Human Adaptation I
Humans and the Changing Environment
- Humans occupy a wide geographic range, living under all kinds of environmental
- It is important to mention that the environment not only comprise external factors, such
as temperature or humidity, but internal factors as well, such as infectious diseases.
o I.e., Malaria many regions of the genones have been selected based on the
genome of malaria
- In this lecture we will review ways in which humans respond to environmental
Some Ways to Respond to the Environment
- There are four main ways in which humans respond to environmental stresses
o Cultural practices and technology
o Developmental adjustment
o Genetic adaptation
- We will review very briefly each category and study in more detail different examples of
- Note: biological responses
- Note: involves inherited genetic changes
Cultural Practices and Technology
- There are uncountable examples on how culture and technology have allowed humans to
adapt to multiple environments.
- Since the origin of anatomically modern humans, this has become our main adaptive
- Of course, humans have been perhaps too successful with this approach.
- We are increasingly a driving factor causing environmental changes that can affect us and
every other life form in the planet.
- Acclimatization can be defined as the physiological adjustment of individual
organisms to different conditions (e.g., temperature, altitude, photoperiod).
- Acclimatization is a reversible process, which entails no genetic change.
- The length of time in which these reversible changes occur can be quite variable. Some
times they occur very quickly (short-term acclimatization, or acclimation), some times
they can take much longer, even years (long-term acclimatization).
Examples of Acclimatization
- Increase in sweating in hot temperatures.
- Increase in respiration rate, heart rate, and red blood cell production when moving to
- Tanning response under increased UV radiation
o Immediate tanning (within 1-2 hours of exposure) fades away during the first 24
It is a redistribution of melanin that you already have
o Delayed tanning (within 2-3 days of exposure), can last several months. Developmental Adjustment
- Developmental adjustment can be defined as anatomical or physiological changes
occurring during growth or development as a result of environmental stresses.
o These changes can be difficult to reverse or even irreversible.
- The ability of organisms to respond physiologically or developmentally to environmental
stresses is often termed plasticity.
Some Examples of Developmental Adjustment
- Reduced body size of adults who had inadequate childhood nutrition, or
- Increased height as adults of persons with good nutrition during childhood.
- Greater chest dimensions and lung capacity in persons that migrated at early age to high-
- Adaptations can be defined as inheritable genetic changes that develop in populations
over long periods of time.
o Related to natural selection (altering the frequencies of alleles it is a slow
- Adaptations are inheritable, acclimatizations are not.
- Adaptations are the result of the action of natural selection, increasing the overall fitness
of a population. This is how evolution works.
o Entails genetic information that is passed from generation to generation
- Through the remaining portion of the lecture, we will review interesting examples of
Some Examples of Adaption
- Perhaps the best known example of adaptation is sickle cell trait.
- In this case, the environmental factor involved is malaria, a tropical disease caused by a
parasite, mainly Plasmodium falciparum (although there are other three Plasmidium
species causing milder forms of malaria).
o This is the nastiest of the 4 plasmodium parasite
Understanding Malaria (Not part of the slide but important)
- Malaria is a tropical disease, common in regions of Central and South America, Africa
- Malaria is caused by protozoa of the genus Plasmodium (P. falciparum, P. vivax, P.
ovale, P. malariae). Plasmodium invades red blood cells, causing the disease
- The disease is spread by the mosquito Anopheles
- Symptoms include cills, fever, shaking, profuse sweating and fatigue
- The most severe form of the disease, cause by P. falciparum, is often fatal
- According to the WHO 2010 Malaria report, there were approx.. 219 million cases of
malaria and approx.. 660,000 deaths in 2010
A Brief History of Malaria in Africa
- Malaria became a very serious problem in Africa only relatively recently.
- The arrival of horticulture to tropical Africa a few thousand years ago, substantially
changed the ecological conditions, which became ideal for the growth and spread of the
- Thus, malaria is a good example of how ecological changes due to human cultural
adaptations can influence disease patterns. Malaria and the Sickle Cell Mutation
- A mutation in the Beta-chain of the hemoglobin molecule (responsible for oxygen
transport) appeared in Africa, and has increased in frequency in areas where malaria is
- This mutation changes the amino acid Glutamic acid normally present in position 6 of the
Beta-chain to the amino acid Valine.
- Sequence of the normal (Hb A) and sickle cell (Hb S) alleles in the Beta chain of
o Responsible for sickle cell anemia, this one change of letter from the ancestral
- The Beta chain gene is located on chromosome 11.
Hb S and Sickle Cell Anemia
- Individuals homozygous for the Hb S allele develop a form of anemia named sickle cell
- The half-life size of red cells of sickle cell patients is much lower than the normal red cell
o Because of this change, the red blood cells will be destroyed at a much faster rate
(relative to normal red blood cell)
- Red blood cells of sickle cell patients change their shape when they release oxygen to the
peripheral tissues of the body.
o When the red blood cells delivers the oxygen, it also changes the elasticity of the
cell that start to attach to each other and start to block pathways that create
- They form hemoglobin polymers that can block cell flow and interrupt oxygen delivery.
o This is a recessive disease heterozygotes are carries but not affects, but can
Inheritance of the HB S alleles
- We have seen that homozygotes for the Hb S allele develop sickle cell anemia.
- Hb AS heterozygotes are phenotypically normal. They are said to have the sickle cell
trait. Although phenotypically normal, they can transmit the Hb S allele to their progeny.
- Take a look at some possibilities of inheritance, d