Describe one behavioural and one phenotypically plastic adaptation to dietary stress

Behavioural Adaptation

Protein Complementation: we have 8 essential amino acids we cannot natural synthesise, must obtain from diet (I.L.L.M.P.T.T.V.H.T.S.)

·         Without these essential amino acids, humans can have nutrition/diet based diseases

·         People will mix staple foods to get all required

Phenotypically Plastic Adaptations

Acclimatization to Nutrition

·        Minnesota Starvation Experiment

o    Create fuel from alternative sources: liver and kidneys convert 160 g glucose/ day for protein, fat cells ↓ in size for lipids (aka weight loss)

o    Reduce Total Energy Expenditure (TEE): drop in lean body mass and basal metabolic rate (which are more NRG expensive than adipose tissue) and overall activity

 A) Why do most people lose the ability to digest lactose early in life?

B) When, where and why do we see the emergence of the ability to digest lactose into adulthood? 

Lactase, the enzyme that allows humans to digest lactose, is typically completely gone by the age of 4. This is because humans don’t require lactase after breast feeding is over.

The Funnel Beaker Culture from Northern Europe were around 5-6 KYA and were the first known culture to continue digesting lactose past weaning age. With 90% of the population lactose tolerant, this mutation developed alongside the emergence of milk processing. This mutation occurred separately another three times in Africa 3-4 KYA alongside the domestication of cattle stock (which was their key to survival)

In 1962 James Neel proposed the thrifty gene hypothesis to explain human variation in obesity.

What is the thrifty gene hypothesis and what can we conclude today about this hypothesis?

It is a genotype that enables a person to get more calories out of a resource than a person without the gene (aka maximize each calorie). He believed that this thrifty metabolism was favored during the first 99% of modern humans’ existence because of the many recurring periods of feast and famine. He believed this would lead to a predisposition of Non- Insulin Dependent Diabetes Mellitus (NIDDM) in current populations because the ability to secrete insulin would be exhausted early in life.

Data today suggests that famines were not recurring as often as required to allow for sufficient selection pressure [for this gene], there 22 genes that are associated with high BMI signatures, and there is not much variation in high BMI cross-culturally.

While the Aymara and the Tibetans are both pastoralists and farmers at a median altitude of 4000 m, the Aymara have lower levels of resting ventilation, hypoxic ventilator response (immediate need for ↑ O2), and higher concentrations of arterial hemoglobin compared to the Tibetans. In other words, in order to overcome hypoxia, the Tibetans have a lifelong/ genetic adaptation to increased breathing while the Aymara have a lifelong/ genetic adaptation increased Hb (hemoglobin) concentrations. 

What is the “Red Queen hypothesis” and how does it relate to human variation?

The Red Queen hypothesis was introduced by Van Valen. He believed that in tightly coevolved interactions (such as a parasite and host), a change to 1 species will result in the extinction of or the corresponding change of the other species (aka each species must run to stay in place).

This is seen in the evolution of certain diseases (that require hosts) alongside humans causing genetic bottlenecks and influence over human variation through death (then evolution to cancel out the trait)

A) When might a parasite and its host evolve a “peaceful coexistence”?

B) When might the parasite be more virulent?

A parasite and a host may have an evolutionary selection that favours both hosts that do not die or become severely ill because then there would be a lack of hosts and parasite reproductive success would be affected.  This is shown in the example of houseflies and parasitic wasps.  Wasps lay their eggs in flies and the populations of flies’ crash when the wasps become too virulent; they reach equilibrium of lower virulence in order to sustain both the wasp and fly population. 

The same is true of rabbits and parasite myxomatosis.  This only occurs if there is an advantage to the parasite keeping its host alive, they must be reliant upon a specific host.  Parasites are more virulent in newly introduced hosts and new regions where there is an abundance of hosts available.  

Describe a genetic adaptation to malaria.

In doing so, make sure you provide evidence which supports the contention that it is a genetic adaptation to malaria.

Sickle cell trait is the most well- known genetic adaptation to malaria; it represents a small mutation in the gene that determines the hemoglobin molecule. Prominent in areas with high rates of malaria, such as many regions of Africa, those who are homozygous for of sickle cell leads to a severe form of anemia that results in early death while those homozygous against sickle cell tend to die of malaria; those who are heterozygous for sickle cell tend not to suffer from anemia and are somewhat resistant to malaria.

In the 1970’s, witnessing the successful the eradication of smallpox and other medical developments, public health officials concluded that humans would soon be free of the burden of infectious disease.

What do you think: will we soon see the end of infectious disease? 

I believe we will never see the eradication of infectious diseases because many of them can survive for years either within a vector or host or without any human reservoir at all. There are diseases that are vector-borne diseases (transferred to humans through a parasite such as malaria), disease passed through direct contact (spread by the droplet route, such as influenza), passed through sanitation routes (mainly through fecal-oral route, such as cholera), and those passed through intimate contact (mainly sexually transmitted disease obtained through bodily fluids, such as AIDS).  There is a theory that there is an HIV/ AIDS resistant gene (seen in 10% of Caucasians today) that is a genetic adaptation originally passed down to European descendants from those developing resistance to the bubonic plague; this is known as the Yersinia hypothesis. 

Define the term balanced polymorphism and provide an example of a balanced polymorphism.

What caused the balanced polymorphism you describe?

A balanced polymorphism is a genetic trait that exists in multiple forms because heterozygotes are selected over homozygotes.

An example of a balanced polymorphism is the sickle cell trait and malaria.

Sickle cell developed as a genetic adaptation to malaria because 2.7 million people die each year from various forms of malaria and the sickle cell changes the gene that determines the hemoglobin molecule; getting hemoglobin molecules to stick together (in the unoxygenated form) which drops the possible molecules that can be infected. However, both those homozygous for and against sickle cell tend to die early (unless under constant medical intervention) compared to those who are heterozygous; either from anemia (severe blood thinning and loss) or from the disease malaria which has been a prevalent selective force throughout our evolutionary history.

In the podcast “81 Words” from This American Life, adherents to both sides of the debate held that they were using “science” to support their arguments.

Briefly summarize the debate.

More importantly, what might we learn in this instance about the use of “science” in the consideration of human variation? 

The psychiatrists that believed that homosexuality was a pathology thought that they had done in depth studies to prove their facts and that they were helping homosexuals.  Over 90% of the psychiatrists on the APA believed that it was a pathology because it had been accepted as such for some time.  The bible claims homosexuality is a crime against humanity, so psychiatrists thought what they were doing was right because it was proving that homosexuality was not the fault of gay people.  Irving Beiber did an in depth study of gay men and concluded that it was caused by close binding mothers and detached fathers.  It was thought that they had done the most in depth work on every aspect of a homosexual’s lifestyle.  However, Evelyn Hooker pointed out that all of the work done on homosexuality was in individuals that were already in therapy, or mental hospitals or prisons or the oppressive environment of the army.  When she did an in depth psycho-analysis of 30 well- adjusted gay men and 30 well- adjusted straight men, professionals were unable to define the results of the individuals as either gay or straight, also 2/3rds of each group were defined as normal.  Alfred Kinsey then did his legendary study where 37% of all men had engaged in a sexual act with another man to the point of orgasm.  This goes to show that science is not only subject to the environment that surrounds it (it does not operate in a vacuum), but also that it is subject to internal prejudices that may not be discernible on the surface.