sex-is-sacred

Previous page in order     Next page in order

Area:

Home page
  Thinking
    Nature


Topics:

Truth

Evolution

Human roots

Why sex?

Complexities

Normal sex

Human sex

Intelligence

Gay sex

Death

Hormones


General:

Links/resources

Parental control

Getting involved

Search

Site map

   JanesGuide rates us as Quality!

Evolutionary Complexities

The logic of natural selection is so simple and straightforward that it's easy to forget how complex its actual mechanisms really are, and to fall into the assumption that what we often observe, or what makes sense in the simple case, must always hold true. 

In recent years, though, a wealth of new observations and analysis have led evolutionary biologists to question many of the "self-evident" assumptions of the past.  Evolution in action often produces results wildly divergent from what the naive engineer might expect. 

Evolutionary parameters

One way of understanding this is to recognize that the process of selection has many parameters.  In fact, given how complex biological systems often are, it may be that in some cases we'll never be able to identify the interaction of these parameters sufficiently to understand the mechanisms that lead to the results we observe. 

Some parameters, on the other hand, are fairly obvious and do lend themselves to analysis.  It's not hard to see, for example, how various characteristics of the ecological niche in which evolution is occurring could affect the process of selection.  Examples of such factors are:

  • Resource fluctuations
  • Risk of resource exhaustion
  • Presence or absence of predation
  • Influence of disease
  • Overall niche stability

Another important class of parameters involve how easily and in what ways the evolving organism can change to adapt to the environment.  Such factors include:

  • Organism design fragility
  • Available mechanisms for rapid adaptation
  • Available mechanisms for gradual adaptation

All of these things may seem extremely obvious, but without considering them carefully, it's easy to jump to overly simplistic conclusions.  Below are some illustrations of what I mean. 

How important is speed of reproduction?

In niches where resources regularly fluctuate widely and rapidly enough over long enough periods, classic "simple" selection patterns often apply. 

For example, if resources increase significantly and rapidly on a regular basis over more than four or five breeding cycles (i.e. long enough for exponential growth rates to kick in), then the ability of an organism to reproduce rapidly is usually selected for.  This is the case for many insect populations with respect to the changes of the seasons, for instance. 

Since in a vague sense all niches can be assumed to be subject to resource fluctuations, it's easy enough to extrapolate that such a pattern of selection always applies — that every species must be designed with a big emphasis on speed of reproduction — and indeed, this still seems to be a tacit assumption of many biologists. 

On the contrary, as Bruce Bagemihl points out in his amazing and wonderful book, Biological Exuberance: Animal Homosexuality and Natural Diversity (page 196 and following), this is not at all the case — in many animal species, large percentages of the population abstain from reproducing altogether.  In some, such as New Zealand Sea Lions, Northern Elephant Seals, and naked mole-rats, as many as 80% to 95% of the population may not participate in reproduction. 

If we discard our simple assumptions, that doesn't actually seem so strange.  For one thing, many of the non-breeders are often males, so the fact that they don't breed has little impact on the overall reproductive speed of the group (since a single male can generally impregnate a great many females). 

But more important, consider that resource fluctuations favor rapid breeding only if the fluctuations themselves occur rapidly.  Gradual changes over decades, centuries or millenia will do nothing to favor the ability to reproduce rapidly.  Instead, ability to adapt to new conditions is much more important, which argues for maintaining greater genetic diversity, which is exactly what we see in a population where there's a significant number of non-breeders. 

Avoiding catastrophic success

There's also an obvious principle that applies to parasites and diseases — if you kill your hosts too successfully, you run out of hosts and then die yourself.  The same principle applies also to the relationship between many animal species and the resources they depend on. 

Any predator, for example, who can too successfully catch its prey will find that its population expands until the entire prey population has been caught, at which point all the predators in their turn starve and die.  To really be successful, a predator can't afford to be too good at catching the animals it depends on for food; instead, predators and prey must match their competence in such a away that their populations remain in symbiotic balance. 

This consideration is clearly relevant to humans, the most dangerous predators of all. 

The balance in question, of course, may be equally important for "prey," which often need predators to escape the same danger of success.  In the absence of adequate predation, herds of herbivores could grow to kill off the very plants they rely on for subsistence, and then die off themselves.


Previous page in order     Next page in order

Except where otherwise noted, material on this site may be copied freely and re-used provided that its authorship is clearly attributed to sex-is-sacred.org.

 Send us feedback! (last updated 24 June 2007)