Biology Reference
In-Depth Information
Fig. B7.1.1
(continued)
Is sexual selection stronger in F than D? It might be, but not if mating is
random. Ideally, we first need to test whether there is greater variance in
male success than expected by chance (Sutherland, 1985). Then we need to
quantify the strength of selection on specific traits (e.g. long tails). However,
this will make cross-species comparisons harder (different species may have
different traits).
Evidence for sexual selection
Traits that improve a male's success in combat
People readily accepted the first part of the process of Sexual Selection that Darwin
proposed, namely selection for the evolution of traits that improved a male's success
in direct combat for mates. There is now abundant evidence that in many species it is
the males with the greatest size, strength or best developed weapons that achieve the
highest mating success. For example, female northern elephant seals,
Mirounga
angustirostris
, haul up on beaches to give birth and then mate again for the production
of the next year's offspring. Because the females are grouped, due to the localized
nature of the breeding grounds, they are a defendable resource and the males fight
with each other to monopolize harems (Fig. 7.4). The largest and strongest males win
