Lecture III: Major Points.

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1 9/20. Lecture III: Major Points. 1. the occupation of voyaging naturalists was conducive to reflection on the origin of species Herbert (1974) a. Darwin s hints. i. Ornithological Notes (1835). Journal of Researches (2 nd edition, 1845). 1 b. Wm. Webster (ship s surgeon HMS Chanticleer): If St. Helena of more recent origin than the continents, presence of distinct species thereon indicates that a successive creation of species goes forward, or that naturalists are wrong in their definition of species. 2. Alfred Russel Wallace. a. Supported himself by collecting S.A. and Malaysia. b. Early work in collaboration with Henry Bates. 1 Later republished as The Voyage of the Beagle. 1

2 c. Inspired by Vestiges to solve the species problem (1847 letter to Bates). d. Sarawak Law paper (W55) triggered a chain of events that led to production / publication of The Origin. 2

9/25. 1. Sarawak Law Paper Every species has come into existence coincident both in space and time with a pre-existing closely allied species. a. Induced from distributional patterns in time and space.

3 9/ Sarawak Law Paper Every species has come into existence coincident both in space and time with a pre-existing closely allied species. a. Induced from distributional patterns in time and space. i. Taxonomic affinity. Tree of life, i.e., dichotomous branching. i Difficulties in classification many branches have no living representative. iv. Geographic replacement of groups the higher the group the greater the required separation e.g., genera (mountain ranges) vs. families (continents). v. Endemism on islands result of age + isolation. vi. Distributions in time. 3

v Rudimentary organs anticipatory or vestigial. b. Necessitates what exists recall Lecture I c. Implications RE diversity of Galapagos finch species. 2.

4 v Rudimentary organs anticipatory or vestigial. b. Necessitates what exists recall Lecture I c. Implications RE diversity of Galapagos finch species. 2. According to his autobiography, Wallace convinced of DwM when writing W55, but had no conception of how or why each new form had come into existence. 3. W55 motivated by Wallace s desire to counter Edward Forbes Principle of Polarity, which AR felt characterized as an absurdity. 4. Darwin-Wallace-Lyell Timeline. 5. Wallace s planned book. 4

5 10/2. 1. Reaction to DW58 was muted. a. England (1997) claims that most i. Saw it as relating to on-going discussions of species and varieties Wollaston s views in particular. Ignored the more radical implications. b. Two negative responses (Boyd, Hussey) i. Did not ignore said implications. Condemned DW58 as wildly speculative. c. A third (Tristram) did ignore said implications and praised DW58 as providing a mechanism for generating varietal variation. 2. The Origin published the following November a. An abstract; no refs. b. Sold out the 1 st day. 5

6 3. Darwin spent the next 20 years completing his Big Species Book piecemeal. Among these later publicatins a. Provisional Hypothesis of Pangenesis (Animals and Plants under Domestication, Vol. II) b. Human evolution (Descent of Man and Selection in Relation to Sex). 4. Today, CD receives the bulk of the credit for having discovered evolution. 5. Wallace remained in the Dutch East Indies until a. Published The Malay Archipelago in b. Father of biogeography; Wallace s Line. c. Published Darwinism in 1889, 7 years after CD s death. d. Thereafter, the leading defender of evolution / Darwin. e. Rejected sexual selection and argued for a guiding hand of supernatural intelligence. 6

7 Wallacea where Oriental and Papuan biotas intermingle. Wallace s line and lines drawn by subsequent authors indicated by dotted lines. Shallow seas that Wallace believed to have been dry land during the Pleistocene shown in lightgray. Figure from Erdelen, W. R Pp In, Metcalfe, I. et al. Faunal and Floral Migration Balkema, Lisse, NL. 7

8 Date Darwin Wallace Lyell 1859 Publishes Origin; Sells out 1 st day. Completes and expands Natural Se- Next 20 years lection piecemeal. Spring Publishes Animals and Plants under Domestication. Includes Provisional Hypothesis of Pangenesis Returns to England Publishes The Geological Evidences of the Antiquity of Man 1869 Publishes Malay Archipelago Publishes Contributions to the 1870 Theory of Natural Selection. Publishes Descent of Man, and 1871 Selection in Relation to Sex Publishes Expression of the Emotions in Man and 1872 Animals Dies 1882 Dies Becomes leading defender of evolution, CD in particular Publishes Darwinism 1914 Post-Origin Darwin-Wallace-Lyell Timeline Publishes The World of Life: A Manifestation of Creative Power, Directive Mind and Ultimate Purpose Dies 8

9 6. DW58: Wallace s Thesis a. Presumed instability of natural varieties not supported by the observation that domestic breeds released into the wild revert to something like the presumed ancestor. i. Based on the assumption that domestic breeds and natural varieties analogous. An equivalence that Wallace rejects because domestic productions are creations of man, not nature. b. Instead ARW proposes a mechanism that can cause both i. Varieties in nature to depart further and further from the parental type, and Domestic breeds escaped into nature to revert. 9

