Chapter 22: Evolution

Chapter 22: Evolution • Historical perspective on evolution • Darwin’s voyage • Darwin’s theory: evolution occurs by natural selection • Evidence supporting the theory of evolution • The Modern Synthesis • The central role of evolution in modern biology

Describe the major ideas on evolution and related topics that had a significant influence on Charles Darwin as he developed the concept of evolution by natural selection.

Historical perspective • divine design and perfection model • fossils • acquired traits • modern geology – Lyell, uniformitarianism, and the ancient Earth • artificial selection • population limits

Historical perspective • divine design and perfection model • from Aristotle, whose ideas dominated most thinking on biology until the renaissance • species were viewed on a scale from simple to complex (which was considered more perfect) • all organisms were seen as moving toward perfection • based on divine intervention and design (thus supernatural, outside the true realm of science) • now discredited in biology, but still part of the social consciousness

Historical perspective • fossils • fossils were known for centuries before Darwin • fossils reveal organisms unlike any living today • the idea that some fossils represent species that had become extinct was recognized even as early as Leonardo da Vinci (1452-1519)

Figure 1.4 A mylodon.Drawing of a giant ground sloth. From A Naturalist’s Voyage Around the World:The Voyage of the H.M.S. Beagle by Charles Darwin (D. Appleton and Co.,New York, 1890).

Figure 1.1 “I was in many ways a naughty boy.”Portrait of young Charles and his sister Catherine. Charles later wrote in hisautobiography, “I was much slower in learning than my younger sister Catherine, andI believe that I was in many ways a naughty boy.” From More Letters of CharlesDarwin: A Record of His Work in a Series of Hitherto Unpublished Letters edited byF. Darwin and A. Seward (D. Appleton and Co., New York, 1903).

Figure 1.2 Charles’ list of his father’s objections to the Beagle voyage.Reproduced by kind permission of the Syndics of Cambridge University Library.

Figure 1.3 The HMS Beagle and Darwin’s quarters.Based on a drawing by shipmate Philip King, with whom Darwin shared hisquarters. From Journal of Researches into Geology and Natural History of the VariousCountries Visited by H.M.S. Beagle by Charles Darwin (facsimile edition of 1839First Edition, Hafner Publishing Company, New York, 1952).

Figure 1.6 HMS Beagle in the Strait of Magellan.Drawing from A Naturalist’s Voyage Around the World: The Voyage of theH.M.S. Beagle by Charles Darwin (D. Appleton and Co., New York, 1890).

Figure 1.7 Map of the Voyage of the HMS Beagle, 1831–1836.Drawn by Leanne Olds.

Historical perspective • birth of modern geology – Lyell, uniformitarianism, and the ancient Earth • prior to the early 1800s, the world view of most was that the Earth is very young (around 6000 years old) • in the early 1800s, geologists began to apply scientific reasoning to studies of geological processes, and quickly recognized that these processes require that the Earth be very old (billions of years) to occur naturally

Historical perspective • this “uniformitarian” model of geological processes was made famous by Lyell’s Principles of Geology, which influenced Charles Darwin • the uniformitarian model is essentially the basis of geology today; confirming tests of this model include dating rocks using radioisotope ratios (more on that later)

Figure 1.7 Map of the Voyage of the HMS Beagle, 1831–1836.Drawn by Leanne Olds.

Figure 1.9 Galapagos finches.Drawing from A Naturalist’s Voyage Around the World: The Voyage of theH.M.S. Beagle by Charles Darwin (D. Appleton and Co., New York, 1890).

Figure 1.8 A Galapagos tortoise.Drawing from A Naturalist’s Voyage Around the World: The Voyage of the H.M.S.Beagle by Charles Darwin (D. Appleton and Co., New York, 1890).

