7 Times Humans Changed Animal Evolution

Summary

This SciShow episode explores the phenomenon of 'evolutionary rescue,' where species rapidly adapt to survive environmental pressures caused by human activities. Examples include cliff swallows evolving shorter wings to avoid cars, fish maturing earlier to dodge commercial fishing, and the London Underground mosquito adapting to a new habitat. The episode also discusses the limitations of rapid evolution, emphasizing human responsibility in preserving biodiversity.

Takeaways

• 🧬 Evolution is often considered a slow process, but some species can adapt rapidly to environmental changes, a phenomenon known as 'evolutionary rescue'.
• 🕊️ Cliff swallows have adapted to living near roads by evolving shorter wings, which provide better maneuverability to avoid cars, showing a change within just a few decades.
• 🌡️ Shorter wings in cliff swallows may also help them cope with climate change by allowing them to catch fewer insects during cold snaps more effectively.
• 🐟 Commercial fishing has led to rapid evolution in fish species like salmon, cod, and herring, with many becoming smaller and reaching sexual maturity at a younger age to avoid being caught.
• 🚇 The London Underground has inadvertently created a unique habitat for a subspecies of mosquitoes that have evolved to prefer mammalian blood and do not hibernate, becoming genetically distinct from their above-ground counterparts.
• 🐍 Turtle-headed sea snakes may be evolving to cope with chemical pollutants through industrial melanism, getting darker to bind and shed ingested heavy metals.
• 🌊 The North Pacific Garbage Patch contains less plastic than expected, possibly due to the rapid evolution of microbes that can digest plastic, although this is still speculative and requires further research.
• 🦋 Edith's Checkerspot Butterflies adapted to a new host plant but faced extinction when environmental conditions changed, showing that rapid evolution is not always advantageous.
• 🐘 Tuskless elephants have become more common in areas heavily affected by poaching, as the lack of tusks provides a biological advantage against ivory hunters.
• 🔄 Rapid evolution can occur in a few generations, especially in species that breed quickly, but it is not a guaranteed solution for all species facing environmental pressures.
• 🌱 While evolutionary adaptations can be impressive, they should not be seen as a substitute for human responsibility in addressing the problems we have caused to the environment and its species.

Q & A

What is the phenomenon known as 'evolutionary rescue'?

Evolutionary rescue refers to the high-speed adaptation that some species can undergo in response to rapidly changing environmental conditions, allowing them to cope with severe population stress.

Why have cliff swallows started building nests on bridge supports instead of cliffs?

Cliff swallows have adapted to building nests on bridge supports due to the availability of such structures, which provide a similar nesting environment to cliffs but are often closer to human settlements.

How have cliff swallows adapted to the threat of cars?

Cliff swallows have evolved shorter wings, which provide them with greater maneuverability, enabling them to quickly take off vertically and evade oncoming cars.

What evolutionary advantage do shorter wings offer to cliff swallows in terms of survival?

Shorter wings allow cliff swallows to be more maneuverable, which is advantageous for evading vehicles and possibly for catching insects during cold snaps, thus helping them survive in changing environments.

How have commercial fishing operations influenced the evolution of fish species like Salmon, Cod, and Herring?

Commercial fishing operations have led to the evolution of these fish species to be smaller overall and reach sexual maturity at a younger age, as larger fish are more likely to be caught, thus favoring the survival and reproduction of smaller individuals.

What is the evolutionary significance of the London Underground mosquitoes' shift in blood meal preference?

The London Underground mosquitoes have evolved to prefer the blood of mammals over birds, likely due to the higher availability of rats compared to pigeons in the underground environment, representing a significant adaptation to their new habitat.

Why have the London Underground mosquitoes evolved not to hibernate and not require a blood meal to lay eggs?

The constant temperature and availability of food in the underground environment may have reduced the need for hibernation and the dependency on blood meals for egg-laying, allowing for year-round reproduction.

How do turtle-headed sea snakes adapt to chemical pollutants in their environment?

Turtle-headed sea snakes are evolving darker coloration due to increased melanin, which binds heavy metals and allows the snakes to store and later shed these pollutants through their skin, reducing their toxic effects.

