Biology: quotes, facts and reflections

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WonderScience

Dolly the sheep, born in Scotland in 1996, was the first mammal cloned from a cell taken from an adult animal.

Dolly was born on 5 July 1996 at the Roslin Institute near Edinburgh. A team led by Ian Wilmut and Keith Campbell used a method called somatic cell nuclear transfer: the nucleus, which holds the genetic material, of a mammary gland cell from a six-year-old ewe was placed into an egg cell whose own nucleus had been removed. Until then many scientists believed a specialised adult cell could not be turned back to build a whole new animal. The team named her after the singer Dolly Parton. Dolly had six lambs of her own. She was put down in February 2003, aged six, after developing a lung tumour caused by a virus common in sheep; she also had arthritis. Her preserved body is on display at the National Museum of Scotland.

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WonderScience

The axolotl, a salamander from the lakes of Mexico City, can regrow a lost leg complete with bone, muscle and nerves, and can repair parts of its spinal cord and heart.

Most salamanders start life in water with feathery gills and later change into land-living adults. The axolotl never makes that change: it grows up, and even breeds, while keeping its gills and staying in the water, a trait biologists call neoteny. After an injury, skin quickly seals the wound and the cells beneath it form a blastema, a bud of cells able to rebuild the missing part. A new limb grows over weeks to months, usually without a scar. In the wild, axolotls now survive mainly in the canals of Xochimilco, the remains of old lakes in Mexico City; pollution, drainage and introduced carp and tilapia have made them critically endangered. Laboratories and aquarium keepers around the world hold large captive populations, which is why scientists can study them so closely.

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WonderEvolution

Archaeopteryx, an animal about the size of a magpie that lived around 150 million years ago in what is now Germany, had feathered wings like a bird but also teeth, clawed fingers and a long bony tail like a small dinosaur. It was one of the first clues that birds are related to dinosaurs.

In 1861 the German palaeontologist Hermann von Meyer described a single fossil feather from the Solnhofen limestone of Bavaria, and the same year a nearly complete skeleton turned up nearby. The limestone was so fine-grained that it was quarried for printing plates, and it preserved even the outlines of feathers. The skeleton was bought by the British Museum and described by Richard Owen in 1863, four years after Darwin's On the Origin of Species. About a dozen specimens are now known, including the fine Berlin specimen found in the 1870s. Archaeopteryx is still usually placed at or near the base of the bird family tree, probably on a side branch rather than as the direct ancestor of modern birds.

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WonderEvolution

Darwin's finches, more than a dozen bird species of the Galápagos Islands, all descend from a single ancestor. Their beaks range from thick nutcrackers for hard seeds to fine tweezers for insects, each suited to the food on its island.

Darwin collected some of these birds in 1835 during the voyage of HMS Beagle but did not realise at the time how closely related they were; the ornithologist John Gould pointed it out after the voyage. Today they are a textbook case of adaptive radiation, in which one ancestral species splits into many, each suited to a different way of life. Despite the name, they are not true finches but belong to the tanager family. Since 1973 Peter and Rosemary Grant have studied them on the small island of Daphne Major. After a severe drought in 1977 left mostly large, hard seeds, birds with bigger beaks survived better, and the next generation's beaks were measurably larger: evolution seen within a few years.

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WonderTrade

The Columbian Exchange is the vast transfer of plants, animals, diseases and people between the Americas and the rest of the world that followed Columbus's voyage of 1492. Potatoes, maize and tomatoes crossed the Atlantic eastwards; horses, wheat, smallpox and millions of enslaved Africans were carried west.

The historian Alfred W. Crosby gave the process its name in his 1972 book The Columbian Exchange. American crops changed diets across the Old World: potatoes helped Europe's population grow, maize became a staple in much of Africa, and chilli peppers reached India and Korea. In the other direction, horses transformed life on the North American plains, and cattle, sugar cane and wheat remade American landscapes. The heaviest cost fell on Indigenous Americans. Smallpox, measles and other diseases they had never met killed a large share of the population within decades, and the plantation economy that followed drove the forced transport of millions of enslaved Africans.

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WonderFood

Fermentation is the work of yeasts and bacteria that feed on the sugars in food and turn them into acids, alcohol or gas. It gives us bread, yoghurt, cheese, wine and pickles, and it kept food safe to eat for thousands of years before refrigerators.

People fermented food long before they knew why it worked: residues in pottery jars from Jiahu in China show that a fermented drink of rice, honey and fruit was made there about 9,000 years ago. For centuries fermentation was thought to be a purely chemical process. In the 1850s the French chemist Louis Pasteur showed that it is the work of living microorganisms, and that different microbes produce different results, some pleasant and some that spoil food. That insight led to pasteurisation, gentle heating to kill unwanted microbes, first used on wine in the 1860s and later on milk.