1831: Leaves on Beagle (age 22) 1836: Beagle returns to England; soon afterwards writes his story of the trip and begins his “secret notebooks” Darwin’s voyage Figure 1.7 Map of the Voyage of the HMS Beagle, 1831–1836.Drawn by Leanne Olds. Figure 1.10 The tree of life.Page from notebook “B,” where Darwin recorded his idea that life is connected like the branches of a tree, with ancestors at the bottom. Reproduced by kind permission of the Syndics of Cambridge University Library.

Darwin’s voyage 1831: Leaves on Beagle (age 22) 1836: Beagle returns to England; soon afterwards writes his story of the trip and begins his “secret notebooks” 1838: Reads Malthus’ Essay on the Principle of Populations 1839: Voyage of the Beagle published 1842: Makes 35-page sketch of theory 1844: Expands sketch to 230 pages 1859: Publishes On the Origin of Species by Means of Natural Selection 1871: Publishes The Descent of Man and Selection in Relation to Sex

Darwin’s voyage • There was much discussion by immediate predecessors and contemporaries of Darwin about: • how the divine design model did not mesh well with observation of the extremes of variation among species • the idea of extinct species represented in the fossil record • functional similarities between the anatomy of extremely divergent species • the idea that evolution occurs thus was “in the air” at the time • attempts to find a convincing mechanism fell short (such as Lamarck’s acquired characteristics model)

Historical perspective • acquired traits • mostly associated with Lamarck (1744-1829) • still focused on a model of organisms driven toward complexity, but involved an explanation with natural causes • postulated that changes or “acquired characteristics” during an organism’s life could be passed on to offspring • famous example was Lamarck’s model for how giraffes developed long necks – he claimed that stretching of the neck in one generation would lead to offspring with longer necks • understanding of genetic inheritance has led to rejection of acquired traits models

Darwin’s theory: evolution occurs by natural selection • Darwin’s theory of evolution was based on four general observations: • overproduction • variation • competition • differential reproductive success • natural selection will produce a population of individuals more suited to their environment through time

Historical perspective • Malthus (1766-1834) wrote the most influential works on this subject • mathematically, populations will grow geometrically if unchecked • food supplies rarely can be expected to grow faster than arithmetically, thus putting a limit on population growth • population limits that would allow selection to act naturally were recognized

Historical perspective • artificial selection • it was well known that domesticated animals and plants had been breed over centuries by humans to produce different varieties • indicates that the characteristics of a species can be modified by selection • some examples: • different breeds of dogs • “wild cabbage” lineage of cabbage, broccoli, cauliflower, Brussels sprouts, collards, kale, etc. • many more

Figure 1.9 Galapagos finches.Drawing from A Naturalist’s Voyage Around the World: The Voyage of theH.M.S. Beagle by Charles Darwin (D. Appleton and Co., New York, 1890).

Darwin’s voyage • Recall Darwin’s theological training – • Darwin was well aware of the impact that a workable, testable theory of evolution would have • …and the intense controversy and scrutiny it would draw… • so, although he worked out most of his theory of evolution shortly after his trip on the Beagle • …he spent 20 years accumulating evidence and doing experiments before finally publishing the idea!

Darwin’s voyage • Darwin was spurred on to publish when Alfred Russel Wallace shared his independent work where he had reached similar conclusions to Darwin • they first presented the theory of evolution by natural selection together in 1858

Figure 3.1. The massive Amazon River system.The main river and its tributaries span more than fifteen thousand miles. HenryWalter Bates spent most of his eleven years in the Amazon on the main river, whileAlfred Russel Wallace ventured far up the Rio Negro. Bates found more than550 species of butterflies at Ega (now Tefé). Drawn by Leanne Olds.

Figure 2.1 Sketch salvaged from fire and shipwreck of the Helen.This drawing of an Amazonian angelfish was one of the few sketches Wallacemanaged to save out of all of his notes and specimens on his doomed voyage home. Itdisplays one of the important talents for naturalists before the age of photography —that of being a good artist. Drawing from the autobiography of Alfred Russel Wallace,My Life (New York: Dodd, Mead, and Co., 1905).

