Survival of the Show-Offs

When you see a peacock strutting
his stuff for a peahen,
you may be surprised that
a drab brown bird is the object of his
affection. There are obvious differences
between the appearances of
male and female peafowl. Many other
animals also exhibit radically different
traits between genders, a phenomenon
known as sexual dimorphism. Secular
theory claims sexual dimorphism
is a result of evolutionary forces that
drove males and females down separate
paths for reproductive success, but
is there a biblical explanation for why
male and female animals aren’t always
identical?

Show-Offs

Contrasts between male and female
animals fall into two main categories:
ornamentation and size. We often see
flashy colors, elaborate dances, and
exaggerated body features used by
males to attract mates, whereas females
are often understated in appearance.
Peacocks are vibrantly colored and have
elegant rear feathers called trains with
striking eye feathers. They display their
tails for peahens, and females select
mates based on the length of their
trains and the number of flamboyant
eye feathers.

Male birds of paradise are brilliantly
colored and perform choreographed
dances to attract mates. Females select
males with the best dances and prettiest
feathers.

One Size Doesn’t Fit All

Size difference is another common
form of sexual dimorphism. Males are
often larger than females, sometimes
to an extreme. Male southern elephant
seals can weigh a whopping 8,800
pounds (~4000 kg), while females
weigh less than 1,800 pounds (~820 kg).

However, males are not always bigger.
Female black widow spiders are
exponentially larger than males. While
females can grow up to 0.5 inch (1.3 cm)
in length, males are often as small as 0.1
inch (0.25 cm).

Combo Anyone?

Some animals are sexually dimorphic
in both ornamentation and size.
The long manes and large size of male
lions make them the most sexually
dimorphic members of the cat kind.

With their luxurious manes and impressive size,
male lions exhibit the most obvious traits of sexual
dimorphism in the cat kind.

Mandrills are the most sexually dimorphic
primates. Male mandrills have
brightly colored faces and backsides and
are also three times larger than females.

Males of most species of deer grow
beautiful antlers despite the cost to
their fitness, since antlers must be shed
and regrown yearly and present a risk
of entanglement. Bucks can also weigh
up to twice as much as does.

Survival of the Fittest

How do Christians explain sexual
dimorphism in animals? Genesis 1
shows how God created a perfect universe
in six 24-hour days 6,000 years
ago. He made the animals according to
their kinds and commanded them to
multiply and fill the earth.

After humans disobeyed God and the
world was cursed (Genesis 3), animals
struggled to survive and reproduce in
an earth affected by sin. Those original
kinds would have undergone a great
deal of natural selection (and other
mechanisms), resulting in species that
best survive in today’s habitats.

Although natural selection and evolution
are often falsely equated, natural
selection is the opposite of evolution.
Natural selection is simply survival of
the fittest. Organisms with the most
favorable traits for a given environment
survive, and organisms with unfavorable
traits are reduced or eliminated.
However, true evolution would require
changing from one kind to another by
the gain of new structures and functions,
a process which has never been
observed. When God created animals,
he gave them all vast genetic potential,
including the genetic programming for
all their sexually dimorphic features.
The sexual dimorphism we see today
has been driven by thousands of years
of natural selection (and other mechanisms)
within animal kinds to best suit
their needs in their environments.

Beauty and Brawn

Ornamentation, such as in male peafowl
and birds of paradise, seems counterintuitive
to survival. Wouldn’t bright
colors and amplified features make
these creatures obvious to predators?
Absolutely, but features needed to attract
mates outweigh the need for camouflage.
Females of these species likely see
these fancy displays as proof of health
and vitality, characteristics that, by God’s
design, they instinctually want to pass
on to their offspring. Since females consistently
choose to reproduce with the
flashiest males, those showy traits carry
on to future generations. In contrast,
since females don’t have to attract mates
but do have to safely raise their young,
the appearances of females may have
been naturally selected for camouflage
rather than display.

Natural selection is also at work when
we see drastic size differences between
males and females. Since male elephant
seals are responsible for protecting their
immense harems of females and offspring,
their enormous size makes them
more successful guardians.

However, black widow females are
considerably larger because producing
hundreds of eggs, spinning egg sacs, and
guarding them requires a lot of energy.
Conversely, it behooves black widow
males to be small. Since the females can
be cannibalistic in our fallen world, the
males need to make quick getaways.

Some animals have been naturally
selected for both ornamentation and
size differences. Studies show that
lionesses prefer thicker, darker manes
on male lions. However, these manes
can take physical tolls on males by raising
their body temperatures. Consequently,
male lions in warmer regions
tend to have thinner manes, but those
in cooler regions tend to have thicker
manes. Also, heavier male lions are
more capable of protecting their prides.

The more testosterone male mandrills
have, the brighter their colors,
which advertises their overall fitness
to females. Additionally, the largest
males have the best chances of winning
in the intense competition for
dominance and mates.

In male deer, the bigger the size
and the more elaborate the antlers,
the more dominant they are and the
greater chance they have of reproducing
and defending themselves from
threats. Therefore, females choose the
largest bucks with the most decorative
antlers, ensuring that their offspring
inherit the best traits for survival.

Sexual dimorphism does not require
a complicated evolutionary explanation.
When we look at beautiful peacocks,
enormous elephant seals, and
magnificent mandrills from a biblical
perspective, we see clear evidence of
created design and natural selection
of favorable traits to best suit them for
survival in our fallen world.

Karina Altman is the animal presenter for Answers in
Genesis. She has a BS in marine biology from Texas A&M
University at Galveston. She has worked in zoos and
aquariums around the US since 2007 and has worked for
Answers in Genesis zoos since 2015.

Leanne Sarkisian holds an MA in biology from Miami
University of Ohio. She is the senior zoo manager for the Ark
Encounter and Creation Museum and has worked for the
Answers in Genesis zoos since 2011.