We are too humane.

Hi CS - Good to see you are still asking some good questions.
There are several issues surrounding potential human evolution that you have raised here, either implicitly or explicitly. Stasis is a perception relative to time scales.
This might appear to be true if we think on the time scale of bacteria or insects, but not if we think on geologic time scales (provided we survive that long). you forgot to include "..before reproducing". I have often pondered this apparent conflict between human ethics and the lessons of population biology. The problem arises because of what is refered to as 'genetic load' in the population - the accumulation of various deleterious alleles in a population that occurs when selection pressures are relaxed.In terms of the frequency distribution of fitness among individuals in a population, however you define fitness, every natural population is like a huge bell curve with a short leading edge (representing a small minority of the 'most fit' individuals) and a much longer trailing edge (representing a large range of relatively 'unfit' individuals). The greater the genetic load of the population, the longer trailing edge becomes relative to the leading edge because selection is neither penalizing the unfit severely enough to curtail their reproductive success (RS), nor providing sufficently increased RS to the most fit in order to push forward the leading edge.So you are correct that by enabling the handicapped to survive to reproductive age (and encouraging their reproduction) we are increasing the frequency of the genes responsible for those particular handicaps. However, the problem is that the same 'physically' handicapped individuals may also possess 'mentally' superior genetics. So, for example, it would be difficult to objectively judge whether humanity would be better served or not by Stephen Hawking having children. Should we propagate the genes for a great intellect, but along with those that predispose ALS ?So on the surface, thinking simply of human evolution in terms of morphology and human physical fitness, it would seem that the consequences of medical interventions frequently defeat the natural evolutionary course of events. The best example I can think of is premature birth. The boundaries for the lowest survivable birth weight seem to be pushed forward every year. This can only mean that, over time, more and more babies will be born prematurely, only to require the same intensive care as their forebears, if not even more.But now let's think beyond the physical realm. There are various mechanisms by which the human species can evolve WITHOUT differential survival of individuals. Differential survival of groups can have a dramatic impact on population structure, and war is as prevalent as ever in our society. However, we don't usually kill off all our vanquished enemies as we might have at one time.A more intriguing, and far less widely recognized, mechanism by which I have little doubt we continue to evolve is sexual selection. Assortative mating can not only bring about unique genetic combinations, but can also affect the survival of alleles at population level. For example, mate-selection on the basis of intellect may be one of the reasons we are as intelligent as we are today. If 'smart' females consistently choose to mate with 'smart' males, this could conceivably accelerate the evolution of intellect in the population without any need for higher mortality among the stupid. This is because of a 'runaway' effect in which the adaptive benefits of intellect are obtained via getting the smartest possible mate and having the smartest possible children who, as a consequence also seek the smartest possible mates. You have to admit, humans are far more intelligent than they need to be just to survive and reproduce, at least until you add the element of group selection via tribal warfare etc. that provides added bonuses for cooperative ability.Another way humans can continue to evolve intellectually (and I would say this is far more important to our species than 'physical' evolution) without dramatic changes in population genetics is through culture. Culture can be thought of as another medium of information storage just like DNA, but one which does not require hundreds or thousands of generations to change at population level. I think this is along the lines of what was mentioned in message 50, except that the physical fusion of the human mind with machinces is not really a requirement for information perpetuation (provided we don't destroy our means of biotic survival).So there are many ways in which the human populations could continue to 'evolve' in some sense, despite increasing genetic loads. As a function of our intellect we are capable of various forms of evolution, both genetic and non-genetic, that other forms of life are not (OK, I'm excluding ID theorists here), even to the point of potentially manipulating / modifying our own gene pool.

