Carl Zimmer connects Bigfoot with an explanation of the history of "null hypothesis" in a Nautilus essay: "Why we can't rule out Bigfoot". He discusses a recent paper by Bryan Sykes' lab, which systematically tested purported Yeti and Bigfoot samples.
Some skeptics have offered up an alternative explanation for Sykes’ finding. It’s possible that the polar bear-like DNA actually comes from a living mammal—perhaps a brown bear—that happened to pick up a few mutations that created a false resemblance to that ancient polar bear DNA.
What these skeptics have done, in effect, is create a null hypothesis. And there’s a straightforward way to set about disproving it. Scientists would need to find more DNA from these mysterious bears. If other regions of the DNA also matched ancient polar bears, then scientists could reject the null hypothesis.
I think this would be a good essay for undergraduate courses introducing science. Zimmer gives a good account of how R. A. Fisher conceived of frequentist statistical testing and the role of the null hypothesis in it.
Applied to Bigfoot, I think we should be very skeptical about the choice of a null hypothesis. That's in part why I think it would be a good essay for a class discussion. I don't think that Sykes approached his study with the null hypothesis that the samples would all represent other mammals. I think he tested the hypothesis that each sample could represent an unknown primate, and refuted it in each case by showing some other animal (from raccoons to bears) is a close genetic match to the sample.
Notable paper: Blasco, R., Finlayson, C., Rosell, J., Marco, A.S., Finlayson, S., Finlayson, G., Negro, J.J., Pacheco, F. G., Vidal, J. R. (2014) The earliest pigeon fanciers. Scientific Reports 4:5971. doi:10.1038/srep05971
Synopsis: Ruth Blasco and colleagues studied 1724 rock dove bones from Gorham's Cave, finding evidence for human processing, cooking and/or consumption of the birds in 11 out of 19 Neandertal contexts, through at least 40,000 years of Neandertal occupations.
Important because: The work documents that hunting and eating these medium-sized birds was a recurrent part of Neandertal (and later modern human) diets. Once it was common to see "small mammal and bird hunting" in lists of behavioral traits limited to modern humans. Now we know that Neandertals regularly took large birds for feathers and medium to large birds for food. This isn't a single occurrence, it is a sampling of the behavior of people over tens of thousands of years.
Plus, who knew? Rock doves are the wild progenitor species of common pigeons, and they are indistinguishable from fragmentary bone remains.
Jonathan Weiner wrote a well-known book about the long-term field studies of Galapagos finches by Peter and Rosemary Grant, titled The Beak of the Finch: A Story of Evolution in Our Time (Vintage). On the publication of their new book about their continued work, Weiner has written an essay of appreciation in the New York Times: "In Darwin’s Footsteps".
They kept up their watch during years of downpours and years of drought — seasons of feast and famine for the finches. And Darwin’s process unfolded before their eyes in intense episodes that illustrated better than anything in the Origin the struggle for existence, and the ways that life adapts and emerges fitter from the struggle.
Weiner describes the most interesting discovery, the establishment of a new population that behaves like an incipient species, from a single founder.
The Grants' book is titled, 40 Years of Evolution: Darwin's Finches on Daphne Major Island.
A photo from outside the Neandertal Museum, in Mettmann, Germany:
The full-size sculpture was originally in a local biergarten, dating to the 1910's, where it entertained patrons for many years.
Notable paper: Coqueugniot H, Dutour O, Arensburg B, Duday H, Vandermeersch B, Tillier, A-M. (2014) Earliest Cranio-Encephalic Trauma from the Levantine Middle Palaeolithic: 3D Reappraisal of the Qafzeh 11 Skull, Consequences of Pediatric Brain Damage on Individual Life Condition and Social Care. PLoS ONE 9(7): e102822. doi:10.1371/journal.pone.0102822
Synopsis: Hélène Coqueugniot and colleagues look closely at a cranial wound on an early modern human skull from Israel, Qafzeh 11. They show that the injury had profound effects on the right frontal lobe of the brain, and argue that the individual suffered a delay in brain development and psychological or developmental disabilities as a result.
Important because: Qafzeh 11 was deliberately buried with red deer antlers apparently placed over the body. The individual seems to represent a child who was a victim of some horrific trauma, who had severe developmental issues, who was nonetheless integrated into a social group and treated with special care when she or he died. It is a window into the social behavior of Middle Paleolithic people.
