Zoals te verwachten was kwam Scientific Ammerican in zijn nummer van Januari 2009 uitgebreid voor met een reeks bijdragen over evolutie, in het kader van het "Darwinjaar 2009".Het loont wel de moeite markante uitreksels van deze bijdragen in het kader van deze blog te vermelden Het is echter wenselijk dit te beginnen met een uittreksel van de inleiding "Dynamic Darwinism" geschreven, door John Rennie (Editor in chief van Scientific American).
-"A billion and half years ago,life on earth was staggeringly dull (ontstellend saai)......Then something happened : some unidentified combination of environmental circumstances and genetic novelty triggered crazy diversification in the variety and complexity of animal life over tens of millions years,climaxing in the so-called "Cambrian explosion"...... When Charles Darwin published "On the origin of species" in 1859,he touched off a cambrian explosion in evolutionary thought.Naturalists had theorized about evolution for centuries before him,but their ideas were generally unfruitful,untestable or wrong.Darwin's breakthrough insight was not that a simple mechanism-natural selection-made evolution possible.Rather it was that in organisms whose environment changed nonrandomly and whose reproductive success in that environment depended on inherited traits,evolution became inevitable.In the decades that followed,Darwin's ideas connected up with the nascent field of genetics and then,at an ever quickening pace,with molecular biology,ecology and embryology.The explanatory power of its concepts proved irresistible.Today,200 years after its birth and 150 years after Origin of species,Darwin's legacy is a larger,richer,more diverse set of theories that he could have imagined........ Just as most of the weird Cambrian monsters eventually went extinct,many current hypotheses in evolution will also wither over time.Those that survive ,however,will be inestimably powerful for explaining the natural world.We humans can also continue to use those ideas to make technologies more adaptable and robust.Why shouldn't we learn from billions of years of nature's experiments?"
Uit de reeks bijdragen werden er drie geselecteerd die een bijzonder blik werpen op de evolutie theorie.Diverse citaten werden dan bijeen gebracht.
1-TESTING NATURAL SELECTION. ,H.Allen Orr. p.44
-"The idea of 'Natural selection'' is simplicity itself.Some kinds of organisms survive better in certain conditions than others do;such organisms leave more progeny and so become more common with time.The environment thus 'selects' those organisms best adapted to present conditions. If environmental conditions change,organisms that happen to possess the most adaptive characteristics for those new conditions will come to predominate.Darwinism was revolutionary not because it made arcane (mysterious) claims about biology but because it suggested that nature's underlying logic might be surprisingly simple."
-"The status of natural selection is now secure ,reflecting decades of detailed empirical work.But the study of natural selection is by no means complete.Rather-partly because new experimental techniques have been developed and partly because the genetic mechanisms underlying natural selection are now the subject of meticulous empirical analysis- the study of natural selection is a more active area of biology than it was even two decades ago.Much of the recent experimental work on natural selection has focused on three goals : determining how common it is,identifying the precise genetic changes that give rise to the adaptations produced by natural selection,and assessing just how big a role natural role plays in a key problem of evolutionary biology-the origin of 'new species'."
-"Fitness,as used in evolutionary biology, is a technical term for this idea : it is the probability of surviving or reproducing in a given environment.The outcome of this selection process,repeated numberless times in different contexts,is what we all see in nature."
-"Most important ,we know something about the effects of mutations on fitness.The overwhelming majority of random mutations are harmful-that is,they reduce fitness;only a tiny minority are beneficial,increasing fitness."
-"Adaptive evolution is a two-step process,with a strict division of labor between mutation and selection.In each generation mutation brings new genetic variation into populations.Natural selection then screens them : the rigors of the environment reduce the frequency of "bad" (relatively unfit)variants and increase the frequency of "good" (relatively fit) ones;"
-"There are serious doubts about the extent of the role natural selection in guiding change at the molecular level."
ON THE ORIGIN OF SPECIES.
-"One of Darwin's boldest (strongest) claims was that it explains how new species arise.But does it ? What role does natural selection play in speciation,the splitting of a single lineage into two ? To this day,these questions represent an important topic of research in evolutionary biology."
-"Most biologists now agree that natural selection is the key evolutionary force that drives not only evolutionary change WITHIN SPECIES but also the ORIGIN OF NEW SPECIES."
PS.What evolutionists mean by "species" (biological species concept).
-"The key idea is that species are reproductively isolated from one another-that is,they have genetically based traits preventing them from exchanging genes."
-"Different species have separate gene pools."
-"It is thought that the populations must be geographically isolated before reproductive isolation can evolve."
-"The genetic drift hypothesis for speciation (about the origin of species) is probably wrong.Rather natural selection plays a major role in speciation."
2-FROM ATOMS TO TRAITS. D.M.KINGSLEY p.52.
Oorspronkelijk Darwinism - 1859 -(Spontaneous variation and natural selection.)
-"Darwin's theory was at once sweeping and simple.He proposed that all living things on earth descended from one or a few original forms.He did not presume to know how life itself arose.Once life began,though,Darwin argued,organisms would slowly begin to change and diversify through completely natural process : all living things vary;the differences are inherited.Those individuals with trait variants that are favorable in the environment they habit will thrive and produce more offspring than individuals with unfavorable variants.Advantageous traits will therefore accumulate over time by an inevitable process of 'natural selection'."
De opinie van John Herschel.
-"Herschel zeroed (focused) in on the fact that 'favorable variations' must occur if anything is to be "effected".Darwin actually knew nothing about the origin of the variant traits (mutations !) themselves,and Herschel felt that if Darwin could not explain the source of variation,he did not really have a theory sufficient to explain the origin of species."
