Why we don't have a penis bone: Scientists say men should blame MONOGAMY
- The penis bone - or baculum - has been described as the 'most diverse' bone
- The baculum first evolved in mammals between 145 and 95 million years ago
- Men no longer have a penis bone as they tend to be in monogamous relationships, and don't need to compete for a partner
It
has been described as the 'most diverse of all bones', yet many
species, including humans, have evolved not to have a bone in their
penis.
A new study has examined how the penis bone – or baculum – evolved in mammals, and the possible function in primates.
Researchers
suggest that humans do not have a penis bone as we tend to be a
monogamous species, and men don't need to compete for a partner.
Researchers suggest that humans do not
have a penis bone as we tend to be a monogamous species, and men don't
need to compete for a partner (stock image)
WHY DON'T MEN HAVE PENIS BONES?
The
study found that prolonged penetration during sex – defined as longer
than three minutes – correlated with baculum presence across the course
of primate evolution.
In humans, men tend to have a short intromission duration, and there is little competition for a female.
Humans tend to be monogamous or, more rarely, polygynous (where one male mates with multiple females).
In these circumstances, only one male has access to a female and sexual competition between males is absent or very low.
Penis bones vary dramatically in length, width and shape in the male mammals where it is present.
For
example, the marmoset's penis bone is only around two millimetres long,
while the walrus's penis bone can reach 60 centimetres in length.
Researchers
from University College London explored why humans do not have a
baculum, yet both ancestral primates and carnivores did.
Their study uncovered that the baculum first evolved in mammals between 145 and 95 million years ago.
The
study found that prolonged penetration during sex – defined as longer
than three minutes – correlated with baculum presence across the course
of primate evolution.
Longer penetration also predicted a longer baculum in primates and carnivores
The researchers also found that high levels of sexual competition between males predicted longer bacula in primates.
Matilda
Brindle, who led the study, said: 'Our findings suggest that the
baculum plays an important role in supporting male reproductive
strategies in species where males face high levels of postcopulatory
sexual competition.
'Prolonging
intromission helps a male to guard a female from mating with any
competitors, increasing his chances of passing on his genetic material.'
Penis bones vary dramatically in length, width and shape in the male mammals where it is present
Humans tend to be monogamous or, more rarely, polygynous (where one male mates with multiple females).
In these circumstances, only one male has access to a female and sexual competition between males is absent or very low.
| Animal | Penis bone size |
|---|---|
| Marmoset | 2 mm |
| Cat | 3.7 mm |
| Gorilla | 5 mm |
| Chimpanzee | 6-8 mm |
| Dog | 7.6 cm |
| Walrus | 60 cm |
Ms
Brindle added: 'Interestingly, humans have neither prolonged
intromission durations, nor high levels of postcopulatory sexual
competition.
'Given the results of our study, this may help to unravel the mystery of why the baculum was lost in the human lineage.'
Chimpanzees
and bonobos - humans' closest relatives - have very small bacula
(between about 6-8mm) and short intromission durations (around seven
seconds for chimpanzees and 15 seconds for bonobos).
But they are characterised by polygamous mating systems, so they experience high levels of competition between males.
The marmoset's penis bone is only
around two millimetres long, while the walrus's penis bone (pictured)
can reach 60 centimetres in length
The researchers suggest that this may be why these species have retained a baculum - albeit a small one.
Dr
Kit Opie, who co-led the study, added: 'After the human lineage split
from chimpanzees and bonobos and our mating system shifted towards
monogamy, the evolutionary pressures retaining the baculum likely
disappeared.
'This may have been the final nail in the coffin for the already diminished baculum, which was then lost in ancestral humans.'
WAS EVE MADE FROM ADAM'S PENIS BONE?
The theory, put forward by revered biblical professor Ziony Zevit, suggests God made Eve from Adam's baculum, or penis bone.
To
support his theory, Professor Zevit said the Hebrew word 'tsela', taken
from the Old Testament, does not translate as 'rib' and instead 'refers
to limbs sticking out sideways from an upright human body.'
The
word 'tzela' or 'tsela' appears a number of times and in different
contexts in the Old Testament, and Professor Zevit said this is what led
translators astray.
He claims that the word was used for any part of anatomy protruding from the body, including feet, arms and penis.
Professor
Zevit said this explains why man has no baculum, unlike most mammals,
and why men don't have an uneven number of ribs compared to women.
Elsewhere,
he added that Genesis 2:21, in which God closes the flesh beneath the
'tsela', refers to the flesh that exists on the underside of the penis.
Defending
his theory, he wrote that his understanding of how Eve was formed is
based on analysis of the use of Hebrew in the Garden story.
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