What is the mystery surrounding the North Pacific Garbage Patch and the missing plastic?

Despite the large amount of plastic that should be present in the North Pacific Garbage Patch, scientists are finding only a fraction of the expected amount, suggesting that other factors, such as the evolution of plastic-eating microbes, may be at play.

How did the introduction of English Plantain impact the Edith's Checkerspot Butterflies?

The introduction of English Plantain led the butterflies to adapt and prefer this new host plant over their natural habitat plant. However, when cattle moved away and the fields became shaded by grasses, the butterflies were unable to switch back and their population went extinct.

What is the impact of poaching on the evolution of African elephants?

Poaching has led to an increase in the prevalence of tuskless elephants, as they are less likely to be targeted by poachers. This trait has become more common in some areas, demonstrating rapid evolutionary change in response to human activity.

Why is rapid evolution not a guaranteed solution for all endangered species?

Rapid evolution is not a guaranteed solution because it depends on the species' ability to adapt quickly over generations, which varies widely. Some species may not be able to adapt fast enough, and evolutionary changes can sometimes have negative consequences, as seen with the Edith's Checkerspot Butterflies.

Outlines

00:00

🐦 Rapid Adaptation of Cliff Swallows

The first paragraph discusses the concept of 'evolutionary rescue,' where species adapt quickly to environmental changes. It uses the cliff swallow as an example, highlighting how they have adapted to living near roads by evolving shorter wings, which provide better maneuverability to avoid cars. The adaptation has led to a decrease in roadkill since the 1980s. Additionally, shorter wings may offer an advantage in catching insects during cold snaps, potentially aiding survival in a changing climate. The paragraph emphasizes the swiftness of this evolutionary change, occurring in less than three decades.

05:04

🐟 Evolutionary Responses to Commercial Fishing

The second paragraph examines how commercial fishing has pressured fish species like Salmon, Cod, and Herring to evolve rapidly to avoid extinction. The fishing industry's preference for larger fish has led to the evolution of smaller fish that reach sexual maturity at a younger age. This rapid evolution is exemplified by the Chinook Salmon, which shrank by about 25% in size within 30 to 40 years after being over-harvested in the 1920s. The paragraph underscores the quickness of these evolutionary changes and the implications for conservation efforts.

10:06

🦟 Evolution of London Underground Mosquitoes

The third paragraph describes the evolutionary changes in a subspecies of Culex pipiens mosquitoes that inhabit the London Underground. Isolated from their above-ground counterparts, these mosquitoes have adapted to prefer mammalian blood, likely due to the abundance of rats. They have also evolved to not require blood for egg-laying and do not hibernate, making them genetically distinct and potentially a new species. The rapid evolution, occurring within a few hundred mosquito generations, showcases the adaptability of species to new environments.

🐍 Adaptation to Pollution in Turtle-headed Sea Snakes

This paragraph explores the phenomenon of industrial melanism in turtle-headed sea snakes, which are adapting to chemical pollutants by becoming darker. The increased melanin not only provides color but also binds to heavy metals, allowing the snakes to store and later shed these toxins through their skin. This adaptation is particularly evident in snakes from the Noumea Lagoon in New Caledonia, where heavy metal pollution is prevalent due to industrial activities. The paragraph highlights the snakes' increased frequency of shedding as a protective mechanism against pollutants.

🌊 The Mystery of the Missing Plastic in Oceans

The fifth paragraph delves into the paradox of the North Pacific Garbage Patch, which contains significantly less plastic than expected. Scientists hypothesize that the rapid evolution of plastic-eating microbes might be responsible for this discrepancy. The existence of plastic waste has potentially driven the evolution of these microbes, which could be breaking down plastics at an accelerated rate. The paragraph also considers alternative explanations, such as plastics sinking due to colonization by marine organisms, and calls for further research to confirm the role of these 'plastivores'.

🦋 The Tragic Extinction of Edith's Checkerspot Butterflies

The sixth paragraph tells the story of the Edith's Checkerspot Butterflies in Nevada, which adapted to lay eggs on an invasive weed, the English Plantain, after ranchers introduced it to their habitat. However, when cattle were removed, and the fields were overtaken by grasses, the butterflies could not switch back to their native host plant quickly enough, leading to their extinction within a few years. This case study illustrates the fragility of rapid evolutionary adaptations and the consequences of ecological imbalances caused by human activities.

