GENETICS TUTORIAL ‑ PART II"Thus the earliest vertebrates, like the earliest amphibia, the earliest mammals, and the earliest primates, were small predators. Over and over again in evolution, the originators of new modes of life were small predators, and the key innovations at each stage conferred a selective advantage in predation." John Morgan Allman, Evolving Brains, 1999, p. 73.
In this chapter I continue describing some basic principles of evolution that apply to all living things. It will serve as a foundation for the more speculative and interesting evolutionary results found in human nature.Pre‑Adaptation
Some genes are "pre‑adapted" for new environments. A gene is pre‑adapted if there was a negligible reward for its presence in the genome at the time some new environmental challenge appears for the first time, and for which the gene then confers a significant genetic benefit.Modern society provides many examples. Computers didn't exist before the mid-20th Century, yet we find that many individuals are naturally talented for computer programming, design, networks, and other aspects of computer use. These people have genes that are pre‑adapted for the computer environment.
Pre‑adaptations are always present, as the following thought experiment illustrates. Imagine any task, and a procedure for reliably measuring performance of that task. The task could be jumping as high as possible, or remembering a sequence of numbers ‑ any task will do provided performance can be measured objectively, producing a continuous range of scores (a binary result, such as pass/fail, does not meet this "continuous range of scores" criterion). After two people have performed the task, there will invariably be a "better" and "worse" performance. After many people have performed the task, the test scores may form something resembling the Gaussian, or "bell curve" distribution, with many scoring near a middle region, and fewer scoring really well and poorly. The top scorers can be described as "pre‑adapted" for the task (provided the task is novel or evolutionarily "new").In real‑world situations, whatever the change in environment, whatever the change in job opportunities, whatever new sporting games are invented, there will always be new consistent winners and losers. Winners in the new task might have been mediocre performers in the old ones (and old winners may become the new losers).
"We are what we're good at," and the forces of selection measure us by what we're good at in the context of our times. Whereas the computer whiz is pre‑adapted to this era, so might a “nobody” of today be pre‑adapted to some future era. We should be careful in judging others, for they might have shined outstandingly in past settings, or be examples of a type that will shine in future ones. Faceless nobodies of times past might have rivaled the best of today's stars, if only given the chance by a change of environment. Chance is everything!Pre‑Maladaptation
But if the winners are pre‑adapted, what are the losers, the "pre‑maladapted." It may seem "unfair" to a civilized mentality to believe that "pre‑ordained" winners and losers will exist when new opportunities appear, but every species has been molded by this unfair rewarding of individuals through abrupt environmental change. We may not like it, but this is the way things work.Anyone feeling gratitude for evolutionary accomplishments should also feel thankful for the diversity of individual performance. Thanks to "inequality" evolution proceeds! But while we celebrate inequality, and rewards for the pre‑adapted, let us also have compassion for the pre‑maladapted, the world's ill‑fated losers, for they cannot be responsible for the changes that doom them.
Over and over, in this book, we shall encounter repugnant examples in nature. Our lesson is to accept that Nature doesn’t take care about individuals, only the genes! And the genes have no qualms about wasting individuals for their sake. Fish lay thousands and millions of eggs, so that on average one or two will survive. Several insect species produce male brains that are programmed to allow the female to make a nutritious meal of him after copulation ‑ to postpone her mating with a competitor or for nourishing his offspring! The historical record shows that humans will send legions of young men to battle, like fodder, who in the prime of their life become maimed or killed. The victors in battle rape the vanquished men's women, then march home as heroes, with greater rights for domestic breeding. In all these settings, the individual is "sacrificed," for he is engaged in risky behaviors with benefits that accrue reliably to only the genes.
