Chapter 12 Life on Earth: The Big Picture Introduction to Philosophy of Biology: Sex and Death

History of life & directionality Weak Particular taxa evolve at particular points in time Strong Particular kinds of taxa evolve at particular points in time

‚Murky‘ Directionality is… Progress (12.1 ) Changes in Disparity (12.2/12.3) disputed and contingency of life‘s history emphasized (12.4) possibly cut down by mass extinctions (12.5)

Directionality is „progress“ Possible conceptualizations of progress: 1)Progression towards homo sapiens 2)Progressive adaptiveness (Dawkins) 3)Arms races (Dawkins) 4)Progressive increase in complexity (Gould)

Progress is adaptiveness (Dawkins) Weak : Organisms of today are better adapted to the environment than earlier ones (i.e. comparing two organisms of one population) Strong : Weak thesis + „…over million of years“ (requiring a ‚general‘ property of adaptiveness)

Progress is visible in arms races (Dawkins) Thesis: Arms races between competing lineages define a direction of progress Problems: -Prolonged arms races reconstruct the environment -May involve a „rock/paper/scissors“ evolutionary shuffle

Progress is Increase in Complexity -Intuitive -Complexity measures -Property status (relative/ objective) 1)Dawkins: ascribed though objective: complexity = length of description of an organism at a fixed level of description 2)Gould: complexity = spread of ‚variation‘

Gould‘s variations Life starts off simply and usually stays there Complexity increases by passive diffusion from a point of origin (undirected, stochastic process) Real change is increase in total variance (bias in the direction of complexity) –Facts, presumably: No mechanism of adaptation/ speciation/ extinction favours complexity Bacteria dominate => Complexity drifts upwards undirected

Smith and Szathmary vs. Gould Thesis: Series of major transitions and hence inherent directionality ( RNA, DNA, eucaryotes, (plants, animals, fungi), human language) Crux (according to Sterelny& Griffith) –Different pictures of variation

Gould vs. S.&S.: Structures of variance Gould: - lower limit to complexity - no upper limit - Gradual spread to higher complexity S.&S.: -„evolution of evolvability“, i.e. dynamic re-limitation - Major transitions= movements of points of max. complexity (=> min. complexity)

Gould‘s challenge (12.2) Claims -expectation that complexity/diversity of life increases gradually over time due to natural selection is mistaken -Therefore the received view is also mistaken

Gould‘s case: The Burgess Shale fauna -Cambrian explosion -7-8 phyla found that are not existent today Therefore: -Orthodox conception of the shape of tree of life is wrong -Diversity increased, but disparity DEcreased

TreesTrees oflifeoflife The received view Gould‘s view

Gould‘s conclusions & interests -„overestimation of the role of selection in evolution“ -Selection plays no role in generating/ reducing disparity -History of life is contingent -Small change (t 0 ) => big change (t 1 ) -Outcomes sensitively dependent on initial conditions => „Survival of the luckiest“

The Concept of Disparity Question: What is it and how (if at all) has it changed? Model: morphosphere= space that represents the physical forms of all actual and possible organisms –Similar forms close together b/c similar sets of physical propertied describe them –Disparity = Size of morphospace for life existing

Disparity and Morphospace Challenges Distances in morphospace (if any) are not measureable) - trait choice, weighting -The Cladist‘s anti-subjectivist argument -Properties important for genealogy ≠ Properties important for disparity -Property lability and retrospective fallacy

Contingency (12.4) Contingency hypothesis= Important features of life are not counterfactually resilient –Importance of particular events in shaping history of life and unpredictability of consequences –Some features of life not predictable by physics No robust process explanations possible

3 Types of Contingency 1)Contingency of specific taxi -Implication of the received view 2) Contingency of Adaptive Complexes -undercuts idea that traits are robustly explained by a selective environment -Inconsistent w/ any kind of empirical adaptionism 3)Contingent Explorations of Morphospace  It seems that: 1 uncontroversial, 2/3 are relatives of Gould‘s anti- adaptionist criticism and besides, hard to test

Mass extinction (12.5) Claim (Whose) -Major transitions of life are defined by mass extinction, not routine or background extinction -Disparity of life depends on extirpation of dominant groups Challenge: -Difference b/w mass and background extinction -Accept importance of mass distinctions but re- evaluate their importance (Sepkowski)

The Importance of Mass Extinction Gould : YES, b/c mass extinctions -Change the ‚rules‘ of evolution -Have a profound effect on biota  Make explanations extrapolating from changes in local populations into ‚ecological time frames‘ impossible Sterelny : NO, b/c mass extinctions -Just change the outcome: normal operations in an abnormal world -Is consistent w/ mass extinction fundamentally reshaping the tree of life  Mass extinction is no threat to the received view

Review: The concepts of Directionality Progress Complexity Disparity Contingency Mass extinctions