evolution

All posts tagged evolution

How important the dimensions are

Published April 19, 2013 by Tony

Penis size influence male attractiveness

No doubt that the research of the ideal partner is done on an aesthetic basis, at least at first glance, because subjectively characteristics affect more than others do.
For example, according to woman preferences, in a man the physical prowess strikes more, like the size of the shoulders and musculature in general, besides the beauty of the face.
But for our ancestors, the prehistoric men, were these same princes worth?
Starting from the fact that our ancestors did not use clothes, a team of Australian biologists wondered if at that time, the male genital organ easily visible, fell within the parameters of choice of a potential partner. It’s to say if penis size interacts with body shape and height to influence male attractiveness.
It’s obvious that going around naked, the sexual organ could be evaluated and taken into account, the same way as other physical characteristics of a male subject.
In particular, the team was asking what role the penis size may have had for women in their partner choice. Given that man is the only primate to have a sexual organs bigger than other, this can be taken into consideration as an element that has been subject of evolution, that is to say that the choices that women did in the past, may have influenced the evolution of the partner, so that those who had a bigger penis was favored to the others. To see whether this kind of evolutionary heritage was still active today, the team of researchers at the University of Ottawa, has analyzed the importance that the penis traits gets in determining the level of a man’s attractiveness.
Using different animated images in 3D, full-size, about male bodies of different height, body shape and size of the penis, coming from a study of Italian men, the researchers recorded the preferences of 105 women chosen for the test.
It came out that in addition to prefer broad shoulders and narrow hips, also the size of the penis had been valued by women as a factor of attractiveness, and that in general the higher dimensions are considered more attractive, although up to certain values. Namely, the extreme dimensions (such as height or size of the penis) were no longer considered as attractive. Therefore, the size of the genital organs helps to determine the masculine appeal, and the study was published in the Proceedings of the National Academy of Sciences (PNAS). These results, furthermore, as authors say, lead to believe that in the past the women’s choices have driven the evolution to promote (genetically) bigger penis in humans, till to reach the existent average size.

.

HUMAN VESTIGIALITY

Published March 14, 2013 by Tony

HUMAN BODY EVOLUTION
11 USELESS ORGANS

From the time of prehistoric man on, the human body has evolved continuously and adapted significantly, and today only a few biological traces of our prehistoric ancestors remains in us which, despite almost without any use, are still part of our body. In the context of human evolution, human vestigiality involves characters, such as organs or behaviors, occurring in the human species that are considered vestigial, in other words having lost all or most of their original function through evolution.
Here’s the main ones.

plica semilunaris11. Plica semilunaris
In the inner part of the eye, the two eyelids form a small indentation called “inner canthus”, occupied by a small red protuberance, the “caruncula lachrymalis”, just external to the small and vertical fold of conjunctiva (that we can see), called “plica semilunaris.” This small fold of tissue near the tear duct, is a vestigial remnant of the nictitating membrane (persisting through evolution) which is drawn across the eye for protection, but performing no function in man. Despite reduced in humans, it represents a third eyelid present and fully functional in many  animals such as birds, reptiles, and fish.

prehistoric man10. Body Hair
Without a doubt, once human being was much more hairy. Up to about 3 million years ago, our body was almost completely covered by hair. Since “Homo erectus” onwards, the different capacity of perspiration (through a better body thermo- regulation) slowly led body to lose hair, now useless.

.

paranasal_sinuses09. Paranasal sinuses
These are a group of four paired air-filled spaces that surround the nasal cavity above the eyes and present in a variety of animals. The human biological role of the sinuses is debated, but a number of possible functions have been proposed among which increasing resonance of the voice or providing a buffer against blows to the face.

