Inventing the Theory of Natural selection It is one thing to observe the results of evolution, but Geometric quite another to understand how it happens. Darwin's progres great achievement lies in his formulation of the hypothe sis that evolution occurs because of natural selection Darwin and malthus Of key importance to the development of Darwins in sight was his study of Thomas Malthus's Essay on the Principle of Population(1798). In his book, Malth Arithmetic ointed out that populations of plants and animals(in- progression cluding human beings) tend to increase geometrically, while the ability of humans to increase their food supply increases only arithmetically. a geometric progression is one in which the elements increase by a constant factor; for example, in the progression 2, 6, 18, 54, number is three times the preceding one. An arithmetic progression,in contrast, is one in which the elements in FIGURE 1.9 crease by a constant difference; in the progression 2, 6, 10, Geometric and arithmetic progressions. A geometric progression each number is four greater than the preced- increases by a constant factor(e. g, X 2 or X 3 or X 4), while an arithmetic progression increases by a constant difference(e. g, units of 1 or 2 or 3). Malthus contended that the human growt Because populations increase geometrically, virtually curve was geometric, but the human food production curve any kind of animal or plant, if it could reproduce un- only arithmetic. Can you see the problems this difference would checked woule the entire surface of the world within a surprisingly short time. Instead, populations of species remain fairly constant vear after vear, because death limits population numbers. Malthus's conclusion provided the key ingredient that was necessary for Dar win to develop the hypothesis that evolution occurs by natural selection Sparked by Malthus' s ideas, Darwin saw that although every organism has the potential to produce more of Can we doult.. that individuals having spring than can survive, only a limited number actually do survive and produce further offspring. Combining an Owns【5 OcT this observation with what he had seen on the voyage of the Beagle, as well as with his own experiences in breed- oLe. wo ld have the best chance of ing domestic animals, Darwin made an important associ- ation(figure 1. 10): Those individuals that possess supe- suzoLUIng and procreating theit hind? On rior physical, behavioral, or other attributes are more ikely to survive than those that are not so well endowed the othet hand, we may feel sute that By surviving, they gain the opportunity to pass on their favorable characteristics to their offspring. As the fre- variation in cn/ullou quency of these characteristics increases in the popula- tion,the nature of the population as a whole will gradu- ally change. Darwin called this process selection. The driving force he identified has often been referred to as survival of the fittest callwatuzal selection An excerpt from Charles Darwins On tbe Origin of species. Chapter 1 The Science of Biology 13Inventing the Theory of Natural Selection It is one thing to observe the results of evolution, but quite another to understand how it happens. Darwin’s great achievement lies in his formulation of the hypothe￾sis that evolution occurs because of natural selection. Darwin and Malthus Of key importance to the development of Darwin’s in￾sight was his study of Thomas Malthus’s Essay on the Principle of Population (1798). In his book, Malthus pointed out that populations of plants and animals (in￾cluding human beings) tend to increase geometrically, while the ability of humans to increase their food supply increases only arithmetically. A geometric progression is one in which the elements increase by a constant factor; for example, in the progression 2, 6, 18, 54, . . . , each number is three times the preceding one. An arithmetic progression, in contrast, is one in which the elements in￾crease by a constant difference; in the progression 2, 6, 10, 14, . . . , each number is four greater than the preced￾ing one (figure 1.9). Because populations increase geometrically, virtually any kind of animal or plant, if it could reproduce un￾checked, would cover the entire surface of the world within a surprisingly short time. Instead, populations of species remain fairly constant year after year, because death limits population numbers. Malthus’s conclusion provided the key ingredient that was necessary for Dar￾win to develop the hypothesis that evolution occurs by natural selection. Sparked by Malthus’s ideas, Darwin saw that although every organism has the potential to produce more off￾spring than can survive, only a limited number actually do survive and produce further offspring. Combining this observation with what he had seen on the voyage of the Beagle, as well as with his own experiences in breed￾ing domestic animals, Darwin made an important associ￾ation (figure 1.10): Those individuals that possess supe￾rior physical, behavioral, or other attributes are more likely to survive than those that are not so well endowed. By surviving, they gain the opportunity to pass on their favorable characteristics to their offspring. As the fre￾quency of these characteristics increases in the popula￾tion, the nature of the population as a whole will gradu￾ally change. Darwin called this process selection. The driving force he identified has often been referred to as survival of the fittest. Chapter 1 The Science of Biology 13 Geometric progression Arithmetic progression 2 6 18 54 4 6 8 FIGURE 1.9 Geometric and arithmetic progressions. A geometric progression increases by a constant factor (e.g., 2 or 3 or 4), while an arithmetic progression increases by a constant difference (e.g., units of 1 or 2 or 3) . Malthus contended that the human growth curve was geometric, but the human food production curve was only arithmetic. Can you see the problems this difference would cause? FIGURE 1.10 An excerpt from Charles Darwin’s On the Origin of Species.