In this article I will examine the relationship between the processes of natural selection,artificial selection and differential reproduction. Whereas these processes are typically discussed in terms of the evolution of species, the context of this article will be populations.
In particular I will propose the introduction of a new term for an existing process (only partially explained as stochastic process), which I call Malthusian selection. Together, these processes form the framework of the Exponentialist theory of evolution and populations, and allow for a form of group selection between populations.
The concept of Malthusian selection was first published in The Australian Humanist (No. 76 Summer 2004) in an article by David Coutts entitled Common Ground - Creationism and Evolutionary Theory.
Thomas Robert MalthusEdit
Thomas Robert Malthus first published An Essay on the Principle of Population in 1798. Today the Malthusian growth model bears his name, and is widely recognised as an approximate physical law of population growth. However, see related article Couttsian Growth Model for a revised Malthusian Growth Model that represents an actual universal physical law.
The term Malthusian selection is thus named after Malthus, in recognition of his contributions to science.
- Mayr acknowledges that it was Malthus who explained the exponential nature of population growth that applies to all species (though Malthus focussed on Mankind), as well as the various checks on population that constrain such growth.
- Mayr referred to "...Darwin's new way of thinking..." as population thinking and considered it "...the foundation of modern evolutionary theory...".
- Mayr acknowledges that Malthus reinforced observations relating to the struggle for existence within limits to growth.
- Mayr acknowledges that it was due to Malthus that Darwin acknowledged the significance of intraspecies competition between populations of the same species.
- Zimmer points out that population thinking also explained how an incipient species could become an established species in very little time.
I will argue that the modern evolutionary synthesis is still a theory of the origin of species, and not even a partial theory of the differential reproduction of populations. The population thinking used is, in fact, too Darwinian and not sufficiently Malthusian.
The only difference between humans and the rest of life is, I suspect, the sophistication and effectiveness of human non-genetic cultural factors (discussed in more detail later).
Malthus (1798) put this well:
"The main peculiarity which distinguishes man from other animals, is the means of his support, is the power which he possesses of very greatly increasing these means."
Darwin (1871) put it even better:
"Man in the rudest state in which he now exists is the most dominant animal that has ever appeared on this earth. He has spread more widely than any other highly organised form: and all others have yielded before him. He manifestly owes this immense superiority to his intellectual faculties, to his social habits, which lead him to aid and defend his fellows, and to his corporeal structure. The supreme importance of these characters has been proved by the final arbitrament of the battle for life."
As noted by Professor Robert M. Young (Malthus On Man - In Animals No Moral Restraint, 1998), in his essay Malthus focussed on Man, and it was Darwin that noted the absence of moral restraint from animals (and plants).
Yet it Malthus, not Darwin, who first proposed that his law of nature (the Principle of Population) applied to all populations of all species:
"Elevated as man is above all other animals by his intellectual faculties, it is not to be supposed that the physical laws to which he is subjected should be essentially different from those which are observed to prevail in other parts of animated nature."
Humanity may well be unique, but we are still subject to the laws of nature.
Malthus (1798) believed in the Biblical creation, and credited God with any tinkering with species:
The powers of selection, combination, and transmutation, which every seed shews, are truly miraculous. Who can imagine that these wonderful faculties are contained in these little bits of matter? To me it appears much more philosophical to suppose that the mighty God of nature is present in full energy in all these operations.
Fortuneatly, this allowed Malthus to focus on the nature of population growth rather than the origin of species. Malthus was the first to thoroughly examine the evidence relating to the differential reproduction of humans:
Taking countries in general, there will necessarily be differences as to the natural healthiness in all gradations, from the most marshy habitable situations to the most pure and salubrious air. These differences will be further increased by the employments of the people, their habits of cleanliness, and their care in preventing the spread of epidemics. If in no country was there any difficulty in obtaining the means of subsistence, these different degrees of healthiness would make great difference in the progress of population...
Particularly from the 2nd edition of his essay onwards, Malthus examined in as much detail as was then possible the causes behind the differential reproduction of discrete human populations around the world, and helped establish the present day field of demography as a result.
A simple rule of thumb to examine Malthus' approach is the Rule of 70. For example, if population A is growing at 1% per annum then it will double every 70 years. If population B is growing at 2% per annum then it will double every 35 years. Population A is thus losing the struggle for existence against population B. If population C halves every 35 years, then it is being selected against and will go extinct.
