Daily Archives: April 10, 2013

Penis Size: Does it matter and why?

A study just published in the Proceedings of the National Academy of Sciences explores the question of penis size and female preference in humans. The study involved making a set of 3D models of human males of various relative body sizes, and fitting them out with various size flaccid penises. These were shown to a sample of Australian women to get their reactions.

ResearchBlogging.orgThe assumption of this study is that at some time in the past humans did not wear clothing, so that information about penis size in men would be available to women who could observe flaccid penises and then choose sexual partners. That assumption is limited, perhaps flawed, in at least three ways:

1) We have no idea when men started to cover their penises on a regular basis. Ethnographically, there are very few cultures where men walk around with exposed penises, though there are several cultures in which men attempt to highlight and perhaps exaggerate the sizes of their mating equipment using various techniques. Since foraging people around the world, who stand in as models for the human “paleolithic,” often cover both male and female groin areas, it stands to reason that the practicer of covering up is old, even if it has not always been practiced. Archaeological evidence of early Homo (African and Asian Homo erectus/ergaster) strongly suggest that our ancestors, well before they became Homo sapiens, lived in a fairly wide range of habitats suggesting but not proving that clothing was developed as far back as just under 2 million years ago. If there was a period of universal exposure of the entire body, it may well have been much earlier than the evolution of anything looking like modern human culture and mating systems.

2) It is highly unlikely that human or pre/proto-human females would determine mating preference on the sole or primary basis of the details of the experience of copulation, assuming that some degree of paternal investment in offspring or the female herself was important. A better model of human mating suggests that females would look for a wide range of features, mostly behavioral, in long term male partners, and these longer term relationships would have more of an effect on selection (for a particular size penis) than a single variable.

3) There is not strong reason to believe that if females were interested in penis size as a factor in copulation that they would use flaccid penises to make assessments. The correlation between erect penis size and flaccid penis size is poor. In addition to this, in a social group in which no one wears clothing, other sources of information about erect penises would certainly be available. Penises would be erect at random times now and then, and in a social system where females make short term decisions about copulation, there would certainly be long term availability of information via the usual linguistic channels, after the evolution of language or proto-language, which would presumably be early(ish) in human evolution.

However, given these caveats, it may be reasonable to carry out the experiment reported in this paper because, well, why not?

The researchers note that human flaccid (visible) penis size is notably larger than that of our relatives, the great apes. This suggests that visual evaluation of penises was a selective force in human evolution. From the abstract of the paper:

Compelling evidence from many animal taxa indicates that male genitalia are often under postcopulatory sexual selection for characteristics that increase a male’s relative fertilization success. There could, however, also be direct precopulatory female mate choice based on male genital traits. Before clothing, the nonretractable human penis would have been conspicuous to potential mates. This observation has generated suggestions that human penis size partly evolved because of female choice. Here we show, based upon female assessment of digitally projected life-size, computer-generated images, that penis size interacts with body shape and height to determine male sexual attractiveness. Positive linear selection was detected for penis size, but the marginal increase in attractiveness eventually declined with greater penis size (i.e., quadratic selection). Penis size had a stronger effect on attractiveness in taller men than in shorter men. There was a similar increase in the positive effect of penis size on attractiveness with a more masculine body shape (i.e., greater shoulder-to-hip ratio). Surprisingly, larger penis size and greater height had almost equivalent positive effects on male attractiveness. Our results support the hypothesis that female mate choice could have driven the evolution of larger penises in humans. More broadly, our results show that precopulatory sexual selection can play a role in the evolution of genital traits.

What have we learned from this study? Perhaps, mainly, something about the reaction a certain subset of Australian women have to male penis size. However, we can also guess that human sexuality, including details such as this, are a product of our rather complex and difficult to parse culture. I am uncomfortable linking these results to either the behavior of paleolithic humans or to a model of sexual selection, given that human sexuality today is so diverse and clearly constructed from exposure to enculturation and lived experience. Is this scientific evidence that when people say things like “size does not matter” or “it’s how you use it that counts,” they are kidding? Perhaps. In Australia. But probably not.

To me, a more interesting study would look at biological and cultural variations in the relationship between flaccid penis size and erect penis size, and how information about these things would be made available in different normative cultural settings. For instance, I would predict that if penis size matters in relation to either female mate choice or male-male competition, this relationship would be strong (and flaccid penises generally larger) in societies where men don’t cover up, but uncorrelated (with little selection on flaccid penis size) in societies where men do cover up.

See also this at The Stochastic Scientist.

Mautz, B., Wong, B., Peters, R., & Jennions, M. (2013). Penis size interacts with body shape and height to influence male attractiveness Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1219361110

Will there be a lot of hurricanes in 2013?

Probably.