Adenoids08. Adenoids
They are a mass of lymphatic tissue situated posterior to the nasal cavity whose function is to be a trap for bacteria, and for this prone to hypertrophy and infection. Normally, in children the adenoids are bigger, often removed to avoid constant infections and  lack of airflow, though their size reduce with age. Useful to protect prehistoric man, over time this gland has lost importance for the improved hygienic conditions of life.

tonsil07. Tonsils
The term most commonly refers specifically to the mass of lymphatic material situated at either side at the back of the human throat. They represents the immune system’s first line of defense against ingested or inhaled foreign pathogens, and because of this tonsillitis are very frequent during youth, obliging their surgical removal. However, the fundamental immunological roles of tonsils have yet to be understood. Tonsils tend to reach their largest size near puberty, and they gradually undergo atrophy thereafter. As for the adenoid, their presence is not indispensable.

coccyx06. Coccyx
The tailbone or coccyx is the remnant of a lost tail. All mammals have a tail at one point in their development; in humans it only is present for a period of 4 weeks, during embryogenesis. The coccyx, located at the end of the spine, has lost its original function in assisting balance and mobility when it was a real tail.

muscles of the auricula05. Erector muscle of hairs / muscles of the auricula.
Diverse muscles in the human body are thought to be vestigial, either by virtue of being greatly reduced in size compared to homologous muscles in other species, by having become principally tendonous, or by being highly variable in their frequency within or between populations. Humans and other primates however have ear muscles that are minimally developed and non-functional, yet still large enough to be identifiable. Among them the arrectores pilorum, and the muscles of the auricula. The Erector muscle of hairs are small muscles attached to hair follicles in mammals whose contraction causes the hairs to stand on end – known colloquially as goose bumps. Useful in many animals, they have lost their utility for humans. Humans and other primates have ear muscles that are minimally developed and non-functional which in other animals give, for instance, the chance to move the ears in various directions.

wisdom Teeth04. Wisdom teeth
These teeth are vestigial (third) molars that human ancestors used to help in grinding down plant tissue. The skulls of human ancestors had larger jaws with more teeth, used to help chew down foliage and compensate the lack of ability to digest the cellulose. As human diets changed, smaller jaws were naturally selected, but the third molars, or “wisdom teeth,” still commonly develop in our mouths. Currently, wisdom teeth have become useless and even harmful to the extent where surgical procedures are often done to remove them.

appendix03. Appendix
The vermiform appendix is a vestige of a small organ that in ancestral species had digestive functions. Darwin argued that it was helpful to digestion during the years in which primitive man ate more plants and vegetables, rich in starch. Therefore, its usefulness is diminished with the evolution, when we started eating more digestible foods.

hymen02. Hymen
It is to say the membrane that surrounds or partially covers the external vaginal opening. Some scientists view the function of hymen in young girls as a protective membrane that protects the reproductive system from infection in the embryonic period and protect the fertility of young girls before mating. Anyhow, this is another organ of which human being wouldn’t feel the lack.

nipples01. Male Nipples
In the anatomy of mammals, a nipple, is a mammary papilla whose physiological purpose is to deliver milk to the infant, produced in the female mammary glands during lactation. The presence of nipples in male mammals is a genetic architectural by-product of nipples in females, best explained as a genetic correlation that over time persists through lack of a better or different evolution of the male.

.

Digit Ratio & Behavior

Published January 29, 2013 by Tony

Evolution of human hands
Fingers & Personality

Show me your hand and I’ll tell you who you are!

The study on the hands never ceases to surprise us, after palmistry, foretelling the future through the study of the palm, others but more serious studies reveal our personality through the length of the fingers.

The digit ratio is the ratio of the lengths of different fingers (or digits).
Hand with index finger being shorter than the ring finger, resulting in the small ratio between  2D/4D, points to a high exposure to testosterone in the uterus.
The 2D:4D digit ratio is sexually dimorphic: while the second finger is typically shorter in both females and males, the difference between the lengths of the two digits is greater in males than females.
A number of studies have shown a correlation between the 2D:4D digit ratio and various physical and behavioral traits. There is some evidence that 2D:4D ratio may also be indicative for human development and growth. Hormones testosterone and estrogen exposure reflects in fetal life. Some authors suggest that digit ratio correlates with health, behavior, and even sexuality in later life. Below is a non-exhaustive list of some traits that have been either demonstrated or suggested to correlate with either high or low digit ratio.

