14 | New Scientist | 10 August 2019COMPLEX feathers might have
originally evolved because birds’
dinosaur ancestors found them
sexually attractive.
Many dinosaurs had simple
feathers on at least some parts of
their body. Palaeontologists think
they know why these first evolved.
“Early dinosaur feathers really are
very hair-like,” says Scott Persons
at the Mace Brown Museum
of Natural History in SouthCarolina. As such, they were
almost certainly for insulation,
like mammals’ fur, he says.
But that makes it hard to
understand why some dinosaurs
then developed feathers that
were more structurally complex
and that eventually became
specialised for flight in birds.
These later feathers are stiffer and
don’t provide much insulation.
Persons and his colleague
Philip Currie at the University
of Alberta, Canada, think it wasn’t
natural selection but sexual
selection that drove complex
feather evolution. If such feathers
helped dinosaurs secure more
mating opportunities, there
would have been a good reason
to evolve and retain them, even
if those complex feathers no
longer provided insulation.
Biologists know that sexual
selection can shape feathers in
dramatic ways. Most famously,
many think peacocks evolved
their elaborate tail feathers largely
to impress peahens. Yet Persons
and Currie say we have never
considered the possibility that
sexual selection could act as
a bridge that helps link two
episodes of natural selection.
In their scenario, dinosaurslike tyrannosaurs evolved simple
feathers through natural selection
for insulation. Sexual selection
then encouraged some dinosaurs,
like oviraptors, to evolve complex
feathers for display. Those feathers
then became sophisticated
enough to allow small dinosaurs
to glide. At that stage, natural
selection then shaped feathers
for flight (Evolution, doi.org/c82d).
Persons thinks we might
eventually find other situations
in which sexual selection serves
as a bridge between episodes
of natural selection. “The
implications may go beyond
this example of dinosaurs and
feathers,” he says. “It’s possible
this process has had a similarly
impactful role in the evolution
of many other organisms for
which we don’t have as clear
a fossil record.”
Sexual selection bridges
might even have had a big impact
on biodiversity: today, birds aremore species-rich than any other
group of land animals, with about
10,000 recognised species.
The idea makes sense, says
Steve Brusatte at the University
of Edinburgh, UK. “The more
feathered dinosaur fossils that are
found, the more it becomes clear
that feathers and even wings did
not evolve for flight,” he says. “If I
had to cast my bets, I reckon that
wings evolved as sexually selected
display structures and then were
later repurposed into aerofoils.”
To nail the idea down, says
Brusatte, we would need to collect
more feathered dinosaur fossils.
If elaborate feathers were unique
to one sex, as they are in bird
species like peafowl, it would
provide strong evidence that
their evolution really was shaped
by sexual selection, he says. ❚EvolutionColin BarrasTOM BEAN/ALAMY STOCK PHOTONews
“ If I had to cast my bets,
I reckon that wings evolved
as sexually selected
display structures”
How birds got their feathers
Dinosaurs’ sexual preferences may have driven evolution of flight
Did sexual selection
shape the feathers
of Archaeopteryx?PregnancyJessica HamzelouMANY women take a folic acid
supplement when trying to get
pregnant. Now, it seems men
hoping to conceive may benefit
from taking it too.
The vitamin folate plays a
role in the healthy division of cells.
Women who don’t get enough in
early pregnancy are more likely to
have babies who have problems
with their brain and spinal cord,
so many are advised to take
supplements of folic acid, a
synthetic version of folate, before
and during pregnancy. In the US and
Canada, folic acid has been added
to foods like bread and cereal on a
mandatory basis since the 1990s.
But mounting evidence suggests
folate might also be important for
fathers-to-be. Studies in rodents
show that the amount of folate
males ingest before conception
influences their offspring’s health.
To explore effects in people,
Nerea Martín-Calvo at the
University of Navarra, Spain,
and her colleagues assessed 108
heterosexual couples undergoing
fertility treatment at a clinic in
Boston in the US and the resulting
113 pregnancies and births.
Participants had to fill out a
detailed food questionnaire, so
that the team could estimate each
person’s levels of dietary folate.
After accounting for factors
like age and the mother’s folate
intake, the group found that men
who had more folate in their
diets had babies with a longer
gestational period. This is generally
thought to be beneficial to health
(Reproductive BioMedicine
Online, doi.org/10/c8zm).
But it is too early to encourage
men to take folic acid, says Sarah
Kimmins at McGill University in
Canada. We haven’t yet identified
the optimum level of folate to
produce the healthiest sperm
and consuming too much may
be detrimental, she says. ❚Folic acid may help
fathers-to-be have
healthier babiesHear how fossils found in the UK tell the evolutionary
story of dinosaurs at New Scientist Live
newscientistlive.com/british-dinosaurs