How New Theories Will Change the Future of Medicine
Second Edition
Summary:
Why do we age? This question has baffled scientists for nearly 150 years and remains a mystery. Scientists disagree over even the general nature of aging. Is aging the result of fundamental limitations that apply to all living things, or are organisms designed by nature to age because a limited life span conveys some advantage? All of the scientific theories either fail to fully explain observed animal characteristics or conflict with generally accepted evolution theory.
This issue has potentially enormous implications for medicine. If aging is the result of fundamental and unalterable forces of nature, then anti-aging medicine is impossible and anti-aging research is futile and foolish. If aging is dictated by species-specific designs, then research may well reveal means for altering the operation of the aging mechanism and thereby improve the treatment of many age-related diseases and conditions.
This book provides a review of theories of biological aging including underlying evolution and genetics issues and describes recent discoveries and theories that favor aging-by-design and therefore suggest that increased research on aging mechanisms would be highly beneficial.
Keywords: Aging Theories, Evolution, Longevity, Gerontology, Anti-aging, Darwin, Evolutionary Theories of Aging, Life Extension, Geriatric Medicine, Ageing, biological clock
Copyright 2003 - 2007 Theodore C. Goldsmith (tgoldsmith@azinet.com). All rights reserved.
Version 6.6 December 6, 2007
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Page numbers in Table of Contents and Index refer to PDF version.
Print Versions:
The Evolution of Aging , Theodore C. Goldsmith, Second Edition, ISBN: 0-9788709-0-5 10/06
Available: Amazon.com, Barnes and Noble, etc.
Earlier version: ISBN: 0-595-28069-2 6/20/2003 trade paperback
Acknowledgements
The author wishes to thank the many people who helped with this book or provided helpful comments and suggestions regarding the underlying material including Joshua Mitteldorf (Temple University), Vladimir Skulachev (Moscow State University), Jeff Bowles, Aubrey de Grey (University of Cambridge), Vicky Cahan (National Institute on Aging), and Joao Magalhaes (Harvard Medical School).
Thanks also to Frann Goldsmith for her editing assistance and Elaine Bailey (Trident Press International) for editorial comments.
Russian Language Version
The Commission for Publication of Biological Monographs (MAIK Nauka-Interperiodika Publishers - Russian Academy of Sciences) has selected an earlier version of this document for publication in Russian. Although translation has been completed, actual publication was cancelled because of budgetary constraints. We are attempting to obtain permission for Internet distribution of the Russian document.
Science Abstract:
In 1882 Weismann formally proposed that aging was an evolved characteristic, an adaptation, which had an evolutionary purpose. Darwin had previously suggested that aging was an evolved characteristic.
Most current theorists have discarded adaptive theories of aging using one or more of the following arguments: Some theorists consider it “impossible” that aging could be an adaptation because adaptive theory conflicts with the theory of natural selection. Some dismiss adaptive theories because of the apparent small or even negligible effect aging has on fitness. Others reject adaptive theories because no mechanism has been demonstrated that would provide for the evolution of a fitness-adverse trait such as aging. Finally, some doubt that aging has evolutionary utility.
This book, written for a wide audience, presents arguments that attempt to refute all of these objections and provides a summary of modern adaptive theories as well as an analysis of the potential public health implications of adaptive theories.
Preface
I am often asked: “Why is digital communications theory important to genetics, evolution, and theories of biological aging?” Biology and space communications certainly seem to be entirely unrelated.
However, there is actually an important and very interesting connection. All living organisms have the ability to communicate their design characteristics to their descendents by means of their genetic codes. This inter-generational genetic communications system is strikingly similar to modern space communications systems. The genetic code is a serial digital data stream. Nature and NASA face similar issues in areas such as data redundancy, error recovery, synchronization, and data merging, and have developed similar solutions. Both systems have benefits and limitations conferred by the fundamental nature of digital communications.
Evolution is the process whereby genetic codes are modified, initially as the result of “transmission error.” Evolution is therefore highly dependent on the details of the genetic communications and data storage scheme including the digital benefits and limitations.
Finally, as the title of this book implies, theories of aging and anti-aging research are very constrained by evolution theory.
The merging of biology and information technology has spawned a number of new fields of science including genomics, and proteomics, under the general term bioinformatics. My main area of scientific interest concerns the consequences of the digital nature of the genetic communications system on evolution theory and thereby aging theory.
Some say: “Darwin was wrong.” Others take the position that Darwin was 100 percent correct and that any valid deviation is “impossible.” This book presents the case that Darwin was perhaps 99 percent correct. Digital genetics analysis and other evidence suggest that minor adjustments to Darwin’s theory are necessary. Although these changes have little effect on our general understanding of evolution, they have a potentially large effect on aging theory.
In order to facilitate worldwide access to this material, especially for students, this book is being made available for free download on the Internet. Distribution via the Internet also allows for frequent additions, revisions, and updates. Communications from readers have been very helpful in making these revisions so please continue sending your comments and criticisms.
Because of these revisions, the initial paperback version of this document, ISBN 0595280692, published in June 2003, is now seriously out of date. A second edition, ISBN 0978870905 was published in October 2006.
If you are reading this on your monitor, the HTML version has hyperlinks from the table of contents as well as links to many on-line references and resources. If you want to print a copy of this document, the PDF version is formatted for 8.5 X 11 inch (216 X 279 mm) paper.
