Imagine you could fly.
Now imagine giving that up.
WHY would you ever do that?!
Hi guys, Lissette here for DNews.
Ostriches, emus, kiwis, penguins… one thing these birds all have in common is that they
can’t fly.
A non-flying bird feels like an oxymoron, but the maybe most surprising thing about
these creatures is that they all once flew.
They all evolved not to fly.
At one point scientists thought that maybe some of the birds living today evolved from
flightless ancestors.
More specifically they thought this about ratites - a diverse group of large, flightless
avians which includes ostriches, emus, and moas.
This has since been proven wrong . Thanks to DNA studies, we now know that all of today’s
flightless birds came from ancestors that flew, but they all independently evolved to
lose their ability to fly.
And they did this all around the world.
Penguins in Antarctica, steamer ducks in South America, emus in Australia, kiwis in New Zealand,
and ostriches in Africa.
It’s astounding to think that given such different environments all these varied bird
populations would go through the same type of evolution- or convergent evolution to be
exact.
But why would the evolution of flight loss happen over and over again?
Well, two possible explanations largely influenced by Darwinian theory, are that changes in the
environment either decreased pressure for flying, or increased pressure to develop another
trait.
This means that nature slowly selected for certain traits over others, and along the
way, took away some birds’ ability to fly.
To illustrate how increased environmental pressures for traits other than flying work
in practice, let’s dive into the biomechanical explanation.
In a study published in the Proceedings of the National Academy of Sciences, researchers
studied different types of flying and wing-propelled diving seabirds.
By analyzing energy costs and morphology, they found that as a bird’s functional ability
to be a good diver increases, its ability to fly decreases - eventually to a point where
flying ceases to be possible.
A larger body and short wings may help seabirds dive and swim better and thereby help them
get more food for example, but this body type makes taking off more difficult.
In other words, penguins may have lost their ability to fly because evolving to be better
swimmers provided a greater advantage than flying - and the two abilities required a
trade-off..
You can’t be both a great flier and swimmer.
So, the environment puts pressure on birds to evolve certain abilities at the expense
of others, but a lack environmental pressures can also lead to change.
If the environment doesn’t strongly require a bird to fly, the bird may lose this ability
over time.
For example, in a study published in the journal Evolution, researchers argue that steamer
ducks eventually lost their ability to fly in part because their South American coastal
environment was suitable to live in year round.
The birds did not have a need to migrate, and thus had little selective pressure to
fly.
Another example of diminished selective pressures is when the dinosaurs went extinct.
During this period, birds were left without predators…
so without the need to fly away from hungry t-rex’s, the birds evolved other qualities
- the ostrich for example became huge and better suited for running rather than flying.
This lack of predation in the environment helps explain why so many flightless birds
are found on islands that were isolated for extended periods of time.
Why use up energy to fly when you can just strut around?
Now, these changes happened slowly over time through natural selection, but I’d be remiss
if I didn’t also mention that you and I and all humans are also making birds flightless
- and very quickly - through artificial selection.
Our turkeys and chickens would look very different if we weren’t breeding them to be large
and meaty for our consumption - So big that they can no longer fly like their ancestors
once did.
Still, while we certainly have a hand in their flightlessness, today’s flightless birds
evolved to be this way.
Which, in some cases might be good.
Could you imagine how terrifying a flying ostrich would be?
On a kind of related note, evolutionary change doesn’t just affect living creatures - it
also affects the technology we use every day.
To find out how much dating technology has evolved since before the Internet, check out
this video from our friends at Seeker Stories:
What trait would you be thrilled to evolve or evolve out of?
I’d kill for a Is there something you would trade in for something else?
Let us know in the comments and remember to subscribe so you never miss an episode of
DNews.
Thanks guys.