- O segredo da vida não será elaborado nos laboratórios
- A transferência horizontal se dá também nos eucariotos
- As extinções e o impacto do Homo sapiens
- Darwin errou feio sobre a seleção sexual como mecanismo evolucionário!!!
Posted: 14 Jan 2013 06:57 AM PST
The secret of life won't be cooked up in a chemistry lab
Life's origins may only be explained through a study of its unique management of information
The Guardian, Sunday 13 January 2013 19.07 GMT
Even the simplest bacterium is incomparably more complicated than any chemical brew ever studied. Photograph: Mads Nissen/ Panos Pictures
The origin of life is one of the great outstanding mysteries of science. How did a non-living mixture of molecules transform themselves into a living organism? What sort of mechanism might be responsible?
A century and a half ago, Charles Darwin produced a convincing explanation for how life on Earth evolved from simple microbes to the complexity of the biosphere today, but he pointedly left out how life got started in the first place. "One might as well speculate about the origin of matter," he quipped. But that did not stop generations of scientists from investigating the puzzle.
The problem is, whatever took place happened billions of years ago, and all traces long ago vanished – indeed, we may never have a blow-by-blow account of the process. Nevertheless we may still be able to answer the simpler question of whether life's origin was a freak series of events that happened only once, or an almost inevitable outcome of intrinsically life-friendly laws. On that answer hinges the question of whether we are alone in the universe, or whether our galaxy and others are teeming with life.
Most research into life's murky origin has been carried out by chemists. They've tried a variety of approaches in their attempts to recreate the first steps on the road to life, but little progress has been made. Perhaps that is no surprise, given life's stupendous complexity. Even the simplest bacterium is incomparably more complicated than any chemical brew ever studied.
But a more fundamental obstacle stands in the way of attempts to cook up life in the chemistry lab. The language of chemistry simply does not mesh with that of biology. Chemistry is about substances and how they react, whereas biology appeals to concepts such as information and organisation. Informational narratives permeate biology. DNA is described as a genetic "database", containing "instructions" on how to build an organism. The genetic "code" has to be "transcribed" and "translated" before it can act. And so on. If we cast the problem of life's origin in computer jargon, attempts at chemical synthesis focus exclusively on the hardware – the chemical substrate of life – but ignore the software – the informational aspect. To explain how life began we need to understand how its unique management of information came about.
In the 1940s, the mathematician John von Neumann compared life to a mechanical constructor, and set out the logical structure required for a self-reproducing automaton to replicate both its hardware and software. But Von Neumann's analysis remained a theoretical curiosity. Now a new perspective has emerged from the work of engineers, mathematicians and computer scientists, studying the way in which information flows through complex systems such as communication networks with feedback loops, logic modules and control processes. What is clear from their work is that the dynamics of information flow displays generic features that are independent of the specific hardware supporting the information.
Information theory has been extensively applied to biological systems at many levels from genomes to ecosystems, but rarely to the problem of how life actually began. Doing so opens up an entirely new perspective on the problem. Rather than the answer being buried in some baffling chemical transformation, the key to life's origin lies instead with a transformation in the organisation of information flow.
Sara Walker, a Nasa astrobiologist working at Arizona State University, and I have proposed that the significant property of biological information is not its complexity, great though that may be, but the way it is organised hierarchically. In all physical systems there is a flow of information from the bottom upwards, in the sense that the components of a system serve to determine how the system as a whole behaves. Thus if a meteorologist wants to predict the weather, he may start with local information, such as temperature and air pressure, taken at various locations, and calculate how the weather system as a whole will move and change. In living organisms, this pattern of bottom-up information flow mingles with the inverse – top-down information flow – so that what happens at the local level can depend on the global environment, as well as vice versa.
