Evolutionary baggage
Encyclopedia
Evolutionary baggage is the part of the genome
of a population that was advantageous in past individuals but is disadvantageous under the pressures exerted by natural selection
today.
s that may have been advantageous in the past may be critically unfit for individuals in today’s environment. Natural selection is not a perfect process; if an organism is “fit enough” to survive a particular environment and reproduce, its genes are passed on to the next generation. Some of these genes may increase an organism’s fitness while some may even be slightly disadvantageous. This seeming paradox is the origin of evolutionary baggage, which is the collectively inherited traits that evolved in a different environment from the present. The result is a “Paleolithic
” genome, which is not adapted to today’s environment and is contributing to “diseases of civilization,” including atherosclerosis
and obesity
. Other hypotheses link evolutionary baggage to genetic diseases. Since all organisms descended from a common ancestor
, evolutionary baggage can be seen universally among organisms.
was advantageous during the extreme cold temperatures of the Ice Age
14,000 years ago. Type I diabetes is deleterious now, but would have conferred an advantage for individuals to survive extremely cold temperatures; this condition prevents production of insulin
, keeping blood sugar
levels high in the blood, which lowered the freezing point of the blood and protected the individuals with the condition. The condition has been linked to variation in the HLA genes. Furthermore, there is genetic evidence of a high prevalence of the condition among Scandinavia
n individuals, who were the direct descendants of the Northern Europe
an populations that endured the most extreme conditions during the Ice Age. This genetic evidence suggests that type I diabetes was a favorable condition in the past, and can be considered evolutionary baggage in individuals today because it can cause severe health problems.
, and type II diabetes
.
The human body adapted over time to crave calorie
-dense foods and to store energy efficiently because our ancestors did not have abundant food; this is called the thrifty gene hypothesis
. These adaptations are genetic baggage today, causing humans to store fat efficiently despite abundant food availability. This leads to obesity, which is an important risk factor
for cardiovascular disease
. However, studies have shown that consuming a Paleolithic-type diet rich in unprocessed foods and lean protein decreased blood pressure
and cholesterol
level while increasing glucose
tolerance.
and scarce food. However, since these conditions are less common in today’s world, individuals with these phenotype
s are at a selective disadvantage. This disadvantage has major implications in the area of health care
because some of the diseases caused by evolutionary baggage are major contributors to the rising cost of health care in developed countries.
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
of a population that was advantageous in past individuals but is disadvantageous under the pressures exerted by natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
today.
Origin
GeneGene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s that may have been advantageous in the past may be critically unfit for individuals in today’s environment. Natural selection is not a perfect process; if an organism is “fit enough” to survive a particular environment and reproduce, its genes are passed on to the next generation. Some of these genes may increase an organism’s fitness while some may even be slightly disadvantageous. This seeming paradox is the origin of evolutionary baggage, which is the collectively inherited traits that evolved in a different environment from the present. The result is a “Paleolithic
Paleolithic
The Paleolithic Age, Era or Period, is a prehistoric period of human history distinguished by the development of the most primitive stone tools discovered , and covers roughly 99% of human technological prehistory...
” genome, which is not adapted to today’s environment and is contributing to “diseases of civilization,” including atherosclerosis
Atherosclerosis
Atherosclerosis is a condition in which an artery wall thickens as a result of the accumulation of fatty materials such as cholesterol...
and obesity
Obesity
Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and/or increased health problems...
. Other hypotheses link evolutionary baggage to genetic diseases. Since all organisms descended from a common ancestor
Common descent
In evolutionary biology, a group of organisms share common descent if they have a common ancestor. There is strong quantitative support for the theory that all living organisms on Earth are descended from a common ancestor....
, evolutionary baggage can be seen universally among organisms.
Type I diabetes
It has been hypothesized that genetically-linked type I diabetesDiabetes mellitus type 1
Diabetes mellitus type 1 is a form of diabetes mellitus that results from autoimmune destruction of insulin-producing beta cells of the pancreas. The subsequent lack of insulin leads to increased blood and urine glucose...
was advantageous during the extreme cold temperatures of the Ice Age
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...
14,000 years ago. Type I diabetes is deleterious now, but would have conferred an advantage for individuals to survive extremely cold temperatures; this condition prevents production of insulin
Insulin
Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....
