Handicapped by sexual selection

Handicapped by Sexual Selection


Hi! I'm Tim Tyler - and this is a video about mate choice, its possible long-term negative consequences, and what they might mean for the future of humanity.

Sexual selection

There are a number of selective mechanisms associated with sexual reproduction. Mate choice, cryptic fertilisation, same-sex rivalry, infanticide, forced copulation, and sperm competition are some of the types of selection involved.

Mate choice

This essay will be concerned mainly with mate choice. Female choice - which is usually what mate choice means - involves females deliberately selecting who they mate with.

The selective criteria which females use may be different from what is supplied naturally by other forms of selection. This can lead to conflicts between the targets of different types of selection.

The selective criteria used by females seem to be quite variable. Like spring fashions, what females like appears to have an unpredictable element. Sometimes utilitarian traits are in vogue - but at other times wild flamboyance is attractive.

To illustrate some more curious choices, consider this superb bird of paradise footage:

[Superb bird of paradise footage - taken from David Attenborough's "Planet Earth" series]

Female choice has some plus points. If male parental investment is rare, female choice can exert a powerful selective force on a population - helping to eliminate mutations and making it harder for pathogens to track their hosts' genomes down the generations.

However, here I want to focus on a particular problem associated with it. Female choice often has the most influence when natural selection is weak. This often happens on isolated islands - where common land predators have not yet arrived.

Once some trait becomes fashionable, it can "take off" - as males which exhibit the desired trait to a greater-than-normal extent act as a super-stimulus to females - and do especially well - transmitting the genes for both the exaggerated trait (and the desire for that trait) into the next generation.

This is known as "runaway sexual selection". In such cases, female choice can have powerful effects on the morphology of adult males.

To illustrate, consider this peacock:

[Peacock footage]

Such exaggerated adaptations can be viewed in a dim light by natural selection when predators eventually arrive on the scene.

The problem can be compounded by what is known as the handicap principle. Females do not choose desirable traits at random. Rather they often choose traits that reflect positive male attributes. Freedom from parasites is often valued - since it indicates good disease-resistance genes - and those are often important.

Females should not choose indicators that can be easily faked. Rather the chosen traits should be difficult to forge - so the results represent honest advertising. That often means that the displays should be costly and difficult for males to produce - so that only the best males can afford to produce them.

To illustrate, here are some Greater Sage-Grouse males, displaying on a Lek:

[Greater Sage-Grouse footage]

These males are handicapped by their sexual ornamentation - making them more likely to wind up as a predator's lunch.


Humanity has already seen the effect of runaway sexual selection - according to many theorists. Sexual selection is thought by many to be primarily what was responsible for inflating the human brain.

Here is Sue Blackmore on the Machiavellian intelligence hypothesis:

[quote from p.74 of The Meme Machine]

There's a nice popular work on the topic, Christopher Wills's The Runaway Brain.

Fortunately, so far, natural selection seems to be smiling on the large human brain. As well as being beautiful, big brains have turned out to be useful. However, mate choice does tend to exaggerate traits beyond what natural selection would produce alone.

Curiously, mate choice by males seems to be a relatively-powerful force among humans - responsible for the female breast, and other aspects of female ornamentation. Of course, females still have their say - most recently making beards blossom on men's faces, and taking away the bone in their penis.

The future

Now, the main reason I am discussing runaway sexual selection is because it closely resembles a phenomena which we might observe in the future.

Mate choice is an example of how the selection criteria that guide evolution can be chosen by intelligent agents - and this is part of a general phenomenon we may well see much more of in the future.

Also, humanity is isolated on a kind of island in space. Resources are abundant - and no predators seem likely to turn up any time soon.

Intra-species competition seems relatively unlikely to keep the effects of sexual selection in check - since we show signs of forming huge cooperative networks, where surveillance is ubiquitous and male combat is prohibited by law.

There may even be an equivalent of the handicap principle. Deviations from the optimisation target selectied by natural selection seem to be aesthetically favoured in some quarters - since they claim that nature's goals do not reflect human values - and that nature is ruthless and cruel - and so on. If such wildly different preferences are adopted en mass, they may well represent something closely analogous to the handicap principle.

It seems to me that our huge brain resembles the elaborate plumage of the birds of paradise. The biological function of love songs - and the like - among our ancestors was to give a signal of health, well being and fertility - in order to advance individual reproductive goals. That resulted in a runaway selection effect - favouring braininess.

All very well - in moderation: the high variance in male reproductive fitness produced by this type of sexual selection may help with the elimination of deleterious mutations and the battle against pathogens.

However, as with most runaway sexual selection processes, the extremes may well have the danger of extinction associated with them. The path involves ignoring utilitaran concerns, until one encounters predators - by which time, it may be too late.

The longer the runaway sexual selection process goes on in an uninhibited manner, the greater the chances that the species will come to a sticky end when predators return to the environment.

The current vast expenditures of resources on pornography and games seem like a sign to me that humanity is following a path much like that taken by the birds of paradise.

While we are isolated on our island paradise, we are busy developing beautiful plumage, in order to stimulate our imaginations - without much thought of possible future predators.

When deciding what we should collectively do, it might be helpful for our species to bear this perspective in mind. We should not blindly walk the path laid out for us by sexual selection - or another similar process of self-directed evolution.

Rather, we should look to the future, consider the probability of us eventually encountering predators - and then act accordingly.



  1. Wikipedia - Sexual selection

  2. Wikipedia - Handicap principle

  3. Tim Tyler - Destroy the Entertainment Industry

Tim Tyler | Contact | http://alife.co.uk/