What is Natural Selection? — Transcript

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1. 0:00This episode of State Clearly was only possible with support from our viewers,
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3. 0:08to patients,
4. 0:09new treatments for Alzheimer's.
5. 0:15Stated Clearly presents:
6. 0:17What is Natural Selection?
7. 0:23Natural selection is one of several key concepts
8. 0:26contained within the theory of evolution.
9. 0:29To understand exactly what natural selection is and
10. 0:32why it's so important
11. 0:33let's first take a quick look at two other evolutionary concepts:
12. 0:37Descent with Modification
13. 0:39and the overarching idea
14. 0:40of Common Descent.
15. 0:44Descent with Modification
16. 0:46is the observable fact
17. 0:48that when parents have children, those children often look and behave slightly
18. 0:51different than their parents,
19. 0:53and slightly different than each other.
20. 0:55They descend from their parents with modifications.
21. 0:59The differences found in offspring
22. 1:00are partially due to random genetic mutations.
23. 1:05Common Descent
24. 1:06is the idea that all life on Earth is related.
25. 1:09We descended from a common ancestor.
26. 1:12through the gradual process of descent with modification over many many
27. 1:15generations,
28. 1:17a single original species is thought to have given rise to all the life we see
29. 1:20today.
30. 1:22the common descent of all life on earth is not a directly observable fact.
31. 1:26We have no way of going back in time to watch it happen.
32. 1:29Instead,
33. 1:30Common Descent as a conclusion based on a massive collection of observable facts.
34. 1:35Facts found independently in the study of fossils
35. 1:38genetics
36. 1:40comparative anatomy
37. 1:42mathematics
38. 1:44biochemistry
39. 1:46and species distribution.
40. 1:48Because the evidence for common descent is so overwhelming,
41. 1:52the concept has been around since ancient times.
42. 1:55In the past however, it was rejected by many philosophers and scientists for one
43. 1:59main reason:
44. 2:00You cannot get order and complexity from random chaos alone.
45. 2:06The bodies and behaviors of living things
46. 2:08are extremely complex and orderly.
47. 2:11Descent with Modification
48. 2:12simply produces random variation.
49. 2:15All through history
50. 2:17no one could explain how complex life arose from simple life through random
51. 2:20variation,
52. 2:21until Charles Darwin discovered Natural Selection.
53. 2:26Charles Darwin, who lived from 1809 to 1882
54. 2:30was a naturalist:
55. 2:31someone who studies nature.
56. 2:33At the start of his career
57. 2:35he traveled the world by ship,
58. 2:36collecting and documenting plants and animals.
59. 2:40During his travels,
60. 2:41Darwin became very interested in the idea of common descent.
61. 2:46He noticed that islands contain species of plants and animals unique to those
62. 2:50islands,
63. 2:51they can't be found anyplace else on earth,
64. 2:53but they often look and behave surprisingly similar to creatures found on
65. 2:57nearby continents.
66. 3:01Tortoises on the Galapagos islands
67. 3:03can be distinguished from those of Africa,
68. 3:05meanwhile,
69. 3:06with the exception of size,
70. 3:07they're almost identical to a species found nearby in South America.
71. 3:12Darwin believed the similarities could be best explained through Common Descent.
72. 3:18Long ago a tortoise from the mainland may have drifted to the islands,
73. 3:22possibly on a raft of storm debris,
74. 3:24and once arriving,
75. 3:26laid her eggs.
76. 3:29Random changes caused by Descent with Modification over thousands of years,
77. 3:33eventually transformed the island creatures and the mainland creatures so
78. 3:36much, that they could no longer be considered the same species.
79. 3:41This idea made good sense to Darwin
80. 3:44except for one thing:
81. 3:46the island creatures he found were not just randomly different from their mainland
82. 3:49cousins,
83. 3:50they were specially adapted for island life.
84. 3:55the Galapagos
85. 3:56is a collection of 18 main islands, many of which are home to tortoises.
86. 4:01The larger islands have lots of grass and vegetation.
87. 4:04Tortoises there grow extra heavy
88. 4:06and have dome like shells.
89. 4:09Some of the smaller islands have very little grass,
90. 4:12forcing the tortoises to feed on island cactus.
91. 4:15the best cactus pads grown the tops of these plants.
