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Born the same day as Lincoln, to prominent (but not aristocratic) family in Kent, England. Father was a country MD. The Evolution of Natural Selection.

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Presentation on theme: "Born the same day as Lincoln, to prominent (but not aristocratic) family in Kent, England. Father was a country MD. The Evolution of Natural Selection."— Presentation transcript:

1 Born the same day as Lincoln, to prominent (but not aristocratic) family in Kent, England. Father was a country MD. The Evolution of Natural Selection Darwin was not a splendid student. "You care for nothing but shooting, dogs and rat-catching, and you will be a disgrace to your family." Went to Edinburgh to study medicine, washed out, partly because he couldn't stomach the brutal conditions. Then to Christ College, Cambridge, with intention of studying for the clergy. Cambridge and theology were a good fit. Darwin did his rat-catching with the best;  Adam Sedgwick (geology),  Whewell (philosophy)  J.S. Henslow, (botany). It was Henslow who set him up for the voyage on the Beagle

2 The Voyage Reported to have taken 2 books with him:  William Paley's Natural Theology, which argued for a literal interpretation of natural history in light of the bible.  Charles Lyell's Principles of Geology, which argued for interpretation from visible evidence. In 1831, signs on as captain’s companion to Capt. Robert FitzRoy aboard the survey ship, H.M.S. Beagle. He left believing implicitly in the former, and returned a convert to the latter.

3 The Voyage Human - 1. Fitzroy had educated Feugian natives in England, having picked them up in an earlier voyage. 2. They were returned to Tierra del Fuego on this voyage, and observed over a year. Darwin got to see the range of "adaptiveness' in humans, and to argue this, and the place and nature of man in the system, with Fitzroy.

4 The Voyage Geology - 1. January 1835: Experienced an earthquake while in Chile - caused a 10 foot uplifting of the coastline. Helped convince him of Lyell's views, especially after seeing fossil shells in Andes. 2.Noted that fossils he collected resembled (but were not identical to) living organisms in the same region. Not consistent with catastrophism. 3.Noted latitudinal replacement of species on the continent, with related forms being geographically close to one another.

5 The Voyage Biology - South American flora and fauna from different regions were distinct from the flora and fauna of Europe. Temperate species of South America were taxonomically closer to species living in tropical regions of South America than to temperate species of Europe. In Patagonia he collected giant fossil ground sloths, elephants, llamas and armadillos- all clearly extinct, but very much akin to he living animals of the area. Observations like these would eventually force him to reject the view that species are immutable.

6 The Voyage Galapagos Islands Tremendous variation among the tortoises.

7 The Voyage Galapagos Islands Variation among the mockingbirds. "...the different islands probably have their representative species or races of the Amblyrhynchus, as well as the tortoise. My attention was first thoroughly aroused by comparing together the numerous specimens, shot by myself and several other parties on board, of the mocking-thrushes, when, to my astonishment, I discovered that all those from Charles Island belonged to one species (Mimus trifasciatus); all from Albemarle Island to M. parvulus; and all from James and Chatham Islands...belonged to M. melanotis." Genus and species Common Name Distribution Nesomimus trifasciatus Charles Mockingbird Champion & Gardner-near Floreana Nesomimus macdonaldi Hood Mockingbird Espanola Nesomimus melanotis Chatham Mockingbird San Cristobal Nesomimus parvulus Galapagos Mockingbird all other islands except Pinzon Dr. Robert Rothman

8 The Voyage Galapagos Islands Variation among the finches.

9 The Voyage Notebook “B”

10 The Voyage Notebook “B” “Each species changes” “Heaven knows whether this agrees with Nature: Cuidado”

11 Returned to England in Contemplates marriage to his cousin, Emma Wedgwood). The Evolution of Natural Selection

12 Returned to England in 1836, married (Emma Darwin, nee Wedgwood). Settled down as moderately wealthy country squire. Moderately famous, makes the rounds among the scientific societies. Ultimately a recluse, worked on a variety of things, much of it just cataloging the specimens from the Beagle. Conducting experiments. Corresponds with the leading scientists and thinkers of his time. The Evolution of Natural Selection

