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Backman Seeds Ghose Milosevic-Zdjelar Read Prepared by: Jennifer West Department of Physics and Astronomy University of Manitoba Chapter 14 and 15 Outer Solar System and Life on Other Worlds 1 Neptune Beyond Uranus lies the outermost major planet in our solar system, Neptune. It wasn’t discovered accidentally! Remember the Titius-Bode rule? a = (4+ 3×2n)/10 AU n=1 a=1 AU real distance 1 AU n=2 a=1.6 AU --,,-- 1.52 AU (Mars) n=3 a=2.8 AU --,,-- 2.77 AU (Ceres, 1801, Piazzi) n=4 a=5.2 AU --,,-- 5.2 AU (Jupiter) n=5 a=10 AU --,,-- 9.58 (Saturn) n=6 a=19.6 AU --,,-- 19.23 (Uranus, 1781, Herschel) n=7 a=38.8 AU ??? 2 Neptune The predicted distance to the next hypothetical planet would be ~39 AU according to T-B ‘law’. The search was on, but the predicted distance didn’t make the discovery any easier. • Two astronomers independently calculated the location of Neptune from irregularities in the motion of Uranus (inspired by a hypothesis of Alexis Bouvard). •British astronomers were a bit slow to respond to calculations of John C. Adams. In the 20th century one of them stole the evidence of how inaccurate the predictions of Adams were. •Urbain Le Verrier (On Sept. 23, 1846, Neptune was discovered by J. Galle within a few degrees of where he had predicted it to be on the sky) 3 Neptune Remember the Titius-Bode rule? It failed at Neptune!.... a = (4+ 3×2n)/10 AU n=1 a=1 AU real distance 1 AU n=2 a=1.6 AU --,,-- 1.52 AU (Mars) n=3 a=2.8 AU --,,-- 2.77 AU (Ceres, 1801, Piazzi) n=4 a=5.2 AU --,,-- 5.2 AU (Jupiter) n=5 a=10 AU --,,-- 9.58 AU (Saturn) n=6 a=19.6 AU --,,-- 19.2 (Uranus, 1781, Herschel) n=7 a=38.8 AU --,,-- 30.1 AU (Neptune, 1846, Galle) Right now, we know that most extrasolar planetary systems do not obey any strict mathematical spacing laws. 4 Neptune • Neptune looks like a tiny blue dot with no visible cloud features. • Thus, astronomers named it after the god of the sea. • In 1989, Voyager 2 flew past and revealed some of Neptune’s secrets 5 Planet Neptune • Neptune is almost exactly the same size as Uranus. • It has a similar interior too. • A small core of heavy elements lies within a slushy mantle of water, ices, and minerals (rock) below a hydrogen-rich atmosphere 6 Planet Neptune However, Neptune looks quite different. • It is bluer • It has active cloud formations. 7 Planet Neptune • The dark-blue tint to the atmosphere is understandable. Its atmosphere contains 1.5 times more methane than Uranus. 8 Planet Neptune • Methane (CH4) absorbs red photons better than blue and scatters blue photons better than red. • This gives Neptune a blue colour and Uranus a green-blue colour. 9 Planet Neptune • When Voyager 2 flew by Neptune in 1989, the largest feature was the Great Dark Spot. • Roughly the size of Earth, the spot seemed to be an atmospheric circulation – much like Jupiter’s Great Red Spot. • Smaller spots (hurricanes) are present 10 Planet Neptune • Recently, the Hubble Space Telescope photographed Neptune and found that the Great Dark Spot is gone and new cloud formations have appeared. • Evidently, the weather on Neptune is changing. 11 Planet Neptune • The atmospheric activity on Neptune is apparently driven by heat flowing from the interior plus some contribution from dim light from the Sun 30 AU away. • Neptune may have more atmospheric activity than Uranus because it has more heat flowing out of its interior. • The reasons for this, though, are unclear. 12 Planet Neptune • Like Uranus, Neptune has magnetic field that must be linked to circulation in the interior. • In both cases, astronomers suspect that ammonia dissolved in the liquid water mantle makes the mantle a good electrical conductor 13 The Neptunian Moons • The two largest moons (out of 13) have peculiar orbits. • Nereid, about a tenth the size of Earth’s moon, follows a large, elliptical orbit – taking nearly an Earth year to circle Neptune once. • Triton, nearly 80 percent the size of Earth’s moon, orbits Neptune backward, clockwise as seen from the north. 14 Neptune with moon Triton 15 The Neptunian Moons • These odd orbits suggest that the system was disturbed long ago in an interaction with some other body, such as a massive planetesimal. 16 The Neptunian Moons • With a temperature of 37 K, Triton has an atmosphere of nitrogen and methane about 105 times less dense than Earth’s. 17 The Neptunian Moons • A significant part of Triton is ice. • Deposits of nitrogen frost are visible at the southern pole. 18 The Neptunian Moons • Many features on Triton suggest it has had an active past. • It has few craters, but it does have long faults that appear to have formed when the icy crust broke. • Also, there are large basins that seem to have been flooded repeatedly by liquids from the interior. 