92. 4:19Fortunately,
93. 4:20tortoises on these islands are equipped with expanded front legs and saddle like
94. 4:24shells
95. 4:25allowing them to stretch their necks extra long to reach their food.
96. 4:30It's almost as if these island creatures
97. 4:32have been perfectly sculpted to survive within their unique environments.
98. 4:37How did this sculpting take place?
99. 4:40Random Descent with modification alone
100. 4:42could never do such a thing.
101. 4:44Darwin drew upon his knowledge of selective breeding
102. 4:47to answer this question.
103. 4:50For thousands of years,
104. 4:51farmers have been taking wild plants and animals,
105. 4:54and through the process of selective breeding,
106. 4:56have sculpted the original wild forms
107. 4:58into new domestic forms,
108. 5:00much better suited for human use and consumption.
109. 5:04The process is slow but simple
110. 5:07if a single plant produces a hundred seeds,
111. 5:09most will grow to be nearly identical to the parent plant.
112. 5:13A few however, will be slightly different.
113. 5:15Some variations are undesirable:
114. 5:17smaller size,
115. 5:19bitter taste,
116. 5:20vulnerability to disease and so on.
117. 5:22Other variations are highly valued!
118. 5:25Thicker sweeter leaves for example.
119. 5:28If a farmer only allows the best plants to reproduce and creates seeds for the
120. 5:32next crop,
121. 5:34small positive changes will
122. 5:36add up over multiple generations,
123. 5:38eventually producing a
124. 5:39dramatically superior vegetable.
125. 5:44You might be surprised to hear that broccoli
126. 5:46cauliflower, kale,
127. 5:48brussels sprouts,
128. 5:49and cabbages, are all just different breeds of a single type of weed
129. 5:54commonly found along the shores of the English Channel.
130. 5:57The evolution of this original plant
131. 5:59into all the varieties we see today
132. 6:01was carefully guided by different farmers around the world,
133. 6:04who simply selected for different traits.
134. 6:08It's important to note,
135. 6:09that the farmer doesn't actually create anything.
136. 6:12Random Descent with Modification creates new traits.
137. 6:16The farmer simply chooses which of those new creations are allowed to reproduce,
138. 6:20and which
139. 6:20are not.
140. 6:22Darwin proposed that nature itself
141. 6:25is also capable of selection.
142. 6:28It may not have an intelligent brain like a farmer,
143. 6:31but nature is an extremely dangerous place in which to live.
144. 6:34There are germs which can kill you.
145. 6:37Animals that can eat you. You could die of heat exhaustion.
146. 6:41You could die of exposure to the cold.
147. 6:45When parents produce a variety of offspring,
148. 6:47nature,
149. 6:48simply by being difficult to survive in, decides which of those variations get to
150. 6:53live in reproduce,
151. 6:54and which do not.
152. 6:57Over multiple generations,
153. 6:58creatures became more and more fit for survival and reproduction within their
154. 7:02specific environments.
155. 7:04Darwin called this process Natural
156. 7:07Selection.
157. 7:09Since Darwin first put forth his idea in the mid 1800s
158. 7:13Natural Selection has been studied and witnessed
159. 7:16numerous times in nature and in the science lab.
160. 7:19What started out as a mere idea is now officially
161. 7:23an observable fact!
162. 7:26Darwin's discovery has greatly expanded our understanding of the natural world
163. 7:30it has lead to amazing new breakthroughs,
164. 7:32and it finally allowed scientists
165. 7:34to seriously consider the idea of Common Descent.
166. 7:39So to sum things up,
167. 7:40What exactly is natural selection?
168. 7:43Natural Selection
169. 7:45is the process by which random evolutionary changes are selected for by
170. 7:49nature
171. 7:50in a consistent
172. 7:52orderly
173. 7:53non random way.
174. 7:55Through the process of descent with modification, new traits are randomly
175. 7:59produced.
176. 8:00Nature then carefully decides which of those new traits to keep.
177. 8:04Positive changes add up over multiple generations,
178. 8:07negative traits are quickly discarded.
179. 8:10Through this simple
180. 8:11ongoing process,
181. 8:13nature,
182. 8:14even though it may not have a thinking mind,
183. 8:17is capable of producing incredibly complex
184. 8:20and beautiful creations.
185. 8:22I'm Jon Perry,
186. 8:24and that's Natural Selection stated clearly!
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