A Better Alternative To Differential K Theory

Famine-Resistant Vs Disease-Resistant Populations

1. What is R/K Selection Theory?

R/K selection theory claims the following:

Some species are adapted to live close to the carrying capacity (K-selected), whereas others are adapted to live below the carrying capacity (R-selected).
K-selection favors greater parental investment than R-selection.
K-selection and R-selection cause two sets of mutually-exclusive characteristics (see table below).

I agree with all the reasoning in Blithering Genius’s essay, “Why R/K Selection Theory is Bogus”, as to why these claims are false. However, I don’t believe that all the patterns proposed in the third claim are entirely non-existent. Instead, I propose that some of the patterns are oversimplifications and consequences of a more accurate ecological model. As it pertains to modern humans, this model is partly described in “Life is Violent” by Blithering Genius and Life History Theory. I recommend reading all three of the prior linked pages if you haven’t already, since they are necessary for understanding the rest of this webpage.

The following characteristics are claimed to be associated with R-selected and K-Selected species:

Characteristic	R-selected	K-Selected
Environment Type	Unstable, Density-Independent	Stable, Density-Dependent Interactions
Size of Organism	Smaller	Larger
Energy Invested Into Offspring	Lower	Higher
Average Number of Offspring	Greater	Fewer
Maturity	Earlier	Later, usually after prolonged parental care
Life Expectancy	Shorter	Longer
Reproduction Times	Each individual only reproduces once	Individuals can reproduce more than once in their lifetime
Survivorship	Type III Survivorship Pattern	Type I or II Survivorship Pattern
Lifespan	Most individuals die within short time	Most individuals live to near maximum lifespan

The observations that brood sizes tend to decrease with (adult) body mass, and that lifespan increases with gestation period were recorded as far back as Aristotle.

2. Further Problems And Clarifications For R/K Selection Theory

The characteristics listed in the table above are often associated with each other, but not always.

“Why R/K Selection Theory is Bogus” notes how the density of environments is poorly defined.
The octopus is an exception to the theory that more intelligent organisms have longer lifespans. Octopuses are very intelligent, yet they only have a lifespan of 3-4 years at most.
Taller humans tend to have shorter life expectancies. This is contrary to how the R/K selection theory proposes that larger organisms should have longer life expectancies.
The size of R-selected and K-selected humans doesn’t follow the rest of the pattern. R-selected and K-selected humans can both be tall or short:

Physique is mostly determined by the energetics of food production. People who herd animals tend to be taller, whether Nords or Maasai. People who grow rice tend to have short legs and light upper bodies. People who use hoes to farm yams have big butts. Europeans tend to be relatively strong and tall, because their ancestors used animals extensively for food and traction.

– Blithering Genius, Discord

Furthermore, most R/K selection theorists tend to categorize all organisms as being either “R-selected” or “K-selected”. This is fallacious because different organisms have different life cycles, which affect their abilities to reproduce. It’s not meaningful to compare organisms that have significantly different life cycles. To do so would be to compare apples with oranges.

A bacterium reproduces by simple cell division, so it only has 2 “offspring” at most. (As with most things in biology, there are some weird exceptions.)

Reproduction is not a contest between men, bacteria, salmon and oak trees. It is not necessarily a contest, although it often involves a struggle for resources or mates, especially with other members of one’s species.

Different types of life have different life-cycles. Some produce millions of offspring, of which very few survive to adulthood. Humans have relatively few offspring, compared to oak trees and oysters. It does not follow that we are less successful, on average. The life-cycles of oak trees, oysters and humans are all successful reproductive strategies. That’s why oak trees, oysters and humans exist.

– Blithering Genius, “Responding to Conundrum, Again”

The R/K selection dichotomy is thus only meaningful when comparing between different taxa that are closely related. Closely related taxa tend to have more similar life cycles and tend to occupy more similar niches. Categorizing different human races as “R-selected” or “K-selected” thus has some meaning, but not as much as the improved terminology that I propose. This essay focuses mainly on comparing different human races.

