Mate selection in Humans: Revision.

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Sexual selection

 

Behavioural ecology is the study of how behaviour contributes to survival and then of course, reproduction.

Thus determining the 'fitness' of the individual.  

 

In this terminology, 'fitness' means the survival of one to pass on its genes (offspring).  Viability basically.  It doesn't mean going to the gym!!

 

Today it is believed that If a trait is changed and it increases sexual success, it will be favoured by selection even though it may lower the probability that the individual will survive.  Majority of animals have one goal in life and that is to keep their genes going by reproducing. Darwin thought that sexual selection was actually a special case of natural selection.  Traits associated with mating success and partner choice could reduce fitness.  This however is not the view that we have today.

 

Choosing

Most often than not Females exercise more choice because:

  • Gametes are bigger and are more energetically expensive to produce
  • The femal gametes are limited, so limited opportunities to breed
  • Usually exhibit more parental care.

Things that females may find 'attractive' are the general things like body size, general health, colouration and adornments, territory quality.  In human terms, are you Mr. Muscles?  Are you healthy?  Tall, dark and handsome?  Rich, posh house?  If not then according to nature, you'll never mate... ;)  

 

There are two main types od selection:

 

Inter-selection: where males attemopt to persuade females 

Intra-selection: where males compete with other males for femal access

 

This has led to sexual dimorphism: the phenotypic differences between males and females.  

Often males are bigger, brightly coloured and have some sort of ornament or defining feature.  In Peacocks it is the tail, in some birds it is the song calling and then in deers its the antlers.  majoirty of females tend to be brown or grey in colour when the males may be blue, red, green etc and so can be seen apart.  The brighter the colours then the more likely the male is to be selected by the female.  These such features are seen as 'strong' and signal to the female good genes.

 

Fisher (1930) said that sexual preference of a particualr kind may confer a selective advantage and may become established in the species.  So how did female choice for adornments come about?

 

It is a 2-step process. 

Of course there is natural genetic variation.  eg. longer tails = better survival and so this has then been passed onto offspring as females have mated with long-tailed males and their sons survive better.  So there is also genetic variation in female choice; alleles for longer tails and alleles that make females prefere longer tails spread Together 

 

Males with longer tials are then favoured as they survive better and have better mating success (sexy-sons hypothesis).  A feedback runway process develops and then tail length only stops decreasing when higher mortality balances the mating advanage.  In simpler terms, if the tails becomes too long that it impedes escape from a predator then it will die and the too-long tail gene won't be passed on.  

 

Other explanations are that males traits are still directly related to fitness.  Zahavi (1977):

  • male colouration indicates low parasite load
  • fluctuating asymmetry
  • colour intenisty therefore related to fitness.  Colour therefore is an honest representation of fitness of an animal and cannot be 'faked' or hidden.  

2 examples of this are the LONG-TAILED WIDOW BIRDS & SWALLOWS

 

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