I agree with the demographic breakdown you present - that is the inescapable 'trailing edge' I was talking about. But consider this. The 'not smart' only win in a *quantitative* sense.
Quantitative measures of RS are only important for 'r-selected' organisms that produce large numbers of offspring and make a minimal investment in each. We are 'K-selected' animals - long-lived and producing few offspring, each of which requires a large investment to be 'successful'. In such species, an individual's RS is MUCH more determined by offpsring *quality* than by offspring *quantity*. The cost of fewer offspring is easily offset by the production of 'fitter' offspring (fitness in the human case being defined by societal values). Don't underestimate the potential power of sexual selection (SS). We have a thread discussing some of its implications in the Biological Evolution forum if you are interested. I don't think so either. We are no longer subjected to any physical forces on a day-to-day basis that might select for morphological changes that might be necessary to ensure our survival (fastfood commercials notwithstanding). We control our environment for the most part. Besides, our generation time is so long, significant morphological changes would take thousands of years to accomplish even with strong selection. I don't think any 'non-biotic' form of 'life-transposition' to some mechanized entity would afford me any solace above and beyond death itself. I am only concerned with the reasonable life expectancy of the human race within the lifespan of our sun. After I re-read what I wrote here, I thought geez - I hope no one thinks I was implying anything like eugenics. The problem with any manipulation of the human gene pool is that it requires one of three things:
-selective juvenile survival
-selective juvenile mortality
-genetic alteration of germ cell lines (eggs and sperm)Number 3 will likely never by deemed ethical by society or the scientific community (but you never know these days), and
can you imagine our Christian friends' reactions to either 1 or 2?This message has been edited by EZscience, 06-02-2005 09:33 PM

Let's make one thing clear. A 'deleterious allele' is a faulty copy of a particular gene. It cannot be equated to the person carrying that gene. It is of obvious interest and benefit to the human race to eliminate alleles that are clearly recognized as 'deleterious' from the gene pool of the population. That doesn't necessarily imply being 'inhumane' towards the carriers. Take for example, the deleterious allele causing phenylketonuria. The population would be better off without any copies of this gene in circulation (some would probably still be produced de novo by mutation at some rate) but how do we accomplish this without denying reproductive rights to known carriers? Education may help, because with recognition of the known risks, many heterozygote carriers may opt not to have children. Same is true of Huntington chorea , which in this case is caused by a deleterious autosomal dominant allele.We are ethically required to be 'humane' to individuals - but have no such oblication to individual genes. There may still be take steps we can take to reduce the frequency such alleles. Going back to Stephen Hawking, I have no doubt that if you asked him, he would be in favor of any humanitarian means of reducing the chances of future generations of people receiving this particular allele that caused his predisposition to ALS. We need to remember that there are various ways our human gene pool might be improved (equals evolution) if we can manipulate the survival of individual *genes*. Thsi does not necessarily equate to having to eliminate all handicapped *genotypes* from the population. This is absolutely true. But it doesn't mean we need not be concerned about predictable increases in the genetic load of our populations. Go back to the example of premature babies. This is an effect of human artificial selection (medically) for earlier and earlier birth. In evolutionary terms, we are providing a 'payoff' for genes that permit premature parturition where none existed before. There is not a single deleterious allele involved, and I don't think there has been any attempt to characterize genetic attributes of premature babies, but evolutionary theory tells us that the more we artifically enhance survival to reproductive age of these babies, the more and more premature births we are going to have over time. We can be virtually certain that this is going to become an increasing and very costly problem for developed societies. But what to do about it? Here is where the conflict arises: human ethics dicatates one thing, evolutionary implications, the opposite, and human ethics will always win out politically.

Sounds great in theory, but what about cost?
What do you think our beloved medical establishment would charge for that? Think Blue Cross would cover it ?My point is that all these 'after the fact' fixes you propose are always going to be very expensive and not options for everyone. Prevention is always cheaper than cure. Yes, of course, unless we somehow managed to eliminate the possiblity of mutations in human germ cell lines. This raises an important point because whether some alleles are deleterious or not will often depend to some degree on the genetic background of the individual and sometimes on environmental factors (e.g. keep foods with phenylalanine out of the diet of PKU children and phenylketonuria is not a problem). So 'deleterious' is often a relative thing, even when applied specifically to one gene. And don't forget than many mutations can be 'neutral' - they may lead to a slightly different protein product, but one that is functionally equivalent in most ways. Thus mutations can also create genetic diversity without necessarily being subject to selection for or against.This message has been edited by EZscience, 06-03-2005 11:51 AM