The Tropical Meteorology Project at Colorado State University makes annual predictions of hurricane season activity, and they released one of these predictions today. This particular group has a good track record, although I would worry that they tenaciously hold to the idea that global warming is not a factor in hurricane development despite the fact that some of the factors (a disrupted ENSO and high SST) that are most affected in the Atlantic by global warming actually drive their predictions. Still, their predictions seem to be based on good empirical data and are probably robust. (Other season forecast information is to be found below).

El Nino conditions tend to reduce hurricane activity, and the warmer the waters in the North Atlantic, the more likely hurricanes are to form from tropical depressions, the stronger they are likely to be, and the longer they are likely to last.

This year, El Nino conditions are unlikely to develop, and sea surface temperatures in the North Atlantic are unusually high as they have been for a few years.

The TMP has released this PDF of their report, which states:

We anticipate that the 2013 Atlantic basin hurricane season will have enhanced activity
compared with the 1981-2010 climatology. The tropical Atlantic has anomalously
warmed over the past several months, and it appears that the chances of an El Niño event
this summer and fall are unlikely. We anticipate an above-average probability for major
hurricanes making landfall along the United States coastline and in the Caribbean.
Coastal residents are reminded that it only takes one hurricane making landfall to make it
an active season for them, and they need to prepare the same for every season, regardless
of how much or how little activity is predicted.

TMP predicts that there is a 72% chance of at least one category 3 or above hurricane landing somewhere on the US coastline (the average probability over the last century is 52%). There is a 48% of such a landfall along the Atlantic coast plus Florida not counting the panhandle (compared to the century average of 31%) and a 47% probability for the Gulf Coast on the Florida Panhandle and points west to Brownsville (compared to 30%). The chance of at least one category 3 or stronger hurricane hitting points in the Caribbean is 61% (compared to 42%).

The forecast predicts that there will be 18 named storms active over 95 days, of which 9 will be hurricanes, active over 40 days, of which 4 will be Category 3 or above.

The Weather Channel is saying the following about the 2013 season:

The Weather Channel released its first 2013 Atlantic hurricane season outlook on April 8, 2012, calling for another active season.

The forecast calls for a total of 16 named storms, 9 of which are expected to become hurricanes, including 5 major hurricanes (Category 3 or higher on the Saffir-Simpson Hurricane Wind Scale).

These forecast numbers are above the long-term average from 1950-2012 (12 named storms, 7 hurricanes, 3 major hurricanes) and slightly above the averages for the current active era from 1995-2012 (15 named storms, 8 hurricanes, 4 major hurricanes).

The Weather Company’s WSI says this:

Weather Services International (WSI) expects another active tropical season this year, with 16 named storms, nine hurricanes, and five intense hurricanes expected (16/9/5). This compares to the 1950-2012 normals of 12/7/3 and the more recent “active period” (1995-2012) normals of 15/8/4.

Researchers at UCL, UK (PDF) predicts 3-4 “intense hurricanes” out of 7-8 hurricanes with 15-16 tropical storms:

The TSR (Tropical Storm Risk) April forecast update for Atlantic hurricane activity in 2013 continues to
anticipate an active hurricane season to moderate probability. Based on current and projected climate
signals, Atlantic basin tropical cyclone activity is forecast to be about 30% above the 1950-2012 longterm norm but slightly below the recent 2003-2012 10-year norm. The forecast spans the period from 1st
June to 30th November 2013 and employs data through to the end of March 2013. TSR’s two predictors
are the forecast July-September trade wind speed over the Caribbean and tropical North Atlantic, and the
forecast August-September 2013 sea surface temperatures in the tropical North Atlantic. The former
influences cyclonic vorticity (the spinning up of storms) in the main hurricane track region, while the
latter provides heat and moisture to power incipient storms in the main track region. At present, TSR
anticipates both predictors will have a small enhancing effect on activity.

Weather Underground’s MAweatherboy1 posted this last month:

I foresee a season that will see near to above average activity. One of the main factors we look at to determine this is the ENSO, which involves the temperature of waters in the Pacific Ocean. Warm Pacific waters, called El Nino if the anomaly is greater than 0.5 degrees Celsius, tend to suppress activity in the tropical Atlantic, while cooler than average Pacific waters, called La Nina if the anomaly is greater than 0.5 degrees Celsius, tend to enhance activity. … This year, I am expecting a very neutral ENSO, with average, season-long (June 1-November 30) Pacific water temperatures that are in the key regions likely not averaging more than 0.2 degrees Celsius above or below average, although I would favor the cooler end of that range if anything. The Southern Oscillation Index (SOI) is an important component in determining ENSO. Positive SOI values promote cooler Pacific waters, and vice versa. SOI values have been mostly negative this winter, though not by much, and I do not foresee any huge changes in this. Neutral conditions like this tend to promote near normal, or in some cases above normal activity. The record breaking 2005 hurricane season was primarily influenced by neutral ENSO conditions.


