George+Mivart++Genesis+of+Species++Chapter+2_Excerpts

Chapter II: The Incompetency of Natural Selection

Natural Selection and Incipient Structures

• Mr. Darwin's theory suggests that Natural Selection acts via slight variations which must be immediately beneficial.

• Difficulties arise in accounting for the beginnings of useful structures through Natural Selection.

• Examples challenging Natural Selection: Giraffe neck, mimicry in insects, vertebrate limb origins, whale-bone development, kangaroo young, and structures of sea-urchins.

Darwin's Position on Variations

• Darwin claims that natural selection can explain significant modifications after they arise but struggles with tiny, rudimentary beginnings.

• Quotes from Darwin:

  • "Slight individual differences suffice for the work..."

  • "Natural Selection acts only by the preservation of small inherited modifications."

• Emphasizes that if complex organs exist that cannot be formed by slight modifications, his theory would collapse.

Case Study: Giraffe Neck

• Giraffe's long neck seems advantageous during droughts, enabling high feeding, thus favoring those with longer necks.

• Critique:

  • If true, similar modifications should have occurred in other ungulates, but they haven't.

  • The argument suggests too many species should develop similar traits if they faced identical pressures.

Variability in Ungulates

• Observations indicate ungulates have diverse adaptations without similar elongation of necks.

• Proposes that different species have varying survival adaptations beyond high-reaching abilities.

Biological Mechanics of Size Increase

• A substantial increase in size due to natural selection may present physiological challenges:

  • Larger animals require more food.

  • Increased size reduces strength-to-weight ratio, complicating survival.

Limitations on Evolutionary Time Frame

• Evolution's immense duration is finite, questioning the notion that favorable and unfavorable variations could effectively balance each other.

Mimicry as Protective Adaptation

• Wallaces studies on mimicry highlight its role in species survival via resemblance to harmful species.

• Notable examples of mimicry include:

  • Heliconidae butterflies in South America with protective coloration and odor.

  • Kallima butterflies resembling leaves in both color and behavior.

Imperfections in Evolutionary Theories

• Natural selection struggles to explain complex adaptations like the asymmetrical heads of flatfish or intricate mimicry found in certain insects.

• Observations suggest that minute early variations would not lead to the full development of mimicry or structural features.

Conclusion

• The chapter underscores significant challenges to Darwinian mechanisms in explaining the origins and developments of complex biological structures.

• Many proposed adaptations via slight variations lack clear pathways, challenging the sufficiency of Natural Selection.

Mivart thinks that Natural Selection cannot explain the unique reproductive features of kangaroos, particularly the development of their young in pouches, as this trait involves a complex adaptation that appears too specialized to arise solely from gradual variations.