Polar Bear Rapid Evolution Lets Them Be Fat Fit

A triple bacon cheeseburger seems like a heart attack on a plate.

So how can polar bears thrive on their version, seal blubber?

Blubber is the fat of whales, seals, and similar sea animals.
例句1：Blubber is the fat of whales, seals, and similar sea animals.
例句2：If someone blubbers, they cry noisily and in an unattractive way.
例句3：The baby whale develops a thick layer of blubber to protect it from the cold sea./幼鲸长出一层厚厚的鲸脂，以抵御寒冷的海水。

Turns out they've stocked up on genes that let them clear fats from their blood.

That's according to a study in the journal Cell.

Polar bears are well adapted to life on the sea ice.

Up to half their body weight's fat, which gives them extra insulation and buoyancy, and provides them with a ready source of energy.

buoyancy /'bɔɪənsi/ n. Buoyancy is the ability that something has to float on a liquid or in the air.
例句1：Buoyancy is the ability that something has to float on a liquid or in the air.
例句2：Buoyancy is a person's ability to remain cheerful, even in sad or unpleasant situations.
例句3：Buoyancy is a feeling of cheerfulness.
例句4：There is economic buoyancy when the economy is growing.

But how can an animal so fat also be so fit?

Researchers compared the genomes of polar bears with those of brown bears, and found that polar bears have accumulated genetic changes that boost their heart health and fat metabolism.

Your metabolism is the way that chemical processes in your body cause food to be used in an efficient way, for example to make new cells and to give you energy.
例句1：a metabolic process/disorder / 新陈代谢过程╱紊乱
例句2：The body's metabolism is slowed down by extreme cold./严寒可以使身体新陈代谢的速度下降。

One gene in particular, called ApoB, helps move cholesterol out of the blood—where it causes problems in humans—and into cells.

These genomic changes happened quickly, evolutionarily speaking.

Polar bears and brown bears diverged from a common ancestor less than half a million years ago.

But if that seems super speedy, the ability to digest lactose didn't spread through human populations until we domesticated cows, just 10,000 years ago.

Lactose is a type of sugar which is found in milk and which is sometimes added to food.

A moving testament to the power of natural selection.

本文节选自《60-Second Science American》