Photo Credit: NASA Goddard Photo and Video via Compfight cc

Penis Size: Does it matter and why?

A study just published in the Proceedings of the National Academy of Sciences explores the question of penis size and female preference in humans. The study involved making a set of 3D models of human males of various relative body sizes, and fitting them out with various size flaccid penises. These were shown to a sample of Australian women to get their reactions.

The assumption of this study is that at some time in the past humans did not wear clothing, so that information about penis size in men would be available to women who could observe flaccid penises and then choose sexual partners. That assumption is limited, perhaps flawed, in at least three ways:

1) We have no idea when men started to cover their penises on a regular basis. Ethnographically, there are very few cultures where men walk around with exposed penises, though there are several cultures in which men attempt to highlight and perhaps exaggerate the sizes of their mating equipment using various techniques. Since foraging people around the world, who stand in as models for the human “paleolithic,” often cover both male and female groin areas, it stands to reason that the practicer of covering up is old, even if it has not always been practiced. Archaeological evidence of early Homo (African and Asian Homo erectus/ergaster) strongly suggest that our ancestors, well before they became Homo sapiens, lived in a fairly wide range of habitats suggesting but not proving that clothing was developed as far back as just under 2 million years ago. If there was a period of universal exposure of the entire body, it may well have been much earlier than the evolution of anything looking like modern human culture and mating systems.

2) It is highly unlikely that human or pre/proto-human females would determine mating preference on the sole or primary basis of the details of the experience of copulation, assuming that some degree of paternal investment in offspring or the female herself was important. A better model of human mating suggests that females would look for a wide range of features, mostly behavioral, in long term male partners, and these longer term relationships would have more of an effect on selection (for a particular size penis) than a single variable.

3) There is not strong reason to believe that if females were interested in penis size as a factor in copulation that they would use flaccid penises to make assessments. The correlation between erect penis size and flaccid penis size is poor. In addition to this, in a social group in which no one wears clothing, other sources of information about erect penises would certainly be available. Penises would be erect at random times now and then, and in a social system where females make short term decisions about copulation, there would certainly be long term availability of information via the usual linguistic channels, after the evolution of language or proto-language, which would presumably be early(ish) in human evolution.

However, given these caveats, it may be reasonable to carry out the experiment reported in this paper because, well, why not?

The researchers note that human flaccid (visible) penis size is notably larger than that of our relatives, the great apes. This suggests that visual evaluation of penises was a selective force in human evolution. From the abstract of the paper:

Compelling evidence from many animal taxa indicates that male genitalia are often under postcopulatory sexual selection for characteristics that increase a male’s relative fertilization success. There could, however, also be direct precopulatory female mate choice based on male genital traits. Before clothing, the nonretractable human penis would have been conspicuous to potential mates. This observation has generated suggestions that human penis size partly evolved because of female choice. Here we show, based upon female assessment of digitally projected life-size, computer-generated images, that penis size interacts with body shape and height to determine male sexual attractiveness. Positive linear selection was detected for penis size, but the marginal increase in attractiveness eventually declined with greater penis size (i.e., quadratic selection). Penis size had a stronger effect on attractiveness in taller men than in shorter men. There was a similar increase in the positive effect of penis size on attractiveness with a more masculine body shape (i.e., greater shoulder-to-hip ratio). Surprisingly, larger penis size and greater height had almost equivalent positive effects on male attractiveness. Our results support the hypothesis that female mate choice could have driven the evolution of larger penises in humans. More broadly, our results show that precopulatory sexual selection can play a role in the evolution of genital traits.

What have we learned from this study? Perhaps, mainly, something about the reaction a certain subset of Australian women have to male penis size. However, we can also guess that human sexuality, including details such as this, are a product of our rather complex and difficult to parse culture. I am uncomfortable linking these results to either the behavior of paleolithic humans or to a model of sexual selection, given that human sexuality today is so diverse and clearly constructed from exposure to enculturation and lived experience. Is this scientific evidence that when people say things like “size does not matter” or “it’s how you use it that counts,” they are kidding? Perhaps. In Australia. But probably not.

To me, a more interesting study would look at biological and cultural variations in the relationship between flaccid penis size and erect penis size, and how information about these things would be made available in different normative cultural settings. For instance, I would predict that if penis size matters in relation to either female mate choice or male-male competition, this relationship would be strong (and flaccid penises generally larger) in societies where men don’t cover up, but uncorrelated (with little selection on flaccid penis size) in societies where men do cover up.

See also this at The Stochastic Scientist.

Mautz, B., Wong, B., Peters, R., & Jennions, M. (2013). Penis size interacts with body shape and height to influence male attractiveness Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1219361110