This is what is meant in this article by differential reproduction. Think of it as differential population growth.
Richard Dawkins (1982) defines natural selection as:
"...the process whereby replicators out-propagate each other."
This definition fails to mention the evolution of species, and would actually serve better as a description of differential reproduction (or differential replication).
Dawkins' Law of Differential SurvivalEdit
Dawkins (1976) proposed a general principle of nature that applies to all life:
"This is the law that all life evolves by the differential survival of replicating entities."
I agree, and I believe that the process of Malthusian selection (in concert with artificial selection and natural selection) supports Dawkins' proposal (though I doubt that Dawkins had group selection in mind). But what does differential survival actually mean, in practical terms?
"Much of the differential survival and reproduction in a population are not the result of selection, but rather of chance."
So Mayr does not see chance (stochastic process) as a selective force, yet it is a significant cause of differential survival and reproduction.
Dr. Philip Whitfield (1993) put the demarkation between species persistence and species extinction in an especially Malthusian manner:
"The extinction of a species does not usually involve the sudden death of all its individual members. Rather, it is a function of the dynamics between rates of birth and death. Species will persist when their overall birth rate equals or exceeds their death rate. But if the latter exceeds the birth rate for a long enough period, replacement of one generation by the next ceases to exist. If no new factor intervenes then the species will go extinct."
What Whitfield describes is group selection. Of course, species are frequently made up of more than one discrete population. The fate of the species is sealed by the fate of all its populations.
The Malthusian approach to variable population doubling periods demonstrates the nature of the differential survival of persistent species, on a population by population basis. Who is fit, and who is the fittest? For a given population this can be demonstrated by successive population doublings. The period of population doubling is an indicator of population fitness, with shorter periods indicting greater fitness.
For species that are going extinct, a similarly Malthusian approach to variable population halving periods can demonstrate the nature of the differential extinction of species, on a population by population basis. Who is unfit, and who is the least fit? For a given population this can be demonstrated by successive population halvings. The period of population halving is an indicator of a lack of population fitness, with shorter periods indicting less fitness.
The well-known state of dynamic equilibrium is Nature's balancing act. There is no guarentee that a population that persists will continue to persist, or that a population experiencing negative growth will go extinct. However, so far, all extinct species have remained extinct.
For species that persist, they compete for resources within Malthusian limits to growth. Inevitably, any population that grows too successfully for too long will hit the limits to growth, and be forced (perhaps just temporarily) onto the pathway of negative growth and extinction.
Natural selection also affects rates of population growth, as Darwin (1859) argued:
In looking at Nature, it is most necessary to keep the foregoing considerations in mind - never to forget that every single organic being around us may be said to be striving to the utmost to increase in numbers; that each lives by a struggle at some period of its life; that heavy destruction inevitably falls either on the young or old, during each generation or at recurrent intervals. Lighten any check, mitigate the destruction ever so little, and the number of the species will almost instantaneously increase to any amount. The face of Nature may be compared to a yielding surface, with ten thousand sharp wedges packed close together and driven inwards by incessant blows, sometimes one wedge being struck, and then another with greater force.
In other words, life within limits to growth is a zero-sum game. A gain by one species is a loss by another. The incessant blows are the geometric nature of population growth, the rate of which varies from year to year, population to population, and species to species.
Mayr (2001) defines natural selection as:
"The process by which in every generation individuals of lower fitness are removed from the population."
The survival of the fittest here relates to the individuals eliminated from the population.
Wikipedia defines natural selection as:
"...the name Charles Darwin gave to the principal process through which new species emerge, or evolve."
Clearly, natural selection is seen as Darwin's answer to the questions of the origin and evolution of species.
Wikipedia does acknowledge the role of environment in natural selection:
"In one environment, a trait may be adaptive and increase the fitness of the individual (that is, enable it to produce more offspring that are more likely to survive). In another environment, this same trait may be maladaptive and decrease the fitness of the individual. It is the environment, or nature, that determines whether a given trait will increase or decrease in frequency within a population over time."
However, the emphasis is on the selection for or against individuals (based on the interplay of genetic traits and environment), and the resultant evolution of new species. There is no attempt to explain the effect of environment on population growth rates.
Wikipedia does discuss the process of differential reproduction, but as a subsidiary process to natural selection.