Read more here/Leia mais aqui: The Guardian
Posted: 14 Jan 2013 04:23 AM PST
Widespread horizontal transfer of retrotransposons
Ali Morton Walsha, R. Daniel Kortschaka, Michael G. Gardnerb,c, Terry Bertozzia,c, and David L. Adelsona,1
aSchool of Molecular and Biomedical Science, University of Adelaide, Adelaide, SA 5005, Australia;
bSchool of Biological Sciences, Flinders University, Adelaide, SA 5005, Australia; and
cEvolutionary Biology Unit, South Australian Museum, Adelaide, SA 5000, Australia
Edited by W. Ford Doolittle, Dalhousie University, Halifax, NS, Canada, and approved December 5, 2012 (received for review April 6, 2012)
In higher organisms such as vertebrates, it is generally believed that lateral transfer of genetic information does not readily occur, with the exception of retroviral infection. However, horizontal transfer (HT) of protein coding repetitive elements is the simplest way to explain the patchy distribution of BovB, a long interspersed element (LINE) about 3.2 kb long, that has been found in ruminants, marsupials, squamates, monotremes, and African mammals. BovB sequences are a major component of some of these genomes. Here we show that HT of BovB is significantly more widespread than believed, and we demonstrate the existence of two plausible arthropod vectors, specifically reptile ticks. A phylogenetic tree built from BovB sequences from species in all of these groups does not conform to expected evolutionary relationships of the species, and our analysis indicates that at least nine HT events are required to explain the observed topology. Our results provide compelling evidence for HT of genetic material that has transformed vertebrate genomes.
transposon interspersed repeat
1To whom correspondence should be addressed. E-mail: firstname.lastname@example.org.
Author contributions: A.M.W. and D.L.A. designed research; A.M.W. and T.B. performed research; A.M.W., R.D.K., M.G.G., and T.B. contributed new reagents/analytic tools; A.M.W., R.D.K., T.B., and D.L.A. analyzed data; and A.M.W., R.D.K., M.G.G., T.B., and D.L.A. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Data deposition: The survey sequence data have been deposited in the Dryad database, http://datadryad.org [doi nos.: 10.5061/dryad.f1cb2/23 (Amphibolurus norrisi), 10.5061/dryad.f1cb2/46 (Eremiascincus richardsonii), 10.5061/dryad.f1cb2/47 (Glaphyromorphus douglasi), 10.5061/dryad.f1cb2/26 (Gehyra variegate), 10.5061/dryad.f1cb2/27 (Gehyra lazelli), 10.5061/dryad.f1cb2/6 (Bothriocroton hydrosauri), 10.5061/dryad.f1cb2/28 (Hydrophis spiralis), 10.5061/dryad.f1cb2/15 (Isoodon obesulus), 10.5061/dryad.f1cb2/16 (Macrotis lagotis), and 10.5061/dryad.f1cb2/19 (Petaurus breviceps)]; and European Bioinformatics Institute Sequence Read Archive (EBI SRA), http://www.ebi.ac.uk/ena/ (accession nos. ERS195148 [Tiliqua rugosa (Sleepy Lizard) paired end reads], ERS195147 [Egernia stokesii (Skink) paired end reads], and ERS154930 [Tachyglossus aculeatus (Echidna) paired end reads], validation sequences deposited in GenBank with accession nos. KC352670, KC352671, KC352672, KC352673, and KC352674).
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1205856110/-/DCSupplemental.
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Posted: 14 Jan 2013 03:24 AM PST
Q&A: Extinctions and the impact of Homo sapiens
Robert M May
Correspondence: Robert M May email@example.com
Department of Zoology, University of Oxford, The Tinbergen Building, South Parks Road, Oxford OX1 3PS, UK
BMC Biology 2012, 10:106 doi:10.1186/1741-7007-10-106
Received: 13 December 2012
Accepted: 19 December 2012
Published: 20 December 2012
© 2012 May; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Extinctions have happened ever since life began - is there anything different about man-made extinctions?