19 The Neptunian Moons • Even more interesting are the dark smudges visible in the southern polar cap. • These are interpreted as sunlight-darkened deposits of methane erupted out of liquid nitrogen geysers. 20 The Neptunian Rings • Neptune’s rings are faint and very hard to detect from Earth. • • • • Maybe seen in 1846 by Lassell (discoverer of Trition)) Recorded in 1968 stellar occultation but missed Found in 1984 (occultation) Imaged 1989 (Voyager 2) 21 The Neptunian Rings • 5 Neptune’s rings, named after the astronomers involved in the discovery of the planet, are similar to those of Uranus, but contain more dust relative to stones • The moon Galatea is gravitationally producing short, incomplete arcs in the outermost ring, called • Egalite, Fraternite, Liberte, Courage 22 The Neptunian Rings • The Egalite, Fraternite, Liberte, Courage, • the semi-transparent arcs are changing their brightness and some are shifting the azimuthal position. • In 2003 Liberte disappeared 23 The Neptunian Rings • The rings are a bit mysterious: some have been observed to consist of braids like a rope • Their dynamics (mechanics of arcs) is not yet fully understood • The rings are semi-transparent, they absorb less than 10% of light passing through them 24 Pluto: Planet No More • Out on the edge of the solar system orbits a family of small, icy worlds. • Pluto was the first to be discovered, in 1930. • However, modern telescopes have found more. 25 Pluto: Planet No More • Out on the edge of the solar system orbits a family of small, icy worlds. • Pluto was the first to be discovered, in 1930. • However, modern telescopes have found more. •Hubble Space Telescope view of • Pluto and its moon Charon : 26 Pluto: Planet No More • You may have learned in school that there are nine planets in our solar system. • However, in 2006, the International Astronomical Union voted to remove one of them, Pluto, from the list of planets. 27 Pluto: Planet No More • Its orbit is highly inclined and so elliptical that it actually comes closer to the Sun than Neptune at times. 28 Pluto: Planet No More •To understand Pluto’s status, you must use comparative planetology to analyze Pluto and then compare it with its neighbours. 29 Pluto: Planet No More • Pluto is very difficult to observe from Earth. No space probes visited it yet • It has only 65% of the diameter of Earth’s Moon. In Earth-based telescopes, it never looks like more than a faint point of light, but some features are seen by the HST 30 Pluto – a dwarf planet 31 Pluto: a dwarf planet • Orbiting so far from the Sun, it is cold enough to freeze most compounds you think of as gases. • Spectroscopic observations have found evidence of nitrogen ice. • It has a thin atmosphere of nitrogen (N2) and carbon monoxide (CO) with small amounts of methane (CH4) 32 Pluto: a dwarf planet and its moons • Pluto has three five moons. • Two – Nix and Hydra – are small. • Charon, though, is relatively large – half of Pluto’s diameter. 33 Pluto and Charon • Charon orbits Pluto with a period of 6.4 days in an orbit highly inclined to the ecliptic. • Pluto and Charon are tidally locked to face each other. • So, Pluto’s rotation is also highly inclined 34 Pluto: a dwarf planet • Charon’s orbit size and period plus Kepler’s third law reveal that the mass of the system is only about 1/500 of Earth mass. • Most of the mass is Pluto – about 12 times the mass of Charon • • • • • Historical mass estimates for Pluto 1931: 1 Earth 1948: 1/10 Earth 1976: 1/100 Earth 1978: 1/500 Earth 35 Pluto • Knowing the diameters and masses of Pluto and Charon allows astronomers to calculate that their densities are both about 2 g/cm3. • Thus, Pluto and Charon must contain about 35% ice and 65% rock. 36 What Defines a Planet? • To understand why Pluto is no longer considered a planet, you should recall the Kuiper belt. • Since 1992, new, large telescopes have found a thousand icy bodies orbiting beyond Neptune. • There may be as many as 100 million objects in the Kuiper belt larger than 1 km in diameter. They are understood to be icy bodies left over from the formation time of the outer solar system. 37 What Defines a Planet? • Some of the Kuiper-belt objects are quite large. • One, named Eris, is 5 percent larger in diameter than Pluto. • Three other Kuiper-belt objects found so far – Sedna (named after the Inuit sea goddess), Orcus, and Quaoar – are half the size of Pluto or larger. 38 Pluto: Planet No More • Its orbit is highly inclined and so elliptical that it actually comes closer to the Sun than Neptune at times. 39 TNOs – Trans-Neptunian Objects • Many of these objects have moons of their own. • In that way, they resemble Pluto and its moons. 40 What Defines a Planet? • Comparative planetology shows that Pluto is not related to the Jovian or terrestrial planets. • It is a member of a newfound family of icy worlds that orbit beyond Neptune, much larger than comets. 