Theodore. C. Goldsmith
November, 2004 Rev 3/07
Annapolis, Maryland
Contents
The Theory of Natural Selection
Variation and Incremental Steps
Darwinian Evolution Requires Individual Benefit
Unresolved Discrepancies with Darwin’s Theory
Weismann’s Theory of Programmed Death
Accumulation of Damage Theories
4. Traditional Theories of Aging
Medawar’s Mutation Accumulation Theory
Williams’ Antagonistic Pleiotropy Theory
Common Problems with Traditional Theories
5. Digital Genetics and Evolution Theory
Biological Plans and Schedules
Evolutionary Genetic Processes
6. Discoveries Affecting Aging Theory
Progeria and Werner’s Syndrome
7. New Theories of Evolution and Aging
Completeness of Natural Selection Theory
Group Selection and Evolutionary Immediacy
Inheritance Efficiency and Individual Advantage
Genetic Diversity and Individual Advantage
Genetic Diversity and Evolution
The Selfish Gene Theory of Evolution
Information Based Evolution Concepts
Evolutionary Disadvantages of Immortality
Anti-Aging Morality and Ethics
Public Opinions on Anti-Aging Research
Biological Control Systems - Hormones
Maintenance Functions Versus Complex Mechanisms
11. Conclusions – Implications for Medicine
If You Think You Can’t, You’re Right
New Adaptive Theories of Aging
Appendix – Aging Attitudes Survey
1. Introduction
Why Do We Age?
The importance of this question is determined by your preconception of the answer.
If you think aging is an inescapable biological reality, an inevitable fact of life, or otherwise caused by a process that is so fundamental, so immutable, and so central to the process of life that no alteration is possible, then determining the cause is academic and of little importance. If you think this, there is nothing that can be done about the root cause of aging. Spending much effort or money on finding the cause is foolish. Geriatrics research should be confined to the amelioration of symptoms and treatment of specific age-related conditions such as Alzheimer’s disease, heart disease, and cancer.
If, on the other hand, you think aging is caused by something more like a genetic disease, then the answer to the question “Why do we age?” is critically important. Finding the answer to this question will lead us in the right directions to finding major treatments that will eventually have a monumental effect on people’s lives. A treatment for aging could result in delaying or relieving age-related diseases that now kill more than 80 percent of the people who die in the developed world and substantially extend the length and quality of countless lives.
This book is dedicated to demonstrating that aging is not inevitable, is not inescapable, and that anti-aging research if aggressively conducted could result within a reasonable time in major new treatments for aging as well as many age-related diseases.
Many people are amazed to find that in the twenty-first century there is still major scientific disagreement regarding the fundamental nature of aging. The problem has not been lack of clues. The problem is that the many clues point in different directions resulting in drastically different conclusions. In addition, compared to most areas of scientific inquiry, aging is surrounded by factors that tend to confuse both popular and scientific thought. Understanding the current situation therefore requires an understanding of these confusion factors as well as the historical sequence in which scientists made important discoveries and developed important theories. A major portion of this book is devoted to covering these aspects of aging theory.
Most medical advances have been the result of experimentation. Some major discoveries have been essentially accidental. Aspirin works. We found that out by trial and error. Why it works is of interest, but secondary.
Aging, however, because it is a relatively long-term process, is a difficult subject for experimentation. An experiment to determine if a medication is effective in relieving pain, increasing kidney function, or suppressing a certain infectious organism, could be performed in a matter of days or weeks. An experiment to determine if a medication increases longevity in animals or humans could take years, decades, or even many decades to perform.
Other processes tend to mask the relatively gradual and mild effects of aging. As an illustration, researchers have been able to determine the functions of various glands by removing a gland from a laboratory animal and observing the results. However, removal of most glands is rather immediately fatal. If a gland had an effect on the aging process, observation of that effect would be masked by the gland’s more critical functions. Until recently, experimental approaches have been unable to shed much light on the causes of aging.
As a consequence, scientific theories of aging are primarily the result of logical analyses of the functional, externally observable, characteristics of various organisms. You can readily picture the difficulties associated with this approach. Imagine trying to deduce the existence of, much less the detailed functioning, of the endocrine system, or other largely internal system, merely by observing how animals live and die. It is difficult or impossible to prove such a logical theory without experimentation, which remains difficult. Various theories of aging, some dating from the 1800s, are still debated.
In any field, theories and assumptions that have remained unchallenged for relatively long periods tend to acquire the appearance of facts. NASA uses an analytic technique called zero-base analysis in which previously made assumptions are reevaluated in light of current information. This book is essentially a zero-base examination of scientific and popular beliefs regarding aging.
Another typical engineering process applied in this book is limit analysis in which scientists vary the parameters of a system model and assess the results. “In the limit” a parameter can be set to zero or infinity. In the current context, we might explore what would happen to an animal population if the animal’s life span were longer or shorter or if it did not age at all.
Finally, the development of modern digital communications systems has led to insights into the properties and issues associated with the fundamental nature of digital data. The mechanism of inheritance in all living organisms involves the transmission of digital data in the form of genetic codes. The properties of digital data therefore constrain inheritance, which in turn constrains evolution, which in turn affects aging theory. Accordingly, this book provides a discussion of digital genetics or the impact of the digital nature of inheritance on evolution theory.
Virtually all current physicians, health professionals, and medical researchers were taught the traditional scientific theories of aging in “Biology 101.” These traditional theories, developed mainly in the 1950s, are very pessimistic regarding the possibility of meaningful anti-aging treatments. In fact, one of the most respected traditional theories teaches that significant medical intervention in the aging process is “a scientific impossibility.”
