Innholdsfortegnelse for EG06 i New Scientist - The Essential Guides

“THERE is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.” There can be no better words to introduce this latest New Scientist Essential Guide than those with which Charles Darwin closed his magisterial work of 1859, On the Origin of Species. The theory of evolution by natural selection introduced by Darwin in that book has few equals in the history of human intellectual achievement. It is an idea in its kernel so simple, yet in its scope so grand and its detail so…

Lamarckism is mentioned in biology textbooks as shorthand for a pre-Darwinian theory of evolution in which species were thought to evolve via the inheritance of characteristics acquired during an organism’s lifetime. According to this, the giraffe got its long neck by intentionally stretching to reach the top of trees. This slightly stretched neck was then passed on to offspring, and so on. But this version of Lamarckism is a terrible caricature. The biologist Jean-Baptiste Lamarck did not originate this idea – which many naturalists, including Darwin, continued to accept–and this was not the core of his theory. Instead, Lamarck’s central idea was that there is a tendency for life to progress up the scale of perfection according to a “complexifying force”. New species originated continuously via spontaneous generation (the appearance…

“THE proprieties of the Association have been outraged.” So wrote civil servant Arthur Munby in his diary on 1 July 1860. And no wonder: the previous day, at the annual meeting of the British Association for the Advancement of Science in Oxford, there had been a most ungentlemanly discussion. An American called John Draper had suddenly become the meeting’s hot ticket. His subject, Darwin’s evolutionary theory, was of wide and topical interest. On the Origin of Species had been published only seven months earlier, and emotions were running high. But Draper wasn’t the attraction: word was that evolution’s fiercest opponents, including the Bishop of Oxford, Samuel Wilberforce, were planning to make a stand. Only the library in the University of Oxford’s new museum could hold the anticipated crowd, and even…

EVOLUTION by natural selection is a two-step process, and only the first step is random: mutations are chance events, but their survival is often anything but. Natural selection favours mutations that provide some advantage, and the physical world imposes very strict limits on what works and what doesn’t. The result is that organisms evolve in particular directions. Consider any kind of creature that lives underwater and has to chase its prey, for instance. Random mutations will result in some offspring having different shapes. Those with shapes that allow them to move faster with less energy are much more like to survive and reproduce than those whose shapes slow them down. The result is that all fast-swimming creatures evolve a streamlined shape, as we see in animals as diverse as squid,…

FOR all the glorious complexity it has produced, evolution often takes away rather than adding. For instance, cave fish lose their eyes, while parasites like tapeworms lose their guts. Such simplification might be much more widespread than realised. Some apparently primitive creatures turn out to be the descendants of more complex creatures. For instance, it appears the ancestor of brainless starfish and sea urchins had a brain. Nevertheless, there is no doubt that evolution has produced more complex life forms over the past 4 billion years. The tough question is: why? It is usually simply assumed to be the result of natural selection, but it seems complexity might actually initially arise when selection is weak or absent. To see why this might be, suppose an animal has a gene that…

MODERN SYNTHESIS The major directing influence in evolution is natural selection. It alone explains why the properties of organisms are adapted to match those of their environments. Genes are the only widespread system of inheritance. Acquired characters – non-genetic traits that develop during an organism’s lifetime – are not inherited and play no role in evolution. Genetic variation is random. Mutations that occur are not necessarily fitness-enhancing. It is mere chance if mutations give rise to features that improve the ability of organisms to survive and thrive. Evolution typically occurs through multiple small steps, leading to gradual change. That’s because it rests on incremental changes brought about by random mutations. The perspective is gene-centred: evolution requires changes in gene frequencies through natural selection, mutation, migration and random losses of gene…

For someone who devised a revolutionary idea, Charles Darwin lived a remarkably quiet life. In 1842, Darwin and his wife Emma moved from London to rural Kent in southern England. They already had two children then, and would go on to have eight more. Darwin had very regular habits. He rose early and went for a walk. After breakfast he worked in his study until 9.30 am, his most productive time of the day, then read his letters lying on the sofa before returning to work. At midday he would go for another walk accompanied by his dog, stopping at his greenhouse to inspect his botanical experiments. Then he would proceed to the sand walk, a gravel path around a strip of woodland. While strolling on this “thinking path”, Darwin…