13 Settled down as moderately wealthy country squire. Moderately famous, makes the rounds among the scientific societies. Ultimately a recluse, worked on a variety of things, much of it just cataloging the specimens from the Beagle. Conducting experiments. Corresponds with the leading scientists and thinkers of his time. Darwin with eldest son, 1842 E.g. Thomas Robert Malthus. Malthus was among first to recognize that population growth is a multiplicative (or exponential) process. A couple have two offspring, which go on to produce 2 offspring each, and so on: 2->4->8->16->32->64->128

14 Thomas Robert Malthus (1766 – 1834) - English cleric - Interested in all things regarding populations. - Was Professor of History and Political Economy at East India Company College in Hertfordshire. Most famously known for his manifest: An Essay on the Principle of Population (1798) “I think I may make fairly two postulata. First, that food is necessary to the existence of man. Secondly, that the passion between the sexes is necessary and will remain nearly in its present state... Assuming then my postulata as granted, I say, that the power of population is infinitely greater than the power in the earth to produce subsistence for man. Population, when unchecked, increases in a geometrical ratio. Subsistence increases only in an arithmetical ratio. A slight acquaintance with numbers will show the immensity of the first power in comparison of the second. By the law of our nature which makes food necessary to the life of man, the effects of these two unequal powers must be kept equal. This implies a strong and constantly operating check on population from the difficulty of subsistence. This difficulty must fall somewhere and must necessarily be severely felt by a large portion of mankind....”

15 Thomas Robert Malthus (1766 – 1834) “This natural inequality of the two powers, of population, and of production in the earth, and that great law of our nature which must constantly keep their efforts equal, form the great difficulty that appears to me insurmountable in the way to the perfectibility of society...The checks which repress the superior power of population, and keep its effects on a level with the means of subsistence, are all resolvable into moral restraint, vice and misery. “... this constantly subsisting cause of periodical misery has existed ever since we have had any histories of mankind, does exist at present, and will for ever continue to exist, unless some decided change takes place in the physical constitution of our nature.”

16 Joseph Dalton Hooker(1817 – 1911)

17 Alfred Russell Wallace In 1858, he received a letter from Alfred Russell Wallace. Wallace was a naturalist and explorer who had spent several years in the Malay Archipelago, asking his advice about a paper he (ARW) was planning to write (it was already written) which outlined a theory of evolution essentially identical to CD's. "Wallace map archipelago" by Alfred Russel Wallace, translator P.J. Veth ( ). - Dutch translation of Alfred Russel Wallace, The Malay Archipelago: 'Insulinde: het land van den orang-oetan en den paradijsvogel', Van Kampen, Amsterdam, Translation by P.J. Veth ( ).. Licensed under Public Domain via Wikimedia Commons

18 The Abstract Writes a 513 pp manuscript – “The Abstract” The first printing of 1,250 copies sells out in the first day. The arguments he presents in favor of evolution are still among the strongest ever given, and many subjects he presented are still being worked on today.

19 The Building Blocks to the Theory Variation under domestication Upon his return to England, he joined pigeon-fanciers groups and takes up pigeon breeding. Produces 15 different varieties, all very different from each other, but all from the same species. Tells his buddy Lyell that if they had been found in the wild, they might be classified not only as separate species, but separate genera! - which are groups of species.

20 The Building Blocks to the Theory Variation in barnacles "If there are a continuous grade of varieties of a plant that range from red flowers through pink to white flowers, they are classified as races of a single species. But if the intermediate races go extinct, we will be left with only the red and white extremes, and classify them as distinct species. Varieties can be interpreted as incipient species. (species beginning to come into being) Likewise, the difference between two species within a genus may foreshadow the origin of two new genera." He wrote that in many of these cases, "natural selection probably has come into play & according to my views is in the act of making two species."