"Differential reproduction due to natural selection can result from differences in functional performance at many levels of biological organization, not only at the level of individual organisms (see unit of selection), but historically the emphasis has been on the selection of individual organisms that differ in some trait(s) which affect individual performance and result in a higher or lower reproductive output (so called positive and negative selection). "
In other words, differential reproduction in the context of natural selection is about the reproductive genetic fitness of a population. There is no attempt to explain the effect of such reproductive fitness on population growth rates.
Instead of recognising the true significance of the Malthusian Principle of Population, evolutionist Elliot Sober (1984) repeats the typical party line that:
"Malthusianism is not a proper starting point for the theory of natural selection for reasons made abundantly clear by Fisher (1930, pp.46-47)."
Malthusianism may well be an improper starting point when looked at from the context of the evolution of species, but natural selection itself is an improper starting point when looked at from the context of the differential reproduction of populations.
What is lacking from the modern evolutionary synthesis is an overarching theory of the differential reproduction of populations that embraces all contributing subsidiary processes. This is provided by Exponentialist theory, which has population as the context, not the origin of species.
Natural selection is only one process that can affect differential rates of reproduction. Artificial selection and Malthusian selection also affect differential rates of reproduction.
"Charles Darwin originally coined the term in order to contrast this process from what he called natural selection. He noted that many domesticated animals and plants had special properties that were developed by intentionally encouraging the breeding potential of individuals who both possessed desirable characteristics, and discouraging the breeding of individuals who had less desirable characteristics."
Once again the emphasis is on the evolution of species, this time through artificial selection. There is no attempt to explain the effect of artificial selection on the differential rates of reproduction of populations.
Yet often the point of artifical selection is to improve reproductive success, or minimise mortality, for the species in question. Thus, rates of population growth must be affected.
In evolutionary terms, stochastic processes are said to eliminate less fit individuals on a day to day basis, or result in rare and haphazard mass extinctions (Mayr, 2001).
The theory of evolution, encompassing as it does natural selection, artificial selection, and stochastic processes does not clearly explain why human populations have differential rates of population. In evolutionary theory, stochastic process is a lame concept that neither clearly explains nor quantifies anything in terms of rates of differential reproduction.
In terms of population dynamics, populations are affected by exogenous factors and endogenous factors ("population feedback").
Exogenous factors (though sometimes called "noise"), are considered "...important biological processes affecting population change..." (Turchin, 2003) and are not to be ignored. Exogenous factors are typically modelled in a stochastic process, though non-random factors such as seasons are recognised.
In population dynamics, stochastic processes is a complex concept that neither clearly explains nor quantifies anything in terms of rates of differential reproduction. There seems little explanatory power in population dynamics for how stochastic processes affect evolution.
The solution, intended to enhance the explanatory power of evolutionary theory, is to introduce the concept of Malthusian selection.
Malthusian Selection DefinedEdit
Malthusian selection is a process that results in differential rates of reproduction of populations. For Malthusian selection to be occur, neither natural selection nor artifical selection can completely explain any evidence of the differential reproduction of populations.
Malthusian selection is used to describe normal environmental factors (eg. altitude, day, night, tides, seasons, weather, earthquakes, tsunamis, floods, volcanoes, fire) and extinction events (such as asteroid impacts, gamma ray bursts, ice ages).
Malthusian selection also includes non-genetic cultural factors (eg. government, medicine, religion, hygiene, diet, family planning, gardening, agriculture, technology) that affect rates of differential reproduction for competing populations within limits to growth.
All Malthusian selection factors affect either birth rates, or death rates, and thus affect the growth rates of populations. The result is differential rates of reproduction.
An Example of Malthusian SelectionEdit
The pace of Malthusian selection can be compared to the pace of evolution by examining the differential rates of reproduction of populations of the human species throughout time and in the present day.
A simple example of Malthusian selection is to consider the populations of the United States Of America and Australia over time. In both cases, the indigenous peoples were displaced by Europeans. It can be argued that European germs were effectively a tool of natural selection which favoured the Europeans. However, non-genetic cultural factors (such as technology, medicine and government) also played their part. These factors are Malthusian selection factors.
Australia has always supported a much lower population with a much lower population density than the United States Of America. This is largely due to the fact that Australia is mostly desert or semi-arid, lacking the water resources of the United States Of America. Such factors are environmental Malthusian selection factors.