41 What Defines a Planet? • One of the IAU’s criteria for planet status is that an object must be large enough to dominate and gravitationally clear its orbital region of most or all other objects. Pluto does not meet the criterion. 42 What Defines a Planet? • Eris (formerly called Xena) and Pluto – the largest objects found so far in the Kuiper belt – do not meet the standard. Eris and its moon Dysnomia Neither does Ceres, the largest body in the asteroid belt. 43 What Defines a Planet? • However, all three (Pluto, Eris, Ceres) are large enough for their gravity fields to have pulled them into spherical shapes. (That’s a requirement for a planet.) • Hence, they are the prototypes of a new class of objects defined by the IAU as dwarf planets. 44 Pluto and the Plutinos • Over a dozen Kuiper-belt objects are known that are caught with Pluto in a 3:2 resonance with Neptune. • That is, they orbit the Sun twice, while Neptune orbits three times. • These Kuiper-belt objects have been named plutinos. • how were they caught in resonances? 45 Pluto and the Plutinos • Models of the formation of the planets suggest that Uranus and Neptune may have formed closer to the Sun. • Sometime later, gravitational interactions among the Jovian planets could have gradually shifted Uranus and Neptune outward. • As Neptune migrated outward, its orbital resonances could have swept up small objects like a strange kind of snowplow. 46 Pluto and the Plutinos • The migration of the outer planets would have dramatically upset the motion of some of these Kuiper-belt objects. • Some could have been thrown inward, where they could interact with the Jovian planets. • Some may have been captured as moons (Triton?) 47 Pluto and the Plutinos • Other objects may have impacted bodies in the inner solar system and caused the late heavy bombardment episode especially evident on the surface of Earth’s moon. • The small frozen worlds on the fringes of the solar system may hold clues to the formation of the planets 4.6 billion years ago. 48 Chapter 15 -- Life in the Universe • The atoms of carbon, oxygen, and other heavy elements that are necessary components of your body did not exist at the beginning of the universe. • They were created by successive generations of stars. • We are made of stardust 49 • The elements from which you are made are common everywhere in the observable universe. As a matter of fact, both you and your planet consists mostly of one element (by mass). Do you know which? • So, it is possible that life began on other worlds and evolved to intelligence there as well. • If so, perhaps these other civilizations will be detected from Earth. 50 Your goal in this lecture is to try to understand the most intriguing of puzzles – the origin and evolution of life on Earth and (in the next lecture) possibly the other worlds. 51 The Nature of Life • What is life? Life is a process by which an organism extracts energy from the surroundings, maintains itself, and modifies the surroundings to promote its own survival and reproduction. 52 The Physical Basis of Life • The physical basis of life on Earth is the element carbon (C). • Due to the way carbon atoms bond to each other and to other atoms, they can from long, complex, stable chains that are capable of storing and transmitting information. • Life needs to store a large amount of information • hydrocarbons 53 The Physical Basis of Life • Carbon may not be absolutely necessary to life. • Silicon could in principle be substituted for carbon because the two elements share some chemical properties. • However, this seems unlikely because silicon chains are harder to assemble and disassemble than their carbon counterparts and can’t be as long. • J. Haldane, "The Origins of Life", New Biology, 16, 12–27 (1954). Suggested that an alternative biochemistry could be based on liquid ammonia. 54 The Physical Basis of Life • Even stranger life forms have been proposed based on electromagnetic fields and ionized gas. • None of these possibilities can be ruled out • These hypothetical life forms make for fascinating speculation • However, only a speculation…. 55 The Physical Basis of Life • Even carbon-based life has its mysteries. • What makes a lump of carbon-based molecules a living thing? • An important part of the answer lies in the transmission of information from one molecule to another. 