🐘 The Rapid Evolution of Tuskless Elephants

The seventh paragraph discusses the impact of poaching on the evolution of African elephants, particularly the increase in tuskless elephants due to the survival advantage it provides against poachers. The Mozambique Civil War led to a significant rise in elephants without tusks, as they were less likely to be targeted. This trait has become common in some populations, with up to 98% of female elephants in South Africa's Addo Elephant Park being tuskless. The paragraph emphasizes the speed of this evolutionary change over a few generations and the potential drawbacks of losing tusks, which are beneficial for finding food and other activities.

🌱 The Limitations of Evolutionary Rescue

The final paragraph addresses the misconception that rapid evolution can solve all environmental problems caused by humans. It clarifies that evolutionary rescue is not a universal solution, as it occurs over generations and varies in speed depending on the species' reproductive rate. The paragraph highlights that some species, like polar bears, cannot adapt quickly enough to survive current threats. It concludes by emphasizing the responsibility of humans to address the environmental challenges we have created, rather than relying solely on the process of evolution.

Keywords

💡Evolution

Evolution refers to the process by which species of organisms change over time through genetic variation and natural selection. In the video, it is the overarching theme as it discusses how species adapt to environmental pressures. An example from the script is the cliff swallows evolving shorter wings to better evade cars.

💡Evolutionary Rescue

Evolutionary rescue is a concept where a species rapidly adapts to cope with fast-changing environmental conditions, often as a response to severe population stress. The video uses the term to describe how some species, like the cliff swallows adapting to roads and cars, can quickly evolve to survive new threats.

💡Cliff Swallows

Cliff swallows are a species of bird that traditionally nest on cliffs but have adapted to nesting on bridge supports near roads. The video highlights how they have evolved shorter wings to better evade cars, demonstrating rapid adaptation in response to a new environmental challenge.

💡Maneuverability

Maneuverability in the context of the video refers to the ability of an organism to move quickly and easily, especially to avoid predators. The cliff swallows' shorter wings provide them with greater maneuverability, allowing them to evade oncoming cars more effectively.

💡Commercial Fishing

Commercial fishing is the activity of catching fish and other seafood for profit. The video discusses how commercial fishing operations have led to rapid evolution in fish species like salmon, cod, and herring, which have become smaller and mature at a younger age to avoid being caught.

💡Industrial Melanism

Industrial melanism is an evolutionary phenomenon where darker-colored individuals within a species become more common due to industrial pollution. The video describes how turtle-headed sea snakes are getting darker, possibly as a way to protect themselves from chemical pollutants by storing heavy metals in their melanin-rich skins.

💡Plastic-eating Microbes

Plastic-eating microbes are organisms that have evolved to consume plastic, potentially as a response to the abundance of plastic waste in the environment. The video suggests that these microbes might be responsible for the reduction in expected plastic waste in the oceans, although this is still a hypothesis.

💡Tuskless Elephants

Tuskless elephants are individuals in a population that do not develop tusks. The video explains that in areas heavily affected by poaching, tuskless elephants have an advantage as they are less likely to be targeted for their ivory, leading to a rapid increase in the prevalence of this trait within the population.

💡Adaptive Advantage

An adaptive advantage refers to a characteristic that increases an organism's chances of survival and reproduction in a particular environment. The video uses the term to describe how certain traits, such as shorter wings in cliff swallows or a preference for different host plants in butterflies, can provide an advantage in new or changing conditions.

💡Extinction

Extinction is the complete disappearance of a species. The video discusses the rapid extinction of an isolated population of Edith's Checkerspot Butterflies due to a combination of factors, including the introduction of an invasive plant and changes in the local ecosystem.

💡Rapid Evolution

Rapid evolution refers to the process by which species evolve and adapt to new conditions at a faster rate than usual. The video provides several examples of rapid evolution, such as the London Underground mosquito adapting to a new diet and environment, and fish species evolving to be smaller to avoid fishing nets.

Highlights

Evolution is not always a slow process; some species can rapidly adapt, a phenomenon known as 'evolutionary rescue'.