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WonderFood

A sourdough starter is flour and water in which wild yeasts and lactic acid bacteria live together. The yeasts make the gas that raises the bread; the bacteria make the acids that give it its sour taste and help it keep longer.

Until commercial baker's yeast became common in the 19th century, much leavened bread was made this way, by keeping back a piece of each day's dough to start the next batch. In 1971 the US Department of Agriculture researchers Kline and Sugihara isolated the bacterium behind the famous sour taste of San Francisco bread, later named Fructilactobacillus sanfranciscensis; it has since been found in starters all over the world. It lives beside a yeast that cannot use maltose, the sugar the bacterium prefers, so the two share the dough without competing. Temperature and how often the starter is fed decide which microbes gain the upper hand, and so how sour the bread turns out.

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WonderOcean

Coral reefs cover less than 1 per cent of the ocean floor, yet they support about a quarter of all known marine species. They also shield coasts from storm waves.

A reef is built by coral polyps, tiny animals related to jellyfish that lay down skeletons of limestone. Most reef corals carry single-celled algae inside their tissue; the algae photosynthesise and pass food to the coral in return for shelter, and they also give it its colour. When the water stays too warm for too long, corals expel the algae and turn white, which is called bleaching; if the heat lasts, they starve and die. A global bleaching event from 2014 to 2017 hit about two-thirds of the world's reefs, and a fourth, from 2023 to 2025, the most severe on record, reached about 84 per cent of reef area.

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StillnessOcean

Mangroves, salt marshes and seagrass meadows draw carbon dioxide from the air and lock it away in waterlogged coastal mud, often for centuries. Scientists call this stored carbon 'blue carbon'.

The term was popularised by a 2009 United Nations report. Coastal mud holds so little oxygen that dead roots and leaves rot very slowly, so carbon keeps building up in the soil instead of returning to the air. These habitats cover only a small fraction of the seabed, yet they are thought to account for about half of all the carbon buried in ocean sediments. Mangroves also break waves, trap sediment and shelter young fish and crabs among their roots. When the wetlands are drained or cleared for shrimp farms or building, the stored carbon can escape back into the atmosphere.

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WonderOcean

Hydrothermal vents, hot springs on the deep ocean floor, support dense communities of animals in total darkness. Their food chain starts not with sunlight but with microbes that make food from chemicals in the vent water, a process called chemosynthesis.

In February 1977 the geologist Jack Corliss and colleagues took the submersible Alvin down about 2,500 metres to the Galápagos Rift, a crack in the Pacific seafloor, expecting bare rock. Instead they found warm vents ringed with clams, mussels, crabs and tube worms. Vent water is rich in hydrogen sulphide, a gas poisonous to most life, but some bacteria can draw energy from it to build sugars, much as plants use sunlight. Giant tube worms, which have no mouth or gut, house these bacteria inside their bodies and live on what they make. The find changed ideas about where life can exist, on Earth and possibly beyond it.

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WonderMigration

Every year more than a million wildebeest, joined by hundreds of thousands of zebras and gazelles, walk a great loop through Tanzania's Serengeti and Kenya's Maasai Mara, following the rains to fresh grass.

The herds have no fixed route; their path shifts each year with the rain. Early in the year hundreds of thousands of calves are born within a few weeks in the southern Serengeti. As the plains dry out the herds move north and west, reach Kenya's Mara in the middle of the year and return south when the short rains begin. The most dangerous moment is crossing the Mara River. A 2017 study found that on average about 6,250 wildebeest drown there each year, and their carcasses, some 1,100 tonnes, feed fish, crocodiles and vultures and fertilise the river for years. Grazing herds also keep the grasslands healthy.

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WonderMigration

European eels live in the rivers of Europe and North Africa but begin life some 5,000 kilometres away in the Sargasso Sea, in the western Atlantic. Adults swim back there to breed, yet no one has ever seen them spawn.

How eels breed puzzled people for more than 2,000 years; Aristotle thought they arose from mud. In the early 1900s the Danish biologist Johannes Schmidt spent almost two decades netting eel larvae across the Atlantic and found that they grew smaller the further west he went, until the tiniest turned up only in the Sargasso Sea. The larvae drift to Europe with the Gulf Stream and turn into transparent 'glass eels' as they near the coast. In 2022 researchers reported the first direct evidence of adults reaching the Sargasso Sea, after tracking satellite-tagged eels released in the Azores. No eggs or spawning adults have yet been found. The species is now critically endangered.

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WonderEvolution

In the Cambrian explosion, which began about 538 million years ago, most of the major animal groups alive today appeared in the seas within roughly 20 million years, among them the first arthropods, molluscs and early relatives of vertebrates.