56 Information Storage and Duplication • Almost every action performed by a living cell is carried out by chemicals it manufactures. • Cells must store recipes for all these chemicals, use the recipes when they need them, and pass them on to their offspring without too much error. • Hence Deoxyribonucleic acid (DNA), a digital code transmitter • Analog transmission of information, not in the form of a symbolic code but, say, proportions of chemicals would not support life on Earth 57 Information Storage and Duplication • There are three important points to note about DNA. 58 Information Storage and Duplication One, the chemical recipes of life are stored in each cell as information on DNA molecules. • These molecules resemble a ladder with rungs that are composed of chemical bases: A, C, T (U), G • Adenine, Cytosine, Thymine (alt.: Uracil), Guanine The recipe information is expressed by the sequence of ladder rungs, providing instructions to guide chemical reactions within the cell. Information Storage and Duplication • Two, DNA instructions normally are expressed by being copied into a messenger molecule called RNA that causes molecular units called amino acids to be connected into large molecules called proteins. • Proteins made of amino acids serve as the cell’s basic structural molecules or as enzymes that control chemical reactions. Information Storage and Duplication • Three, the instructions stored in DNA are genetic information passed along to offspring. (One strand calles chromosome can have 220 millions of nucleotides) • The DNA molecule reproduces itself when a cell divides; Information Storage and Duplication • To produce viable offspring, a cell must be able to make copies of its DNA. • Surprisingly, it is important for the continued existence of all life that not all the copies be exact duplicates. 62 Modifying the Information • Earth’s environment changes continuously. • To survive, species must change as their food supply, climate, or home terrain changes. • If the information stored in DNA could not change, then life would quickly go extinct. • The process by which life adjusts itself to its changing environment is called biological evolution. 63 Modifying the Information • When an organism reproduces, its offspring receives a copy of its DNA. • Sometimes external effects such as radiation alter the DNA during the parent organism’s lifetime, and sometimes mistakes are made in the copying process. • 40-50 nucleic acids are damaged per DNA molecule per second, when you sunbathe. The damage is mostly repaired by proteins. In any case, any dmage is not passed on to offspring. • This is an example of mutation, which can also occur due to viruses or chemicals. 64 Modifying the Information • Most mutations make no difference. • Some, however, are fatal, killing the afflicted organisms before they can reproduce. • In rare but vitally important cases, a mutation can actually help an organism survive. 65 Modifying the Information • These changes produce variation among the members of a species. • All the squirrels in the park may look the same but they carry a range of genetic variation. • Some may have slightly longer tails or fastergrowing claws. 66 Modifying the Information • These variations make almost no difference until the environment changes. • If the environment becomes colder, a squirrel with a heavier coat of fur will, on average, survive longer and produce more offspring than its normal contemporaries. • Similarly, the offspring that inherit this beneficial variation will also live longer and have more offspring of their own. 67 Modifying the Information • These differing rates of survival and reproduction are examples of natural selection. • Over time, the beneficial variation increases in frequency, and a species can evolve until the entire population shares the trait. • In this way, natural selection adapts species to their changing environments – by selecting, from the huge array of random variations, those that would most benefit the survival of the species. 68 Modifying the Information • It is a common misconception that evolution is random, but that is not true. • The underlying variation within species is random. • Natural selection, though, is not random because progressive changes in a species are directed by changes in the environment. 69 Life in the Universe • It is obvious that the 4.5 billion chemical bases that make up human DNA (in each cell) did not just come together in the right order by chance. • The key to understanding the origin of life lies in the processes of evolution. 70 Life in the Universe • This means that life on Earth could have begun very simply, even as simple a form as carbon chain molecules able to copy themselves. • Of course, this is a hypothesis for which you can seek evidence. • What evidence exists regarding the origin of life on Earth? 