change opin­ion.

The orig­i­nal flurry of in­ter­est over that sight­ing has sub­sided, with both sides hold­ing to their orig­i­nal views. But just in the last few months, the ivory­billed wood­pecker has reared its head again — lit­er­ally. In Jan­uary 2017, am­a­teur birder Michael Collins pub­lished im­ages of what he called an ivory-bill, col­lected while pad­dling 1,500 hours on the Pearl River near the Mis­sis­sippi-louisiana border with a cam­era at­tached to his kayak pad­dle.

At the risk of re­veal­ing my own bi­ases, I’d say this re­cent ev­i­dence (even an im­age of a bird’s head held at the char­ac­ter­is­tic ivory-billed angle) is less con­vinc­ing than the 2004 video.

But it doesn’t mat­ter: there are still many who think that the ex­ist­ing amal­gam of poor video, vague sounds and wooden mod­els is per­sua­sive, and they will con­tinue to search. There is a cu­ri­ous par­al­lel here to the search for Big­foot: the same tech­niques and ar­gu­ments are de­ployed in favour of the ev­i­dence. One is sci­ence (af­ter all, the bird did ex­ist once); the other is not.

What all such sto­ries have in com­mon is be­lief, un­shake­able be­lief, driven by the de­sire of dis­cov­ery. In each and every case, that be­lief colours the ad­mis­si­bil­ity of ev­i­dence. It’s not true that there are two ways of think­ing, log­i­cal and ir­ra­tional. Rather it is that hu­man thought is en­tan­gled with both.1

SCI­EN­TIFIC EV­I­DENCE AND “PROOF,” IT TURNS OUT, ARE VERY MUCH IN THE EYE OF THE BEHOLDER

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