Name: 人類の進化は加速しているのか、それとも減速しているのか？- ローレンス・ハースト (Is human evolution speeding up or slowing down? - Laurence Hurst)
Uploaded: 2021-01-14T11:23:53.000Z
Duration: 5 min 48 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

The Tibetan high plateau lies  about 4500 meters above sea level,

様態の副詞

While visitors and recent settlers  struggle with altitude sickness,

This ability comes not from training  or practice,

but from changes to a few genes  that allow their bodies

These differences are apparent from birth—

Tibetan babies have, on average,  higher birth weights,

and are much likelier to survive than  other babies born in this environment.

These genetic changes are estimated  to have evolved

over the last 3,000 years or so,  and are ongoing.

but would be the fastest an adaptation  has ever evolved in a human population.

It's clear that human evolution isn't over—

And will our technological and scientific innovations impact our evolution?

many populations have evolved genetic  adaptations to their local environments.

People in Siberia and the high arctic are  uniquely adapted to survive extreme cold.

and can continue to use their hands  in subzero temperatures

They've undergone selection  for a higher metabolic rate

Further south, the Bajau people  of southeast Asia can dive 70 meters

and stay underwater  for almost fifteen minutes.

Over thousands of years living  as nomadic hunters at sea,

they have genetically-hardwired unusually  large spleens that act as oxygen stores,

enabling them to stay underwater  for longer—

an adaptation similar  to that of deep diving seals.

Though it may seem pedestrian  by comparison,

the ability to drink milk  is another such adaptation.

All mammals can drink  their mother's milk as babies.

After weaning they switch off the gene  that allows them to digest milk.

But communities in sub-Saharan Africa,  the middle east and northwest Europe

that used cows for milk have seen  a rapid increase in DNA variants

that prevent the gene from switching off  over the last 7 to 8000 years.

At least in Europe, milk drinking may  have given people a source of calcium

to aid in vitamin D production,  as they moved north and sunlight,

the usual source of vitamin D,  decreased.

all of these changes improve people's  chance of surviving to reproductive age—

the force behind all these  evolutionary changes.

Modern medicine removes  many of these selective pressures

sometimes combined  with infectious diseases,

Antibiotics, vaccines, clean water  and good sanitation

all make differences between our genes  less important.

Similarly, our ability to cure  childhood cancers,

surgically extract inflamed appendixes,  and deliver babies

whose mothers have life-threatening  pregnancy-specific conditions,

all tend to stop selection by allowing  more people to survive

But even if every person on Earth  has access to modern medicine,

it won't spell the end of human evolution.

That's because there are other aspects  of evolution besides natural selection.

that would have been subject  to natural selection

subject to what's called  genetic drift instead.

With genetic drift, genetic differences  vary randomly within a population.

On a genetic level, modern medicine  might actually increase variety,

because harmful mutations don't kill  people and thus aren't eliminated.

This variation doesn't necessarily  translate to observable, or phenotypic,

Researchers have also been investigating  whether genetic adaptations

to a specific environment  could appear very quickly

through epigenetic modification:  changes not to genes themselves,

but to whether and when certain genes  are expressed.

These changes can happen  during a lifetime,

but so far researchers are conflicted  over whether epigenetic modifications

and lead to lasting changes  in populations.

There may also be other contributors  to human evolution.

Modern medicine and technology  are very new,

even compared to the quickest,  most recent changes by natural selection—

so only time can tell how our present  will shape our future.