听力文摘：冰河世纪动物如何生存（在线收听）

During the last ice age, rapid swings in temperature occurred within decades or less, meaning populations of organisms had to adjust quickly to new environments or face extinction.

在最后一个冰河世纪中，温度在数十年甚至更短的时间内迅速变化，这意味着生物种群不得不快速调整来适应新的环境，否则等待它们的只有种族灭绝。

Scientists knew there wasn't time for the genetic code to mutate within individuals and spread throughout large populations. So, how did animals respond? Ancient bison preserved in the Canadian arctic have given scientists a clue.

科学家知道那时基因编码没有时间在个体中产生变异并在种群中大范围地传播。那么，动物们是如何应对的？在加拿大北极圈内保留的古代野牛标本给科学家们提供了一些线索。

When genes were first identified, scientists thought they were hard wired. One gene made one protein and was unalterable. Today we know the story is much more complex. Part of that complexity is known as epigenetics, a process by which genes are modified by environmental factors.

第一次识别古代野牛的基因时，科学家们认为它们是固定相连的。一个基因对应一个蛋白质并且无法改变。如今我们知道故事远没有那么简单。其中一部分复杂性来自表观遗传学，它是基因通过环境因素发生改变的过程。

The genetic code stays the same, but certain molecules attach to the code to prevent specific genes from working or to change how they are expressed. Other molecules can affect the chromosome and alter the way the DNA unwinds, affecting how genes work.

基因密码保持不变，但是某个为阻止某个特定基因工作或变更的密码附属分子发生了变化。而其它分子可以通过影响染色体并改变DNA解旋的方式来影响基因的表达。

Extracting DNAScientists examining twenty six thousand year old bison bones looked for evidence of epigenetic changes in extracted DNA. They analyzed the genetic code for a particular kind of epigenetic change called DNA methylation. They not only found methylations, they found them in locations where they occur in modern cattle. That suggested they weren't due to DNA degradation, but were true epigenetic changes.

DNA提取科学家检查了已有26000年历史的古代野牛的骨头，试 图在提取的DNA中找到表观遗传变异的证据。他们分析了一种特定种类的表观变化（被称为DNA甲基化）的基因密码。他们不但找到了甲基化，而且发现它们跟 现代牛群体内发现的位置是一样的。这表明它们不是发生了DNA退化，而是真正的表观遗传变异。

This is just the first step in solving the ice age adaptation puzzle. Scientists plan to gather more DNA samples from animals that lived before and after the dramatic climatic shifts. That way they'll have genetic snapshots to compare. If comparisons prove successful, the next step will be to determine exactly how the epigenetic alterations changed the gene expression.

这仅仅是解决冰河世纪适应谜团的第一步。科学家计划在气候剧烈变化前后生存过的动物身上收集更多的DNA样本。如此一来，他们就有更多的基因用来比较。如果比较的结果证明是之前的推断是正确的，那么下一步是确定表观变化是如何影响基因表达的。