At the same time the general public, mostly for reasons having little scientific credibility, also thinks of aging as inescapable, inevitable, and unalterable as it has been for thousands of years. More profoundly, educated people tend to think that those who believe that aging might be a treatable condition are uneducated or naive.
It should therefore come as no surprise that the anti-aging research budget is relatively miniscule.
However, a group of theorists, using more recent data, has developed theories indicating that the fundamental causes of aging may actually be much more treatable than predicted by the traditional theories. In addition to producing their own theories, these theorists have discovered many logical flaws and inconsistencies in the traditional theories. The potential health implications are staggering since most of the people who currently die in developed countries die of age-related diseases and conditions such as cancer, heart disease, and stroke.
What Is Aging
Aging refers to the time-sequential deterioration that occurs in most animals including weakness, increased susceptibility to disease and adverse environmental conditions, loss of mobility and agility, and age-related physiological changes. Aging is usually understood to include reductions in reproductive capacity. In this book, it is assumed that aging includes changes in reproductive capacity including behavioral patterns such as reproductive vigor or strength of the urge to mate. Reproductive capacity and aging have similar theory issues as will be discussed later.
A non-aging animal is such a foreign concept that discussing it in English is awkward. Some scientists use the term senescence to indicate the deteriorating effects of aging as opposed to the simple passage of time. In this book, aging means the deteriorating effects. A non-aging animal does not age but does get older and has increasing “calendar age.”
We will be examining two major questions about aging:
1. What is the fundamental nature of aging? Is aging a feature of an organism’s design that evolved because it confers some benefit, or, is aging not an evolved characteristic but rather a limitation, a defect that confers no benefit?
2. Are there potentially medically treatable factors that are common to the various manifestations of aging such that a single treatment could delay or ameliorate many different manifestations? Is aging itself a potentially treatable condition or are we limited to treating the various manifestations separately?
Scientific attitudes regarding these questions vary dramatically depending on discipline. Biologists currently tend to believe that it is impossible for aging to be an evolved characteristic. (Biologists have been arguing about this question for nearly 150 years.) Medical scientists are more likely to accept either answer for question 1 but consider the question itself to be very academic, “What difference does it make?” As we will see, question 1 has very significant implications for question 2, which does have obvious impact on medicine.
Human Mortality
Developed countries have been keeping fairly careful birth and death records for hundreds of years partly because this data is central to calculations involved in life insurance, pensions, and annuities. The curve shown in Figure 1 shows mortality[1] in the United States in 1999 as a function of age. That is, the curve shows the fraction (equivalent to probability of death) of the people that age that died in 1999. The curve shows that the probability of dying approximately increases exponentially with age. The chance of dying during any given year is less than 1 percent until age sixty and rises to 30 percent at age ninety-seven.
Figure 2 shows the same information displayed on a logarithmic vertical scale to make it easier to see the detail at the lower ages. Data for males (top curve) and females (bottom curve) has been added to the curve for the total population (middle curve). On this figure you can clearly see the infant and early childhood mortality that declines to approximately age 4, and the childhood period where death rates are extremely low (< .02 percent). Then we see a sudden jump to another plateau between ages 18 and 30 where death rates are about .1 percent and where a dramatic difference between males and females is apparent. From age 30 onward, death rates nearly follow the exponential curve, doubling approximately every seven years. A 30 year old has a .1 percent chance of dying while 30; a 101-year-old has a 40 percent chance of dying before reaching 102. Biologists have long been curious as to why death rates level off for very old people.
Some actuaries use a simple exponential equation to approximate the probability of death as a function of age. This Gompertz Approximation (developed by Benjamin Gompertz 1779 – 1865) would appear as a straight line on figure 2 and is useful since the deviations between the actual curve and a straight line at very young and very old ages are relatively insignificant in an actuarial context.
Figure 3 again shows the same data as a survivor’s curve based on the ages of people who died in 1999 and showing the fraction of the people left alive as a function of age. This curve shows that 90 percent of the people who died in 1999 were over fifty-eight years old. Of those that died, 50 percent were more than seventy-eight years old.
Aging and Disease
It is obvious from the foregoing that we have been largely successful in conquering diseases that kill people more or less indiscriminately with regard to age or that strike children or young people preferentially. Except for infant mortality, diseases that kill large numbers of people such as heart disease, cancer, and stroke all have incidences that are very highly related to age. Here are the leading causes of death in the total U.S. population:
|
Cause of Death (USA 2000 Data) |
Percent |
|
Heart Disease |
29.6 |
|
Cancer |
23.0 |
|
Cerebrovascular Diseases |
7.0 |
|
Lower Respiratory Disease (asthma, COPD) |
5.1 |
|
Accident |
4.1 |
|
Diabetes |
2.9 |
|
Influenza and Pneumonia |
2.7 |
|
Alzheimer’s Disease |
2.1 |
|
Other |
23.5 |
Some age-related diseases involve processes that are plausibly a simple function of the passage of time. For example, some heart disease involves buildup of deposits in blood vessels that would appear to gradually increase as time passed. Cancer is thought to involve multiple sequential mutations that would also be increasingly likely as time passed.
However, animals that have much shorter life spans also develop heart disease and cancer. How is this explained?