Humans who ponder the consequences of what I'm calling a pre‑maladaptation have grounds for bemoaning their bad luck. I like the thought that each person "has their time," a time when they would have some maximum of pre‑adaptation, and since people are born into times "at random," they most often are "out of their preferred time." Imagine how frustrating it would have been for Beethoven to have been born before pianos existed, and before orchestras. Or for Einstein to have lived before the preliminaries of 19th Century physical theory had been set. Delay
's birth a century; would he have become the giant we know today? Bring to the 21st Century such notables as H. G. Wells, Lucretius, Democritus, Shakespeare, Homer, and others; what would become of them? We cannot know how fortuitously attuned to their age these giants were, or what nobodies they might have been had the "roll of their genes" occurred at some other time. Darwin
Species Shaping ForcesPre‑adaptation is a useful concept calling attention to the fact that whatever an organism's make‑up it will have some kind of “match” to every hypothetical new environment, and the match of some individuals will be adaptive. It might be adaptive whether or not the environment in question has ever existed before, and whether or not any of the organism's ancestors have been exposed to that environment. In such cases, we should not say that the organism has become adapted to the environment in question, just because it fares better than some of its cohorts. Rather, it is adapted due to a pre‑adaptation.
Most organisms will be pre‑maladapted to the new environment. Thus, most individuals will fall behind, watching a minority of pre‑adapted individuals leap forward. The greater the number of changes to the environment, the greater will be the disparity in relative rewards between the pre‑adapted and pre‑maladapted. A species should evolve "faster" at such times.When I refer to changes in the "environment" I mean to include not only the climate for a region, and the disappearance of a food staple (plant or animal), or appearance of new foods, but also the appearance of a new predator, the invasion of a new parasite, or the adoption of a new element of "culture" (in the case of humans, and perhaps chimpanzees).
There is a special case, unique to humans, in which culture has created an entirely new environmental condition: the removal of most of the natural threats to survival.An advanced civilization shields people from diseases, animal predators, and, in some cases, the need to work. It even shields people from each other to a great extent, by reducing the frequency of outbreaks of "tribal warfare." In this environment genes that in harsher, unforgiving environments would be maladaptive would now be neutral. Only the most severe genetic defect will be eliminated from a human genome shielded this way.
Under these conditions we might want to think in terms of "potential pre‑adaptation" and "potential pre-maladaptation." Today's genome is accumulating a large reservoir of potential pre‑maladapted genes, carried unknowingly by individuals who may be reproductively successful only because they are not subjected to selective forces.At the risk of getting ahead of my story, I believe that such genes will become apparent only after natural forces of evolution are restored, and put "the squeeze" on our burgeoning global population. Winners and losers in this new environment will not be close‑call winners and losers, they'll be clear‑cut winners and losers. The disparity between those now destined to win and those destined to lose is greater than ever, and growing faster than ever. The complexion of Humanity could change dramatically apre le deluge.
To understand a species we must consider the selective forces that have "shaped" it. In other words, we must learn what kills individuals before they reach reproductive age, what factors determine which individuals reproduce after reaching maturity, what foods are eaten, and how precarious is the supply.
For example, if our ancestors 5 million years ago were eaten by lions the survivors would have been good at avoiding lions. This might have rewarded the evolution of bipedality, which would have enabled standing tall and running fast. It might also have rewarded the capacity for social cooperative strategies, a precursor to intelligence.
Another theory speculates that our ancestors had to learn how to find and store root plants that would have grown on the grasslands (Wrangham and Peterson, 1996). This would have rewarded the creation of digging tools, and the ability to carry extra roots to a storage place at a home base, which in turn would have rewarded bipedalism and a self‑control that provisioning requires.
Whichever environment accompanied the branching of bipedal chimpanzees from their jungle‑dwelling forebears 5 million years ago, we can be sure that the forces of selection rewarded individuals carrying genes for dealing with whatever were the causes of mortality in their new environment, whether they were escaping from lions or digging and storing roots.
Perhaps 500,000 years ago some humans migrated to the edge of constantly‑moving glaciers. Mortality in this new setting would have been climate‑related, such as cold and hunger. We may presume that genes for planning and foresight were rewarded. To the extent that large animals were hunted, and meat became an essential food source, genes for a strategic type of cooperative hunting would also have been rewarded.
