 Welcome to Learning English, a daily 30-minute program from the Voice of America. I'm Ashley Thompson. And I'm Dan Novak. This program is designed for English learners, so we speak a little slower, and we use words and phrases, especially written for people learning English. Coming up on the program, John Russell and Anna Matteo have a story on new research into the genetics of Neanderthals and Denisovans. Brian Lin has this week's science report about the de-orbiting of the International Space Station. Later, Andrew Smith and Jill Robbins present the English lesson of the day. Neanderthals live on within us. These ancient human relatives, and others, called Denisovans, once lived alongside our early Homo sapiens ancestors. The groups mixed and had children. As a result, some of the Neanderthals and Denisovans live on in our genes. And science is starting to show just how much that shapes us. Mary Prendergast, a Rice University archaeologist, said, we're now carrying the genetic legacies and learning about what that means for our bodies and our health. In the past few months, researchers have linked Neanderthal DNA to a serious hand disease. The shape of people's noses and other human traits. They even placed a gene carried by Neanderthals and Denisovans into mice to investigate its effects on biology. The researchers found that the gene gave the mice larger heads and an extra rib. Research of the human story remains a mystery. But Dr. Hugo Zieberg of the Karlinska Institute in Sweden, said new technologies and research are helping scientists begin to answer the questions. Who are we? Where did we come from? And the answers point to a deep reality. We have far more in common with our ancient cousins than we ever thought. Until recently, the genetic legacy from ancient humans was invisible. But there has been a number of discoveries from ancient DNA, an area of study developed by Nobel Prize winner Svante Pebo. He was first in creating a Neanderthal genome. Research shows some African populations have almost no Neanderthal DNA, while those from European or Asian backgrounds have up to 2%. Denisovan DNA is rarely found in most parts of the world, but makes up 4 to 6% of the DNA of people in Melanesia. This Pacific Ocean area extends from New Guinea to the Fiji Islands. That may not sound like much, but it adds up. Even though only 100,000 Neanderthals ever lived, half of the Neanderthal genome is still around, in small pieces scattered around modern humans, said Zeeberg, who works closely with Pebo. It is also enough to affect us in very real ways. Scientists studying the subject say the DNA can be both helpful and harmful. For example, Neanderthal DNA has been linked to autoimmune diseases, like Graves disease and Rheumatoid arthritis. When Homo sapiens came out of Africa, they had no immunity to diseases in Europe and Asia. But Neanderthals and Denisovans already living there did. Chris Stringer is a human evolution researcher at the Natural History Museum in London. Stringer said that by mating with Neanderthals and Denisovans, Homo sapiens got a quick fix to our immune systems, which was good news 50,000 years ago. Stringer added, the result today is, for some people, that our immune systems are oversensitive and sometimes they turn on themselves. In 2020, research by Zeeberg and Pebo found that a major genetic risk factor for severe COVID-19 came from Neanderthals. We compared it to the Neanderthal genome and it was a perfect match, Zeeberg said. The next year, they found a set of DNA variants along a single chromosome inherited from Neanderthals had the opposite effect, protecting people from severe COVID. Much less is known about our genetic legacy from Denisovans. Although some research has linked genes from them to fat processing and better performance at high altitudes. Manasa Raghavan, a human genetics expert at the University of Chicago, said Tibetans carry an amount of Denisovan DNA. She noted that the population continues to live and do well in low oxygen environments today. John Hawks of the University of Wisconsin-Madison said that human evolution was not about survival of the fittest and extinction. Instead, he suggested, it is about interaction and mixture. Researchers expect to learn more as the science continues to develop. Even when ancient bones are not available, scientists today can get DNA from soil where ancient humans once lived. And there are less explored places in the world where researchers hope to learn more. Zeeberg said biobanks that collect biological materials will likely be established in more countries. As researchers go deeper into humanity's genetic legacy, scientists expect to find even more evidence of how much we mixed with our ancient cousins and all they left us. Perhaps, Zeeberg said, we should not see them as so different. I'm John Russell. And I'm Anna Mateo. VOA Learning English has launched a new program for children. It is called Let's Learn English with Anna. The new course aims to teach children American English through asking and answering questions and experiencing fun situations. For more information, visit our website learningenglish.voanews.com. The American Space Agency, NASA, has a new plan for de-orbiting the International Space Station, or ISS. The plan involves developing a new spacecraft to safely guide the ISS during its final reentry through Earth's atmosphere. NASA cooperates with four other space agencies on the station. These include the Canadian Space Agency, the European Space Agency, Japan's Aerospace Exploration Agency, and Russia's Roscosmos. The ISS began serving as a space research center more than 22 years ago. It has been widely praised as a scientific success, but NASA and its international partners say the ISS has a limited technical lifetime. NASA has said it will keep operating and sending astronauts to the ISS until 2030. After that, the U.S. Space Agency plans to use privately developed space laboratories for its space research needs. NASA says this will permit it to pay space station operators only for the goods and services it needs. NASA has already chosen several American companies to develop future space stations. These privately operated stations will aim to serve the science needs of NASA as well as other nations, space