This is important because this theory of a “biological guiding hand� supports their assertion that hunter gathers did not and will not need to be consciously concerned about population control.

Most hunter-gatherers have cultural practices that limit their population, as well. Extended breastfeeding periods are not only healthier, but they also space out birth. Consciously, though, foragers tend to identify these as freeing the mother from carrying children more than spacing out births. Emic and etic.

I asked for a reference.

That’s difficult–it’s a fairly basic tenet of ecology, and basics are always difficult to cite, since everyone takes it for granted. Dr. Thornhill addresses this in detail in his video with Daniel Quinn, “Food Production and Population Growth.”

This is important because this theory of a “biological guiding hand� supports their assertion that hunter gathers did not and will not need to be consciously concerned about population control. In this way they were and will be exempt from the tragedy of the commons.

I am at a disadvantage because my background is in electronic control systems and not in anthropology or biology. However I have a strong intuition that this theory is false. I need more time to critique it properly. I intend to do that, but I don’t want to participate in a “pissing contest� now.

Jason: The last time you responded with this answer, (http://anthropik.com/2006/01/thesis-26-collapse-is-inevitable/#comment-4457) I asked for a reference. You didn’t give one but, as I indicated above, I have found some.
Although this natural world is full of suffering, I don’t consider it cruel as that would require intention.

In fact, it almost never comes to that. When the lion population grows, the herds of gazelle decrease. Fewer gazelle are harder to find, so lionesses spend more time hunting–and less time having sex. That lowers the birth rate, which lowers the population. With less predation, the gazelle population goes up, making them easier to find, so the lionesses don’t have to spend so much time hunting. That gives them more time to have sex, so the birth rate goes up, so the lion population expands, and so much predation brings down the gazelle population. Rinse, wash, repeat.

Starvation is only the most extreme control available–and rarely used.

As far as I know all mammals will reproduce at a rate fast enough to keep their population increasing. If other environmental stress (predators, weather, disease, lack of water, fire, etc.) doesn’t prevent it, the population will increase until some individuals starve.

What is here being referred to as “environmental stress” are in fact all completely natural factors in the living systems of this planet. Of course any population will increase if there are zero factors affecting lifespan other than “old age”. But that is a straw argument if ever there was one — it will never happen, has never happened. Predators, weather, drought, etc., are all factors that have and will ALWAYS be around and impact populations (especially mammals), so what is the point being made here?

It strikes me that you are describing the mechanisms of ‘Punctuated Equilibrium’ but in a way that suggests that that speciation event occurs constantly…

To back up a little…

Evolutionary Biology has two primary schools of thought. Punctuated Equilibrium and Stable State. Both consider the mutation rate to be statistically constant.

What they disagree on is the way that these mutations move through a population. Obviously direct, fatal mutations are always self eliminating, but then we need to consider adaptions that slightly improve or hinder organisms.

In Punctuated Equilibrium, these adaptions build up within a population with little or no effect until an environmental change occurs. The smaller the population size and the more isolated it is, the more dramatic these changes will be as a result. This is the point where you normally see speciation events… assuming that the affected adaptions (mutations) have spread through the population effectively, once the crisis is passed there is a decent chance that the remaining population is distinctly different from the original.

In Stable State, the argument is that mutation rates AND adaptive changes in the population overall both occur at a relatively stable rate. So what happens is that slight improvements in adaptive traits confer slight advantages to the host animal allowing them to be slightly more successful doing all of the things that allow them to survive and propogate.

In my mind, both of this scenarios occur in natural populations. Gradual genetic drift over time combined with dramatic events in times of stress. This, to me, is the most logical and complete view of both drift and speciation.

Now, I would like to point out that if you decide to read up on PE that you be a bit cautious. I have described PE as originally presented by Gould et al back in the `70’s. However, since that time, the theory has been driven into more extreme territory — that ALL change ONLY occurs during puctuation events, perhaps some hints of group selection (which is blantantly and demonstrably false, IMHO) etc. Even Gould himself appears to have gone along with some of this… but that is distinctly different from what I am talking about and willing to consider plausible.

On your last question: natural selection can select the more fit, simply by MORE, more fit individuals being born into the population. At the end of the day, ALL selection CAN BE reproductive… ie, a really good hunter is more likely to survive to reproduce than a poor one, someone that walks a little more silently is slightly more like to avoid predation… so one, and so forth. Very subtle effects that can and do affect the whole population on an extremely large time scale (and then magnified, for short sudden bursts in times of stress.)

Janene

Selection for abilities to survive environmental stress requires those with the least ability to die.

You keep saying it, but it keeps not being true.

I think in context you should have seen that I meant natural selection. Selection that occurs because of mating choice or elimination of variations unable to reproduce will not select for adaptations that improve a species ability to survive environmental conditions. Only artificial selection, where mates are intentionally selected for survivable qualities, can accomplish this.

Natural selection is based on the principle that all species increase exponentially until they reach environmental limits by producing more than enough young to maintain a constant population. When the environmental limit is reached the death rate must meet the birth rate to maintain a constant population. At this time those individuals least able to survive die and the species adapts to its environment A species that evolved the ability to control its birth rate and prevent this process would be an exception to this principle. When the population is not yet environmentally stressed, sexual selection occurs. This process will select for reproductive ability and qualities that affect mate preference.
If you know how natural selection could select the more fit individuals without eliminating some of the unfit please explain.

Selection for abilities to survive environmental stress requires those with the least ability to die.

You keep saying it, but it keeps not being true.

When surviving in spite of environmental limitations is the selecting factor, only a few of those of the disadvantageous variation must die. This process does gradually select for more advantageous traits although only a few are dying from environmental stresses.
The process you are speaking of works well for traits that affect reproduction. However, for traits that improve survivability only to the extent they also improve reproduction. This will only happen in the real world while a species is increasing to fill its nitch. A species that had unlimited resources and no enemies that caused deaths would evolve in this manner while improving its reproductive rate. If it were in a non-infinite environment, however, it would reach the limits of its resources and revert to normal natural selection with deaths.
This scenario will only be avoided if births are limited either naturally or intentionally. If this is the case, however, an increased reproductive ability will not be an advantage. We are left with genetic drift or, if under intentional control, artificial selection.

Because the ponies with the advantageous gene would be able to find more food at times when it is scarce. So when mating season comes along, they would be stronger and healthier, more likely to concieve, more likely to successfully give birth and more likely to bear healthy offspring.

Otherwise, you are relegating natural selection to only a negative mechanism: it would NEVER be able to select among advantageous genes, only lethal ones…

Janene