After the last glacial cold period, that peaked 19,000 years ago, humans had to adapt to an ever‑warming climate. For some, this meant adopting an agricultural lifestyle. Those who were pre‑adapted for farming would have prospered, provided they could also band together for mutual protection from raiders. Others remained nomadic, and targeted the new farmers. Thus, the main killer of Man became other men (it probably has been "other men" for the past 100,000 years, at least). As farming achieved unprecedented success, urban living became possible, sometime after 3000 BC. This created opportunities for microbes, which competed with Man as the main killer of men. Our ancestors are the ones with immune systems that afforded protection against "urban" diseases.
In every step of this evolution toward modern Man, the change in what killed people was a principal selective "force."
H. G. Wells made the point, 100 years ago, that long‑lived life forms cannot adapt to fast changes of conditions, unlike short‑lived forms, that can adapt. This leads more often to the demise and replacement of long‑lived large creatures by other large creatures, both of whom are competing with small, short‑lived creatures. He warns that humans, with a long life span, are vulnerable on this account.
The looming threat to Humanity posed by viruses and bacteria may become a classic example of this evolutionary dynamic. How ironic if our demise, or loss of greatness, which is most often portrayed in terms of dramatic events, such as global thermonuclear war, instead is dealt by tiny viruses!
If in fact viruses produce large‑scale human die‑offs during the 21st century (Garrett, 1995), the survivors will be those with pre‑adapted immune systems; not the physically strongest or most intelligent. This possibility illustrates in dramatic fashion the principle that "a species is shaped by what kills its members."
How Many Genes Can Compete?
Human tribes are supposed to have numbered 50 to 100 individuals throughout much of our prehistory. The number of adults in such a tribe would have been about half this number, half of whom would have been adult males (12 to 25 in number). It is tempting to think that fewer than this number of genes can be evolving in the tribal genome. But such an assumption is erroneous, as I will illustrate.
When a man goes into the world "to be measured," it is his phenotype that is being measured. And his phenotype could be the result of many genes (interacting with each other to produce a unique phenotype). Consider the extreme case where each of the men in a tribe differs from "an average" by just one allele. Consider 4‑year intervals, during which each woman of child‑bearing age bears one baby. During each 4‑year interval, if only one man prospers and is accorded sole breeding status, then every 4 years one allele can be declared a winner over it's competitor(s). In a lifetime, 10 alleles can be declared winners (where we imagine the environment places great importance upon different aspects of phenotype each 4‑year period). After 80 years, 20 alleles could be declared winners, etc.
Even though this is a thought experiment, it proves that there is no fundamental, mathematical reason forbidding the number of gene sites for allelic competition to exceed the number of adult males in a self‑sufficient tribe, or the total number of tribe members. (A "multiple regression" statistical argument is also possible, and more persuasive for me, but I shall spare my readers of this daunting argument.)
Every individual is a carrier for many genes that are competing with allele counterparts. The number could be 50, or 500; and it doesn't matter if the individual is a member of a tribe with only 50 or 100 members.
Migration, New Gene Competition, and Pace of Evolution
The number of gene loci hosting allelic competitions has undoubtedly increased in number since the advent of urbanization, and the more recent globalization of our species. A tribe of Africans may be homozygous for genes influencing skin color, but if they were captured and brought to
as slaves their ancestors would find that those same genes influencing skin color had become a factor in determining individual welfare in the non‑African society. The same argument would apply to many genes. America
The inescapable conclusion is that the more diverse a population becomes, due to migration, the more genes there are in competition with each other. Does this mean human evolution is progressing faster today, or slower? If a person's "measure" is affected by more genes, it must take longer for all genes to have their measure taken. Stated another way, when more genes enter the fray of competition, those already in competition may feel a decrease of selective pressure influencing their fate. Aspects of a person which were important in the tribal setting suddenly recede in importance, as other genes, which had been firmly established many generations earlier, resume their competition with alleles they had never before encountered, or had encountered long ago and had triumphed over. The coming together of ethnicities must introduce major changes to the set of genes that are subject to evolutionary forces, in terms both of which genes are in competition and the relative strength of selective forces upon specific genes. These considerations suggest that the pace of evolution has slowed in modern times.