3. Differential K Theory Lacks Predictive And Explanatory Power

Differential K Theory is an attempt to apply R/K selection theory to human races. It proposes that the evolution of every race was affected by a “K factor”, which theoretically affects and explains multiple race differences in fertility, IQ, criminality, and sexual anatomy and behavior. Europeans, East Asians, and other intelligent races are supposedly K-selected, while less intelligent races are supposedly R-selected. Parental investment presumably favors quality offspring in the former, while favoring quantity in the latter.

However, Differential K only raises the question as to what factors affect the K factor. There are no coherent answers to this question. It’s not clear how different K factors would affect the selection for intelligence in different populations around the world. It’s also not clear how different levels of parental investment are related to genetic differences or selection for intelligence.

Labeling a population as R-selected or K-selected is only a binary distinction. This limits the amount of information that these terms can convey. Not all K-selected populations are the same as each other, nor are all R-selected populations the same as each other. For example, the R/K selection framework doesn’t make it clear how “K-selected” populations like Europeans and East Asians are different from each other, nor does it describe how “R-selected” populations like sub-Saharan Africans and Latinos are different from each other. R/K selection doesn’t describe the different selectionary pressures these populations went through.

Even if the patterns associated with R-selected and K-selected species seemingly map well onto some human races, it’s still ambiguous whether some races should be classified as “R-selected” or “K-selected”. Supposedly, K-selected races have lower fertility rates and higher average IQs. However, fertility rates are largely dependent on environmental factors. Fertility rates will be low if a population has large amount of birth control. Fertility rates also drop during times of war and/or famines, and they increase during economic booms. It’s thus not meaningful to classify populations as “R-selected” or “K-selected” based on their fertility rates. Even if a population has a relatively higher average IQ, it’s more descriptive and straight-forward to simply say that instead.

Differential K Theory is popular among many race idealists, since it justifies their ideology. The race idealists want to believe in R/K selection theory because it provides a narrative for explaining why some races have higher or lower intelligence and others. The truth is actually more complex, and it probably doesn’t have anything to do with different levels of parental investment.

4. Explaining Patterns In Human Races Without R/K Selection

All populations evolved to live near the carrying capacities of their respective environments, not just “K-selected” populations. It’s thus more descriptive to describe every population by the main factor that had historically kept them below the carrying capacities of their respective environments.

As mentioned in “Life is Violent”, human populations have historically been limited by a combination of disease, famine, and war. All human populations are known to have dealt with these causes of death at one point or another in their histories, but most populations were affected by each of these factors to different degrees.

War is not an alternative to peace and prosperity. War is an alternative to famine and disease, and famine almost always leads to war. If you and your children are facing death by starvation, then you will kill other people to get food. So, unless disease kills most children before adulthood, population growth will eventually lead to war. That is why war is a human universal. Our ancestors fought to survive. We inherited the genes and memes of the winners, not the losers.

– Blithering Genius, “Life is Violent”

For recent human history, it’s accurate to make some generalizations about human populations:

Eurasian populations were mainly limited by diseases.
South Asian populations were more limited by famines and malnutrition, in the past few hundred years.
Amerindian, Austronesian, and sub-Saharan African populations were mainly limited by famines, malnutrition, and wars.

Words like disease-resistant and famine-resistant are thus better descriptors for summarizing and describing the adaptations of modern human populations. However, they aren’t the only descriptors that we can use. We can brainstorm many other terms and statistics, such as “shorter gestational lengths”, “early pubertal development”, “higher intelligence”, etc. For an information-dense continuous variable, we can graph and calculate the Ancestral Premature Death Rate (APDR) for every race.

Disclaimer: I’m not an expert on the evolutionary history of every human population. Throughout this page, I’ve only written and mentioned information that I already know about. The conclusions that I propose are based on what I know. Someone with greater knowledge could probably expand upon these ideas to write more conclusions.