But... Despite the fact that it's an undeniably severe injury, we may not be able to infer that much about the life of this individual. His or her brain was small for age, but well within the range of developmentally normal adults today.
Experimental psychology has recently become embroiled in a controversy about whether replication of high-profile findings should be a serious goal of new research. Bioethicist Michelle Meyer and psychologist Christopher Chabris have a weighty essay in Slate about the problem: "Why Psychologists’ Food Fight Matters".
They focus on the complaints that some experimenters have raised, that they feel "persecuted" or "bullied" by other scientists who are attempting to replicate their findings. In some cases, young researchers worry that their job prospects or tenure cases may suffer as other scientists unjustifiably discredit their earlier work, without being given an opportunity to respond in print in a timely way.
My first reaction to this was, "Oh, really? Well, that's science." But there are some real cases of boorish behavior. For example,
Once the journal accepted the paper, Donnellan reported, in a much-tweeted blog post, that his team had failed to replicate Schnall’s results. Although the vast majority of the post consisted of sober academic analysis, he titled it “Go Big or Go Home”—a reference to the need for bigger sample sizes to reduce the chances of accidentally finding positive results—and at one point characterized their study as an “epic fail” to replicate the original findings.
Now, I think that reflects worse on the replicator than on the original researcher. But it's easy to see how it puts a responsible scientist into an impossible position. What we need is a less confrontational attitude toward replication, one that sees replicability as a hallmark of good science and accepts replication studies into journals without needing a "crisis of replication" to make them newsworthy.
Some have legitimate complaints about "failures to replicate" that do not correctly implement the experimental protocol, or change some key aspect that leads to a different outcome. Meyer and Chabris do a good job of presenting the nuances of such concerns, which basically revolve around competence. Are researchers capable of describing what they've done accurately, so that the results can be replicated? Or does every result depend on some "special skill" that the original lab has developed, that somehow cannot be described?
We should remember the cases in experimental psychology where the "special skill" involved falsifying results.
I agree with most of Meyer and Chabris' suggestions, particularly the concept that replication should not depend upon the original researchers' cooperation.
Replicators have no obligation to routinely involve original authors because those authors are not the owners of their methods or results. By publishing their results, original authors state that they have sufficient confidence in them that they should be included in the scientific record. That record belongs to everyone. Anyone should be free to run any experiment, regardless of who ran it first, and to publish the results, whatever they are.
In sciences with unique specimens, cell cultures, or other materials, this principle means that the original materials must be available for examination or use by qualified researchers. Where substantial investment or assistance has been provided by the original researchers to enable replication, obviously they should be included as authors. Many journals now provide a standard format for reporting contributions to a paper, and "provided reagents or samples" is one of the standard entries. There are cases where the contribution does not rise to the level of authorship, but at least such assistance should be acknowledged.
Paleoanthropologists often ignore the fundamental principle of replicability. But providing the full ability to replicate paleoanthropological work really is not very hard. Just make sure that qualified researchers can access the specimens. Many of the observations that paleonthropologists depend upon are simple measurements that could be replicated easily on 3-d models. Heck, in many cases nowadays the original measurements may have been taken on 3-d models.
That means there should never be any question of access to the same models for replication.
Personally, I wonder whether we should make grant funding contingent on first replicating some prior finding. Yes, that would take time that researchers might otherwise devote to new work. But to do effective research most experimentalists already need a pipeline capable of replicating earlier work in the same area of research. And they need to convince a grant panel that they are already prepared to carry out such work. Replication studies are a good way to accomplish both goals, and might sometimes actually lead to rejection of overhyped bad ideas.
Besides, we know that most grant applications that are funded actually describe work that already exists in pilot form. They may as well be doing something for the good of the science. Instead of rehashing their own old results, they could rehash other people's!
Many futurists and not a few science fiction writers hold the idea that computer technology is developing toward a point where artificial intelligence will begin to develop new technology instead of people. At that near-future time, they argue, the progress of technology will no longer be predictable. It is a "singularity", beyond which no laws of technological progress can apply.
This idea has been around for many years and has its merits. I just wanted to point to a comment by the physicist Sabine Hossenfelder, who suggests that word doesn't mean what they think it means: "What is a singularity?".
What one typically means with a singularity is a point where a function behaves badly, so that one or several of its derivatives diverge, that is they go to infinity. The ubiquitous example in school math is the poles of inverse powers of x, which diverge with x to zero.