, keeping blood sugar
Blood sugar
The blood sugar concentration or blood glucose level is the amount of glucose present in the blood of a human or animal. Normally in mammals, the body maintains the blood glucose level at a reference range between about 3.6 and 5.8 mM , or 64.8 and 104.4 mg/dL...
levels high in the blood, which lowered the freezing point of the blood and protected the individuals with the condition. The condition has been linked to variation in the HLA genes. Furthermore, there is genetic evidence of a high prevalence of the condition among Scandinavia
Scandinavia
Scandinavia is a cultural, historical and ethno-linguistic region in northern Europe that includes the three kingdoms of Denmark, Norway and Sweden, characterized by their common ethno-cultural heritage and language. Modern Norway and Sweden proper are situated on the Scandinavian Peninsula,...
n individuals, who were the direct descendants of the Northern Europe
Northern Europe
Northern Europe is the northern part or region of Europe. Northern Europe typically refers to the seven countries in the northern part of the European subcontinent which includes Denmark, Estonia, Latvia, Lithuania, Norway, Finland and Sweden...
an populations that endured the most extreme conditions during the Ice Age. This genetic evidence suggests that type I diabetes was a favorable condition in the past, and can be considered evolutionary baggage in individuals today because it can cause severe health problems.
Diet
It is a fundamental biological concept that organisms are most fit if they eat the same diet which their evolution has adapted them to. Throughout history, humans adapted to a diet by living off the land. Today, humans maintain the same genes that have been evolved from our ancestors and adapted to the diet they consumed. This has created a mismatch between the modern diet and lifestyle (which has emerged in evolutionary terms very recently), and the diet and lifestyle to which the human body has slowly adapted to over thousands of years. This phenomenon can be considered evolutionary baggage because the deviation from the Paleolithic diet and lifestyle has led to “diseases of civilization” such as obesity, hypertensionHypertension
Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...
, and type II diabetes
Diabetes mellitus type 2
Diabetes mellitus type 2formerly non-insulin-dependent diabetes mellitus or adult-onset diabetesis a metabolic disorder that is characterized by high blood glucose in the context of insulin resistance and relative insulin deficiency. Diabetes is often initially managed by increasing exercise and...
.
The human body adapted over time to crave calorie
Calorie
The calorie is a pre-SI metric unit of energy. It was first defined by Nicolas Clément in 1824 as a unit of heat, entering French and English dictionaries between 1841 and 1867. In most fields its use is archaic, having been replaced by the SI unit of energy, the joule...
-dense foods and to store energy efficiently because our ancestors did not have abundant food; this is called the thrifty gene hypothesis
Thrifty gene hypothesis
The thrifty gene hypothesis was proposed by geneticist James V. Neel in 1962 to resolve a fundamental problem. Diabetes is clearly a very harmful medical condition. Yet it is quite common, and it was already evident to Neel that it likely had a strong genetic basis...
. These adaptations are genetic baggage today, causing humans to store fat efficiently despite abundant food availability. This leads to obesity, which is an important risk factor
Risk factor
In epidemiology, a risk factor is a variable associated with an increased risk of disease or infection. Sometimes, determinant is also used, being a variable associated with either increased or decreased risk.-Correlation vs causation:...
for cardiovascular disease
Cardiovascular disease
Heart disease or cardiovascular disease are the class of diseases that involve the heart or blood vessels . While the term technically refers to any disease that affects the cardiovascular system , it is usually used to refer to those related to atherosclerosis...
. However, studies have shown that consuming a Paleolithic-type diet rich in unprocessed foods and lean protein decreased blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
and cholesterol
Cholesterol
Cholesterol is a complex isoprenoid. Specifically, it is a waxy steroid of fat that is produced in the liver or intestines. It is used to produce hormones and cell membranes and is transported in the blood plasma of all mammals. It is an essential structural component of mammalian cell membranes...
level while increasing glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
tolerance.
Implications
Evolutionary baggage from our ancestors may be causing disease in individuals today. In our ancestors, these phenotypes conferred selective advantage against harsh climate, infectious diseaseInfectious disease
Infectious diseases, also known as communicable diseases, contagious diseases or transmissible diseases comprise clinically evident illness resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism...
and scarce food. However, since these conditions are less common in today’s world, individuals with these phenotype
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
s are at a selective disadvantage. This disadvantage has major implications in the area of health care
Health care
Health care is the diagnosis, treatment, and prevention of disease, illness, injury, and other physical and mental impairments in humans. Health care is delivered by practitioners in medicine, chiropractic, dentistry, nursing, pharmacy, allied health, and other care providers...
because some of the diseases caused by evolutionary baggage are major contributors to the rising cost of health care in developed countries.