N.B. Among the "random variations" there are possibly "favorable variations" so that "natural selection" could occur.
Erfelijkheid van variaties.
-"Darwin believed in blending inheritance, the idea that offspring take on characteristics intermediate between the parents.But even Darwin recognized that the theory was problematic."
-"Mendel's experiments changed the general perception of heritable variants from ephemeral and blendable to discrete entities passed from parents to offspring,present even though they are not always visible."
-"J.Watson and F.Crick had proposed a structure for the DNA molecule in 1953,with stunning implications for our physical understanding of heredity and variation."
Moleculaire basis van variatie.
-"Today scientists know that spontaneous changes in DNA are the simple "WHY" of variation,but to answer to "HOW" those mutations translate into traits differences is more complex and makes for an active field of research with implications far beyond evolution studies."
-"A subspeciality that has come to be known as EVO-DEVO concentrates on studying the effects of changes in important developmental genes and the role they play in evolution."
-"Herschel's most persistent objection to Darwin's theory was his feeling that useful new traits could never appear from simple random variation (??)... He argued that such characteristics would always require "mind,plan,design,to the plain and obvious exclusion of the haphazard (disorganized) view of the subject and the casual (accidental) concourse of atoms.Herschel was correct to point out that the origin of variation was still a mistery in 1859.After 150 years of additional research,however,we can now catalogue a variety of spontaneous DNA sequence variants that occur everytime a complex genome is passed from parents to offspring.Only a tiny fraction of these changes are likely to improve,rather than degrade the original heredity information and the traits that are derived from it....Thus the casual concourse of atoms clearly can generate interesting new traits and the intrinsic variability of living organisms continue to provide the raw material by which,in Darwin's famous words at the end of the "Origin of species",endless forms most beautiful and most wonderful,have been and are being evolved."
'Zo wordt Darwin toch in ere hersteld !!!)
3-EVOLUTION IN THE EVERYDAY WORLD. D.P.Mindell p.82
Implicaties van de evolutietheorie in het dagelijks leven.
-"Our progress in comprehending the history and mechanisms of evolution has led to powerful applications that shape a wide variety of fields today."
Gezondheidsgebied.
-" In health care,phylogenic analysis ( studies of DNA sequences to infer the evolutionary relatedness or genealogy)of a pathogen such as bird flu op West Nile virus can lead to vaccines and to guidelines for minimizing the disease's transmission to and among people.A laboratory process called " directed evolution" that rapidly evolves proteins can imrove vaccines and other useful proteins."
Bacteriële diversiteit (metagenomics).
-"A recently developed approach known as 'metagenomics' has revolutionized scientist's ability to survey the kinds of microbes living in a region,bringing about the most dramatic change in our understanding of microbial diversity since the advance of microscopes."
Vogelgriep H5N1
-"In 1997 scientists barely contained a potentially catastrophic outbreak in Hong-Kong of H5N1,when they convinced authorities to slaughter all domestic fowl (domesticated birds),the local virus source. Although future pandemics are a question of "WHEN",not "IF",our knowledge about evolutionary sources,hybridization among genomes and the host-shifting capability of the viruses helps us to minimize risks."
Evolutie en geneeskunde.
-"Applying an evolutionary perspective in understanding our susceptibilities and promoting health is known as evolutionary or Darwinian medicine.A vital step in this new endeavor is integration of basic evolutionary science into the curricula for medical and public health students.The matching of human genotypes with particular diseases has given rise to the possibility of personalized medicine, in which physicians can specify medications and dosages for individuals based on particular gene traits."
In vivo and in silico.
-"Researchers are now borrowing from evolution's drawing board,using directed evolution to enhance useful functions of proteins.These molecular biologists intentionally mutate genes,produce the proteins the genes encode,measure the proteins functional performance,and the select sets of top performers for subsequent bouts (intensive activity) of mutation and testing.Repeating this cycle millions of times often yield impressive results."
(PS-De biotechnologie is, in die zin,de logische hedendaagse opvolger van de evolutie !)
Kritische ecosystemen en bevolkingsaangroei.
-"As humankind's numbers continue to grow and cause environmental changes at a rapid pace,concerns mount about conserving biological diversity and sustaining human populations over time.We rely on healthy ecosystems,made of organisms and their environments, to provide us with usable water,arable land and clean air.These critical ecosystem services are essential for human well-being, yet we have little understanding of their regulation and the consequences of changes in ecosystems.....These are different questions that evolutionary method and knowledge help to answer."
Metagenomics.
-"Collect the DNA from an entire community of microbes of various species in some location and you have a metagenome.....The known microbes and their genes play important roles in development of our immune systems.... Metagenomics analyses suggest that changes in the occurrence,abundance and interactions of both known and unknown microbes play a role in human diseases."
-"Turning to external ecosystems and sustainability,metagenomic analyses of water samples from seas and oceans indicate that a vast amount of oceanic biological diversity,including many viruses,remains to be discovered and understood."
-"We have yet to see applications arising from microbial metagenomics and evolutionary ecology,but possibilities abound."
-"Evolution is the unifying principle for comprehending all life on earth,and applying its lessons about the history and mechanisms of change can promote human well-being.What was once a curiosity is now a powerful tool."
PS-Deze paragrafen zullen verder uitgewerkt worden met berichten over:"Evolutionary developmental biology"-"Epigenetics" and "Biotechnology".Dit zal nodig zijn om een beter begrip van hedendaags Darwinisme.!