UNIQUE among scientific disciplines, evolutionary biology finds its roots in a popular book by a single author. The grey-bearded genius presented a new and radical view of existence: that life has changed over time and space, in part through a simple process called natural selection. Charles Darwin called his work “one long argument”. To a 21st-century reader it seems lengthy indeed, with only a single illustration to enliven its 150,000 words. But Darwin was a clear thinker and the book is an impressive piece of advocacy, moving from the familiar – how animals on farms have changed – to the less so, embryos and instinct included. Darwin also shows how what might seem to be problems for his argument, such as the uncanny perfection of complex structures like the eye,…

OUR understanding of evolution today stems from the combination of two very different ideas. One came from a monk who studied pea plants in a Moravian monastery in the 1850s. The other came from a Victorian gentleman who spent five years as a naturalist on a voyage around the world, 20 years previously. Although Gregor Mendel and Charles Darwin were alive at the same time, they never met and Darwin wasn’t aware of Mendel’s work. With hindsight, the union of the two men’s work seems like a marriage made in heaven (or hell, if you’re a creationist). In fact, for many years, it wasn’t obvious that Mendel’s studies of heredity had any relevance to Darwin’s theory of evolution by natural selection. It would take nearly 60 years for this jigsaw…

IT IS a theme repeated endlessly in wildlife documentaries: how perfectly animals are adapted to their environment. It is, however, seldom true. Take the UK’s red squirrel. It appeared perfectly well adapted to its environment – until the grey squirrel arrived, and proved itself rather better adapted to broadleaf forests thanks, in part, to its ability to digest acorns. There are many reasons why evolution does not produce “designs” that are as good as they could be. Natural selection’s only criterion is that something works, not that it works as well as it might. The classic example of an evolutionary botched job is the panda’s thumb, which it uses to grasp bamboo. “The panda’s true thumb is committed to another role. So the panda must… settle for an enlarged wrist…

“IT IS really laughable to see what different ideas are prominent in various naturalists’ minds, when they speak of ‘species’… It all comes, I believe, from trying to define the undefinable.” Strong stuff – and from a surprising source. Charles Darwin wrote those lines in a letter to fellow naturalist Joseph Hooker, just three years before the publication of On the Origin of Species. Darwin clearly had a problem with the word to which his name is now so intimately linked. It turns out he is not alone. Today, some 160 years after he revolutionised biology, how to define a species is more problematic than ever. You probably learned that a species is a group of individuals that can breed to produce fertile offspring, but this is just one of…

EVOLUTION is the most revolutionary concept in the history of science. Nothing else has more radically changed our understanding of the natural world and ourselves. The work of Charles Darwin showed, irrefutably, that humans are just another animal occupying a small branch on a vast tree of life. No divine spark is needed to explain our existence and traits. But how exactly did Darwin devise his theory of evolution? What ideas did he build on? Where does the naturalist Alfred Russel Wallace, who proposed a similar theory, fit in? And how shocking was the idea to the Christian society of the time? The story of the uncovering of this great revelation has been retold countless times since the publication of Darwin’s On the Origin of Species in 1859. In the…

1795 Erasmus Darwin, Charles’s grandfather, foreshadows Darwin when he writes: “Would it be too bold to imagine that all warm-blooded animals have arisen from one living filament… with the power of acquiring new parts” 1798 The doom-mongering An Essay on the Principle of Population by Thomas Malthus warns of the dire consequences of unrestricted population growth. It is a key influence on Charles Darwin 1809 French naturalist Jean-Baptiste Lamarck publishes Philosophie Zoologique, outlining his idea of evolution according to a “complexifying force” 1809 Charles Robert Darwin is born in Shrewsbury, UK, the fifth of six children in a prosperous family 1813 French zoologist Georges Cuvier publishes an Essay on the Theory of the Earth, setting out his idea that new species appear after catastrophes such as floods 1823 Alfred Russel…

Darwin’s ideas about evolution rest on three pillars: variation, inheritance and selection. In the “modern synthesis” of evolution, which combines Darwinian theory with genetics, variation arises in the form of genetic mutations. DNA sequences change at random as the result of external forces, such as radiation, and internal ones, such as damage to DNA or RNA caused by highly reactive molecules called free radicals. Most of these changes are either neutral or detrimental to life, but a few lead to the adaptations on which evolution is built. Mutations may occur in any cell, but only those in germ cells, such as eggs and sperm, are passed down the generations to produce genetically distinct individuals: this is the basis of inheritance. One of Charles Darwin’s greatest insights was the realisation that…