Cliff swallows have adapted to living near roads by evolving shorter wings for better maneuverability against cars.

Since the 1980s, the number of road-killed cliff swallows has declined due to the evolutionary advantage of shorter wings.

Shorter wings in cliff swallows may also help them cope with climate change by being more maneuverable to catch insects during cold snaps.

Commercial fishing has led to rapid evolution in fish species, with some becoming smaller and reaching sexual maturity at a younger age to avoid extinction.

The London Underground has inadvertently created a habitat that led to the evolution of a distinct mosquito subspecies that feeds on mammals and doesn't hibernate.

Turtle-headed sea snakes may be evolving industrial melanism to protect themselves from heavy metal pollutants by storing them in their darker skins.

The rapid evolution of microbes that eat plastic could be responsible for the missing plastic in ocean garbage patches.

Edith's Checkerspot Butterflies evolved to prefer an invasive plant but went extinct when the cattle that maintained the habitat were removed.

African elephants are evolving to be tuskless due to the advantage it provides against poaching, especially in areas with civil unrest.

Rapid evolutionary changes usually take ten to a hundred generations, depending on the species' reproductive rate.

Evolutionary rescue is not a guarantee for all species, and some may not be able to adapt quickly enough to survive.

The rapid evolution of certain traits can sometimes have negative consequences, as seen with the tuskless elephants and their struggle to find food.

Evolution should not be seen as a solution to environmental problems caused by humans, but rather a natural process that can sometimes offer temporary relief.

SciShow encourages viewers to learn more about evolution and its misconceptions through linked episodes.

Transcripts

[INTRO]

A lot of people think evolution on Earth happens a little something like this:

a slimy creature crawls out of the ocean, and hundreds of millions of years later

its descendants peel themselves off the sofa,

wondering how they managed to binge-watch all five seasons of Breaking Bad in less than three days.

-- In other words,

evolution is a long, slow process.

But it's not always that way--

Some species can rapidly adapt to cope with fast changing environmental conditions like:

human encroachment;

invasive species;

climate change;

you know-- things that are 100% our fault.

Biologists call this high-speed adaptation

"evolutionary rescue."

Though that kind of makes it sound awesome--

when really

it's how some species are able to respond in times of severe population stress.

Take cliff swallows, for example--

that's a species of swallow that builds nests on cliffs.

Except, lots of them don't do that anymore.

Today, many cliff swallows make their nests on bridge supports.

That, of course, means there are large populations of cliff swallows living next to roads.

Birds that live next to roads face a strange new enemy.

They're fast,

they're hard-

-they're cars.

It seems like cliff swallows are quickly adapting to this threat.

In fact-- since the 1980s

the number of road-killed swallows has declined-

-even though there are more birds than ever nesting next to roads.

That's probably because populations near roads

have rapidly evolved shorter wings.

Biologists studying the birds have found that road-killed cliff swallows

tend to have longer wings than the not road-killed variety,

a little over 5% longer, on average;

and they think that's because shorter wings give the swallows an advantage against vehicles.

Longer wings are better for air speed and gliding, but shorter wings make the birds more maneuverable-

-so they can quickly take off vertically and evade oncoming cars.

What's really impressive is that the change in wing length

happened in less than three decades.

Also, shorter wings may help the swallows cope with climate change.

In 1996, half of a cliff swallow population that scientists were studying starved to death during a cold snap -

probably because the freezing temperatures killed a lot of the insects they normally eat.

What was really noticeable though,

was that the birds that survived had shorter wings.

Researchers think the birds with shorter wings were much more maneuverable,

and that made them better at catching the few insects that didn't freeze.

So it's possible the short wings they evolved for dodging cars

will help them survive the more frequent and severe cold snaps brought on by a changing climate.

Commercial fishing operations catch a lot -A LOT - of fish every year.

In fact, they catch so much

that species -like Salmon, Cod, and Herring- have all evolved quickly to avoid extinction.

Basically, they're now living fast and dying young.

You see, human fishing tends to favor larger specimens;

so many species evolved to be smaller overall,

or are becoming sexually mature at a younger age,

or doing both of those things.