4.1. Disease-Resistance In Eurasia

As it turns out, the races that are usually theorized to be “K-selected” (i.e. European, Jews, and East Asians) were usually limited by diseases and such. We could describe them as disease-resistant¹. Eurasia had multiple factors that contributed to the spread and number of diseases, compared to the Americas and Africa:

Animal Domestication: Eurasia had more domesticable large mammals like cattle, pigs, sheep, and horses. Close proximity to these animals facilitated the transmission of zoonotic diseases - illnesses that can jump from animals to humans. Diseases like smallpox, influenza, and measles likely originated from animal populations in Eurasia.
Population Density and Settlements: Early agricultural societies in Eurasia developed larger, more concentrated settlements. Dense populations living close to domesticated animals created ideal conditions for diseases to spread and mutate.
Geographical Connectivity: Eurasia is a large, horizontally-oriented landmass that allowed for easier migration of people, animals, and subsequently, pathogens. This connectivity meant diseases could spread more widely and quickly compared to the more fragmented and vertically-oriented continents of the Americas and Africa. Historically, most civilizations were horizontally shaped. It was easier for civilizations to spread east or west than north or south since the former directions were easier for adapting to climates and growing crops.
Continuous Population Mixing: Trade routes like the Silk Road facilitated constant human movement across Eurasia, allowing pathogens to spread and evolve more rapidly than in more isolated regions.
Population Bottleneck in the Americas: The Amerindians went through a population bottleneck in a very cold area (the Beringia land bridge) before setting foot on the American continent. The cold temperatures and the lack of pathogens carried with them, as well as lack of genetic diversity from the small population and the ensuing founding effect all likely reduced the disease immunity of their future descendants.

4.2. Disease, Civilization, And Higher Intelligence

Historically, disease-resistant races built more stable civilizations, which thus enabled higher populations in the long-term. Higher populations made it easier to spread diseases, which thus selected for disease immunity. There was thus a feedback loop between disease prevalence and higher populations.

Diseases have the potential to decrease populations in the short-term, and they have occasionally threatened the prosperity of civilizations. It may thus seem paradoxical to recognize the connection between disease prevalence and higher populations and civilizations, but the reasoning still stands. By contrast, populations with a strong history of famines or wars have little historical record of building complex long-term civilizations. This is likely because war was destructive to building thriving civilizations.

It’s well known that larger brain sizes correlate with higher intelligence. Bigger brains and higher intelligence both correlate with higher energy consumption. Higher energy consumption burns more calories at a faster rate, which causes lower famine-resistance. There are thus trade-offs as to whether a population becomes more intelligent versus more famine-resistant. Famine-resistant likely selects for smaller and less intelligent brains, because they burn fewer calories. This reaffirms the theory that the populations of the smartest races in the world were mainly limited by diseases.

Historically, increases in IQ seem to be linked to the growth of civilization: laws, money, writing, math, etc, or things that require abstract reasoning. The causal chain of Diseases -> Civilization -> Increased Intelligence is far superior to other theories of intelligence selection and adaptation, such as the Cold Winters Hypothesis. Elaborating on this topic would probably require writing another essay. For now however, the causal chain between disease prevalence and observed intelligence offers a likely explanation for why strong disease immunity and higher intelligence often appear together in populations that have one or the other (e.g. Europeans, Jews, East Asians, etc).

4.3. Famine-Resistance

Human populations that were mainly limited by famines and malnutrition have been relatively rare. Usually, most human populations that were primarily limited by famines chose to fight wars to steal land, food, food-producing capital in order to limit the further starvation and malnutrition of their people. Famine-resistant populations thus tend to have histories filled with lots of warfare. Wars tend to destroy civilizations, which tends to reduce natural selection in favor of higher intelligence.

I thus propose that famine-resistant populations tend to only exist for short periods of time or rare circumstances, until war and/or disease become the main cause of death among the population. When a different major cause of death becomes more prominent or prevalent for long periods of time (compared to famine), some famine-resistance traits may wither away over time, but only if the famine-resistance adaptations aren’t adaptive in the absence of famine (being the main cause of death).