However, such poles are not malign, you can remove them easily enough by multiplying the function with the respective positive power. Of course this gives you a different function, but this function still carries much of the information of the original function, notably all the coefficients in a series expansion. This procedure of removing poles (or creating poles) is very important in complex analysis where it is necessary to obtain the “residuals” of a function.
Hossenfelder points out that von Neumann first introduced the analogy in reference to technology.
Notable paper: Eren MI, Roos CI, Story BA, von Cramon-Taubadel N, Lycett SJ. 2014. The role of raw material differences in stone tool shape variation: an experimental assessment. Journal of Archaeological Science 49:472-487. doi:10.1016/j.jas.2014.05.034
Synopsis: Metin Eren and colleagues show in a large experimental study that the properties of raw materials do not constrain the shape of handaxes, at least not in the hands of a skilled knapper.
Important because: If differences in artifact shapes between sites or regions actually reflect raw material type, they tell us nothing about ancient culture, knowledge or learning. By showing that raw material doesn't matter, Eren and colleagues raise the potential of studying ancient cultural differences. Demonstrating that handaxes in particular are not constrained by raw material means that the Acheulean -- with a diversity of handaxe shapes and sizes in different places -- is not as monolithic as many archaeologists have claimed.
But... Toolmakers really do prefer some raw materials over others, and traveled some distance to obtain them, even among the earliest Oldowan toolmakers. Toolmakers who were forced to work with shoddy materials probably had a harder job, and would have had a harder time transmitting their knowledge to novices. So raw material obviously matters to the kinds of artifacts we should expect to find, even if it does not constrain artifact shape in any absolute way.
Michael Eisen reflects on the suicide of a Japanese stem-cell researcher whose lab has become enmeshed in a scientific fraud investigation: "Yoshiki Sasai and the deadly consequences of science misconduct witchhunts". As Eisen reports, his own father committed suicide under similar circumstances in 1987 as an NIH researcher, after a member of his lab was shown to have produced fraudulent results.
Eisen emphasizes that in such cases, laboratory heads face strong opprobrium even when they are trying to investigate and uncover evidence of the fraud.
Of course everyone will point out that Sasai was overreacting – just as they did with my father. Neither was accused of anything. But that is bullshit. We DO act like everyone involved in cases of fraud is responsible. We do this because when fraud happens, we want it to be a singularity. We are all so confident this could never happen to us, that it must be that somebody in a position of power was lax – the environment was flawed. It is there in the institutional response. And it is there in the whispers – I still remember how the faculty in my graduate department talked about David Baltimore during the Imanishi-Kari incident.
The result is an atmosphere in which some researchers would rather cover up fraud than create a laboratory environment that prevents it. Nevertheless, in several recent cases, laboratory heads with years of track record have been the prime perpetrators of frauds, and students or trainees have been whistleblowers.
I agree with Eisen that researchers who "overhype" their results help perpetuate circumstances in which other researchers and students are likely to perpetrate fraud. Science is rather like magic -- we need to keep our minds open to the idea that when something unexpected happens, it's possible we're being tricked. We need to emphasize replication and open access to data.
The team also used their simulation to predict what would happen if they removed each of the partners from the dance. If they took out Bmp, Sox9 activity also died away and the fingers didn’t form at all; instead, the virtual limb bud continued growing as a shapeless lump. If they took out Wnt, Sox9 became active everywhere and the spaces between the fingers disappeared. If they blocked Bmp and Wnt together, these effects partly cancelled each other out but the number of fingers decreased.
The team then checked these predictions by applying drugs that block Wnt and Bmp to isolated limb buds growing in Petri dishes. In every case, the reality matched the predictions.
Nice case study in evo-devo, with a clear importance given the widespread nature of these gene systems.
Carl Zimmer has been writing about chimerism in the New York Times: "Having More Than One Set of DNA Carries Legacy of Risk". As he points out, this condition can cause some interesting consequences in humans:
The results suggest that some people can have serious genetic diseases without any symptoms. That’s because they have the defective version of a gene in only some of their cells, and their other cells compensate for them.
But such people are unknowingly at risk of having children with full-blown versions of their diseases, if the mutation appears in their reproductive cells. Dr. Lupski said that as technology improved, clinical geneticists should test people for this hidden risk.
In humans, somatic mosaicism is fairly rare -- although Zimmer reports on a new study that finds it is a bit more common than anyone had previously guessed.
