Sexual dimorphism in water

Assignment on water related sexual dimorphism in man

Humans; NASA Pioneer 11 plaquette

Orientation
Understand what is meant by sexual dimorphism; http://en.wikipedia.org/wiki/Sexual_dimorphism and do find out what is stated about SD in man.

If you succeeded in finding this information, you observe the resemblance with the anatomical "stereotypes"of males and females.
Paleoantropolgists do think, based on skeletal finds (Australopithecus), that the observed dimorphism was stronger in the past and diminished (but not a 100%) in the course of our evolution.

A number of these differences between men and women could be related with a more amphibious past.
The differences do have a strong significance for social behaviour in man. We know this intuitively and ethological research with "stereotypic" models acknowledges this. This does not mean, that the differences are there, because of signaling functionality. Biologically it is more likely, that the basis are gender specific adaptations for different functions of men and women in our species. The strong signal value in social behaviour, courting and mating, is in this view secondary; a stronger signal is intuitively related to greater "fitness"..
This phenomenon is observed in a lot of totally different species. It is the basis for the research in this assignment.

As mentioned before SD was probably stronger in our evolutionary past. The relative loss of SD is ascribed to our "self-domestication", in concordance with the effect seen in wild animals we have domesticated realising an easier life with less "natural" selective forces working. Wild boars versus bio-industry pigs are a prime example.)

In the AAT there are a number of adaptive traits mentioned, that could be related to a more aquatic specialisation of females compared to man;
- a more sophisticated streamline, for swimming and diving.
- more subcutaneous fat means more isolation against heat loss in cold water.
-     better floating properties as a result of a more even distribution of body mass; essential in caring for a ( floating) baby suckling.

Two are easy to investigate;:

1. The fat / body mass relation; use a modern digital balance that differentiates between lean mass and fat, preferably carried out in a swimming pool.

- Enter a general person in the memory of the balance system (man/female without distinction). Take measures of about ten men and women of approximately the same age group (in swimming ware). You can encounter problems in finding volunteers among women, as an effect of the widely distributed "I am to fat" obsession in modern women. Do state that all measuring is anonymous registrated.

NB; Use only fully grown people, minimum age for males 18 and females 16. It is best to select a narrow age range (e.g. 16 - 25) and of course male and female in equal quantities.

- sort the results by sex percentage of total fat (spreadsheet)
- calculate mean values and check if the AAT statement is correct.If this is not possible you can find sites on the internet that have values at hand for different age groups (health promoting, medical or fitness related).

2. Find volunteers (the same?) that are willing to demonstrate their floating abilities in the swimming pool. Ask them to take a passive horizontal position on their backs, facing up. Note the number of F/M that can maintain this position without sinking to a more vertical position.

3. Sort again and try to use formal statistics on this phenomenon; is the difference in numbers significant or not (ask math for help on this)..
NB: the number of observations is probably to small to be certain, but work it through anyway as a lesson to learn.


Babyswimming
A part of sexual dimorphism is described in my project Aquatic reflexes in newborn humans




water babies © Urchin rock