Looked at in the large, the history of life on Earth is one of continuous change, driven by the interplay between evolutionary processes and the altered environments that can result. Some of these environmental events have had external causes (for example, the asteroidal impact that caused the most recent of the so-called Big Five mass extinctions, which eliminated the dinosaurs), while others have arisen from changing interactions among species (for example, the early appearance of oxygen in the atmosphere, resulting essentially from biogeochemical processes in primitive ecosystems). Are the recent past and impending future extinctions, unambiguously caused by humans, different? Yes and no. No, in the sense that the explosive growth of the animal species Homo sapiens can be seen as just another evolutionary process with increasingly serious ecological consequences for other species. Yes, in the sense that - unlike earlier extinctions - the causative agent (that's us) is aware of what is happening and could act to reverse current trends. Unfortunately, we show few signs of doing so.
What are the major causes of extinctions (man-made or otherwise)?
The causes of recent, human-associated extinctions are usually listed under three headings: over-exploitation, habitat destruction, introduced aliens. But you could, with a bit of a stretch, brigade many past extinctions under one or more of these headings. The above-mentioned demise of the dinosaurs, or the massive wave of marine extinctions which mark the end of the Mesozoic, could be called 'habitat change'. The opening and closing of land bridges, as tectonic plates moved around over the past billion years and more, introduced 'invasive aliens', which restructured many ecosystems. More generally, over geological time-scales, natural evolutionary processes created changes within plant and animal populations, with new winners and new losers. In that sense, humans look like being the main agents of the Big Sixth wave of extinctions, on whose breaking tip we currently stand.
How are the man-made versions distinct?
The very big difference between past extinctions and the current human-associated ones is we understand what is happening. And we can, in principle, choose to modify our behavior to preserve the awe-inspiring diversity of plant and animal life we have inherited. Even were we to do this - and we show few signs of it - there would still, over relatively long time-scales, be changes. They would, however, be more likely to be the pseudo-extinctions technically referred to as 'relay and replacement', as in the series of differently named species along the continuum as Eohippus evolved into today's horse.
How much do we know about the rate of extinction before humans started interfering?
As in so many areas of science, we know quite a lot, and continue to learn more. One measure of our knowledge is indicated in Table 1, by Raup, which gives the estimated average lifetime, from origination to extinction, of a variety of animal groups. Figure 1 complements this by showing numbers of families (remember the taxonomic hierarchy: species, genus, family,...) of marine animals over the sweep of geological time. The figure testifies to increasing diversity and species richness, interrupted by episodes of mass extinction. Overall, these data suggest average life-spans of animal species in the fossil record to be around 1 to 10 million years, with significant variation within and among taxonomic groups, and with the higher end of the range being more common.
Posted: 14 Jan 2013 03:00 AM PST
Darwin Was Wrong About Dating
By DAN SLATER
Published: January 12, 2013
A COUPLE of evolutionary psychologists recently published a book about human sexual behavior in prehistory called “Sex at Dawn.” Upon hearing of the project, one colleague, dubious that a modern scholar could hope to know anything about that period, asked them, “So what do you do, close your eyes and dream?”
Actually, it’s a little more involved. Evolutionary psychologists who study mating behavior often begin with a hypothesis about how modern humans mate: say, that men think about sex more than women do. Then they gather evidence — from studies, statistics and surveys — to support that assumption. Finally, and here’s where the leap occurs, they construct an evolutionary theory to explain why men think about sex more than women, where that gender difference came from, what adaptive purpose it served in antiquity, and why we’re stuck with the consequences today.
Lately, however, a new cohort of scientists have been challenging the very existence of the gender differences in sexual behavior that Darwinians have spent the past 40 years trying to explain and justify on evolutionary grounds.
Of course, no fossilized record can really tell us how people behaved or thought back then, much less why they behaved or thought as they did. Nonetheless, something funny happens when social scientists claim that a behavior is rooted in our evolutionary past. Assumptions about that behavior take on the immutability of a physical trait — they come to seem as biologically rooted as opposable thumbs or ejaculation.