What most people don't know is that there are some primates where chimerism is nearly universal. The callitrichid monkeys are small anthropoid primates found in South and Central America, and include marmosets and tamarins. Twinning is very rare in most anthropoid primates -- in humans, it amounts to between 0.5 and 2 percent of births in different populations. Marmosets have a very high frequency of twin births, and triplet births are more common than singletons, meaning that most marmosets were born as twins or triplets.
In humans, twins sometimes exchange blood through their placentas. With identical twins this exchange is much more common but does not lead to noticeable chimerism, because the twins are genetically identical. Occasionally, identical twins who share a placenta, called monochorionic twins, will have a significant difference in their blood supply, leading to twin-twin transfusion syndrome. This can cause significant differences in development between the twins, and in extreme cases one twin's development is severely compromised.
Even fraternal twins can exchange blood through their placentas. This kind of exchange can remain evident in the blood, with a small fraction of an individual's hemapoietic stem cells actually borrowed from her twin -- a condition called hemapoietic chimerism. Surveys of blood in fraternal twin children have found that up to 8 percent of such twins have a very small fraction of blood cells (as low as 0.01 percent) expressing the blood types of their twin (van Dijk et al. 1996).
Primatologists have long known that marmosets and tamarins have hemapoietic mosaicism. Twins and triplets have placentas that fuse early in development, developing anastomoses that allow blood to move from one developing embryo to the other (or others). Corinna Ross and colleagues (2007) investigated this phenomenon, reviewing what was then known about it:
Genetic chimerism, the mingling of two or more genomic lineages within an individual (1), is rare in mammals, but chimerism is prevalent in the hematopoietic tissues of marmosets and other callitrichid primates (2, 3). In these species, fraternal twins exchange cell lines through chorionic fusion during early development (2, 4, 5). On the basis of karyotypic evidence from Callithrix jacchus (2, 3), estimates are that 95% of pregnancies result in the birth of hematopoietic chimeric twins. Chorionic fusion of the twins' placentas begins on day 19 and is complete by day 29, forming a single chorion with anastomoses connecting the embryos, which are still at a presomite stage in development (4–7). The fusion of the chorions and a delay in embryonic development at this stage allows the exchange of embryonic stem cells via blood flow between the twins (2, 8). As a result, the infants are genetic chimeras with tissues derived from self and sibling embryonic cell lineages (2, 3, 8).
Ross and colleagues found that chimerism in marmosets was not limited to the blood but occurred in every tissue type that they examined, from kidneys to hair. Two out of twenty-one deceased animals they examined had chimerism in the gonads, four out of seven live animals had chimeric sperm. Those findings show that marmoset males may commonly be fathering the genetic offspring of their twins.
Also, there is this:
We determined that individuals in 5 of the 15 families passed on alleles to their offspring that represented gene lineages inherited horizontally from the sibling (see examples in Fig. 1 and SI Fig. 4). One breeding female, whose uterine twin was a male, produced offspring that inherited her sibling's alleles. This documents the possibility that an XY primordial germ cell is capable of maturing and producing viable eggs in a female, a phenomenon that has not been documented for primates. Although we are not currently able to document the fate of the Y chromosome during development of the female's oocytes, our data suggest the intriguing possibility that a female may pass on a Y chromosome to her offspring.
A genetically male stem cell producing eggs in a chimeric female.
The authors discuss some of the consequences of chimerism from the point of view of the unique social system of callitrichids. Their system of twin births depends on extensive help from males and from other females besides the mother. Help, in an evolutionary perspective, depends on relatedness, and the extent of chimerism affects the relatedness between twins and between individuals in a group:
Based on the prevalence of chimerism, the proportion of cells within a tissue that carry sibling alleles, and the probability of the direction of exchange obtained from our data, we estimate that male twins are on average related by r = 0.574 (see SI Text for calculations). More specifically, in a case of unidirectional exchange in which the soma of the donating twin is nonchimeric, he is related to the sperm of the recipient twin by an average r of 0.625 (see SI Text ). The relatedness calculations suggest that chimeric callitrichid siblings are more closely related to each other than typical nonchimeric mammalian siblings.
Callitrichids may be, in the limited sense of relatedness, nearly as comparable to social insects as to other primates. Genes that promote cooperativeness should have a greater payoff considering that they will sometimes be expressed in siblings' bodies and behavior. Yet germline chimerism might give rise to some very interesting genomic conflict between twins in utero. Callitrichids do have a fairly high rate of fetal loss and perinatal mortality.