In some populations the change is really dramatic,

like: the average adult fish is 20% smaller than the species used to be,

and lives only 75% as long.

The advantage of this is pretty obvious -

smaller fish are less likely to be harvested by humans.

So--fish that stay small -or reach sexual maturity sooner,

can pass their genes on before they end up someone's dinner.

Fishes: well-done. and

these changes can happen really quickly.

For example: after they were over-harvested in the 1920s,

Chinook Salmon took only about 30 to 40 years to get roughly 25% smaller;

and that's great, for them--

unless we start letting people catch smaller fish to keep up with the demand.

When the London Underground was built in 1863,

workers inadvertently created a tidy isolated habitat for the world's favorite bug--

the mosquito.

Standing water would collect in the tunnels,

which made a perfect breeding ground for the bloodsuckers.

Humans discovered this the hard way during World War Two,

when the tunnels were used as overnight bomb shelters

and the mosquitoes took to feasting on those people.

It's bad enough when you're underground trying to avoid getting exploded,

without being covered in blood-sucking bugs.

What's actually weird about this is that they were biting people at all.

Because the mosquitoes that live in the London Underground are a subspecies of Culex pipiens -

a species that -above-ground- usually feeds on birds.

So in the eight decades or so it had spent apart from its kin,

the London Underground mosquito has switched to preferring the blood of mammals.

Probably because rats are a bit more common than pigeons in the new habitat.

And that's not the only difference between the underground mosquito and the species it evolved from--

Unlike the above-ground version,

the London Underground mosquito doesn't hibernate in the Winter,

and the females don't need blood in order to lay their eggs.

In fact, the two types are now so genetically distinct

that they can't mate and produce offspring.

So the metro mosquitoes are arguably a new species -

not just a subspecies.

Anyhow, whatever you want to call them,

researchers think it only took a few hundred mosquito generations for this new pest to evolve.

So like,

"yay evolutionary-rescue" i guess

Okay, all sorts of garbage and pollution get dumped into the sea,

but one species may have evolved a trick to survive this refuse onslaught.

Turtle-headed sea snakes seem to be adapting to chemical pollutants

through an evolutionary phenomenon called industrial melanism -

in other words, they're getting darker.

All members of this species of Australian sea snake have black and white stripes

or they did

until recently.

Around 17 years ago, researchers noticed that the turtle-headed sea snakes living in the Noumea Lagoon in New Caledonia

were mostly black instead.

They get that color from the pigment melanin

and it just so happens that it not only gives black animals their color,

it's also very good at binding to heavy metals.

Heavy metals are substances like zinc, lead and arsenic,

which can accumulate in animals tissues

and being toxic, eventually cause their death;

the waters around New Caledonia are full of heavy metals,

from nearby nickel mining activities and industrial runoff.

Scientists actually collected shed skins from New Caledonia snakes

and found higher amounts of zinc, nickel and lead.

So they think the snakes are protecting themselves from these pollutants by

storing the heavy metals they ingest inside their melanin-rich skins.

Then they can shed that skin,

effectively ridding themselves of the dangerous substances--

which is probably why researchers have found

that blacker snakes shed their skins about twice as often as their striped relatives.

Speaking of oceans full of garbage,

let's talk about garbage patches.

There are large areas of the ocean where our trash collects,

thanks to water circulation patterns.

The North Pacific Garbage Patch alone contains about 79,000 tons of plastic

in an area about the same size as the state of Alaska.

And that's a massive amount of plastic,

but it's not as massive as it should be.

Scientists say they're only finding about a hundredth of the plastic they expect to find in the ocean.

The garbage patches don't appear to be getting any bigger,

though they definitely should be.

Now, no one is entirely sure why this is;

but some scientists think it's because of the rapid evolution of microbes that eat plastic.

The mere existence of all our trash could be acting as a strong selective pressure

driving the evolution of molecular pathways for chopping up plastics

Plastic-eating microbes have been documented in other places.

Scientists were recently able to isolate a type of bacteria called Ideonella Sakaiensis,

which was nomming on plastic outside a bottle recycling facility.

Considering the kind of plastic garbage they eat has only been a thing for around 70 years,

they evolved really quickly;

so it's possible that that's happening in the oceans too,

but this is a guess.