Another slowing influence is the declining rate of infant and childhood mortality. Unless something important has been overlooked, these arguments suggest that the pace of evolution has slowed in modern times (Kondrashov, 1988).
Conservation of Selective Pressures: Pleiotropy and Polygenes
When selective forces suddenly reward a new capability the species undergoes a quick disintegration in other, more recently‑acquired capabilities. This is due to the random, unintended deleterious effects that any mutation produces, which places a brake on the speed with which new capabilities can be acquired.
To understand this, recall that a gene has many effects, referred to as pleiotropy. This is most dramatically illustrated when a mutation occurs that has no redeeming consequences. For example, one mutation causes its carrier to have 6 fingers, short stature and heart murmurs (Ellis‑van Creveld syndrome). These phenotypic effects are seemingly unrelated, yet they are caused by just one allele. Mutations that are adaptive, judged by the fact that they have been selected during the course of evolution, will also have many effects, with perhaps just one of them being adaptive to a far greater extent than the numerous, small negative effects. Thus, whenever a mutation occurs and confers an increment of adaptive advantage, its future in the gene pool will depend not only on how well it performs its adaptive task, but also upon how many unintended, deleterious effects come with it.
Assuming for the moment that there are only 40,000 genes in the Human genome, since there are more than 40,000 properties defining a human, each gene must have more than one beneficial effect. This implies that after a gene is "in place" it can be modified over time to produce more desired effects. An "old gene" may thus have several beneficial effects, in addition to a few small negative ones. The selection of a modified, dual‑purpose (or multi‑purpose) gene must occur with "painful slowness" since the original function of the gene should not be disturbed appreciably, and since every mutation is likely to produce other unwanted effects. To get things "just right" must require many generations and many small compromises.
Whenever a new selective force becomes important, the other selective forces must lose importance, else the population will drop to dangerous levels. This "partitioning" of selective pressure leads to a more conservative behavior of our genome, causing already established gene alleles to remain longer than otherwise.
By the same reasoning, a recently‑established gene allele is more likely to be disrupted with deleterious effects than a long‑established gene allele. This "genetic entrenchment" is due in part because of the rewards of redundancy for genes that are important enough to respond to selective forces for long periods of time. A task that must be done by a gene will be less vulnerable to mutation to that gene if it has been exposed to mutations and selection for a long time. In addition, genes that exist for a long time may become "depended upon" by other genes that are selected after the first gene and which in some way depend upon the presence of the first gene for its new effect to be expressed properly. When two or more genes must be present to produce a specific phenotypic trait that has adaptive value, those two or more genes are referred to as a "polygene" group. Genes that are members of a polygene are more difficult to get rid of, provided they have not become harmful. New genes have not had this opportunity to achieve robustness, or become entrenched, and they are thus more likely to be lost by random mutations because they are likely to have small phenotypic consequences. The concept of "genetic entrenchment," and a culturgen counterpart to this concept, is treated at greater length in Chapter 16.
For humans it has been estimated that at least 20% of the genome influences the brain. This is not to say that 20% of human genes are present exclusively for brain wiring, since many genes will exist mainly for other purposes which have "acquired" brain wiring roles. If one of these genes mutates it is more likely to affect its new brain task than the older, original task. Undoubtedly some genes are mostly brain‑related, and probably some genes are exclusively brain‑related. Whether a gene is partly, mostly, or exclusively brain‑related, if it recently acquired this role it is likely to be more vulnerable to random mutation than the other parts of the genome, or to older genes that mostly affect anatomy or physiology.
