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← Origins of Life: Astrobiology & General Theories for Life - The Multiple Origins of Life - Part 4

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Showing Revision 3 created 07/13/2020 by Alexis McMillan-Clifton.

  1. So why does
  2. an understanding
  3. of what an evolutionary agent is
  4. help us
  5. understand the origin of life,
  6. and in particular
  7. the multiple origins of life.
  8. And it's worth starting
  9. with a case study here
  10. This is Sol Spiegelman
  11. and he was a virologist
  12. and he was interested in the evolution
  13. of very simple viruses.
  14. And the virus he worked with
  15. was called Q Beta Phage.
  16. And this is a very small RNA virus.
  17. And he asked the following question:
  18. What is the minimum genome
  19. the Q Beta has to possess
  20. in order to successfully complete
  21. its life cycle?
  22. But he tricked the virus.
  23. He put a population of viruses
  24. in a test tube,
  25. along with enzymes
  26. that normally
  27. it would have to encode itself.
  28. But he ensured that those enzymes
  29. were always present.
  30. And what he observed,
  31. over multiple replication rounds
  32. of the virus
  33. in this new environment that he created,
  34. was that the virus became
  35. smaller and smaller and smaller,
  36. until it eliminated
  37. all the traces
  38. of the enzyme that now existed
  39. with certainty
  40. in the environment
  41. in which it was evolving.
  42. So we can interpret this experiment
  43. in the following way:
  44. here's a Venn diagram
  45. in one set
  46. of the viral genome V
  47. and another set, the environment,
  48. H, the host.
  49. And the intersection of these two sets,
  50. a gene shared
  51. by the virus and the host
  52. or the virus and its environment,
  53. and what Spiegelman discovered
  54. is that if you make
  55. the environment certain,
  56. then,
  57. the virus minimizes itself.
  58. It throws away all genes it doesn't need
  59. because they're already there.
  60. This is minimalogy.
  61. But he could have performed
  62. an alternative experiment,
  63. and made the environment
  64. very uncertain.
  65. And when environments are very uncertain,
  66. that is, you can't throw things away
  67. because you know they won't be there,
  68. then you have to encode them
  69. intrinsically.
  70. So a good example for us
  71. are vitamins.
  72. With respect to vitamins,
  73. we're minimal,
  74. because we know
  75. they're always there,
  76. we don't have to synthesize them,
  77. right,
  78. but many other genes we can't
  79. be certain we can acquire
  80. from the environment,
  81. so we have to encode them
  82. and transmit them ourselves.
  83. And we call that autonomy.
  84. So these are two different configurations
  85. for an adaptive agent.
  86. Now, many people would call
  87. a virus "non-living"
  88. because it depends on its host
  89. to replicate,
  90. but of course,
  91. we depend on the environment to replicate,
  92. too, because we need vitamins.
  93. So really there is a spectrum
  94. of adaptive agency.
  95. On the one hand,
  96. there are organisms that live
  97. in very certain environments.
  98. And they become simple.
  99. There are other organisms
  100. that live in very uncertain environments,
  101. and they become complex.
  102. They encode more and more
  103. in their genes.
  104. And life spans
  105. this informational spectrum,
  106. from organisms
  107. that encode very little about the world
  108. because they don't need to,
  109. to organisms that encode a great deal
  110. about the world,
  111. because they need to,
  112. to complete their life cycle.
  113. And when you think about it
  114. it in this information theory term,
  115. the way an organism,
  116. or life,
  117. or an agent really is,
  118. is a mechanism
  119. for acquiring adaptive information
  120. about the world that it
  121. propagates forward in time,
  122. then computer viruses,
  123. the block chain,
  124. the Constitution,
  125. and many, many other cultural forms,
  126. are essentially living.
  127. There's nothing special
  128. about
  129. the biochemical example,
  130. a replicated cell,
  131. because a replicating cell
  132. is simply a
  133. somewhat autonomous
  134. informational entity that is
  135. able to propagate itself
  136. forward in time,
  137. just like a Constitution
  138. can.
  139. But like a virus,
  140. the Constitution requires us.
  141. We are
  142. the vitamins
  143. of the Constitution.
  144. And this leads to a very open question
  145. that's worth debating.
  146. On one hand,
  147. we could be fundamentalist.
  148. We could say look,
  149. all of life depends on chemistry,
  150. and so finding the simplest chemistry
  151. that is capable of encoding
  152. adaptive information about the world
  153. is where life really started.
  154. But another possibility say,
  155. well not really, because at any scale
  156. that you can find this basic
  157. set of mechanisms,
  158. you're entitled to call it life.
  159. And you're even
  160. entitled to call it an independent
  161. origin of life.
  162. So by analogy,
  163. someone might say,
  164. "To understand architecture,
  165. to understand Gothic and Renaissance,
  166. or Baroque,
  167. or Rococo architecture,
  168. you need understand quantum mechanics."
  169. And I think that would be foolish,
  170. because all of them of course
  171. ultimately depend on quantum mechanics,
  172. but it's not the differences
  173. in the physics
  174. that explain
  175. the differences in the architecture.
  176. That requires a higher level
  177. of understanding.
  178. And so the pluralist approach
  179. to the multiple origin of life
  180. says that every level,
  181. we need to find those unique mechanisms
  182. that can support
  183. propagation of information.
  184. And there isn't
  185. a "correct,"
  186. most basic level.
  187. It depends on
  188. the question that you're asking
  189. and the variation
  190. that you're trying to explain.