10 7. Wallace s Argument in Detail a. Abundance in nature determined by resource availability, not reproductive rate example of passenger pigeon. b. Principle of Malthus numbers that die enormous; those that perish, the least fit. c. Selection ubiquitous. i. Equilibrial densities of homogeneous populations, each of a different type, determines which types will survive and which will be extinguished. 2 In today s parlance, carrying capacity, K i, of the i th type a measure of fitness d. Scenario for replacement of one variety by another. i. Within population winnowing of formerly inferior, but nonetheless coexisting, types during bad times If a superior variety then arises, it will outcompete the original even if good times return. 2 Given 19 th century ignorance of hereditary mechanisms, this was about the best anyone could do. 10

11 e. Selection not frustrated by chance because the numbers are enormous. f. Domestic varieties i. Would not evolve absent human intervention because they cannot survive under natural conditions. Must therefore revert or perish. g. Acquired characters not inherited giraffe scenario. h. Trade-offs: varieties in which an unbalanced deficiency occurred could not long continue their existence. 8. Wallace anticipates impt. contemporary ecological ideas: a. Equilibrium density determines competitive outcomes. b. Invasibility a criterion of fitness. c. Coexistence of inferior and superior forms. d. Winnowing effect of periods of resource scarcity. 11

12 10/3. 1. Darwin Contributions to DW58: I. From the 1844 essay. a. Excess biotic potential. b. Changing environmental conditions induce variability. c. Struggle for existence. d. Natural selection. e. Sexual selection. 2. Darwin Contributions to DW58: II Letter to Asa Gray. a. Artificial selection. b. Darwin s Demon. c. Natural selection. d. Environmental change induces variability. e. Principle of Divergence 12

13 3. Principle of Divergence (PoD) a. Necessary to account for dichotomous branching. Its genesis a topic of continuing interest. b. CD claimed not to have figured it out til 1857 when he wrote about it to Asa Gray, but PoD appears to have been anticipated in the 1844 essay c. Richards (2012) argues that CD s thinking evolved: i. Decreasing emphasis on physical environment, and Increasing emphasis on ecological interactions: Natural selection, also, leads to divergence of character; for more living beings can be supported on the same area the more they diverge in structure, habits, and constitution. [Darwin (1859, ) quoted by Pfennig and Phennig (2010). Emphasis added] i Decreasing emphasis on allopatric speciation. iv. Increasing emphasis on sympatric speciation. d. Cat-mouse-bumblebee-clover system. 13

14 4. CD s theory of evolution. a. Sources of variability: i. Use and disuse Conditions of life i Inherent b. Indirect vs. direct action of the Conditions of Life, i.e., the environment. i. Indirect via the reproductive tissues random. Direct via the soma adaptive. c. Placed increasing emphasis on use and disuse and direct action of conditions of life in response to mounting criticism. d. Single vs. individual differences qualitative vs. quantitative differences. e. Selection theory compatible with, but doesn t necessitate evolutionary progress. 14

15 10/5. 1. Darwin vs. Wallace: Similarities. a. Darwin s Facts were Wallace s Facts b. Natural selection the principal evolutionary driver. c. Extinction of ancestral populations by descendent competitors the source of gaps in affinity among living species e.g., isolation (anatomical / physiological) of egglaying mammals. 2. Darwin vs. Wallace: Differences. a. Individual (Darwin) vs. group selection (Wallace) conflicting claims by historians, b. Variability i. Darwin: Partitioned as to kind (individual vs. single differences) and source (conditions of life acting on the germ and soma) Wallace: Intrinsic variability ubiquitous; sources unimportant and unknowable. 15

16 c. Domestication: i. Darwin (focusing on induced changes): Natural selection analogous to artificial selection which we know to be a vera causa see Ruse (1975). Wallace (focusing on varietal stability): What holds for domestic productions (tendency to revert) does not necessarily hold for natural varieties because the former are products of man, not Nature. d. Evolutionary Mechanisms i. Darwin: Selection one of several material forces. Wallace: Selection the only material force, but immaterial forces also important. e. Sexual Selection i. Darwin: Male-male combat and female choice. Wallace: Truth in advertising; no opportunity for females to choose in monogamous species with 1:1 sex ratios. 16

17 f. Sufficiency of secondary laws: i. Darwin: Yes. Continuity of variation. Wallace: No. Lack of utility; irreducible complexity. g. In sum: i. Darwin: a materialist. Wallace: An intelligent designer. h. Scientific differences complemented differences in age, social / economic status and politics. 17

Darwin s On the Origin of Species

Darwin s On the Origin of Species In search of a mechanism What is Darwin lacking? A mechanism no understanding of how these patterns arose September 1838:for amusement Darwin read the Essay on Population