4.4. Famine-Resistance In South Asians

In recent history, South Asians are an example of a primarily famine-resistant population with a relatively low record of deaths from warfare. South Asia had 10-15 major famines within 200 years in the 1700-1900s (Link 2, Link 3). As a consequence, South Asians evolved traits that are adaptive to surviving famines, including: smaller frames, low lean muscle mass, insulin resistance, and higher body fat percentages.

South Asia has some of the lowest average IQ scores on the entire Eurasian continent. This suggests that something happened to either bottleneck or reverse the selection for intelligence in South Asia, compared to the rest of the continent. Given the aforementioned reasoning, I suspect that the famines of recent history selected for smaller brains and lower intelligence among South Asians. If this is true, then I’d estimate that South Asia’s IQ scores would be closer to the IQs found in Middle Eastern countries, if the South Asian famines in the past 300 years never happened.

We also have to keep in mind that the population of South Asia (and the world in general) was increasing from the 1700s to the present, due to the introduction of New World crops and technological advancements. Since the world’s carrying capacity rose during this time, famines and wars were less common in our timeline over the past 300+ years than they otherwise would’ve been.

British rule probably partially caused some famines in South Asia, but its rule probably also prevented some wars in South Asia, since it had strong political authority and superior technology for settling conflicts and disputes.

4.5. Famine-Resistant Populations Tend To Have Higher Obesity Rates

Populations that weren’t historically limited by diseases tend to have higher obesity rates. This makes sense, since such populations would’ve had more deaths due to famines, which would’ve selected for traits for surviving famines. Traits for conserving body fat (and hence energy) more strongly can plausibly increase the probability of survival from famines. In the presence of abundant food and the absence of famines, such traits can also increase obesity and diabetes rates.

Many Austronesian countries have the highest obesity rates in the world. This can be mainly attributed to unhealthy changes in their diets, but it’s likely that genetics and culture are also contributing factors.

In the United States, blacks, Hispanics, and American Indians have higher obesity rates than whites and Asians. While different diets are once again a contributing factor, it seems likely that blacks, Hispanics, and American Indians are probably more famine-resistant than Europeans, East Asians and Southeast Asians.

4.6. R-Selection Characteristics In Humans

I established that human populations were mainly limited by disease, famine, and war. I also defined disease-resistant populations and famine-resistant populations. One may follow these patterns and assume that there should also be “war-selected” humans, or humans who evolved to survive and win wars (e.g. American Indians, sub-Saharan Africans, etc). However, this doesn’t seem to be a very useful distinction in practice. Upon closer examination, there aren’t any notable differences between “famine-resistant” or “war-selected” populations, or at least not any that I have noticed.

Either way, populations that were not mainly limited by diseases are usually what R/K selection theorists think of as being “R-selected”, or having fast-paced life and reproduction strategies. “R-selected” human races tend to have earlier pubertal development, shorter pregnancies, higher impulsivity, and lower abstract intelligence. Each of these traits have tradeoffs, but they would theoretically make it easier to have more children within shorter periods of time.

Even then, although R-selected humans populations have many characteristics that are associated with the concept of R-selection, the differences in some of these traits aren’t very large. The gestational length between R-selected and K-selected races is only about one week.² Additionally, R-selected races only start puberty about one to two years earlier than the most K-selected races. In other species however, it’s plausible that the differences between R and K selected subspecies could be much greater.

Bigger brains generally have more neural connections and greater complexity, so it makes sense that it would take longer for them to develop both inside and outside the womb. The relatively smaller brains of R-selected races is likely a contributing factor as to why humans from such races usually have relatively smaller gestational periods and earlier pubertal development. However, there could be other reasons as well, which would need to be determined with further research and analysis.

5. Misconceptions About Population Densities And Fertility Rates

Populations have lower fertility rates in environments that have high population densities.

This is fallacious because “high density” and “crowdedness” are not well-defined. R/K selection theory proposes that R-selected species evolved to live beneath the carrying capacity. However, this is a false assumption because all organisms evolved to reproduce up to the carrying capacity, as mentioned before.

