Evolution: quotes, facts and reflections - Page 2

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WonderEvolution

The Mexican tetra, a small river fish, has colonised caves several times, and cave after cave its populations have evolved tiny or missing eyes and lost their colour, giving biologists natural repeats of the same experiment.

About 30 cave populations are known in a limestone region of San Luis Potosí and southern Tamaulipas in north-eastern Mexico, while their eyed relatives still live in rivers nearby. Genetic studies suggest the caves were entered at least five separate times, and that the cave forms are recent, less than about 20,000 years old. When fish from two different caves are crossed, some offspring can see, a sign that eye loss happened partly through different genes. Cave life brought other changes too: taste buds all over the head, a very sensitive lateral line (the row of pressure sensors along a fish's side), and bodies that store about four times more energy as fat, which helps them survive long gaps between meals.

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WonderEvolution

Bread wheat carries six sets of chromosomes, two from each of three wild ancestral grasses. Organisms with more than two complete sets of chromosomes are called polyploid, and they are common among plants.

Most animals, including humans, have two sets of chromosomes, one from each parent. Wheat gained its extra sets in two steps. Long before farming, two wild grasses, Triticum urartu and a relative of Aegilops speltoides, crossed to produce wild emmer, with four sets. After farming began in the Near East, cultivated emmer crossed with a third wild grass, Aegilops tauschii, adding two more sets and creating bread wheat. The oldest known bread wheat, identified from its DNA, comes from Çatalhöyük in Turkey and dates to about 6400 to 6200 BC. Extra gene copies can take on new roles, one reason polyploid crops are often large and hardy. Potatoes, cotton, Arabica coffee and cultivated strawberries are polyploid too.

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WonderArchaeology

The Schöningen spears, found in a German coal mine in the 1990s, are among the oldest known hunting weapons: wooden spears shaped and balanced for throwing. Their exact age, once put at about 400,000 years, is still debated.

A team led by the archaeologist Hartmut Thieme uncovered ten wooden weapons between 1994 and 1999 in an open-cast lignite (brown coal) mine at Schöningen in Lower Saxony, where waterlogged lakeside mud kept the wood from rotting. Most were carved from spruce trunks, one from pine, and in some the thickest point lies in the front third of the shaft, as on a modern javelin. When athletes threw replicas, they reached targets 15 to 20 metres away. The spears lay among the bones of an extinct wild horse, many with butchery marks. Their age has changed with each dating method: first 380,000 to 400,000 years, then about 300,000 to 337,000; a 2025 study argued for about 200,000 years, which would make Neanderthals their likely makers.

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