Download “Vestigial or not vestigial” that is the question?

“Vestigial or not vestigial” that is the question?
Sample Response
Definition
Vestigial structures are structures of organisms in a species whose original
function is considered to have been lost, or reduced during evolution. These are
either in a degenerate, atrophied, imperfect condition or form, or in a similar
state.
Vestigial organs - evolution or devolution?
First, it is in principle not possible to prove that an organ is useless, because
there is always the possibility that a use may be discovered in the future. This
has happened with over a hundred alleged useless vestigial organs that are now
known to be essential.
Second, even if the alleged vestigial organ were no longer needed, would it
prove devolution or evolution? The creation model allows for deterioration of a
perfect creation. However the particles-to-people evolution model needs to find
examples of nascent organs, i.e. those that are increasing in complexity.
However, we now know that many, if not all, of the considered vestigial organs
do have a function of their own. In the context of human evolution structures
usually called ‘vestigial’ are largely entirely functionless but they may have
retained lesser functions or developed new ones. But what about the organs that
have never been considered to have a function in their own right, e.g. the male
nipple? Can these be considered as vestigial?
Why do men have nipples?
- Men are women in the womb
A well-trained embryologist cannot visually tell the difference between a male
and a female embryo if the embryo is less than seven weeks old. At that early
stage of prenatal life, there is a fork in the road of development. If there are no
hormonal changes in the prenatal environment, the embryo develops into a
female. If, however, the embryo is destined to become a male, its Ychromosomes trigger the production of testosterone (the male hormone), which
masculinises the brain and genitalia (internal as well as external) of the embryo.
But it takes no female hormone to produce a female, as this is the default state of
the developing embryo (only at age ten or later does the female body begin to
produce the hormones that transform the girl into a woman).
It seems obvious that for females, these structures have a function, both to
mother and child. But wouldn’t it be just as useful for the child to have access to
milk from both parents? In many species, food is provided for offspring by both
male and female parents, to the obvious advantage of the young. This is a
common behaviour in birds, for example. Why, then, are male mammals so
selfish?
There is absolutely no physiological reason why men couldn’t nurse babies - all
the equipment is there. The development of mammary glands in embryonic
development happens independently of sex. These glands remain
indistinguishable between the sexes until puberty, during which there is exposure
to hormones from the ovaries, adrenal glands, and pituitary gland in the female
body. Pregnancy further enhances the development of these glands, especially
the hormone prolactin, which is produced in the pituitary gland at the base of the
brain. But exposure to the same kinds of hormones at the same times would
give the same results for men, or, more specifically, removing (or reducing) the
effect of the masculinising hormones like testosterone. Mutations of the
testosterone pathway can cause males to be born without recognizable
masculine genitalia, and they develop usually into women carrying the Y
chromosome, simply because they’ve had their masculinisation progress
impaired. Therefore, genetically and genitally they’re still male - they have
internal testes, not ovaries.
However, men can lactate - there is no physiological barrier. So why don’t they?
The reason is not physiological, but evolutionary. In the vast majority of
mammalian species, offspring are born and raised solely by the female - the
male plays no parental role at all. His evolutionary interests are best served by
having children with as many females as possible, and so he doesn’t gain any
advantage to sticking around to help raise one or two of them. According to the
general consensus of evolutionary selection, the organisms that pass on the
most copies of their DNA are the most successful.
What about those species for whom males do play a role in the parenting of their
offspring e.g. humans? We see that the male contributions in these species
include things like bringing back food for the female, chasing off potential
competitors within its species, and looking out for predators from other species.
These alternatives to lactation are well-adapted traits for the species in which
they’re found, and offset any benefit which male lactation would provide
evolutionarily. But this doesn’t preclude the existence of any species for which
male lactation would be an evolutionary benefit, and in fact one has been
recently discovered, a fruit bat found in Malaysia. Males of this species were
discovered with functioning mammary glands, both full and drained, indicating
that they were providing milk to their young. This species hasn’t been studied
enough to determine why male lactation was advantageous for development, but
as you should know already, the physiological requirements would already have
been in place. As bats are closely related to humans (just outside of the
primates), this seems to suggest that male lactation in humans is only a few
environmental variables away from becoming commonplace.
More than two?
All mammals can develop an extra nipple. It is not widely known, but about one
in 50 women and one in 100 men have a third nipple. Polymastia refers to the
appearance of the additional nipple along with the presence of mammary glands.
The third nipple is merely one of those anomalies that arise in human
populations. The third nipple usually forms along the two vertical “milk lines”
which start from the armpit, run down through the breasts, and further down to
the groin in both women and men. These milk lines are clearly seen in other
mammals e.g. dogs who have larger ‘litters’ than humans and therefore require
many ‘feeding stations’ for their brood.