•    Lowered sperm counts and high digit ratio
•    Increase risk for heart disease in males and high digit ratio
•    Risk of obesity and metabolic syndrome in males and high digit ratio
•    Reduced risk for prostate cancer and high digit ratio
•    Reduced birth size in males and high digit ratio
•    Increased risk for depression in males and high digit ratio
•     Reduced risk of alcohol dependency and high digit ratio
•    Increased Anxiety in males and high digit ratio
•    Reduced performance in sports and high digit ratio
•    Assertiveness in females and low digit ratio
•    Aggression in males and low digit ratio
•    Personality traits correlated with low or high digit ratio
•    Higher exam scores among male students and high digit ratio
•    Musical ability in males and low digit ratio

Paraphilic (or extreme fetish) sexual interest in males and high digit ratio.
• Bem female sex role score in women and high digit ratio; “feminine” erotic sex role preference in gay men and low digit ratio. [Finger-length patterns vary with gender, sexual orientation and birth order. Among heterosexuals, the mean 2D:4D ratio is larger in women than in men, especially on the right hand. The right-hand 2D:4D ratio of homosexual women is more masculine (that is, smaller) than that of heterosexual women. Men with more than one older brother are more likely to be homosexual and have a significantly more masculine right-hand 2D:4D ratio than men without older brothers.]

•    A smaller ratio between the second and fourth fingers is linked to a longer stretched penis size, (as reported by researchers in the Asian Journal of Andrology). [In this study, researchers at Gachon University Gil Hospital in South Korea recruited 144 volunteers 20 years of age and older who were going to undergo urological surgery. While the men were under anaesthesia, the researchers measured their finger lengths and both their flaccid and stretched penis lengths. Since shorter members stretch more than longer ones, the stretched measurement —used by the researchers— is more telling about the size of an erect penis, giving back that stretched penis length is statistically correlated to the size of the penis when fully erect. The average flaccid penis length, the researchers found, was 3.0 inches (7.7 centimetres), with a range of 1.6 to 4.7 in. (4 to 12 cm). Stretched lengths ranged from nearly 3.0 to 6.7 in. (7.5 to 17 cm), with an average of 4.6 in. (11.7 cm).The average ratio between the two fingers was 0.97, with a range of 0.88 to 1.12, making the differences hard to make out with the unaided eye. But the lower the digit ratio, the study found, the longer the penis was likely to be.]

It has been suggested by some scientists that the ratio of two digits in particular, the 2nd (index finger) and 4th (ring finger), is affected by exposure to androgens e.g. testosterone while in the uterus and that this 2D:4D ratio can be considered a crude measure for prenatal androgen exposure, with lower 2D:4D ratios pointing to higher androgen exposure. Studies in mice indicate that prenatal androgen acts primarily by promoting growth of the fourth finger.

Peter L. Hurd is an academic specialising in biology and his research primarily focuses on the study of the evolution of aggressive behavior, including investigation of aggression, communication and other behavior. He conducted a study on digit ratios suggesting a positive correlation in males between aggressive tendency and the ratio of the lengths of the ring finger to his index finger. Many studies on both human, and non-human, animals suggest that inter-individual variation in adult aggressiveness is largely organised by prenatal exposure to androgens. Men who have the ring finger longer than the index are more aggressive and quarrelsome.
Hurd demonstrated that men with more feminine typical-digit ratios showed lower aggressive tendency than males with more masculine-typical digit ratios. Hurd demonstrated that men with more feminine typical-digit ratios showed lower aggressive tendency than males with more masculine-typical digit ratios
.

Another study says that fighting may have shaped the evolution of the human hand, according to a new study by a US team. The University of Utah researchers used instruments to measure the forces and acceleration when martial artists hit a punch bag. They found that the structure of the fist provides support that increases the ability of the knuckles to transmit “punching” force.  David Carrier from the University of Utah, USA, suggests that the human hand may have also evolved its distinctive proportions for a less enlightened reason: for use as a weapon. According to Carrier and colleague Michael Morgan, modern chimpanzees have long palms and fingers with a short thumb, while the human palm and fingers are much shorter and the thumb longer and stronger. Carrier explains that this squat arrangement allows us to clench our hand into a fist when we fold the thumb across the fingertips; however, chimp fingers form an open doughnut shape when curled.