During the past few centuries, we have seen dramatic differences in the national rates of reproduction of these two nations, and no evidence of the evolution of Americans or Australians whatsoever. Americans and Australians are still very much Homo sapiens.
In fact, our global homogenous population is increasingly mobile and intermixed and thus subject to stablising selection (i.e. genetic steady-state), preventing natural selection from having much effect.
The Human Population PieEdit
Currently, the idea of group selection at the population level is explicitly rejected by modern evolutionists. For example Richard Dawkins (1982) clearly expresses his disdain for the idea of populations as the unit of selection for Natural Selection:
"Populations may last a long while, but they are constantly blending with other populations and so losing their identity. They are also subject to evolutionary change from within. A population is not a discrete enough entity to be a unit of natural selection, not stable and unitary enough to be selected in preference to another population."
Yet, ever since censuses began, the historical reality of the differential reproduction of human populations has been clearly documented (even allowing for complicating factors such as immigration and emigration, or revolutions and new nations). Projections indicate that this will continue. Nature (2001) provided a region by region estimate of world population in 2000. They then projected figures for 2075 and 2100. Imagine a pie chart of the human global population. The pie itself starts at 6,055 millions, grows to 8,951 then shrinks to 8,414. Here are some examples of the competing human population wedges of that pie:
- The North American wedge starts at 5% and stays there
- The South American wedge starts at 9%, grows to 10%, and reaches 11%
- The Western European wedge of the human population pie starts at 8%, then levels off at 5% from 2075
- The China region wedge starts at 23%, falls to 16%, and falls again to 15%
- South Asia (incl. India) starts at 22%, then levels off at 24% in 2075
- The Sub-Saharan African wedge starts at 10%, rises to 17%, and rises again to 18%
Whilst I agree with Dawkins that population categories blend and merge, these examples demonstrate that some populations are being selected "for", and some are being selected "against" in the struggle for existence, the survival of the fittest. This is not natural selection, nor artificial selection. It is not Social Darwinism, for it is too neutral and too disinterested a process for that. It is Malthusian selection.
As the human population expands, so too does our slice of the pie chart of life on Earth. So too do the slices of the pie chart used to feed and sustain the global human population (crops, fish, livestock, grass for livestock, trees etc). However, nobody has ever suggested that the pie chart of life on Earth is getting any bigger. Instead, as Darwin suggested, the evidence suggests that as one wedge is driven in, other wedges are being driven out or squashed into extinction.
To get an idea of the global human impact on life, consider an example from The Atlas Of The Living World (1989), edited by David Attenborough, in which it was estimated that humanity makes use of 27% of the Earth's plant production for our own purposes.
Common ground for creationists and evolutionistsEdit
As such, Malthusian selection represents something that is not supposed to exist - namely, common ground for creationists and evolutionists. Otherwise, how else do we explain the differential rates of population growth of the human species in the absence of natural selection?
As a concept, Malthusian selection is implicit in the theory of evolution, but not explicit. For example, Ernst Mayr (2001) refers to "chance" (i.e. stochastic factors) as a separate factor to natural selection:
"Owing to unequal survival and reproductive success of its individuals, there is a continuing genetic turnover in each population as a result of chance and natural selection."
This explanation is fine, as far natural selection goes, but it fails to explain the consequences of reproductive success in terms of population growth. If reproductive success is unequal, then it also fails to provide an explanatory framework for differental rates of reproduction. The fate of a population is sealed by the fate of its individuals.
Malthus' essay on the Principle of Population (which ended with two chapters on natural theology) was embraced enthusiatically by Archdeacon William Paley in his Natural Theology (1802). Yet Paley seemed to miss the point that Malthus was making regarding the inevitability and constancy of the struggle for existence, due to the power of population over the means of subsistence. As explained by Professor Robert M. Young (1985):
"Paley almost exclusively stressed harmony and benevolence at the expense of the unpalatable facts. Harmony, not struggle, was the keynote."
Another natural theologian, Thomas Chalmers did use the Malthusian Principle of Population to actually emphasise Malthus' focus on the struggle for existence, but only to moralise about God's punishment of sin and vice, and to advocate Malthusian moral restraint.
Yet as a concept, Malthusian selection is actually absent from the theory of creationism, and absent from the theory of Intelligent Design. There is no debate in the so called Creation-Evolution controversy, nor the Teach The Controversy agenda, regarding the fact that - in the supposed absence of evolution - populations of all species demonstrate differential rates of reproduction and thus the survival of the fittest still applies regardless of whether or not species evolve.