The name makes it sound sudden, but the Cambrian explosion unfolded over millions of years and built on the simpler life of the preceding Ediacaran period. What changed was the sheer variety: eyes, legs, shells and hard skeletons appear, along with burrows and the first clear signs of predators hunting prey. Two exceptional fossil beds preserve even soft tissue: Chengjiang in China, about 518 million years old, and the Burgess Shale in Canada, about 508 million years old. Trilobites, armoured sea-floor arthropods, appear early in the period and survived for some 270 million years. Leading explanations for the burst include rising oxygen in the oceans, new genetic tools for building bodies, and an arms race between predators and prey.

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WonderEvolution

In industrial Britain, the dark form of the peppered moth, first recorded in Manchester in 1848, became common where soot blackened the trees and hid it from birds. When the air was cleaned up in the twentieth century, the pale form returned.

The peppered moth became a textbook example of natural selection. By the 1890s nearly all peppered moths around Manchester were dark. In the 1950s Bernard Kettlewell's field experiments suggested that birds ate more of the moths that stood out against the bark, though critics later questioned his methods. After clean-air laws such as the UK's Clean Air Act of 1956 cut soot, the dark form became rare again. The geneticist Michael Majerus answered the critics with a six-year experiment in Cambridge involving 4,864 moths; published after his death, in 2012, it confirmed that birds took more of the conspicuous moths. In 2016 scientists traced the dark colour to a piece of mobile DNA inserted into a gene called cortex around 1819.

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WonderEvolution

Most adults in the world make little lactase, the enzyme that digests milk sugar, after childhood. In several peoples with a long history of dairy farming, genetic changes that keep the enzyme working for life spread through natural selection, a trait called lactase persistence.

In Europe the most common variant sits in a stretch of DNA that switches the lactase gene (LCT) on and off; a widely cited estimate puts its first spread at roughly 7,500 years ago. Different mutations with the same effect arose independently among cattle herders in East Africa and pastoralists in the Middle East, so evolution reached one solution several times. Scientists call this gene-culture coevolution: a cultural habit, keeping animals for milk, changed which genes helped people survive. The story is more complicated than it first looked. A 2022 study in Nature found that Europeans used milk for thousands of years while the variant stayed rare, and suggested it spread fastest in famines and epidemics, when milk could make people without it seriously ill.

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WonderBiology

The yellow slime mould Physarum polycephalum, a single-celled organism with no brain, can grow a network of tubes between scattered pieces of food that balances short routes, backup links and low cost, much as engineers try to do.

Despite its name, a slime mould is not a fungus: Physarum lives as one giant cell with many nuclei that creeps over damp logs, feeding on bacteria and fungal spores. In a 2010 study in the journal Science, a team led by Atsushi Tero of Hokkaido University placed oat flakes in the pattern of 36 cities around Tokyo and set the slime mould on the spot marking Tokyo. Bright light, which it avoids, stood in for mountains and sea. Within about a day it had linked the oats with a network that closely matched the real Tokyo rail system in efficiency, cost and resistance to breaks. The team then turned the organism's simple local rules into a mathematical model for designing networks.

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WonderOcean

Whales feed at depth and release nutrient-rich faeces near the surface, fertilising the phytoplankton, tiny drifting algae, at the base of the ocean food chain. Scientists call this the whale pump.

The term comes from a 2010 study by the marine scientists Joe Roman and James McCarthy, who looked at whales and seals in the Gulf of Maine, off the north-eastern United States. Many whales dive to feed and then rest and breathe at the surface, where they release loose, floating plumes of faeces rich in nitrogen. The researchers estimated that marine mammals return about 23,000 tonnes of nitrogen a year to the sunlit surface layer of the Gulf, more than all the rivers flowing into it combined, and that before industrial whaling the flow was probably much larger. Other studies found a similar effect with iron in the Southern Ocean. Because phytoplankton also absorb carbon dioxide, recovering whale numbers may help both ocean productivity and carbon uptake.

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WonderMigration

Pronghorn from Grand Teton National Park travel up to about 240 km (150 miles) between their summer range and their winter range in Wyoming's Upper Green River Basin. Roads, fences and new building now cut across this ancient route.

Pronghorn look like antelopes but are the last surviving members of a family found only in North America. They can reach about 88 km/h, a speed beaten on land only by the cheetah, yet they rarely jump: faced with a fence, they look for a gap to crawl under, so tight wire fencing can block a route completely. At Trappers Point, a narrow bottleneck on the route, archaeologists found remains of pronghorn hunts about 6,000 years old. In 2008 the US Forest Service designated the Path of the Pronghorn, the first federally protected wildlife migration corridor in the United States. In 2012, overpasses and underpasses built on US Highway 191 near Pinedale gave the herds a safe way across the road.

