Reading 1

• What is the main topic of Chapter XV?

  Recapitulation and conclusion of Natural Selection

  
• What does the author acknowledge about the theory of Natural Selection?

  Many serious objections can be raised
• What is the author's stance on the complexity of organs and instincts?

  They are perfected by slight variations
• What propositions does the author believe support the theory of Natural Selection?

  Individual differences, struggle for existence, gradations
• What is a significant challenge in understanding the perfection of structures?

  Conjecturing the gradations of structures
• How does the author view the existence of defined castes in ants?

  It presents a curious difficulty for Natural Selection
• What contrast does the author mention regarding species and varieties when crossed?

  Species are often sterile, varieties are fertile
• What does the author suggest about the sterility of crossed species?

  It is incidental to reproductive system differences
• What conclusion does the author draw from the results of reciprocal crossing of species?

  It shows significant differences in fertility
• What does the author say about domestication and sterility?

  Domestication tends to eliminate sterility
• What does the author imply about the effects of slight changes in life conditions?

  They can increase vigor and fertility
• What happens when individuals of the same variety are subjected to uniform conditions?

  Benefits from crossing diminish or disappear
• What is the outcome for species under new and changed conditions?

  They may perish or become sterile
• What does the author suggest about hybrids produced from distinct species?

  They are often few in number and sterile
• What does the author say about geographical distribution and species descent?

  Species descended from common parents
• What does the author believe about the migration of species?

  It has occurred over long periods
• What does the author state about the geological record?

  It is more imperfect than believed
• Why does the author argue against expecting many linking forms in geological records?

  Due to the imperfection of the geological record

  
• What does the author suggest about the classification of linking forms?

  They may be misclassified as new species
• What does the author imply about the discovery of fossil links in the future?

  Many fossil links may remain undiscovered
• What does the parent form of species not represent?

  All characters of its modified offspring
• Why can't we recognize a species as a parent of another?

  We lack most intermediate links
• What is a limitation of the geological record?

  It is imperfect
• What happens if linking forms are discovered?

  They may be classified as new species
• What do many species do after formation?

  Become extinct without modified descendants
• Which species vary most frequently?

  Dominant and widely ranging species
• What is a characteristic of local varieties?

  They spread only after considerable modification
• What do fossiliferous formations require for accumulation?

  Much sediment on subsiding sea beds
• What happens during periods of subsidence?

  More extinction occurs
• What hypothesis is mentioned regarding the Cambrian formation?

  Older formations may lie buried beneath oceans
• What is a significant objection to the theory of organic change?

  Insufficient time for assumed organic change
• What does geology declare about species over long time intervals?

  Species have all changed
• How do fossils from consecutive formations compare?

  They are more closely related
• What is the relationship between the geological record and the theory of descent?

  The geological record supports gradual change
• What governs variability in domesticated species?

  Complex laws and conditions of life

  
• What can be inferred about inherited modifications?

  They can persist for many generations
• What role does man play in variability?

  He exposes beings to new conditions
• How does man influence breed characteristics?

  By selecting individual differences
• What is the result of unconscious selection by man?

  Formation of distinct and useful breeds
• What does the struggle for existence arise from?

  High geometrical ratio of increase