Parts of the modern human brain evolved during the past 100,000 to 200,000 years, and some people speculate that for the past 40,000 years little has changed. I will argue later that brain genes continue to evolve in response to changing social conditions, which add in subtle ways to the repertoire of human behaviors. For now, I merely claim that behaviors which are uniquely human, and which are recently evolved, are most vulnerable to disruption by the appearance of new selective forces.
If a new adaptation has been selected for strongly, it might acquire robustness even in a relatively short time. Human language, which may have appeared 200,000 years ago, is a candidate example. Language played such a crucial role during its evolution that the genes that code for it are probably already robust.
The capacities for reading and writing have a briefer evolutionary history, and the genes that code for these abilities are more vulnerable. Until recently, few people engaged in reading and writing. These genes provided a niche to only a small fraction of the population during the past 4000 years. It is therefore not surprising that dyslexia affects several percent of the population, whereas verbal language impairment is virtually unknown.
Unintended Deleterious Effects
I suffer from occasional 20‑minute blind spells, called "scintillating scotoma." It is an impairment produced by a gene that in women produce migraine headaches. As I type with difficulty through a flashing zig‑zag blind‑spell pattern, it occurs to me that I am paying a penalty for some genetic mutation that is doing good somewhere else. Every mutation does many small bad things for every big good one, and the sum of bad ones found in most people must be worth their penalty; otherwise the gene allele would not have evolved.
In the case of my blind‑spells a dilated blood vessel is putting pressure on a nerve fiber carrying signals from my eyes to my brain's occipital lobe. What if the dilation occurred elsewhere within my brain? I might not know that it was occurring since I could not see it. But it might nevertheless have subtle effects upon mood or thought. There must be people, probably many people, who do indeed experience mild mental afflictions, lasting 20 minutes for example, which are counterparts to my scintillating scotoma. We should be prepared, then, for the possibility that a certain amount of irrational human behavior is caused by genes that are conferring a greater adaptation benefit in some other behavioral realm, with the unintended side effect that behavior is mildly irrational in a different realm.
I frequently think about the penalties that are paid when evolutionary pressures for one trait rise above the others. Sure, you can quickly evolve skin color in response to latitude migrations, but you'll pay with other unintended defects that accumulate, until the new skin has been achieved and a better balance of evolutionary forces has been established.
Only 12,000 years ago, just after the climate warmed but before the glaciers had melted enough to raise the world's sea level, people in Siberia migrated across Beringia to the new world. As they moved south, generation after generation they would have lost their need for light skin. Central American Indians are dark‑skinned, and this must have been achieved in less than 10,000 years. But those who continued their migration southward, past the equator, they would have needed to re‑achieve light skin. Perhaps at each migration juncture those who were best adapted to the latitude stayed behind and the others continued the migration. This could have minimized the risks of unintended deleterious mutations, but it is more likely that the southward migration was so hurried that skin color played no role.
Such fast adaptations must have produced defects in other aspects of the American Indian. Perhaps they lost the ability to metabolize alcohol; we shall probably never know what compromises the genes had to make to adapt quickly to the need for a different skin color.
Cancer may afflict humans more than most other species because we have recently undergone a rapid evolution under strong selective forces that rewarded brain re‑wiring (to accommodate behavioral adaptations) and immune system enhancements (to fight pathogens seizing the opportunities offered them by the newly evolved super‑tribe human lifestyle). To achieve these new traits, genes must have been selected that would normally not be acceptable because of their unintended deleterious effects, and a defense against cancer may have been one such compromised ability.
The Dangers of Fast Evolution
Species evolve at different rates. Even a given species may remain genetically static many generations, then respond to an abrupt change in climate by evolving fast. Rates of change must vary by orders of magnitude, with long eras of equilibrium punctuated by short periods of disruptive change. Mammals lived throughout most of the dinosaur era, and flourished only after the meteorite impact of 65 million years ago (which killed the dinosaurs because of a brief, disruptive climate change lasting several years).
The equilibrium periods are available for "clean up" of unintended deleterious effects created during the fast evolving times.
