Monday, August 4, 2008
Tuesday, July 1, 2008
While carrying out field work in Papua New Guinea in the late 1980s, Dr. Pritchard, an immunologist-biologist at the University of Nottingham (foto to the left), noticed that Papuans infected with the Necator americanus hookworm (foto to the right), a parasite that lives in the human gut, did not suffer much from an assortment of autoimmune-related illnesses, including hay fever and asthma.
His explanation for this phenomenon is that "the allergic response evolved to help expel parasites" and that "the worms have found a way of switching off the immune system in order to survive...".
To test his theory, and to see whether he can translate it into therapeutic pay dirt, Dr. Pritchard infected himself with hookworms: In 2004, David Pritchard applied a dressing to his arm that was crawling with pin-size hookworm larvae, like maggots on the surface of meat. He left the wrap on for several days to make sure that the squirming freeloaders would infiltrate his system. “The itch when they cross through your skin is indescribable,” he said. “My wife was a bit nervous about the whole thing.”
Hookworm infiltrates a victim’s system when the larvae, hatched from eggs in infected people’s excrement, penetrate the skin, often through the soles of the feet. From there, they enter the bloodstream, travel to the heart and lungs, and are swallowed when they reach the pharynx. They mature into adults once they reach the small intestine, where they can subsist for years by latching onto the intestinal wall and siphoning off blood. After sieving the fecal samples to extract hookworms eliminated when the worm treatment pill was given, the team reached an intriguing conclusion: Villagers with the highest levels of allergy-related antibodies in their blood had the smallest and least fertile parasites, indicating that these antibodies conferred a degree of protection against parasite infection.
And the hookworms seemed equipped to retaliate. After colonizing a digestive tract, the host often showed signs of a blunted immune response, leading Dr. Pritchard to suspect that the worms were reducing the potency of the body’s defenses to make their environment more hospitable.
Saturday, February 23, 2008
Friday, February 22, 2008
Li et al. (2008) conducted a large-scale genome-analysis of 938 humans from 51 populations. He found a clear-cut relationship between haplotype heterozygosity and geography, which not only supports the "out of africa"-hypothesis of a single origin in sub-Saharan Africa. The correlations also indicate our genetical proximity and therefore can show us details on the history of our way out of africa (see Figure 1).
Figure 1: Individual Ancestry Diagram. Each individual isrepresented by a vertical line partitioned into colored segments whose lengths correspond to his/her ancestry coefficients in up to seven inferred ancestral groups.
In detail the findings show that the mean heterozygosity across autosomal haplotypes is negatively correlated with distance from Addis Ababa, Ethiopia, with a correlation coefficient r of –0.91 and a slope of –1.1 × 10−5 per km (see Figure 1). This trend supports a serial founder effect, a scenario in which population expansion involves successive migration of a small fraction of individuals out of the previous location, starting from a single origin in sub-Saharan Africa.
Figure 2: Analysis of molecular variance and correlation between haplotype heterozygosity
and geographic distance.
Li et al. 2008. Worldwide Human Relationships Inferred from Genome-Wide Patterns of Variation. Science. Vol. 319, pp. 1100-1104
Thursday, February 21, 2008
Wednesday, February 6, 2008
Thursday, January 31, 2008
A few days ago I was confronted with the proposition that we cannot learn anything from evolution for the field of psychology. The main argument of my collocuter was that already between different species of primates there are huge differences so there would be no possibility to derive some new insight from a comparative view to our species.
While there are of course eminent persons like Konrad Lorenz, Norbert Bischof or Gerhard Vollmer who do not share this opinion I feel personally bound to answer this argument stating my own point of view regarding the value of the evolutionary approach to psychology. I will do this in 10 propositions:
1) All of our human biology, including our perceptional system and our brain, are formed by evolution. This leads to the point that we can only perceive and think in ways we are adapted for. In this situation: Why should our thinking about the human mind not gain insight from understanding evolutionary processes.
2) If we want to understand a complex system, what would be a more promising approach: a) Looking at it from inside, perceiving just a part of the system or b) Looking at it also from outside, conceiving the whole system.
3) Although we are and always behave as body and mind, psychology tends to forget the body and constructs cognitive theories which are floating over the reality like clouds. Evolutionary thinking helps us to tie our mental theories to evolutionarly developed bodies.
4) Psychology does not find a unifying way in its thinking. There are always emerging new paradigms like new fashions but up to now no paradigm could integrate all existing theory in one consistent framework. Evolutionary psychology can do this and can even integrate clinical psychology.
5) The evolutionary approach helps psychology with its way of asking the right questions. One important question thereby is "Why?". Only by asking the right questions we can get to the right answers.
6) Evolutionary psychology can also integrate the social and cultural dimension of humans and thus does not leave us in a field of cultural ambiguity. Culture is also an evolutionarily pre-formed expression of humans.
7) Evolutionary psychology also offers a dynamic view on the human mind, making the human lifetime development easily understandable
8) Evolutionary psychology does not neglect or suppress gender differences only because distinct political correctness is asking for it
9) Evolutionary psychology concentrates on the big issues in human life like sociality, sexuality, risk, foraging etc.
10) Evolutionary psychology is looking at what unites us with our environment and with other species rather than concentrating on - of course also important cultural delicacies. However, without knowing their bigger natural meaning and heritage we will not be able to fully understand these delicacies - and they will never taste as delicate as they do if we know how precious they are