Also, there is evidence that even deposits of material causing heart disease can increase or decline based on other factors such as cholesterol levels.
Finally, a disease (See Werner’s Syndrome) causing accelerated aging also causes accelerated incidence of heart disease and at least some cancers.
It is therefore clear that many “age-related” diseases are significantly caused by whatever causes aging. Putting it another way, a “major treatment” for aging could reasonably be expected to delay the average onset age of many or even most age-related diseases.
Although a “cure” for many diseases has eluded us, “major treatments” have dramatically increased life spans of victims of diseases such as diabetes, cancer, heart disease, and even AIDS. We might think of a major treatment for aging as something that would eventually extend average life span by 50 percent or more. As we shall see, such a development is no longer in the realm of science fiction.
Aging Variations in Animals
Life spans vary enormously from species to species. In the wild, animals are subject to attack by predators and competitors, difficulty in finding and competing for food, and adverse environmental conditions such as harsh winters. Older or otherwise weaker animals often do not survive. Under laboratory or zoo conditions, animals have food provided and are protected from other animals of the same or different species as well as from environmental conditions. Zoo animals receive some medical care and typically live much longer than wild animals. The average life span of wild animals is therefore shorter than for zoo animals while the maximum recorded life spans while usually higher for zoo animals are sometimes higher for wild animals.
Some fish and reptiles have extremely long maximum life spans and will be further discussed in Chapter 6.
Humans have the greatest authenticated maximum life span (122 years) of any mammal. However, some researchers think that a bowhead whale killed in Alaska by Eskimos was 211 years old.
The following table lists maximum recorded life spans (in years) for some animals.
|
Species |
Age |
|
Laxmann’s shrew Sorex caecutiens |
2 |
|
Human Homo sapiens |
122 |
|
Highland desert mouse Eligmodontia typus |
0.8 |
|
Asian elephant Elephas maximus |
80 |
|
Little Brown Bat Myotis lucifugus |
30 |
|
Eastern gray squirrel Sciurus carolinensis |
23.5 |
|
House canary Serinus canarius |
22 |
|
American robin Turdus migratorius |
12.8 |
|
American Crow Corvus brachyrhynchos |
14.6 |
|
African gray parrot Psittacus erithacus |
73 |
|
Red-breasted parrot Poicephalus rufiventris |
33.4 |
|
White-winged crossbill Loxia leucoptera |
4 |
|
American white pelican Pelecanus erythrorhynchos |
54 |
|
Brown pelican Pelecanus occidentalis |
31 |
|
Beluga sturgeon Huso huso |
118 |
|
Lake sturgeon Acipenser fulvescens |
152 |
|
Rockfish Sebastes aleutianus |
140 |
|
Pacific ocean perch Sebastes alutus |
26 |
|
Pink salmon Oncorhynchus gorbuscha |
3 |
|
Sockeye salmon Oncorhynchus nerka |
8 |
|
Halibut Hippoglossus vulgaris |
90 |
|
Aldabra tortoise Geochelone gigantea |
152 |
|
Wood turtle Clemmys insculpta |
60 |
|
Eastern box turtle Terrapene carolina carolina |
75 |
|
Coahuilan box turtle Terrapene coahuila |
9.4 |
This table seriously underestimates the maximum age potential for longer-lived animals relative to humans. This is because humans have greater medical support and because life spans of humans are much better monitored. We have measured the life spans of at least several hundred million people. If we measured several hundred million rockfish what would be their maximum age? Most of the people lived under conditions where they could survive even though seriously weakened by age. What would be the maximum age of rockfish if similarly protected and medically supported?
Evolution Fact and Theory
Evolution theory is very central to scientific theories of
aging. Understanding the history and current status of evolution theory is
therefore essential in order to understand the history and current status of
biological aging theory. In this connection it is very important to recognize
that “evolution” has several aspects that possess different degrees of
scientific certainty.
First, we have the fact of evolution. Did evolution of life on Earth occur? Are humans and other current species descended from earlier, different, and generally simpler species? There is overwhelming scientific evidence supporting the fact of evolution. Darwin presented much of this evidence in 1859. Since Darwin, a huge mass of additional evidence has accumulated further confirming that evolution of life on Earth has occurred. As a result, there is essentially no scientific disagreement with the fact of evolution. Evolution is one of the major foundations of biology. We can say that convergence has applied to the fact of evolution in that our certainty has more or less steadily increased with time.
Another aspect concerns the mechanics of evolution. How does evolution work? What factors are important to the process of evolution? Why have organisms evolved in a certain way? Darwin[2] presented a mechanics concept that included “natural selection” and “natural variation.” However, even in Darwin's time, there were significant discrepancies and issues concerning evolutionary mechanics. Since Darwin, scientific discoveries have confirmed that Darwin's mechanics are generally valid but have also disclosed additional issues and questions. As a result, there exists significant scientific disagreement regarding the details of evolutionary mechanics. A number of evolution mechanics concepts have been developed that are essentially additions to or modifications of Darwin’s mechanics. In this book, “Darwinian evolution” or “orthodox Darwinism” means Darwin’s mechanics (along with any obvious inferences). Convergence regarding mechanics has not occurred. Certainty regarding mechanics has decreased for reasons to be described.
The “theoretical” part of evolution has to do with mechanics. The disagreements have a relatively minor effect on general biology but are very significant in connection with aging theories. (Aging was one of the original discrepancies.)