Using evolutionary psychology to back up these assumptions about men and women is nothing new. In “The Descent of Man, and Selection in Relation to Sex,” Charles Darwin gathered evidence for the notion that, through competition for mates and sustenance, natural selection had encouraged man’s “more inventive genius” while nurturing woman’s “greater tenderness.” In this way, he suggested that the gender differences he saw around him — men sought power and made money; women stayed at home — weren’t simply the way things were in Victorian England. They were the way things had always been.
A century later, a new batch of scientists began applying Darwinian doctrine to the conduct of mating, and specifically to three assumptions that endure to this day: men are less selective about whom they’ll sleep with; men like casual sex more than women; and men have more sexual partners over a lifetime.
In 1972, Robert L. Trivers, a graduate student at Harvard, addressed that first assumption in one of evolutionary psychology’s landmark studies, “Parental Investment and Sexual Selection.” He argued that women are more selective about whom they mate with because they’re biologically obliged to invest more in offspring. Given the relative paucity of ova and plenitude of sperm, as well as the unequal feeding duties that fall to women, men invest less in children. Therefore, men should be expected to be less discriminating and more aggressive in competing for females.
It was an elegant, powerful application of evolutionary theory to the mating game. The evolutionary psychologists of the 1980s and ’90s built on Mr. Trivers’s theory to explain a wide array of stereotypical gender differences in mating.
In 1993, David M. Buss and David P. Schmitt used parental investment theory to explain why men should be expected to “devote a larger proportion of their total mating effort to short-term mating.” Because men invested less time and effort in their offspring, they evolved toward promiscuity, while women evolved away from it. Promiscuity, the researchers hypothesized, would have been more damaging to the female reputation than to the male reputation. If a man mated with a promiscuous woman, he would never be able to ensure his paternity. Men, on the other hand, could potentially enhance their status by pursuing a short-term mating strategy. (Think Kennedy, Clinton, Spitzer, Letterman and so forth. My space is limited.)
One of the earliest critics of this kind of thinking was Stephen Jay Gould. He wrote in 1997 that parental investment theory “will not explain the full panoply of supposed sexual differences so dear to pop psychology.” Mr. Gould felt that the field had become overrun with “ultra-Darwinians,” and that evolutionary psychology would be a more fruitful science if it didn’t limit itself “to the blinkered view” that evolutionary explanations accounted for every difference.
BUT if evolution didn’t determine human behavior, what did? The most common explanation is the effect of cultural norms. That, for instance, society tends to view promiscuous men as normal and promiscuous women as troubled outliers, or that our “social script” requires men to approach women while the pickier women do the selecting. Over the past decade, sociocultural explanations have gained steam.
Take the question of promiscuity. Everyone has always assumed — and early research had shown — that women desired fewer sexual partners over a lifetime than men. But in 2003, two behavioral psychologists, Michele G. Alexander and Terri D. Fisher, published the results of a study that used a “bogus pipeline” — a fake lie detector. When asked about actual sexual partners, rather than just theoretical desires, the participants who were not attached to the fake lie detector displayed typical gender differences. Men reported having had more sexual partners than women. But when participants believed that lies about their sexual history would be revealed by the fake lie detector, gender differences in reported sexual partners vanished. In fact, women reported slightly more sexual partners (a mean of 4.4) than did men (a mean of 4.0).
In 2009, another long-assumed gender difference in mating — that women are choosier than men — also came under siege. In speed dating, as in life, the social norm instructs women to sit in one place, waiting to be approached, while the men rotate tables. But in one study of speed-dating behavior, the evolutionary psychologists Eli J. Finkel and Paul W. Eastwick switched the “rotator” role. The men remained seated and the women rotated. By manipulating this component of the gender script, the researchers discovered that women became less selective — they behaved more like stereotypical men — while men were more selective and behaved more like stereotypical women. The mere act of physically approaching a potential romantic partner, they argued, engendered more favorable assessments of that person.
Read more here/Leia mais aqui: The New York Times
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