Figure 2.2 The Malay Archipelago.Map by Leanne Olds.

Figure 2.3 The Golden Birdwing butterfly.Wallace discovered this form (Ornithopteracroesuslydius) on the island of Batjan.Photograph by Barbara Strnadova.

Figure 2.4 The Wallace Line.

Darwin’s voyage • Darwin published his first version of the book On the Origin of Species by Means of Natural Selection in 1859 • in it, he laid out the entire argument with all of the evidence that he had been gathering ever since his voyage on the Beagle

Darwin’s voyage • Darwin’s book had immediate and dramatic impact • the force of his argument and evidence convinced many scientists quickly • of course it stirred tremendous controversy as well • Darwin made several revisions of his work in response to some of the most reasonable criticisms • He also focused on human evolution in The Descent of Man (1871)

Describe the major ideas on evolution and related topics that had a significant influence on Charles Darwin as he developed the concept of evolution by natural selection.

Describe the logical reasoning behind Darwin’s concept of natural selection.

Darwin’s theory: evolution occurs by natural selection • Darwin’s theory of evolution was based on four general observations: • overproduction – each species produces more offspring than will survive to maturity • variation– individuals in a population vary, and some of the variation is heritable (this was expanded by others later, as genetics came to be understood) • competition– there is competition among the individuals of a population for limited resources (struggle for existence) • differential reproductive success – individuals that possess more favorable characteristics (in the pool of variation) are more likely to survive and reproduce; those with less favorable characteristics are less likely to survive and reproduce • thus, natural selection will produce a population of individuals more suited to their environment through time

Darwin’s theory: evolution occurs by natural selection • when populations are separated (such as the geographic separation of islands from each other and a nearby continent), natural selection on two separate populations can produce two distinct populations with different characteristics – resulting in two separate species • note that for this theory to explain the current variety of species on Earth, there is a need for a long amount of time for natural selection to produce the variety observed; thus, the idea of an ancient Earth hundreds of millions to billions of years old is crucial

Describe the logical reasoning behind Darwin’s concept of natural selection.

Explain the terms microevolution and macroevolution (in their true scientific meanings), and describe how microevolution can lead to macroevolution.

Darwin’s theory: evolution occurs by natural selection • two major branches: microevolution, or changes of a population over time, and macroevolution, or the formation of species • http://evolution.berkeley.edu

Explain the terms microevolution and macroevolution (in their true scientific meanings), and describe how microevolution can lead to macroevolution.

Discuss these major lines of evidence for evolution: • fossil record • anatomical evidence (comparisons, vestigial structures, “design” flaws) • distribution of organisms • developmental comparisons • molecular comparisons

Figure 3.1. The massive Amazon River system.The main river and its tributaries span more than fifteen thousand miles. HenryWalter Bates spent most of his eleven years in the Amazon on the main river, whileAlfred Russel Wallace ventured far up the Rio Negro. Bates found more than550 species of butterflies at Ega (now Tefé). Drawn by Leanne Olds.

Figure 3.2 Mimicry in butterflies.This is an original plate from Bates’ 1862 paper reporting the discovery of mimicry.The butterfly at the center (5) is Leptalis nehemia, the typical butterfly of the family.The other Leptalis butterflies (1–8) deviate greatly from this pattern, as they aremimics of other species. Each pair (3/3a, 4/4a, 6/6a, 7/7a, 8/8a) illustrates mimicrybetween Leptalis and species of other families. Specimens 3a, 4a, and 6a are membersof the genus Ithomia that mimic varieties of Leptalis theonoe found in the area of SaoPaulo. Specimens 7a and 8a are members of the Mechanitis and Methona genera thatmimic Leptalis amphione and Leptalis orise.

Figure 3.3 Caterpillar mimic of snake head.First discovered by Bates, a number of species mimic the appearance of snakeheads. This is the Spicebush Swallowtail caterpillar (Papiliotrollus).Photo by Mary Jo Fackler.

Chapter 22: Evolution