Finally, we have “derivative work”, theories that are based on a particular evolutionary mechanics concept. We will be discussing several theories of aging that are based on Darwinian mechanics as well as several that are based on post-Darwin mechanics concepts.
Biological Design
We can consider design as referring to all of the aspects of an organism that contribute to the performance of useful functions. Living things have some unique capabilities. They can reproduce and they can pass information regarding their designs to their descendents. Their descendents can then construct themselves in such a way that they have the same or similar design as their parents. Therefore, duck eggs always produce ducks and goose eggs always produce geese.
Evolution theory says that the designs of organisms have been accumulatively progressing with the passage of time such that there currently exist organisms having much more complex designs than existed, say, one billion years ago. Design features (evolved characteristics) of organisms can involve incredible complexity (more complexity than anything else known to science). Design features of organisms involve coordination and cooperation between many different tissues and supporting functions. For example, vision in an eagle involves muscles, sensory cells, nerves, brain functions, and inherited behaviors, all of which must be supported by other systems and tissues.
The most important question to be discussed in this book is: Are living organisms designed to age? If so there are consequences. If aging is a function like vision we can expect it to have characteristics common to other evolved functions including complexity and coordination.
2. Evolution Theory
Scientific theories regarding the cause of aging are intimately bonded to theories of evolution, particularly those of Charles Darwin.
Charles Darwin (1809 – 1882) was born in Shrewsbury, England to a family with long experience in medicine, and studied medicine at Edinburgh, Scotland. Darwin found medicine boring, and disliked the sight of blood, and so eventually became interested in the study of plants and animals. At one time, he spent several years studying barnacles. Eventually he sailed as naturalist on the HMS Beagle during a survey mission to South America from 1831 to 1836.
Darwin’s book, initially published in 1859, The Origin of Species by Means of Natural Selection or, The Preservation of Favoured Races in the Struggle for Life was a best seller and immediately controversial, both because of scientific disagreement and religious issues. Darwin’s primary conclusion, that species are descended from other species, was a lightning rod for controversy. Another English naturalist and contemporary of Darwin named Alfred Wallace (1823 – 1913) had a similar theory and is considered by some to be a co-discoverer of the evolution theory, though much less well known.
It is difficult to overstate the impact Darwin had on biology. In the more than 140 years since, there is no other theory in the field of evolution that has anywhere near the scientific acceptance of Darwin’s theory of natural selection. Popularly, most adult Americans easily associate “Darwin” with “evolution” and vice versa. Darwin’s books are still carried by most bookstores.
Darwin and the theory of natural selection resulted in aging being considered a substantially different type of biological property from teeth and most other animal characteristics.
The Theory of Natural Selection
Darwin proposed that random changes occurred in the inheritable designs of organisms. Through the process of natural selection, the changes that produced a beneficial result were retained in subsequent generations of the organism. Changes that were adverse were rejected.
Many of Darwin’s conclusions reached in Origin were based on comparison of the generic characteristics of wild plant and animal species with those of domesticated plants and animals. Darwin was especially interested in the differences or variations between individual members of species and between different species. The wild species were the result of natural selection or what was later called “survival of the fittest” while the domestic species were partly the result of selective breeding by humans. Wild species were subject to predator attack, intra-species warfare, starvation, and exposure to adverse weather. In contrast, domesticated species are protected and provided with food. Wild species survived based on survival traits. Domesticated species were bred for specific qualities desired by human breeders. Most domesticated species would not survive long in the wild. Domesticated species were frequently bred for externally obvious characteristics where natural selection would affect any characteristic, internal or external, if it affected survival. Darwin noted that the differences between members of domestic species such as dogs were grossly larger than the differences between members of wild species. Domestic species represented a proof that “selection”, that is selecting successive generations for the same property, could eventually result in very large changes to organisms.
Darwin determined that most characteristics or traits of organisms were evolved adaptations that aided the organism in surviving. That is, if sharper teeth resulted in animals of a given species surviving longer and therefore having more descendents than other animals with dull teeth, eventually, most of the animals in the population would have sharper teeth because the genetic design for sharper teeth would be passed to the larger number of descendents. Sharper teeth resulted from the process of evolution, the process of adapting to conditions in the animal’s external world.
The mechanics or how-it-works aspect of Darwin’s theory of natural selection is very simple and readily understood. There is no need for advanced mathematics or other major complexity. High school students can readily understand survival of the fittest.
Even the slowest reproducing species, would, if allowed to breed in an uncontrolled manner, occupy the entire planet in a relatively short period of time (an idea earlier put forth by Thomas Malthus (1766 – 1834)). This is the idea of geometric progression where one rabbit has two progeny, and they each have two, and they each have two, etc.
The growth of the populations of all species is therefore checked by a variety of external factors such as predators, diseases, food supply, and environmental conditions so that in a stable population each individual has an average of only one descendent which survives to produce one descendent and so on. All wild organisms are in competition for survival with other species and even more acutely with members of their own species.
A major clue as to the nature of evolution was found in the geographical distribution of various plants and animals. (Darwin’s expeditions provided very extensive data in this area and Origin has two chapters on geographical distribution.)
