10 things I'd tell Darwin
Guest post by Nick Lane, author of Life Ascending: The Ten Great Inventions of Evolution
When Matt Ridley read Nick Lane’s new book he said “If Charles Darwin sprang from his grave, I would give him this fine book to bring him up to speed.” We asked Nick to write a quick 10-point primer for the father of evolution about our current understanding of the science of life.
"Darwin knew everything and nothing about evolution. Everything, because nobody grasped the priciples of natural selection better than he. Nothing, because almost all of today’s proofs of his theory are written in the languages of genes and molecules that he knew nothing about.
Darwin would be amazed and delighted by the scope and details of our current understanding of life. In Life Ascending: The Ten Great Inventions of Evolution I take life’s most celebrated ‘inventions’, each one of which transfigured our planet, and trace what we know of how they came to be"
Here’s what Nick would tell Darwin:
1. The Origin of Life
Darwin famously speculated about life beginning in some warm pond, but recent research has framed a far grander setting – the hydrothermal vents at the bottom of the ocean. One type of vent bubbles hydrogen gas into the oceans, giving rise to a myriad of honeycomb cells with delicate mineral walls. These natural cells replicate spontaneously under the pressure of the vents. What’s more, they concentrate organic molecules, including DNA, up to amazingly high levels, and generate energy across a membrane just as living cells do today. There’s lots to learn, but as a setting for the origin of life, it brooks no equal.2. DNA
In 1953, Francis Crick and James Watson walked into The Eagle in Cambridge and declared they knew the secret of life – the structure of DNA. It immediately provided the mechanism of heredity so sorely missed by Darwin. But Watson and Crick didn’t know how DNA coded for proteins. The story of the code within the DNA code is one of the best (and least known) scientific detective stories of the 20th century – and it also points to life’s origins in deep sea vents. Most unexpectedly, the detailed mechanism by which DNA is replicated implies that life actually emerged from the vents twice from a common ancestor that lived inside.
3. Photosynthesis
Without photosynthesis, life wouldn’t be up to much. It provides us not only with all the food we need to live, but also with the oxygen needed to burn it up to provide our energy. And yet true photosynthesis arose only once in the whole history of evolution – in bacteria that were later captured by algae and plants and put to work. The trick depends on an enzyme that splits water to extract hydrogen, releasing oxygen as waste. The core of the water-splitting enzyme is similar to a mineral in its structure. Knowing how it works at the atomic level could help to solve the energy and climate crises of our planet.
4. The Complex Cell
Complex life, like photosynthesis, arose only once on earth. The differences between plants, animals, fungi and algae suggest that plants arose from one type of bacteria and animals from another, but that’s not what happened. Compared to bacteria, our cells are virtually identical to those of a daffodil: we are in fact closely related. Complex cells arose in an unprecedented merger between bacteria. That vital step was not anticipated by Darwin, who saw organisms as diverging rather than converging. Yet without that improbable chimera, natural selection may never have got beyond bacteria, and none of us would be here.5. Sex
Sex is absurd. Not only does it cost a small fortune to find a partner, but it transmits horrible venereal diseases and parasitic genes, and randomises all successful combinations of genes. Worse, sex requires males, viewed by implacable feminists and evolutionists alike as a waste of space. So why we all have sex anyway was viewed as the queen of evolutionary problems in the 20th century. An old explanation for the benefits of sexual recombination has risen in a new guise, and helps explain not only why we have so much sex, but also why it got going in the first place in simple cells.
6. Movement
Muscle is the invention that sets us animals apart. Yet the two molecules that make muscles work, the chain-like proteins actin and myosin, are found in all organisms, even those without any muscle. Nothing would have given Darwin more pleasure than the finding that the same molecules that power muscular contraction evolved from simpler forms that propel amoebae around, support plant cells, and help bacteria to divide. Or that they they work by forming a dynamic scaffold in cells in the same way that a variant form of haemoglobin does when it distorts red blood cells in sickle-cell anaemia. Selection fashioned such spontaneous quirks into the might of muscle.
7. Sight
Darwin himself pondered the evolution of ‘organs of extreme perfection’ such as the eye, and it’s been an icon ever since. What use is half an eye, say detractors, yet the eyeless rift shrimp reabsorbs its fully formed larval eyes and replaces them with a naked retina – literally half an eye – as it moves down to the black-smoker vents. We now know how eyes evolved in more detail than any other organ. Surprisingly, it looks as if the critical light-sensitive protein at the centre of it all, rhodopsin, evolved from an ancestor in algae where it is used to calibrate light levels in photosynthesis. Some bacteria even use rhodopsin for a type of photosynthesis.8. Hot Blood
Hot blooded animals keep their thermostat jammed on hard at 37°C, regardless of need. Many small mammals need to eat as much in a day as a lizard eats in a month, and a serious penalty is smaller populations. One big benefit is stamina, yet dinosaurs like Velociraptor apparently combined stamina with a low resting metabolism. But hot blood may also solve an interesting problem with diets rich in carbon and low in nitrogen, such as leaves. Vegetarians get enough nitrogen from leaves only if they eat a lot and get rid of the excess carbon. We hot bloods just burn it off, and that enables herbivores to survive on a much lower quality diet.9. Consciousness
There’s no doubt that consciousness evolved, and that many animals are aware of themselves and their surroundings, perhaps right down to bees. But still there are deep uncertainties about what consciousness actually is. We simply don’t know yet how neurons firing in the brain can generate a feeling of anything. This is what philosophers call the hard problem, and it may be solved by studying the behaviour of animals like bees that apparantly gain neural rewards for finding nectar. I’d tell Darwin that consciousness is the last great challenge for understanding natural selection.
10. Death
But death is no challenge. Without death, natural selection would count for nothing, and life could never have evolved the majesty of consciousness at all. Yet death benefits individuals, or rather their genes, in some way. Mitochondria, the power-houses inside our cells, hold the key. They generate reactive free radicals that ultimately undermine our health. The problem is that in the short term, free radicals optimise respiration, making us as strong and energetic as we can be when young. Antioxidants disrupt that. So sadly the penalty for vigour in youth is decreptitude in old age. But there’s hope. Birds leak fewer free radicals and live longer than mammals, without losing their vigour. And that means the anti-ageing pill is not a myth.
Thursday, May 28, 2009
Nick Lane - 10 things I'd tell Darwin
Very cool to see how much we know now that we didn't when Darwin was alive - and how close he was to the truth anyway.
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