21 The Building Blocks to the Theory Heritability It is the proportion of the variation observed in a population that is due to variation in the effects of genes.

22 The Building Blocks to the Theory The struggle for existence Darwin recalls Malthus - uncontrolled growth of populations. He observed in nature that there is not uncontrolled growth. How come? Most individuals born don't survive. Incorrect On average, the most fit individuals pass their genes onto more offspring than less fit individuals.

23 The Building Blocks to the Theory Is Survival and Reproduction Nonrandom? Great question by Darwin! He considered the null hypothesis. Were the observations he was making solely due to chance alone? Those individuals that possess the traits that make them best suited for the environment (or most successful at surviving) will go on to reproduce. More importantly, they will produce more offspring than those individuals that do not have the trait that is as well suited. Natural selection requires more than surviving, it means surviving to reproduce. And it means reproducing more than other phenotypes.

24 The Building Blocks to the Theory This leads to - Natural selection. 1. Natural selection is the differential success in reproduction, and its product is adaptation of organisms to their environment. "This preservation of favorable variations and the rejection of injurious variations, I call Natural Selection." 2. Even slight advantages of some variations will accumulate in a population over many generations of being perpetuated by natural selection. 3. Natural selection thus occurs from the interaction between the environment and the inherent variability in a population. 4. Variations in a population arise by chance, but natural selection is not a chance phenomenon since environmental factors set definite criteria for reproductive success.

25 1.Thus, variation + inheritance + struggle for existence = evolution by natural selection. If these three preconditions are met, evolution necessarily results. 2. Results in adaptation - a structure, behavior or other feature of an organism that enables it to survive or reproduce more successfully than it otherwise would under the existing environmental conditions. To summarize natural selection The Building Blocks to the Theory

26 a.Entirely materialistic and mechanistic - depends entirely on forces or factors that can be observed. b.No limit to the amount of change possible. c.Non-progressive - proper icon for history of life isn't ladder (Scala naturae), but tree. Every branch has a history as long as any other. Each represents a lineage evolving adaptively to survive and reproduce in its habitat (not trying to become human, or anything else). i.Species are not more or less advanced - no linear order to life. ii.Evolution is not goal directed or teleological. Important implication: Natural selection favors only successful individuals, not coexistence of species. Contrast with popular views on the harmony of nature. Improvement of one species can even  extinction of another. Unique features of Darwin's theory: The Building Blocks to the Theory

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28 Postulate 1: Individuals Differ from one another. Darwin’s Postulates Postulate 2: The variation is inherited Postulate 3: Individuals vary in their success at surviving and reproducing Postulate 4: Survival and Reproduction are non-random.

29 Postulate 1: Individuals Differ from one another. Darwin’s Postulates Peter and Rosemary Grant – Princeton University Isla Daphne Major Medium ground finch?

30 Postulate 1: Individuals Differ from one another. Darwin’s Postulates Variation in beak depth of medium ground finches (Geospiza fortis) in 1976.

31 Darwin’s Postulates Heritability of beak depth in medium ground finch (Geospiza fortis). Postulate 2: The variation is inherited

32 Darwin’s Postulates Postulate 3: Individuals vary in their success at surviving and reproducing Drought in Medium ground finches did not even attempt to breed. “The decline in the number of finches was simultaneous with a decline in the availability of seed the birds eat.”

33 Darwin’s Postulates Tribulus plant (Tribulus cistoides)

34 Darwin’s Postulates Beak depth in surviving medium ground finch (Geospiza fortis) before and after the drought. Postulate 4: Survival and Reproduction are non-random.

35 Darwin’s Postulates Did evolution occur? Beak depth of finches hatched the year before the drought versus the year after the drought.

36 The Nature of Natural Selection  Natural Selection acts on the individual but its consequences are seen at the population level. During the drought of 1977, the beaks of individual finches did not become larger. However, more finches with larger beaks survived the drought event. After the drought, the mean size of finches and the mean beak depth changed in the population.