If an inheritable beneficial change occurred in an organism, we would expect its descendents possessing that change to propagate radially (or radiate) from the point of origin. Natural barriers such as oceans would tend to prevent the free migration of land animals and many plants. If species were descended from other species, we would expect substantial differences between such descendent species that were separated by such a barrier. “Families” of species that lived in one area would tend to resemble each other more than they resembled species in another area just as individuals in a geographic area resemble each other more than they resemble individuals that lived in a distant place. Sure enough, Darwin found flora and fauna to be “utterly dissimilar” between barrier-isolated geographic areas that were otherwise similar such as Australia, Western South America, and South Africa. Areas that had greater difference in their climates or otherwise represented different habitats but were not separated by migration barriers tended to have more similar organisms.
Darwin recognized that changes to inheritable characteristics that had no particular survival advantage or disadvantage, (survival neutral characteristics), could also geographically propagate and eventually become widespread.
Variation and Incremental Steps
Darwin proposed that small random changes to the inheritable characteristics of organisms (mutations) were the driving force behind evolution.
The probability that an animal will live longer and have more descendents is determined by the combination of all the characteristics possessed by that animal. For example, suppose some herbivore species in Africa becomes heavily predated by lions. We can suppose that “faster” might be a desirable characteristic for these animals. However, “faster” is actually the result of many characteristics. If we were redesigning this animal for more speed we might give it longer leg bones and reduce the size of other bones and systems to save weight. We might want to reduce heavy defensive characteristics such as horns. Internally, we would need to increase the size of some muscles and joints. Nerves, brain, and inherited behavior patterns would all need modifications.
All these changes are individually adverse and only have full survival benefit when applied in a specific combination. Larger leg bones without larger muscles would be a disadvantage. Larger muscles without stronger ligaments, tendons, and joints would be a disadvantage. A mutation that caused a large change in leg bone size would be adverse because it would not be accompanied by the other necessary complementary changes that are required in order to result in a beneficial effect.
Darwin was of course aware that occasional mutations caused large changes in animals. Darwin referred to these as “monstrosities” because such mutations (such as two-headed animals) were adverse and ugly.
Therefore, beneficial mutations in more complex organisms would be confined to those that caused only minor changes. A small increase in leg bone size might be beneficial. Subsequent mutations that resulted in small changes in associated muscles, tendons, or nerves might also be beneficial. Yet subsequent small additional increases in bone size might now be beneficial because the tendons and muscles had developed to match the original change in bone size. Eventually, in tiny increments, an animal with dramatically larger legs might evolve. If we examine the differences that currently exist between normal members of a wild species, they are indeed relatively minor in terms of their survival effect. We can use the term propagatable mutation to describe a mutation that had a sufficiently small effect that it could plausibly spread in the population. Such a mutation might have no physiological effect or might even have a very small negative effect.
This example also illustrates that characteristics of animals involve tradeoffs. In this case, we are giving up heavy defensive features such as horns, long sharp claws, and strong jaws in favor of saving weight in order to be faster.
Variation in inheritable characteristics between individuals in a population is thus a required property of life to support Darwin’s evolution theory. (Some contemporaries thought new species were created instantaneously by massive mutation in a single individual.) Natural selection operates upon this variation. Our increasing knowledge of the details of inheritance (see Genetics) provides increased support regarding the essential evolutionary role of variation.
In connection with variation, Darwin recognized that genetic diversity was a benefit to survival. Highly inbred domestic animals and plants were generally weaker, less hardy, and more susceptible to disease than crosses between more diverse specimens.
Darwin concluded for reasons described above that evolution took place by means of tiny increments. Each generation was only minutely different from its parents. Webster’s defines “evolution” as “…gradual development.”
These two features, evolution by means of natural variation and evolution in tiny incremental steps were the center of Darwin’s mechanics theory. When Darwin referred to “my theory”, he was referring most specifically to these features in addition to the idea that species evolved from other species in the same manner.
In addition to physical characteristics, Darwin included instincts and inherited behavior patterns in traits that evolved through natural selection. Behaviors would need to evolve in parallel with physical characteristics. A wing has no survival value unless used to fly. An eye is useless unless used to see. Flying and seeing would need to be supported by the appropriate brain and nervous system characteristics including inherited behaviors that lead to learning to fly and learning to see. Even a light sensitive spot on a worm would have no added survival value unless it somehow altered the behavior of the worm.
Some important implicit requirements of the theory of natural selection should be mentioned.
First, the natural variations in characteristics in a population of animals must be genetically programmed and thereby inheritable. Variations that were not genetically recorded could not participate in evolution because they would not affect the genetic content and therefore the design of subsequent generations.
Second, evolution requires a population. Evolution results from the difference in statistical life spans between animals that have a beneficial trait and those that do not.
Third, in order to evolve, a trait must be expressed or displayed by the organism in such a way that it affects the differential in life span. A latent characteristic which was present but not expressed at the time of an animal’s death could not have affected whether it lived or died. The death of that animal therefore could not have contributed to evolution of that characteristic.
Finally, and very important, the probability that an individual animal would live longer and/or breed more is determined by the combined effect of all its characteristics.
As you will see later in this book, these requirements are central to discriminating between various theories of aging.
Few scientists of the time would have argued against the idea that natural selection could cause a species to evolve. After all, humans had for thousands of years been causing domesticated species to change by selective breeding. If small dogs were bred with small dogs for a long time, men could produce a Chihuahua. If fast dogs were bred with fast dogs for long enough a Greyhound would result. If you go back far enough, Chihuahua and Greyhound are descended from the same dog.
The argument was whether all the species that now exist could have evolved from a single original primordial species (probably a single-cell organism on the order of pond scum) simply by the effects of natural selection acting in slow small increments on individual variation caused by random mutation. It was a much greater leap to believe that humans evolved from pond scum than to believe that fast dogs developed from slow dogs.
