Download to read offline
Animal Behaviour – SEXUAL SELECTION IN ANIMALS
- 1.
- 2. SEXUAL SELECTION • Specialtype of natural selection • Natural Selection – “Struggle for Existence” • Sexual Selection – “Struggles for Mates” • Male competition; female choice
- 3. THEORY OF SEXUAL SELECTION •Proposed by Charles Darwin in 1871 • “…the advantage, which certain individuals have over others of the same sex and species, in exclusive relation to reproduction.” • An explanation for beautiful plumage of peacock
- 4. • Considered itsignificant for the gradual perfection of the sexual process • Attributes to the development of plumage, courtship dances, songs, other secondary sexual characters and even female’s choice of mates THEORY OF SEXUAL SELECTION
- 5. INTRASEXUAL & INTERSEXUAL SELECTION Thedifferences in individuals’ breeding success rate depends on two factors: • Competition within one sex (mostly males) for access to members of opposite sex – Intrasexual selection • Choice by individuals of one sex (mostly females) for members of opposite sex – Intersexual selection
- 6. INTRASEXUAL SELECTION • Involvesthe male-male competition for a potential mate – mate rivalry • Observed in many species of birds and mammals • Examples include mate rivalry between two male red deers, elephant seals or sunfish
- 7. • Best explainedthrough the competition between two stags of red deer, Cervus elaphus • Initially, the males challenge each other by roaring • If the roaring capacity of both stags is same then they approach and walk parallel to each other • In some cases, they fight by interlocking antlers and pushing each other. MATE RIVALRY IN RED DEERS
- 8. MATE RIVALRY INELEPHANT SEALS • It is influenced by the female • When a male tries to copulate, the female elephant seal will make a loud call to alert all other males. • Then the males will fight and the first male to prove its dominance will get to copulate the female.
- 9. MATE RIVALRY IN SUNFISH •The males defend territory until the female comes and lays eggs. • As the female lays eggs, the male fertilizes them. • However, subordinate males (female mimics) may quickly dart-in between them • Thus, the male of choice and the subordinate male has the chance to fertilize the eggs of the female.
- 10. INTERSEXUAL SELECTION • Femalechooses a male based on certain traits • Huxley called it epigamic selection Bright, extravagant and colourful fins of fishes, long colourful tail of peacock, dancing as seen in birds of paradise and mating calls
- 11. CONTROVERSY • Wallace arguesthat male-male competition is a part of natural selection – form of struggle for existence • Bright and attracting features of males - attraction for predators • Argued that for the development of these features, lot of energy is required - against the principle of natural selection.
- 12. SEXUAL SELECTION IN HUMANS •Darwin (1871) thought sexual selection was more important than natural selection in the evolution of the differences between the human races • Geoffrey Miller – humor, music, visual art, verbal creativity & even vocabulary – not survival benefits but courtship adaptation favored by sexual selection Example: Miller (2000) proposed that greater vocabulary demonstrate intelligence (fitness) to potential mate Experiment: Males use greater lower-frequency vocabulary when in romantic mindset (Rosenberg & Tunney, 2008)
- 13. SEXUAL SELECTION IN HUMANS •Secondary sexual characters like facial hair, vocal characteristics appear to have been shaped by sexual selection • Men’s secondary sexual traits like robust face, beard and deep voice are more effective in intimidating men than attracting women • Men’s dominance and social status – preferences of women • Women’s physical appearance – competition for male choice (Puts, 2016)
- 14. CONCLUSION Though there aremany oppositions, it provides an explanation for certain features that cannot be explained by Natural Selection
- 15. REFERENCES – BOOKS #McFarlandD., Animal Behaviour – Psychobiology, Ethology and Evolution, Longman Group UK Ltd, 1985. #Gundevia H.S., Singh H.G., A Textbook of Animal Behaviour, 2nd Edition, S. Chand & Company Ltd., New Delhi, 2006. #Chattopadhyay S., LIFE – Evolution, Adaptation & Ethology, 2nd Edition, BOOKS & ALLIED (P) LTD., Kolkata, 2009. #Verma P.S., Agarwal V.K., Cell Biology, Genetics, Molecular Biology, Evolution and Ecology, Multicolor Edition, S. Chand & Company Ltd., New Delhi, 2009.
- 16.
- 17. REFERENCES – ARTICLES #Kirkpatrick,M. (1987). Sexual selection by female choice in polygynous animals. Annual Review of Ecology and Systematics, 18(1), 43-70. #Kirkpatrick, M. (1982). SEXUAL SELECTION AND THE EVOLUTION OF FEMALE CHOICE. Evolution, 36(1), 1-12. #Pellegrini, A. D., & Long, J. D. (2003). A sexual selection theory longitudinal analysis of sexual segregation and integration in early adolescence. Journal of experimental child psychology, 85(3), 257-278. #Puts , D. (2016). Human Sexual Selection. Current Opinion in Psychology, 7, 28-32.
- 18.