The great diversity of human anatomy, relative to other animals, testifies to the great potential for fast human evolution. Strong selective forces must have superceded such things as head shape, for example.
When a species is suddenly subjected to a strong selective pressure, a few gene sites will suddenly grow in importance. More than two alleles may exist at each "hot" site (if only one allele exists, it won't be a site for selective pressure). Other sites, being relegated to lesser importance, are likely to accumulate mildly deleterious mutations with less consequence than before the fast evolution (to use a metaphor, it's as if no one is "minding the store" when a new one appears). Humans, who have been evolving fast for the past 7 million years (since separating from the chimp lineage) must have many multi‑allelic gene sites. The more alleles that are in competition, the greater the fraction of maladaptive offspring. Thus, the faster evolution occurs in response to some new selective pressure, the greater the likelihood of a low offspring survival rate in order to prevent a proliferation of the unfit.
Is it not ironic that today, after coming out of a phase of extremely fast evolution in several traits, humans have just achieved what must be the highest offspring survival rate ever? Does this not mean that humans also must be exhibiting the greatest rate of survival of maladaptive individuals? How long can this last? This topic will be returned to in Chapters 6 and 8.
Lag and Regression
An abrupt environmental change, such as those at the onset of an interglacial (occurring every 120,000 years, typically), must set evolution in motion in new directions. Until a new "optimum" has evolved, producing stasis (and genetic consolidation), there will be "lag." Some things are easier to evolve than others, and they will lag less. Skin color may be one example.
Because adaptation takes time, there could be a lag in many traits after an environmental change. Present aspects of human nature should "make sense" only in the Pleistocene context, not necessarily in that of the Holocene (the past 12,000 years). For this purpose it has been useful to create the term "environment of evolutionary adaptation" (EEA), also referred to as the Ancestral Environment (AE). Common behaviors that were adaptive 20,000 years ago need not be "adaptive" today (Symons, 1979).
The Yanomamo Indians of South America appear to be more "primitive" than their Asian stock who began migrating to the
New World~12,000 years ago. How can this happen? Could the forces of evolution actually cause a population to regress? Yes! And maybe this happened with the Yanomamo. Their regression is only in relation to what was adaptive in their former setting. By definition, they must be better adapted to the Venezuelan jungle than were the original Siberian stock, or even the partially modified Central American Indian stock.
The longer the race, the greater the disparity between the contestants – especially between winners and losers. This is certainly true for a foot race, but is it true in evolution? Consider that our ancestry traces back to a chimpanzee‑like animal 7 million years ago, or 2 billion years ago to a one‑celled life form, and 3 or 4 billion years ago to strands of DNA. Things like those early DNA strands may exist today, as do many one‑celled life forms that may resemble those in our ancestry. So "yes," the longer the race, the greater the spread between the evolutionary contestants (note that all extant living forms are "winners").In human affairs there is a discernible spreading in the quality of life of winners and losers. The most prosperous people of today have a higher standard of living than the most prosperous of yesterday, yet there are people living today who are no better off than the worst off yesterday. Can there be stability in a world where the rich get richer, and the poor stay poor? This is a topic for Chapters 11, 14 and 16.
Random mutations rarely produce benefits to the individual organism (i.e., for the ability of the organism to stay alive, out‑compete its contemporaries and to out-reproduce them). A mutation that alters a gene is likely to have effects on many phenotypic traits (pleiotropy), and usually all or most traits suffer from random mutations. For a mutation to succeed, it must confer some advantage that outweighs damage done to many other traits. "Forward" evolutionary change is thus difficult.
After a genetic mutation spreads throughout a gene pool, it becomes part of a genetic setting that new mutations must deal with. If a new mutation relies upon the presence of the first one, and if this second mutation also spreads throughout the gene pool, then the first gene has a more secure future. This occurs because any challenge to the first gene must confer an advantage that outweighs the contributions of two genes ‑ the first one and the other gene that relies upon the first one for it's proper expression. The longer a gene stays within a genome the greater is the chance that other genes will become dependent on it and therefore provide it with additional security. When this happens, the gene has become "entrenched."