Development of different varieties was driven by geographic separation and differences in conditions. If a mammal lived in an area that contained both mountains and lowlands, it could not be optimized for both areas. The animals in the mountains might tend to develop characteristics that would favor survival in the colder, higher areas such as increased fur. The lowlands animals might develop characteristics favoring their conditions. Since they were somewhat geographically isolated the two groups would tend not to interbreed (genetic isolation). The two new varieties are both more effective at surviving in their particular habitats than the original variety and so would probably replace the original variety. After a long time the two varieties could evolve to be so different, they would become separate species. Eventually, the number of new species and variations being produced would be more or less matched by old species becoming extinct.
Besides natural selection, which is based on survival, Darwin recognized that sexual selection also played a role in evolution. Sexual selection would involve advantages that an individual might have that did not affect its survival but did represent an increase in its probability of breeding such as ability to attract the opposite sex. Darwin considered that sexual selection was weaker than natural selection.
Humans would be classified in Darwinian terms as “domesticated” as opposed to “wild” animals because humans have probably not existed under wild conditions for thousands of years. For example, one would expect the incidence of genetic diseases among humans to be higher than in a wild species because the effects of civilization and medical intervention allow individuals with adverse inherited conditions to survive and propagate in a way not possible in a wild species. Darwin speaks to such aspects of evolution of humans in his later book Descent of Man (1871). Use of human data (such as actuarial data) in an attempt to prove or disprove theories based on natural selection (such as aging theories) is therefore highly suspect although commonly done.
In connection with “survival of the fittest”, the term fitness came to be associated with the ability of an organism to survive and breed. It was apparent that there could be compromises or tradeoffs between various traits that improved survival. Speed in an animal might be a compromise with strength. A faster but weaker animal might be able to survive better than a slower stronger animal. It was also apparent that a tradeoff could exist between survival and reproduction. An animal that was a prolific breeder might be as fit as an animal with better survival capabilities but reduced breeding capabilities. (This particular tradeoff is important to some aging theories.) The fitness concept does not incorporate any aspect leading to increasing the quality of progeny relative to their parents. The quality of progeny is assumed to come from the effects of natural selection on the parents. Most biologists define fitness along the lines of “the ability to produce adult progeny.”
Darwin’s mechanics theory has some other important properties. Evolution does not take place during an organism’s life as suggested by some earlier theorists. The inheritable beneficial characteristics of an organism are fixed during its life.
Evolution is a very slow process. Although mutations might occur occasionally, beneficial mutations might be very rare because most mutations could be expected to be adverse. However, the beneficial effect caused by a beneficial mutation, once it finally happened, would be immediate. The immediate descendents of the mutated organism would live longer and breed more. The immediate “short-term” effect of beneficial mutations is important for theory considerations to be discussed.
Darwinian Evolution Requires Individual Benefit
It is also important to note that because of the mechanics of Darwinian evolution (survival of the fittest and the short-term nature of Darwinian mechanics), Darwinian beneficial mutations are associated with individual animals. Beneficial genetic mutations propagate because the individual organisms possessing those mutations can live longer and breed more. We can speak of “individual” fitness to emphasize the importance of the individual in Darwinian evolution. Specifically, Darwinian evolution theory does not allow for the evolution of traits that are beneficial to “the herd”, or “the group”, or “the species” if they are adverse to individuals. This individual benefit requirement will become very important in discussions to follow.
After original publication of Origin, there was some popular confusion about the term “natural selection.” Some people were interpreting “selection” as meaning a function of God. Subsequently, the expression “survival of the fittest” was used by Darwin and others in an effort to clarify that organisms themselves were actually performing the “selection.”
Darwin’s main conclusion, that species are descended from other species, is supported by overwhelming and growing scientific evidence. As will be described, there remain legitimate scientific disagreements regarding mechanics of Darwin’s theory.
It should be noted that until the nineteenth century, there was little scientific evidence that conflicted greatly with the biblical notion of creation, that is, that the Earth and all the species on it had been created more or less simultaneously in the relatively recent past. It was widely thought that the Earth was not very old, possibly as little as 25,000 years old.
For example, mountains could not be extremely old. Every wind that blows and every rain that falls removes material from a mountain and deposits it in a valley. If the Earth were extremely old, would it not be essentially flat?
The discovery of the occasional odd bone was often attributed to existing but undiscovered species or recently deceased species. There was little evidence that existing species had changed much or new species appeared during the time that people had been making observations, which was a significant fraction of the putative age of the Earth.
However, eventually it became clear that the Earth was very old, on the order of 4.5 billion years old. Mountains and other geological features were being replenished by geological processes such as plate tectonics that, even now, seem fantastic. Methods were developed (eventually including radioisotope dating) for estimating ages of rocks and fossils, which disclosed extreme ages for some fossils and allowed the determination of a time continuum for the appearance and disappearance of various life forms. All of these developments contributed support to the idea that evolution of life on Earth had in fact occurred.
There was great and immediate objection to Darwin’s theories on religious grounds. This controversy greatly contributed to the popularity of and very wide distribution of Darwin’s books. The major objection was of course Darwin’s idea that species were descended from other species as opposed to being individually created by God. The idea that the human species was descended from “monkeys” as opposed to being individually created by God was particularly unattractive.
