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Sexual Selection, An Explosion of Understanding
One-hundred and fifty-seven years since the publication of Charles Darwin’s The Origin
of Species has caused a massive impact in countless scientific, philosophical, and other
fields. Many are aware of these impacts and know they were laid out in his first major
work, but relatively few are aware of the implications mentioned later expounded upon
in his second work, The Descent of Man, and Selection in Relation to Sex. The author’s
primary focus will herein be on concepts expounded upon in this second piece,
specifically on sexual selection. Darwin defined sexual selection as, “the advantage
which certain individuals have over other individuals of the same sex and species solely
in respect of reproduction” (Darwin). While the definition of sexual selection has
remained nearly unchanged since it’s writing. This general definition has exploded in the
modern era to an understanding that better pinpoints how sexual selection occurs and
what use it is within evolutionary constructs. Concepts will be show in a chronological
and thematically organized manner, as both in this regard had a tendency to play off
one another (EG the general concept of sexual selection leading into more developed
ideas in subjects thematically different). Doing so we will explore the concepts initially
produced by Darwin and how they have since been developed in more specific and
organized.
Understanding of sexual selection’s research and development over the course
of the last three centuries requires specific examination of origins. Charles Darwin
initially in The Origin of Species makes a short mention of it, and in the Descent of Man,
and Selection in Relation to Sex published in 1871 was mostly devoted to the subject
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matter. The undertones of the work allude to what Darwin mentions of secondary sexual
traits, or “any of a number of manifestations [of traits], as development of breasts or
beard, muscularity, distribution of fat tissue, and change of pitch in voice, specific to
each sex and incipient at puberty but not essential to reproduction” (Dictionary.com).
These traits, Darwin claimed had purposes in either male-male competition, in aiding
the female mate choice process, or potentially both. Examples are given throughout the
piece of male-male “weapons” which are used to fight for mating rights to females, or
elaborate adaptations like male bird’s plumage (Darwin). Criticism naturally arose after
publishing by the other leading figure of natural selection at the time, Alfred Wallace. He
argued that many forms of competition were not specifically sexual selection but natural
selection traits- serving various other functions (EG peacocks colors to act as
camouflage rather than mate attraction) and therefore adaptive traits. Wallace
additionally claimed physical, ornate traits like peacock’s tails were too complicated for
an animal to differentiate on standards of what is more desirable for mating (Berkley
University). Ironically, in making the argument he delineated from his strict belief in
adaption as the modus operandi of evolution, specifically in concert of his own example
of very complicated designs (like peacock tails) being orchestrated by adaptation. Aside
from this critical review, Darwin’s definition on sexual selection has remained the best
explanation up until the modern day and is his lasting legacy on sexual selection.
Darwin’s definition on male-male competition has surprisingly been considered
to be relatively complete in its definition (Hosken, Jones). Explained as any form of
intra-sex competition to gain mate choice preference, Darwin gave examples including
male narwhal tusk-fencing, scarab beetles battling with horns, and female quails
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fighting. Darwin also addressed potential counter points on male-male competition by
giving some examples of female-female competition. This illustration show the reversal
of roles can also occur but does not deviate from his idea that intra-sex fighting occurs,
and is incredibly important in sexual selection. The concept was relatively obvious in
terms of explanation and example, thus kept short in comparison to female mate choice.
Elaboration on The Descent of Man, and Selection in Relation to Sex therefore
focused on the nuances and faculties of female selection. To understand why one
needs to look through at the observations made by Darwin. In his sightings, much detail
was given by Darwin on males of many species having types of ornamental display and
showing some level of variation within the species ornamental display. The differences