Chimerism conceivably may have bad side effects upon immunity. The immune system may attack chimeric cells, or alternatively the presence of chimeric cells may prevent the immune system from raising up antibodies to certain pathogenic antigens. A marmoset genome sequencing project has been underway for some time, and has this month reported a draft of 90% of the common marmoset genome (Marmoset Genome Sequencing and Analysis Consortium 2014). They investigated whether genes related to immunity might have changed under selection during marmoset evolution. They drew some hits:
Hematopoietic chimerism of marmosets was expected to correlate with marked changes in immune system function. We found positively selected genes related to the immune response significantly enriched in marmoset (threshold of P < 0.05; Table 1). NAIP and NLRC4 homologs, conserved in mammals, were absent in marmoset (Supplementary Table 38). These proteins form the NAIP inflammasome in macrophages, a cytoplasmic complex that triggers macrophage inflammatory death through activation of caspase-1 (refs. 29,30) and could affect reproduction, as human NAIP is expressed in the placenta.
Other positively selected genes potentially involved in circumventing unwanted chimerism-associated responses included CD48, encoding a ligand for CD244 (2B4), which is found on the surface of hematopoietic cells and regulates natural killer cells and the levels of interleukins IL-5 and IL-12B, involved in T cell development and in allergic responses32. Finally, in contrast to the extensive family of KIR genes that are integral to immune system function in humans and other catarrhine primates, the marmoset genome contained only two KIR genes, one of which was partial.
All told, it is impossible to tell whether those instances of selection really are connected to chimerism; similar evidence of positive selection occurs for some immune system genes in every species of primate so far subjected to sequencing. Immunity evolves.
The system of genes related to inflammation is most interesting, as anything that may affect placental health would be under stronger constraints in callitrichids than in any other anthropoid. Likewise, the limited number of KIR genes is provocative, but it is not clear whether that is callitrichid-specific, or whether other New World primates may have a similar system.
UPDATE (2014-08-05): Sweeney and collegues (2012) re-examined the issue of chimerism across cell types in a small sample of marmosets and tamarins. They found much higher levels of chimerism in blood cell lineages than in other tissue types, and suggested that the mechanism of the chimerism is infiltration of the other tissues by hematopoietic tissue.
Taken together, the levels of chimerism in tissues of different origins coupled with other lines of evidence suggest that indeed only hematopoietic cell lineages are chimeric in callitrichids. The chimerism detected in other tissues is likely the result of blood or lymphocytic infiltration. Using molecular methods to detect chimerism in a tissue sample seems to have allowed a substantial increase in the ability to detect these minor cell populations.
They discussed earlier results that found chimerism in sperm, and note that this result is hard to reconcile with purely hematopoietic infiltration.
van Dijk, B. A., Boomsma, D. I., & de Man, A. J. (1996). Blood group chimerism in human multiple births is not rare. American journal of medical genetics, 61(3), 264-268.
Ross, C. N., French, J. A., & Ortí, G. (2007). Germ-line chimerism and paternal care in marmosets (Callithrix kuhlii). Proceedings of the National Academy of Sciences, 104(15), 6278-6282. doi:10.1073/pnas.0607426104
The Marmoset Genome Sequencing and Analysis Consortium. (2014). The common marmoset genome provides insight into primate biology and evolution. Nature Genetics. doi:10.1038/ng.3042
Sweeney, C. G., Curran, E., Westmoreland, S. V., Mansfield, K. G., & Vallender, E. J. (2012). Quantitative molecular assessment of chimerism across tissues in marmosets and tamarins. BMC genomics, 13(1), 98 doi:10.1186/1471-2164-13-98
The Renaissance Mathematicus enlisted the historian Melinda Baldwin to write about the early history of the word, "scientist", originally coined by William Whewell: "The history of 'scientist'". It's a great story about how nineteenth-century thinkers perceived themselves.
“Scientist” became so popular in America, in fact, that many British observers began to assume that it had originated there. When Alfred Russel Wallace responded to Carrington’s 1894 survey he described “scientist” as a “very useful American term.” For most British readers, however, the popularity of the word in America was, if anything, evidence that the term was illegitimate and barbarous.
The Brits vastly preferred the term "man of science", which had the dual advantages of referring only to men, and making it sound like some kind of aristocratic pursuit instead of a profession.
