Sexual Selection and its Role in Evolution Relating to Gender Differences

1
Sexual Selection and its Role in Evolution
Relating to Gender Differences

• Megan Sims
• Biology Department
• Spring 2005

2
Sexual Selection What is it?

• Introduced by Charles Darwin
• Secondary sex characteristics evolve in one
  gender because the other gender prefers to mate
  with individuals having such features

3
Why Sexual Selection?

• Many characteristics are limited to one sex ?
  must be related to reproduction
• Often, these traits are only fully developed at
  maturity during breeding season
• Organisms of one sex are able to feel a strong
  allure or aversion to specific features

4
Sexual Selection Two Types

• Intrasexual selection - individuals of the same
  gender competing with each other to remove rivals
• Intersexual selection - individuals of the same
  sex compete to convince the surrounding females
  to mate with them

5
Fishers Process

• Female preference initially developed to favor
  traits desired by natural selection ? offspring
  are more likely to carry these traits
• Males having the preferred characteristic are
  considered even more fit
• Cycle ? ever increasing selective force favoring
  stronger preferences and more extreme traits

6
Direct Benefits of Fastidiousness

• obtain mate who may provide
• - paternal care
• - territorial defense
• - greater fecundity
• lowered chance of
• - mating with the wrong species
• - having mate who is infested with parasites

7
Ornaments

• Tusks, spurs, antlers, and horns
• Long tails in widowbird males
• Dark and intermediate coloring in
  Parasitic Jaegers
• Large, colorful trains in peacocks

From http//www.gamebird.com/India_Blue_peacock.jp
g
From http//www.illinoisbirds.org/parasitic.jpg
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Behavior (Courtship Rituals)

• Bowerbird of New Guinea
• Female cotton-top tamarins

From www.wanats.iinet.net.au/ LRX2003_p1.html
From http//www.csew.com/cottontop/images/ctop1.gi
f
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Humans

• Males typically score higher in imagined
  rotation, targeting, and maze reading
• Women show an advantage in spatial location
  ability

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Conclusion

• Most differences between males and females are
  primarily due to the process of evolution and
  sexual selection (essentially by female choice)
• These processes are evident not only in humans,
  but in much, if not all, of the remaining animal
  kingdom and certainly should not be neglected

11
References

• 1.   Bleie, T. (2003). Evolution, Brains, and the
  Predicament of Sex in Human Cognition.
  Sexualities, Evolution, and Gender, 5.3. 149-189.
•  
• 2.   Cooijimans, P. (2003). Sex Differences in
  Intelligence. Retrieved March 21, 2005 from
  httpsq.4mg.com/SexIQ.htm.
•  
• 3.   Ehrlich, P., Dobkin, D., Wheye, D. (1988).
  Sexual Selection. Retrieved April 5, 2005 from
  http//www.stanfordalumni.org/birdsite/text/essays
  /Sexual_Selection.html.
•  
• 4.   Sexual Selection. (1994). Retrieved April 5,
  2005 from
• http//www.zoology.ubc.ca/otto/PopGen500/Discuss
  ion3/Overheads.html.
• 5.   Stewart, D. (1995). The Importance of Being
  Flashy. National Wildlife Magazine,
  September/October. Retrieved April 5, 2005 from
  http//nwf.org/internationalwildlife/ornament.html