In 1925 Tennessee passed a law “…prohibiting the teaching of the Evolution Theory in all the Universities, Normals and all other public schools of Tennessee, which are supported in whole or in part by the public school funds of the State, and to provide penalties for the violations thereof.”
Later in 1925, a high-school biology teacher, John Scopes, was charged with illegally teaching the theory of evolution. The subsequent trial, State v. John Scopes, known popularly as “the monkey trial”, pitted three-time presidential candidate William Jennings Bryan as fundamentalist council for the prosecution against famed agnostic lawyer Clarence Darrow for the defense and created an international media circus in the little (pop. 1,800) town of Dayton Tennessee. The trial was eventually transferred into a tent so that thousands of spectators could be accommodated. Bryan also acted as a prosecution witness and was cross-examined by Darrow in a famous exchange, which, by all accounts, Darrow won handily.
Scopes was obviously guilty. The trial was about the constitutionality and reasonableness of the law. Darrow actually requested the jury to find Scopes guilty so the case could be appealed to the Tennessee Supreme Court, which eventually dismissed the case. The international derision resulting from this case inhibited many other states that had been considering anti-evolution laws. Eventually, in 1968, the U.S. Supreme Court found laws prohibiting teaching of evolution in public schools unconstitutional by virtue of the First Amendment (separation of church and state).
Fundamentalist anti-evolution efforts continue today. Creationists favor teaching a biblical version of the creation in public school science classes as an alternative to evolution theory. Creationist texts abound with scientific-sounding arguments, footnotes, and references. However, unless a dramatic rightward shift in the U.S. Supreme Court occurs, teaching the Bible in U.S. public school science classes will remain unconstitutional.
Intelligent Design (ID) is a version of creationism that holds that individual species of living organisms, because of their complexity and for various other reasons, cannot have arisen from random chance and natural selection, and therefore must be the result of the operation of some intelligence. ID proponents avoid mention of God or the Bible. Readers are free to ascribe the intelligence driving the development of different species to little green men, Klingons, or whatever their favorite source of supernatural intelligence might be. Credentialed scientists approach rural local public school boards in religiously conservative states with arguments to the effect that ID represents a legitimate scientific disagreement with evolution theory and should therefore be taught as an alternative.
ID has an advantage over creationism in that ID proponents can choose to believe that the historical record matches that proposed by evolutionists, that various species appeared on the same schedule, and that individual species are derived from prior species. The only difference is now that God or other source of supernatural intelligence directed the design of each individual species. The fossils and other evidence therefore do not conflict with ID as they do with creationism.
However, ID and creationism are actually fundamentally incompatible with science. The development of a scientific theory becomes trivial if the theorist is free to invoke God or other source of supernatural direction anytime he is having difficulty making his theory agree with observed facts. Once it was determined that God was responsible for a certain function or process, further inquiry would be inhibited or could even be prohibited. If, several hundred years ago it had been determined that God was responsible for lightning, would we ever have discovered and harnessed electricity?
Many people are not as opposed to the fact of evolution as to the teaching of evolution. They see teaching evolution, especially in lower grades, as anti-religion, essentially teaching atheism. While the “humans are descended from lesser species” aspect of Darwinism is obviously objectionable to fundamentalists, another aspect, the individual benefit requirement, is more generally objectionable. Most religions, societies, and civilization generally, are built on the concept of individual sacrifice for the greater good. Horrible acts including pogroms and “ethnic cleansing” have been “justified” based on evolution theory.
Anti-evolution efforts in the United States are having a significant effect. A Harris poll in June 2005 found that 54 percent of Americans do not believe that humans developed from earlier species (up from 46 percent in March 1994).
The existence of creationism and ID contribute to a sort of scientific backlash, a “siege mentality”, an atmosphere of “us versus them” in the scientific community. Legitimate scientists feel comfortable in taking positions that attribute more certainty, scope, and comprehensiveness to Darwinian mechanics theory than is actually scientifically justified. See example in chapter 7.
Miscellaneous Objections
In later editions of Origin, Darwin provided a chapter, Miscellaneous Objections to the Theory of Natural Selection, in which he responds to objections raised by contemporary scientists.
If Darwin’s theories were correct, there would have existed sometime in the past individuals possessing all of those little incremental variations extending from that original organism to each current species. One objection was that the fossil record did not seem to support this, as there were times when new species seemed to suddenly appear and there were many “missing links.” Darwin presented extensive geological arguments showing that the geological fossil record itself had gaps that would explain the non-discovery of some intermediate forms. For example, a geological event that caused a coastal area to submerge might cause loss of some part of the fossil record.
Another major objection had to do with the intermediate survival value of various organs and structures. Contemporaries argued that “half a wing” would not be of any value and so a full wing could not have evolved by means of tiny steps. Darwin agreed that his theory would be defeated if a single case could be found where an organ or structure did not have increased survival value in all of the incremental intermediate forms needed to evolve that organ or structure.
For example, the eye is a complex structure that might not appear to have value without all its complex parts including retina, lens, iris, etc. If this were true, there would be no incremental evolutionary path from no eye to complete eye. Darwin was able to show that even in existing living species, there are examples of a continuum of minor variations of optical organs all the way from a light sensitive spot on a worm to an eagle’s eye. He was also able to show that eyes in current animals evolved down at least two different evolutionary paths.
However, although the theory of natural selection explained a great many things, and Darwin was able to successfully respond to many objections (such as those above) f