Adapting People Trivia Quiz

Answer: Serving as an oxygen reservoir

One study compared the Sama-Bajau to a geographically-close but non-diving population and found that the Sama-Bajau have spleens that are around 50% larger in size. The spleen acts as a reservoir for oxygenated blood and splenic contraction, where the spleen-stored blood is pumped into circulation, has the effect of increasing the amount of oxygen available to the diver.

The enlarged version of the spleen makes an estimated 10% more oxygenated blood available for the diver. The enlarged spleen has been linked to a specific gene and is a trait passed onto succeeding generations.

Answer: True

The mammalian diving reflex is found in various air-breathing vertebrates. These are physiological responses to being underwater that override the normal reflexes. These include giving priority to distributing oxygen to vital organs, constriction of the peripheral vascular system, slowed heart rate and release of blood cells stored in the spleen. The response is triggered by submerging the nostrils in water. If continuing to breathe, such as with a snorkel, the response is proportional to decreasing water temperature.

The biggest response is when the person stops breathing with the face underwater. Heart rate reductions range from 10-30% for an untrained person in warm water to 40-50% for trained free-divers such as the Sama-Bajau. The average human has a mild reflex compared to aquatic mammals and birds.

Answer: Lots of swimming

The cornea in the eye loses its ability to refract light when immersed in water, resulting in blurry vision. The Moken children's eyes accommodated this by making the pupil smaller and changing the shape of the lens. This ability is not unique to these children. With training, most children can achieve this neuro-muscular control. The ability can be lost with lack of practice or due to age-related loss of eyeball flexibility.

This is an example of phenotypic plasticity, the ability to make reversible changes to phenotype in response to changes in the environment, rather than a fixed genetic adaptation. The 2004 tsunami resulted in the Thai government moving the Moken people inland so the children probably no longer swim enough to keep up this ability.

Other examples of phenotypic plasticity in free-divers include increased spleen size (as distinct from the genetic Sama-Bajau enlargement), changes in blood composition to improve oxygen transport, an enhanced mammalian diving reflex, increased carbon dioxide tolerance, and increased lung and chest wall flexibility (a held breath decreases in volume with increasing depth).

Answer: High-altitude Sherpa porters

More than 80 million people worldwide live permanently above 2,500 m (8,200 ft) in hypoxic conditions, where levels of oxygen in the air are lower than required for the average human. Over time this generally results in altitude-related problems for the lowland visitor. The Tibetan plateau where the Sherpa people live has an average height of 4,000 m (13,000 ft) over a 2.5 million sq km (965,250 sq mi) region so the population has had to adapt to survive.

Archaeological remains suggest the first human habitation in the area was 30-40,000 years ago. There was an increase in habitation 8-12,000 years ago after the last glacial maximum, however a rapid rise in the genes adapting for high altitude only took place 3-8,000 years ago. This is a very short evolutionary period although the extreme conditions create a strong selective pressure.

Answer: Ethiopia

Each of these populations has co-evolved different ways of dealing with low oxygen levels, none of them involving enlarged spleens. An enlarged spleen is a temporary solution, good for the duration of a dive before it needs recharged with oxygenated blood.

The Tibetans have a near-lowland level of haemoglobin. With larger lungs and a higher breathing rate, this keeps the blood oxygenated and avoids overly thick blood (an effect of higher haemoglobin concentration) which would risk clots and strain the heart. High nitric oxide levels (near double lowland population levels) help dilate blood vessels, leading to high rates of oxygen delivery.

The Andeans of the Peruvian and Bolivian Altiplano have a high haemoglobin concentration which allows for a higher blood oxygen concentration, the downside being that the elderly are more prone to chronic mountain sickness.

The Amharas and other tribes of the Ethiopian Highlands manage to maintain near-sea level haemoglobin concentration but with a higher oxygen saturation. The mechanism is, at the time of writing, unclear.

Answer: Inuit

The traditional diet of the Inuit consists mainly of fish and sea mammals, a diet which is high in fat and protein. Genetic changes associated with lower 'bad' cholesterol and insulin levels are present in the Inuit. This provides a level of protection against cardiovascular disease and diabetes.

Mutations also appear to have had the effect of reducing their height as well, suggesting that there are impacts on the regulation of growth hormones. Shorter, stockier bodies help with preserving body heat and their flat, broad faces are less prone to frostbite.

Answer: Saves energy

Food in the desert can be scarce and shivering too much is a wasteful use of energy. The hormone thyroxine controls body heat production. The seasonal increase in thyroxine boosts the basal body heat without the need for shivering. This is coupled with an adaptation allowing a mild drop in core body temperature at night. Temperatures are rarely so cold that this adaptation does not help.

A campfire can also be useful.

Answer: To increase vitamin D

Melanin is a pigment which is the main factor in determining skin colour and possibly developed in response to people becoming mostly hairless. It is also found in hair and the iris of the eye. Melanin increases the protection against damage to DNA and certain vitamins. In the strong sunlight found near the equator this has resulted in darker skin colouring. Side effects are that melanin in the skin increases the amount of body heat retained (more sweating helps counter that) and reduces the amount of vitamin D produced by the body.

In northern latitudes where the sunlight is not so strong, a lighter skin helps increase vitamin D production. Other adaptations include a change from curly hair (more cooling) to straight hair (traps heat better) and iris colour change from brown towards blue (allows more light into the eye).

Answer: Animal husbandry

Lactase is the enzyme which allows complete digestion of milk. On weaning, most mammals lose much of the ability to digest milk. With domestication of sheep, cattle and goats, non-human milk became available as a food source to humans. In winter and at times of famine, those with lactase persistence could recover extra energy from consuming milk and milk products, thus probably gaining a survival advantage. The reasons for lactase persistence are still the subject of debate.

Archaeological evidence indicates that the pastoralist culture came before widespread lactase persistence. It has arisen independently in several regions of the world. Hunter-gatherer populations remain largely lactose intolerant.

Answer: Sickle Cell Disease

Historically, the inherited Sickle Cell Disease (SCD) is most commonly associated with regions where malaria is endemic. It gives a survival advantage over those people with ordinary haemoglobin, but it is the carriers of SCD (with one copy of the SCD mutation) that do best. They have partial immunity and, if infected by malaria, the blood cells normally do not take on the sickle shape. Any that do are usually destroyed by the spleen, cutting short the parasite's lifecycle.

Those with the full version of SCD-infected blood cells also have some protection from malaria but there are many more sickle cells present, causing health issues. The deformed cells causes blockages in capillaries and, untreated, such people rarely survive to adulthood.