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WonderMigration

The sardine run takes place off South Africa's east coast from about May to July, when vast shoals of sardines follow a band of cool water north along the shore. Dolphins, gannets, sharks, seals and whales gather to feed on them.

Sardines normally live in the cooler waters off South Africa's southern and western coasts. In some winters a narrow strip of cold water forms close to the shore of the Eastern Cape and KwaZulu-Natal, between the coast and the warm Agulhas Current, and the fish move north along it. The shoals can stretch for several kilometres and are followed from the air by spotter planes. Common dolphins herd the sardines into tight balls near the surface, Cape gannets plunge in from height, and sharks, Cape fur seals and Bryde's whales feed on the exposed fish. Scientists are still not sure what sets the run off: in some years it is weak or barely happens, and why is not fully understood.

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WonderEvolution

At Laetoli in Tanzania, footprints pressed into volcanic ash about 3.6 million years ago show that early human relatives already walked upright on two feet. They are among the oldest known footprints of hominins, the group that includes humans and our extinct close relatives.

The hominin prints were found in 1978 by a team led by the palaeoanthropologist Mary Leakey, two years after animal tracks were first noticed at the site. Ash from an eruption, probably of the nearby Sadiman volcano, was dampened by light rain, took the prints of animals and people walking across it, and set hard before more ash buried it. The main trail is about 27 metres long and was left by at least two individuals, most likely of the species Australopithecus afarensis, to which the famous skeleton nicknamed Lucy belongs. The feet show a humanlike arch and a big toe in line with the other toes, so upright walking was established long before large brains or stone tools.

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WonderEvolution

Convergent evolution happens when unrelated organisms independently evolve similar traits, such as streamlined bodies in sharks, dolphins and extinct ichthyosaurs.

Sharks are fish, dolphins are mammals and ichthyosaurs were marine reptiles, yet all three evolved a similar streamlined, fin-driven body built for fast swimming. The same pattern shows up elsewhere: camera-like eyes, with a lens that focuses light onto a retina, evolved independently in both vertebrates and octopuses, and the extinct Australian thylacine looked strikingly like a wolf despite being a marsupial with no close relation to dogs. Convergent evolution does not mean life is aiming for a fixed set of designs. Natural selection simply favours whatever body plan works best under a given set of physical pressures, so unrelated lineages can arrive at strikingly similar answers.

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WonderEvolution

Maize, sugarcane and sorghum grow well in heat and strong sun partly because they use C4 photosynthesis, a way of concentrating carbon dioxide inside the leaf. This method has evolved independently more than 60 times in different groups of plants.

Most plants use C3 photosynthesis, which relies on an enzyme called RuBisCO to capture carbon dioxide. In heat and drought, plants close the pores in their leaves to save water, carbon dioxide inside runs low, and RuBisCO grabs oxygen instead, wasting energy in a process called photorespiration. C4 plants first trap carbon dioxide in their outer leaf cells as a compound with four carbon atoms, which gives the pathway its name, then carry it to inner cells where RuBisCO works and release it there, so the enzyme is surrounded by carbon dioxide. With more than 60 separate origins, it is one of the most often repeated adaptations in plant evolution. Scientists are now trying to engineer the trait into rice.

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WonderNature

Welwitschia, a plant of the Namib Desert in Namibia and Angola, grows only two leaves in its whole life. They keep growing from their base for centuries, and some plants are thought to be more than a thousand years old.

The Austrian botanist Friedrich Welwitsch came across the plant in southern Angola in 1859; he wrote that he knelt and gazed at it, half afraid that touching it would prove it imaginary. It is a gymnosperm, like conifers, which means its seeds form in cones rather than inside fruit, and male and female cones grow on separate plants. Over the years the wind tears the two leaves into many ribbons, so an old plant looks like a heap of leaves. The Namib is one of the driest places on Earth. The leaves catch fog and dew, which drip onto shallow roots, although a 2019 study suggests that rain soaking into the ground is its main water source. The plant appears on Namibia's coat of arms.

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WonderNature

The saiga, an antelope of the Central Asian steppes, has an enlarged, flexible nose that filters out dust in summer and warms and moistens freezing air in winter before it reaches the lungs.

Saigas live on the dry grasslands of Kazakhstan, Russia, Uzbekistan and Mongolia, and herds migrate hundreds of kilometres between summer and winter pastures. Their numbers collapsed after the Soviet Union broke up: poaching of males for their horns, used in traditional Chinese medicine, cut the population by about 95 per cent. In May 2015, during unusually warm, humid weather, a bacterium the animals normally carry harmlessly, Pasteurella multocida, caused a blood infection that killed about 200,000 saigas in Kazakhstan within a few weeks, more than half of all saigas then alive. Protection from poaching has since let the Kazakh herds recover so strongly that in 2023 the International Union for Conservation of Nature moved the species from Critically Endangered to Near Threatened.

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