Gregor Mendel had an unlikely background for someone known as the founder of modern genetics, not least because he carried out his work 50 years before genes were actually discovered. Born in 1822 on a farm in what is now the Czech Republic, he joined the Augustinian friary at Brno and here carried out his work on heredity. In the friary garden he bred thousands of pea plants, noting the presence of characteristics such as flower colour and wrinkliness of seeds. He found, for example, that when he crossed white-flowered plants with purple ones, the resulting plants weren’t a light mauve, as might be expected if parental traits blended together, but appeared as either white or purple in fixed ratios. These observations led him to devise the now famous laws…

“THE chances that life just occurred are about as unlikely as a typhoon blowing through a junkyard and constructing a Boeing 747,” astronomer Chandra Wickramasinghe told a court in Arkansas in 1981 that was hearing an objection against a mandate that schools in the state should give equal weight to evolution and creationism. His colleague Fred Hoyle made the tornado version of this claim famous – proving that even very clever people can utterly misunderstand evolution. A somewhat better analogy would be starting with a million junkyards, painstakingly testing the wreckage left in each one after the tornado to find the most flight worthy, making a million exact copies of that junkyard, unleashing another million tornadoes, running another series of exhaustive tests, and so on, until you produce some kind…

BIOLOGICAL SPECIES CONCEPT A species is a population of individuals that can reproduce to generate fertile offspring, and that is reproductively isolated from other populations. GENETIC SPECIES CONCEPT A species is a population of individuals that can reproduce and has a distinct genetic profile. Occasional interbreeding with other populations can occur if it doesn’t compromise the species’ genetic fingerprint. MORPHOLOGICAL SPECIES CONCEPT A species is a group of organisms whose physical features are consistently and persistently distinct from those of other groups. ECOLOGICAL SPECIES CONCEPT A species is a set of organisms adapted to a particular niche, whose distinct behaviours and morphology result from that adaptation. RECOGNITION SPECIES CONCEPT A species is a group of organisms that recognise each other as potential mates. UNIFIED SPECIES CONCEPT All separately evolving branches…

A FEATHER isn’t just pretty: it’s pretty useful. Strong, light and flexible, with tiny barbs to zip each filament to its neighbours, it is fantastically designed for flight. The mammalian eye, too, is a marvel of complex design, with its pupil to regulate the amount of light that enters, a lens to focus it onto the retina, and rods and cones for low light and colour vision – all linked to the brain through the optic nerve. And these are just the tip of the iceberg of evolution’s incredible prowess as a designer. For centuries, the apparent perfection of such designs was taken as self-evident proof of divine creation. Darwin himself expressed amazement that natural selection could produce such variety and complexity. Even today, creationism and intelligent design thrive on…

RICHARD DAWKINS EVOLUTIONARY BIOLOGIST, EMERITUS PROFESSOR AT THE UNIVERSITY OF OXFORD, UK Which facts about evolution had to be true, and which just happen to be true? Did the genetic code have to be digital in order for natural selection to work? Could any other class of molecules have substituted for proteins? How inevitable was the evolution of sex? Eyes? Intelligence? Language? Consciousness? Was the origin of life itself a probable event, and therefore is life common in the universe? FRANS DE WAAL PRIMATE ETHOLOGIST AT EMORY UNIVERSITY, ATLANTA, GEORGIA Why do humans blush? We’re the only primate that does so in response to embarrassing situations (shame), or when caught in a lie (guilt), and one wonders why we needed such an obvious signal to communicate these self-conscious feelings. Blushing…

WHY is life so diverse? And why are living things so exquisitely suited to their environments? To understand these two striking features of the natural world you need look no further than evolution. Darwin’s beautiful idea explains why there are hundreds of thousands of species of beetles and flowering plants, why birds’ feathers are ideal for flight and insulation, and why a desert plant possesses hairy leaves to reduce water loss. Since On the Origin of Species was published in 1859, time has not eroded Darwin’s insights. Yet all scientific theories must incorporate new ideas and findings, and evolution is no exception. In recent years, our understanding of biology has taken huge strides. Advances in genetics, epigenetics and developmental biology challenge us to think anew about the relationship between genes,…