It’s not always clear what the carrying capacity is. The carrying capacity is a fuzzy number, not an exact number. It’s difficult to calculate and model the carrying capacity because it is usually affected by an innumerous set of factors that are nearly impossible to predict and calculate in an advance. This confusion may cause some people to mistakenly believe that some populations never reach their carrying capacities, even when the population is exceeding what the resources of its environment can support. Other times, people may deny the concept of carrying capacities altogether for ideological reasons.

In spite of the faster reproductive advantages of R-selected populations, all populations have the potential to grow exponentially towards infinity. The R-selection and K-selection dichotomy would only be relevant for understanding population growth when all populations have abundant resources and low birth control usage, lest there be confounding factors.

6. Fertility Rates Are Probably Mostly Environmental, Not Genetic

In modernity, there are abundant resources, and we can observe that sub-Saharan Africans have higher fertility rates than Europeans and East Asians. However, Sub-Saharan Africa has far lower contraception rates than the rest of the world, so it would be inaccurate to attribute to attribute the higher total fertility rate of Africa to R-selected traits.

Birth control has the potential to drastically alter a country’s fertility rates within short periods of time. From 1947 to 1957, Japan’s total fertility rate dropped from 4.54 to 2.04. As another example, the fertility rate in the Philippines fell from 2.7 in 2017 to 1.9 in 2022. It’s not like the Japan and the Philippines suddenly went from being “R-selected” to “K-selected” within just 5-10 years. That rapid change in the fertility rate is best explained by the sudden rise of birth control within the countries.

Additionally, no race would perform relatively well if they were living outside their ancestral environments without abundant resources. For example, if sub-Saharan Africans were placed in pre-industrial Europe or pre-industrial East Asia where scarcity was common, they would not have higher fertility because they are not adapted to those environments. Instead, they would have lower fertility rates than the races that are already adapted to those environments. The same is true for K-selected races, if they were placed in environments associated with R-selected races.

The United States has abundant resources and widely accessible birth control, so it seems like an optimal environment that has eliminated the main environmental factors that might affect fertility rates. In the United States, the R-selected races have slightly higher fertility rates than the K-selected races.

7. Final Thoughts On R/K-Selection Theory

R/K-Selection Theory isn’t defined very well. The theory has multiple falsehoods and contradictions, so the patterns that it proposes don’t always apply consistently. R/K selection also doesn’t have very much explanatory power, since the binary distinction limits the amount of information that it can convey. The information that R/K selection conveys can be somewhat increased by only examining subspecies of the same species and other closely related taxa.

With respect to humans, R/K selection doesn’t explain why some races have higher intelligence than others or why some races have higher obesity rates than others. And while R-selected races have some traits that enable faster reproduction, these differences are too small to cause noticeable population differences, especially when we consider different environments, resource abundance, and the effects of birth control. Differential K Theory fails to explain the patterns that it observes because it doesn’t describe the historical selectionary pressures of populations.

For non-human populations, it’s plausible that some subspecies may have more noticeable different R-selected traits. Non-human animals could also be described with different descriptors, in order to communicate the main barriers that such populations face regarding their survival and reproduction (e.g. predation-resistant). By using better descriptors, the evolutionary reasons as to why some species and subspecies have varying intelligence and other traits than others becomes more clear. For further information, data should be gathered to graph the estimated Ancestral Premature Death Rate (APDR) for various races, species, and subspecies over the centuries.

Footnotes:

Of course, when I say “disease-resistant”, there are many different types of diseases and different populations will be better adapted to different diseases than others. I’m also talking about diseases that mainly affect infant children and survival into adulthood, rather than developmental or elderly diseases. Although the concept of being “disease-resistant” is somewhat ambiguous, phrases like “Europeans are disease-resistant” or phrases like “East Asians are disease-resistant” usually implicitly signify which diseases are being talked about, since races evolved in environments that spread different diseases.

The average gestational length for blacks is ~39 weeks, whereas it is ~40 weeks for whites. South Asians have similar gestational length to blacks, in two UK studies. (Balchin 2007), (Patel 2004). Beyond the given links, there doesn’t seem to be very good information/data available on this topic, especially outside the US, UK, or with ideal racial categories.