Research is needed to confirm plastivores are a thing and can account for the missing plastic.

It could be explained other ways too,

like, maybe this plastic is just sinking as its colonized by marine organisms.

Recent research has suggested some plastics aren't as everlasting as we thought.

-I'm rootin' for the microbes, though-

Human beings cause all kinds of problems for nature all by ourselves;

but sometimes, we go above and beyond,

by introducing plants or animals that wreak havoc on our behalf.

That's what happened to an isolated population of Edith's Checkerspot Butterflies, on a cattle ranch in Nevada.

In their natural habitat, these butterflies lay their eggs on maiden Blue-Eyed Mary plants,

a native species of wildflower;

in this particular location,

ranchers introduced an invasive weed called English Plantain.

It turned out, the butterflies that laid their eggs on plantain

actually fared a bit better

since the plants live longer.

So the butterflies quickly evolved to prefer this new host plant.

Things were going swimmingly--

until the cattle moved away.

When that happened, the fields were almost immediately taken over by grasses

because -you know- they were no longer being eaten by cows.

This grassy vegetation shaded the plantains,

so the caterpillars living on them didn't get the warm sunlight they were used to;

the poor butterflies simply weren't able to switch back to the wildflowers fast enough.

So within a couple of years, the isolated population of Edith's Checkerspot Butterflies went extinct.

This whole process from the introduction of English plantain

to the extinction of the adapted population of butterflies,

only took around a hundred years.

Elephant tusks are highly sought after in the ivory trade.

The presence of poachers gives tuskless elephants a profound biological advantage,

which is probably why African elephants without tusks have become a lot more common in some areas.

During Mozambique's Civil War, elephants were poached in large numbers for their ivory and meat

in order to help sustain the fighting forces and pay for weapons.

Since tuskless females were more likely to survive-

lacking tusks went from being a relatively uncommon trait,

to a common one possessed by up to a third of young female elephants.

A similar thing has happened elsewhere on the continent.

Nowadays in South Africa's Addo Elephant Park,

up to 98% of female elephants never developed tusks.

Incredibly, this has all happened over a period of a couple generations,

that's probably because about 2-4% of females already possessed the tuskless trait.

Sadly, those tuskless females were pretty much the only ones that survived long enough to breed,

and that allowed the mutation to sweep through the population very quickly

despite the fact that elephants reproduce extremely slowly

compared to all of the rest of the animals on this list.

While being tuskless is great when it comes to avoiding poachers,

it's important to note that female elephants in this species had benefited from having tusks up until now.

They're helpful for finding food, among other things.

So while losing their tusks might seem like a win for rapid evolution,

it's not an unqualified one.

It might be tempting to think that we can stop worrying now about endangered species

because this high-speed evolution is gonna swoop down and eat up all the plastic and save the elephants,

evolutionary rescue can't save every species.

Some simply aren't capable of adapting quickly,

because evolutionary change happens over generations not years.

Even hyperspeed adaptations like the ones, we just talked about,

generally take ten to a hundred generations.

Basically, the more babies you have and the quicker you have them,

the faster [that] evolutionary changes can spread through a population.

So we're talking about hundreds of years for species -like polar bears-

to make big changes that might help them survive.

Sometimes rapid evolution can happen faster,

like the species already has an adaptation that helps them respond to a very bad situation,

as we saw with the tuskless elephants;

but for the most part it occurs in animals that breed fast and have lots of offspring.

Even then, evolving quickly can totally backfire --

just ask the Edith's Checkerspot...

So while examples of warp-speed adaptation are fascinating,

we shouldn't see evolution as some superhero that's going save this planet.

That is still on the folks who caused the problems in the first place,

which is us.

Though, I am thankful for many of the wonders that were brought to us as we did it.

Thanks for watching this episode of SciShow.

Don't forget to subscribe to get all of our episodes delivered in to your YouTube inbox.

You can also subscribe to SciShow Psych and SciShow Space,

where we talk about those topics in exclusion of all these other ones.

If you were surprised to learn that evolution can happen so quickly,

you might learn a lot from our episode on Evolution Misconceptions,

so we've linked to it, for you to click on, and watch it.

I hope you enjoy.