71 The Origin of Life on Earth • The oldest fossils are all the remains of sea creatures. • This indicates that life began in (or was brought into) the sea. • However, identifying the oldest fossils is not easy. 72 The Origin of Life on Earth • Fossils billions of years old are difficult to recognize because the earliest living things contained no easily preserved hard parts like bones or shells. • They were microscopic Bacteria & Archea The Origin of Life on Earth • Fossils from western Australia that are more than 3 billion years old contain features that experts identify as stromatolites – fossilized remains of colonies of single-celled organisms, such as cyanobacteria. The Origin of Life on Earth • The evidence, though scarce, indicates that simple organisms lived in Earth’s oceans 3.4 Gyr ago – less than 1.2 billion years after Earth formed. Chemical signs of life exist back to 3.8 Gyr ago, 0.75 Gyr after the Earth fully formed • Where did these simple organisms come from? • Alexander Oparin (1896-1980) thought in 19231936 that they formed on Earth, in a primordial soup rich in hydrogen, methane and ammonia. 75 The Origin of Life on Earth • An important experiment performed by Stanley Miller and Harold Urey in 1952 sought to recreate the conditions in which life on Earth might have begun. The Origin of Life on Earth • The Miller experiment consisted of a sterile, sealed glass container holding water, hydrogen, ammonia, and methane. • An electric arc inside the apparatus created sparks to simulate the effects of lightning in Earth’s early atmosphere. The Origin of Life on Earth • Miller and Urey let the experiment run for a week and then analyzed the material inside. • They found that the interaction between the electric arc and the simulated atmosphere had produced many organic molecules from the raw material of the experiment, including such as amino acids (building blocks of proteins). • Recently re-analysed, the original apparatus produced more than ~20 amino acids that are in use by life on Earth. 78 The Origin of Life on Earth • When the experiment was run again using different energy sources – such as hot silica to represent molten lava spilling into the ocean – similar molecules were produced. • UV radiation present in sunlight was sufficient to produce complex organic molecules. 79 The Origin of Life on Earth • According to updated models of the formation of the solar system and Earth, Earth’s early atmosphere probably consisted of CO2, nitrogen, and water vapour – instead of the mix of hydrogen, ammonia, and methane assumed by both Oparin, Miller, Urey, and Haldane. 80 The Origin of Life on Earth • When gases corresponding to the newer understanding of the early Earth atmosphere are processed in a Miller apparatus, lesser but still significant numbers of organic molecules are created. 81 The Origin of Life on Earth • The Miller experiment is important because it shows that complex organic molecules form naturally in a wide variety of circumstances. • Lightning, sunlight, and hot lava pouring into the oceans are just some of the energy sources that naturally rearrange simple common molecules into the complex molecules that make life possible. 82 The Origin of Life on Earth • amino acids in the primordial soup can link together to form proteins by joining ends and releasing a water molecule. The Origin of Life on Earth • Charles Darwin thought that this must have occurred in sun-warmed, shallow tidal pools, where organic molecules were concentrated by evaporation. • It is now believed that the early linkage of complex molecules more likely took place on the ocean floor – perhaps near the hot springs at midocean ridges. 84 The Origin of Life on Earth • These complex organic molecules were still not living things. Even though some proteins may have contained hundreds of amino acids, they did not reproduce. They linked and broke apart at random. • According to the hypothesis, somewhere in the oceans, after sufficient time, a molecule formed that could copy itself. • At that point, the chemical evolution of molecules became the biological evolution of living things. 85 The Origin of Life on Earth: Problem • The weakness of the hypothesis of Earth origins of life is that it supposedly took only 0.75 Gyr to form fully functional, complex bacteria (called procaryots). • This seems a relatively short time period when compared with ~2 Gyr needed for the early cells to make a relatively minor advance to cells with nuclear membrane and mitochondria (called eucaryots) • Additional ~2 Gyr were needed to evolve into multicellular life some 0.54 Gyr ago. This also seems like a relatively simple modification compared with the assembly of self-replicating bacteria from organic molecules. 86 The Origin of Life on Earth • Since every next step in the evolution took a shorter and shorter time, the unusually quick selforganization of chemicals into a complex bacteria seem a priori unlikely. The process itself seems likely though – it simply could have started outside the Earth. • An alternative theory for the origin of life that ‘solves’ that problem holds that reproducing molecules may have arrived here from space. 