Consider the situation of environmental change that reverses itself at some later time. The first change may lead to the appearance and widespread acceptance into the genome of a mutation. Let us assume that this new gene, which has almost completely displaced an older one, confers an adaptive advantage in the new climate. Suppose, now, that before this new allele has time to become entrenched, the climate changes back to the original state. The few individuals who carry copies of the original gene allele will become a source for the quick re‑emergence of the original allele. Evolution can be said to have "reversed" itself.
If the second climate change occurred much later, however, this evolutionary reversal might not be feasible. First, the original allele may have disappeared, and second, other genes may have become dependent upon the presence of the new allele, making it more difficult to dislodge from its entrenched location. In theory, both difficulties for an evolutionary reversal can be overcome, but they constitute a more insurmountable obstacle to the reversal.
Laboratory evidence exists for "reverse evolution" (Teotonio and Rose, 2000). Fruit flies from a standard stock were selected for various experiments over the course of 20 years (200 generations) and were subjected to new environments to produce variant strains. When fruit flies from these new strains were subjected to the original environment, in every case reverse evolution was observed. In two cases, the reversal was almost complete after only 10 generations; others required 50 generations. In some cases the amount of reverse evolution was small.
At every instant of a species evolutionary history, the most vulnerable genes are the most recently‑acquired ones. This concept will be returned to in later chapters.
Culture can be thought of as a collection of "culturgens" or "memes" ‑ similar to a genome being comprised of a collection of genes (Lumsden and Wilson, 1981). Although some similarities exist between genetic and cultural evolution, the differences are striking. This topic will also be dealt with in a future chapter (Chapter 16), as a unifying theory for understanding the rise and fall of civilizations.
Although the idea of "mutational load" was described by Kondrashov (1988), we owe H. G. Wells it's first brief expression (ironically, in the same journal, almost 100 years earlier). In 1895 Wells wrote: "Has anything arisen to show ... that where the life and breeding of every individual of a species is about equally secure, a degenerative process must not inevitably supervene?" (Wells, 1895).
Primitive people today produce about 7 offspring per woman. Allowing for slightly shorter life spans in past times, about 6 offspring per woman was normal. On average, only 2 survived to adulthood. Is it possible that some of the 4 who died were genetically inferior? Yes, of course.
Approximately half of all conceptions fail to produce a live birth. It is speculated that the half that die are genetically defective due to some incompatibility between the paternal and maternal alleles. It is a small step to suggest that there will be a residue of live births that are also destined to fail to survive childhood due to genetic defects. If this is true, then what would be the genetic consequences of intervening medically to sustain all live births through childhood and into adulthood?
If some of the 2/3 of live births that formerly died were due to genetic defects (a fraction derived from the ratio of childhood mortality rates in primitive and modern societies), and if all live births now live a full and reproductive life, then surely the genetic defects which they carry will be contributed to the gene pool in larger numbers than would have occurred in the ancestral environment (AE). Our gene pool must inevitably accumulate these defective genes at a higher rate than in the past. This phenomenon is called "genetic load" (Kondrashov, 1988).
It may be impossible for a species to average only one offspring per adult for a long time. With no excess of births, the downward pulling force of “genetic load” would degrade the gene pool of the species. Therefore, the survival ratio must be kept well below one if humanity is to maintain a healthy genetic future! We who survive without serious genetic defects should be grateful to those less fortunate, whose deaths in the past made us possible.
I feel sorry for the bent masses of future people, for they will suffer from cruel disabilities that were traditionally weeded out by the neglect of less benign times in the AE. Humanity reaps what it sows, and it is sowing the wrong genes ever more often and preserving defective offspring with an excess of unthinking compassion.
Compassion can be a double‑edged sword. What seems laudable for one generation may in fact create unlaudable consequences for many future generations. I shall return to this moral dilemma in Chapter 11
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