37 The Nature of Natural Selection  Natural Selection acts on the phenotype, but the result is a change in genotype (change in allele frequencies). This is validation for the concept that for natural selection to occur, traits must be hereditary. Even if all of the variation in beak depth had been environmental (the drought leaves behind finches with large beakes), finches with deep beaks would have still been favored in But the next generation of finches would not necessarily have had deep beaks. The range of variation (or population mean) might go back to what it was before the drought. The change in one generation must be passed on to the next.

38 The Nature of Natural Selection  Natural Selection cannot predict the future (and neither can organisms) o The phenotype of a generation is a product of the environment that preceded it. If the environment stays the same, so will the phenotype of the population. But if the environment changes, there is no way the organisms would know that in advance. The finches with deep beaks could not predict the rain and the abundance of small seeds.

39 The Nature of Natural Selection  Natural selection can produce new traits, even though it operates on existing traits. Natural selection can only select from the range of variation that already exists in the population. o Paradoxically, evolution can produce new traits. Not from the range of variation that exists in a starting population, but, As a result of mutations that occur in each generation over time. Coupled with meiosis and fertilization (recombination) more variants are created for Natural Selection to act on. Could you produce a Brassica with more trichomes than in the initial population? Long-term selection for oil content of corn kernels.

40 The Nature of Natural Selection  Occasionally, novel characteristics can be generated through preadaptation (exaptation).  This occurs when a pre-existing trait is used in a novel way and is elaborated upon by selection. Leaves of butterwort (P. moranensis) are covered with glandular trichomes. _03_01_archive.html 3_01_archive.html WEDNESDAY, MARCH 31, 2010 Botanical Flypaper Butterwort plants Non-glandular trichomes

41 The Nature of Natural Selection -activity  Natural Selection does not predict perfection Fig. 1.Collection sites for G. affinis (A) and G. hubbsi (B). Open symbols represent predator- free populations, and filled symbols represent predator populations. Outer labels of maps represent latitude and longitude values. Labeling beside collection localities identifies populations and corresponds with those presented in Fig. 2. Langerhans R B et al. PNAS 2005;102:

42 The Nature of Natural Selection Divergence in gonopodium size, controlling for body size, between predator regimes in G. affinis (A) and G. hubbsi (B). Data were pooled across years for both species. Least-squares means ± 1 standard error from ANCOVAs are depicted. Open bars represent predator-free populations, and filled bars represent predator populations. Population names are as in Fig. 1.Fig. 1 Female mating responses to videos of a male with a small vs. large gonopodium. (A) Females spent more time directly interacting with the large-gonopodium male than the small-gonopodium male (P < ). (B) Females approached the large-gonopodium male within one body length more times than the small-gonopodium male (P = ). Means ± 1 standard error are depicted.

43 The Nature of Natural Selection  Fitness is not Circular Of course cacti are more likely to survive and reproduce in the desert – that’s because they have the traits that permit them to do so. “Survival of the fittest.” (Herbert Spencer, 1864) Of course the fittest survive! The weakness in our thinking is we forget the fundamentals of how natural selection works. For natural selection to operate, there must be a range of variation in the population for a trait. The environment eliminates those individuals who do not possess the trait that permits them to survive. Even if they do survive, they may not reproduce as much as a conspecific that has a different trait. Fitness can be measured = the number of offspring

44 The Nature of Natural Selection  Natural Selection Acts on Individuals, not groups. Groups of individuals are not selected for. Neither are species. The environment acts on each individual separately. An individual that puts its life on the line for the sake of another will be quickly selected against and eliminated from the population. Self-preservation will be selected for. Group selection may seem to occur (kin selection) because individuals in the population are closely related (e.g. social insects, Hymenoptera). Group selection is considered by many to be theoretically possible and has been demonstrated in a laboratory setting.


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