87 The Origin of Life on Earth • Radio astronomers have found a wide variety of organic molecules in the interstellar medium. • Similar compounds have been found inside meteorites. The Miller experiment showed how easy it is to create organic molecules. It is not surprising to find them in space. The Origin of Life on Earth • Whether the first self-reproducing molecules formed here on Earth or in space or on another planet, long before the sun was born, the important thing is that they could have formed by natural processes. • The first reproducing molecule surrounded itself with a protective membrane 89 The Origin of Life on Earth • Experiments have shown that microscopic spheres the size of cells containing organic molecules form relatively easily in water. These are Oparin’s coacervates made of lipids (constituents of fat) • The evolution of the cell membrane occurred The first organisms were single-celled procaryotic bacteria. The Origin of Life on Earth • Stromatolites and other photosynthetic organisms began adding oxygen, a product of photosynthesis, to Earth’s early atmosphere. The Origin of Life on Earth • An oxygen abundance of only 0.1 percent would have created an ozone screen – protecting organisms from the Sun’s ultraviolet radiation and later allowing life to colonize the land. 92 Geologic Time • Life has existed on Earth for at least 3.4 billion years. • There is no evidence, though, of anything more than simple organisms until about 540 million years ago Geologic Time • This sudden increase in complexity is known as the Cambrian explosion. • It marks the beginning of the Cambrian period, about 550 Myr ago • The”explosion” took only 5-10 Myr • The best fossils come from the geographical region of the so-called Burgess shale, which is in Canada 94 Evolution of life • Cambrian Explosion of life forms is near the top of the column. The left-hand column has a linear time scale. Evolution: body segmentation scheme The emergence of vertebrates familiar today – fishes, amphibians, reptiles, birds, and mammals – would be crammed into the topmost part of the chart, above the Cambrian explosion. Upper row – early embryonic stages Lower row – late stages of Different animal embryos. Geologic Time • Humanoid creatures have walked the Earth for about 3 million years. • This is a long time by the standard of a human lifetime, but it makes only a narrow red line at the very top of the diagram. Geologic Time • All of recorded history would be a microscopically thin line at the very top of the column. Geologic Time • Imagine that the entire 4.6-billion-year history of the Earth has been compressed onto a year-long video. First signs of life would appear in March: • Stromatolites, • cyanobacteria 99 Geologic Time • The slow evolution of the first simple bacterial forms would take up the next 6-7 months. 100 Geologic Time • Suddenly, in mid-November(!), you would see the trilobites and other complex organisms of the Cambrian explosion. Geologic Time • You would see no life of any kind on land until…. November 28. Once it appeared though, it would diversify quickly. 102 Geologic Time • By December 12, you would see dinosaurs walking the continents. By the evening of Christmas Day, they would be gone, and mammals and birds would be on the rise. 103 Geologic Time • If you watched closely, you might see the first humanoid forms by suppertime on New Year’s Eve. • By late evening, you could see humans making the first stone tools. • The Stone Age would last until 11:59 PM. • The first towns and cities would then appear. 104 Geologic Time • Suddenly, things would begin to happen at lighting speed. • Babylon would flourish, the Pyramids would rise, and Troy would fall. • The Christian era would begin 14 seconds before the New Year. • Rome would fall. • The Middle Ages and the Renaissance would flicker past. • The American and French revolutions would occur one second before the end of the video. 105 Geologic Time • Imagining Earth’s history as an year-long video gives a perspective on the rise of life. • Tremendous amounts of time were needed for the first simple living things to evolve in the oceans. • As life became more complex, new forms arose more and more quickly as the hardest problems – how to reproduce, how to take energy efficiently from the environment, how to move around – were solved. 106 Geologic Time • The easier problems – what to eat, where to live, and how to raise young – were solved in different ways by different organisms, leading to the diversity that you see today. 107 Geologic Time • Even intelligence – that which appears to set humans apart from other animals – may be a unique solution to an evolutionary problem posed to humanity’s ancient ancestors. • A smart animal is better able to escape predators, outwit its prey, and feed and shelter itself and its offspring. • So, under certain conditions, evolution is likely to select for intelligence. 108