Perhaps it is time for present-day adherents of these opposing points of view to address the common ground of Malthusian selection, not just for human populations but for all populations of all species.
Malthusian selection is proposed as a group selection process that drives the selection of one population over another. It is not a moralistic theory, and does not propose any theory of social progress (or relative cultural superiority), as does Social Darwinism. Malthusian selection, like natural selection, is a neutral and disinterested process. Malthusian selection is not teleological.
It is worth noting that, even for humans, Malthusian selection works in a shorter timeframe (i.e. decades) that is generally allowed for by natural selection (i.e. millennia). In terms of population growth, it is proposed that Malthusian selection is thus generally a more significant factor than natural selection and artificial selection.
Yet in terms of population growth for undomesticated species, natural selection may be the tortoise in the race, as slow and steady wins the race. Once a species has evolved to suit an environmental niche, assuming the niche remains stable, then the hare that is Malthusian selection is asleep and the tortoise that is natural selection will cross the finishing line first.
In terms of population growth for domesticated species, artificial selection can be the key factor. Again, this would require a stable environmental niche.
Malthusian population thinking is the key to understanding the Law of Differential Survival, an overarching theory of differential reproduction (or differential population growth).
Malthusian selection is not proposed in opposition to the theory of evolution, but in support of it. In the context of new species, or the evolution of species, natural selection and artificial selection remain unchanged.
However, in the context of populations, natural selection and artificial selection can now be seen in a new light, as additional group selection processes that work in conjunction with Malthusian selection to affect differential rates of reproduction for populations of all species.
- David Attenborough (editor), (1989). The Atlas Of The Living World. Marshal Editions. ISBN 0-297-79642-9
- David Coutts (2004), Common Ground - Creationism and Evolutionary Theory, The Australian Humanist (No. 76 Summer 2004)
- Charles Darwin (1859), The Origin of Species
- Charles Darwin (1871), The Descent of Man
- Richard Dawkins (1982), The Extended Phenotype. Oxford University Press. ISBN 0-19-286088-7
- Richard Dawkins (1995), River Out of Eden. Phoenix, Orion Books Ltd. ISBN 1-85799-405-1
- Jared Diamond (1997), Guns, Germs and Steel. Vintage. ISBN 0-09-930278-0
- Thomas Robert Malthus, An Essay on the Principle of Population (1st edition, 1798). A Summary View (1830). Penguin Books. ISBN 0-14-043206-X
- Ernst Mayr (2001), What Evolution Is. Weidenfeld and Nicolson. ISBN 0-297-60741-3
- William Paley, 1802), Natural Theology, or Evidences of the Existence and Attributes of the Deity collected from the Appearances of Nature.
- William Peterson (1979, 1999), Malthus, Founder of Modern Demography. Transaction. ISBN 0-7658-0481-6
- Elliot Sober (1984), The Nature Of Selection. Chicago University Press. ISBN 0-226-76748-5
- Nature (2nd August 2001), Population Set To Decline
- Peter Turchin (2003), Complex Population Dynamics. Princeton University Press. ISBN 0-691-09021-1
- Carl Zimmer (WGBH Educational Foundation and Clear Blue Sky Productions, 2001), Evolution, the Triumph of an Idea. Harper Collins. ISBN 0-06-019906-7
- Philip Whitfield (1993),From So Simple A Beginning - The Book Of Evolution (p. 182). Macmillan. ISBN 0-02-627115-X
- MALTHUS ON MAN - IN ANIMALS NO MORAL RESTRAINT article about Malthus' influence on Darwin, by Professor Robert M. Young
- MALTHUS AND THE EVOLUTIONISTS:THE COMMON CONTEXT OF BIOLOGICAL AND SOCIAL THEORY Online chapter from Darwin's Metaphor: Nature's Place in Victorian Culture by Professor Robert M. Young (1985, 1988, 1994). Cambridge University Press. ISBN 0521317428
- Wikipedia (as of 9th January, 2006), articles on natural selection and artificial selection.
- Couttsian Growth Model - a revised Malthusian Growth Model
- List of countries by birth rate
- List of countries by death rate
- Population history of American indigenous peoples
- Indigenous Australians
- World population