A number of papers related to the hominin exploitation of aquatic resources are appearing soon in the Journal of Human Evolution. Two of these in the early online area of the journal.
A research article by Will Archer and colleagues looks at the faunal assemblage at the Koobi Fora FwJj20 locality. At 1.95 million years ago, FwJj20 presents the earliest known evidence of repeated exploitation of fish and turtles by toolmaking hominins. The article begins with an extensive review of the issues related to aquatic resources and some discussion of ethnographic observations of fish consumption in the Turkana area. Unlike some recent papers that emphasized the role of particular fatty acids from fish, Archer and colleagues focus more generally on the value of dietary fat during the dry season:
Ethnographic data suggest that during periods of food shortage, hunter-gatherers intentionally under-utilize foods that are high in protein and low in fat like lean terrestrial meat in favor of foods with higher lipid content (Speth, 1991). Catfish meat in particular is ‘fattier’ in the dry season, a characteristic easily recognizable and sought after by fishermen in the Marsabit district on the eastern shore of Lake Turkana, identified by the butter yellow color of the flesh (Personal communication from indigenous Turkana fishermen).
Mmm...buttery yellow catfish flesh.
One of the most important issues identified by Archer and colleagues is that fish and turtle remains do not present much evidence of human modifications such as cutmarks or percussion marks. A high fraction (upwards of 60%) of terrestrial vertebrate bones may show cutmarks or percussion marks, but only a small fraction of fish bones do, and the pattern of human-induced breaks is largely the same as natural breaks. Archer and colleagues show that the representation of fish remains at FwJj20 is similar to human-accumulated fish assemblages in recent archaeological periods, in that humans exploit relatively few species of fish, and leave more heads than other parts.
The other paper is by José Joordens and colleagues, and I'll be writing about it later this weekend.
Archer, W., Braun, D. R., Harris, J. W., McCoy, J. T., & Richmond, B. G. (2014). Early Pleistocene aquatic resource use in the Turkana Basin. Journal of human evolution doi:10.1016/j.jhevol.2014.02.012
Joordens, JCA, Kuipers RS, Wanink JH, Muskiet FAJ. (2014) A fish is not a fish: Patterns in fatty acid composition of aquatic food may have had implications for hominin evolution. Journal of Human Evolution doi:10.1016/j.jhevol.2014.04.004
In Nautilus David Grinspoon interviews science fiction author Kim Stanley Robinson about his recent work, 2312 and the disconnect between technological optimism and climate pessimism: "An Astrobiologist Asks a Sci-fi Novelist How to Survive the Anthropocene".
Human intelligence is adaptive. It’s given us enormous powers in the physical world thus far. With it, we’ve augmented our senses by way of technologies like microscopes, telescopes, and sensors, such that we have seen things many magnitudes smaller and larger than we could see with unaided senses, as well as things outside of our natural sensory ranges.
But our intelligence has also led to unprecedented problems as our planet reaches its carrying capacity. Is intelligence adaptive enough to adjust to the calamities of its own success? This situation is a completely new thing in history—which means that no one can answer the question now.
I'm interested in the way that authors have taken the concept of "Anthropocene" and are running with it. The idea that we may be terraforming asteroids in various ways in the medium term throws a wrench into the classification of a new geological period that involves only Earth covering the last 100 years or so.
I've had this link on my desktop for a while, a paper by John Ioannidis and colleagues in PLoS ONE: "Estimates of the Continuously Publishing Core in the Scientific Workforce".
Using the entire Scopus database, we estimated that there are 15,153,100 publishing scientists (distinct author identifiers) in the period 1996–2011. However, only 150,608 (<1%) of them have published something in each and every year in this 16-year period (uninterrupted, continuous presence [UCP] in the literature). This small core of scientists with UCP are far more cited than others, and they account for 41.7% of all papers in the same period and 87.1% of all papers with >1000 citations in the same period. Skipping even a single year substantially affected the average citation impact.
I'm not in the 1%, since I didn't start publishing regularly until 2000. Indeed, anyone who began or ended their career in this 15-year-period is likely to be absent (although career-enders might still have papers in the pipeline to keep them on the annual-publishing list).
But this is actually very remarkable, that you can differentiate people by whether they publish at least once a year, every year, and the resulting list of people makes up more than 40% of all papers. It speaks to the multi-authored papers that have become so important in most of the sciences. With multi-author lists in mind, it's less surprising that the same list would include so many of the papers with 1000 citations or more.