agencies, and other organizations. In a report to the U.S. Congress last year, NASA established its plans for the ISS. The report said the agency aims to make the station's final years its most productive. Among the goals NASA declared to support deep space exploration and continue to return medical and environmental benefits to humanity. The agency recently announced its new de-orbiting plan for the ISS after considering other options to retire it. A past plan or option involved the use of several Russian spacecraft, but NASA officials rejected that plan and decided a new specially designed spacecraft would better serve the needs of the de-orbiting operation. Other options included a plan to take apart the space station in space and transport its pieces back to Earth. Another plan would have seen the ISS sent to a higher orbit where it would remain out of service. A third option involved a non-controlled re-entry operation. NASA said none of these met its requirements for safety and effectiveness. The agency recently released a request for proposals to companies interested in building the new spacecraft. NASA calls it the U.S. de-orbit vehicle, or USDV. It says it can be a completely new vehicle or an existing design that is changed to meet all needs of the de-orbiting process. The agency said it is seeking proposals now because the effort will take years to develop, test, and certify. NASA has said when it is time to retire the ISS it will begin taking the first steps to slowly lower its operating altitude. This part of the process can likely be carried out by the ISS and its systems without the need for additional spacecraft. But the final part of the operation, re-entry, will center on guiding the ISS through Earth's atmosphere to a pre-chosen target in an unpopulated area in the ocean. NASA says this final part is expected to require a new or modified spacecraft using a large amount of propellant. The targeted landing spot has been identified as a place called Point Nemo in the South Pacific Ocean. This is a stretch of open water between New Zealand and the southernmost part of South America. The U.S. National Ocean Service identifies Point Nemo as the point in the ocean that is farthest from land. NASA predicts that most ISS equipment will burn up or vaporize during the intense heating that happens during atmospheric re-entry. But it says some denser or more heat-resistant elements are expected to survive and land in the targeted ocean area. I'm Brian Lin. Brian Lin joins me now to talk more about his science report. Thanks for being here, Brian. Sure, Dan. Glad to be here. In this week's report, you looked at a new plan NASA has for de-orbiting the International Space Station. The space station is, of course, currently fully operational and seems to be busier than ever. So why does NASA think it is necessary to retire it? Yes, you're correct about the current status. And as noted in the report, NASA plans on still operating the space lab until 2030. But agency officials have said they knew when the space station was launched more than 22 years ago, it would not last forever. And there are technical systems that simply cannot be replaced at this point. And even if they could, a so-called remodel of the station would also not be possible in space. We know from the report that NASA has decided to turn over the development and operation of a new space station to private companies. What can you tell us about that? So yes, NASA has already chosen three American companies to develop future space stations. And agency officials have said the plan is to have multiple orbiting labs in the years to come. So the idea is that NASA itself would pay for use of these stations for its scientific research along with space agencies from other countries and other organizations. And there are also expected to be more visits by non-astronauts to these future stations. And do we know when those new stations are expected to be completed? Well, at least one team working on a station it calls Starlab says it plans on it being fully operational as soon as 2027, so in plenty of time to replace the current one. Very interesting. Thanks again for being here, Brian. You're welcome. Thank you, Dan. Name is Anna Matteo. And my name is Jill Robbins. And I'm Andrew Smith. We're listening to the Lesson of the Day on the Learning English podcast. Welcome to the part of the show where we help you do more with our series Let's Learn English. This series shows Anna Matteo in her work in life in Washington, DC. Let's jump right in with a short clip from Lesson 20 of the series. We'll play the clip three times in a row. Listen to Anna ask a question and then make a statement. And listen for how she pronounces the small word can. Can you teach? You can be a teacher in a school. Can you teach? You can be a teacher in a school. Can you teach? You can be a teacher in a school. There's a difference between how she pronounces the word can when she asks the question. Can you teach? And how she pronounces it when she makes a statement. Listen one more time. Can you teach? You can be a teacher in a school. With her statement, you can be a teacher in a school. She says the word can a bit faster. And the vowel sound changes from a like an apple to the schwa a. This change of vowel sound is something that happens when we talk faster. That's a funny word schwa, isn't it? When English speakers do not put any stress on a vowel, it sounds like this, a. We write it with the upside down e. Why do you think we have a special word for this sound, Jill? I think we need a special word for it because it can be written using a, e, i, o, u, or y in words. It is the most common vowel sound in English because it represents unstressed vowels. Lesson 20 of Let's Learn English has a pronunciation practice video that explains this change of vowel sound. Let's listen. In slow speech, can sounds like can. In fast speech, it often sounds like can. Listen to Anna talking to Pete about being a teacher. Can you teach? You can be a teacher in a school. But now let's listen to the negative forms of the verb can. These of course are the words cannot and can't. Well it might seem simple. We want you to know how and when native speakers use each form. When we want people to clearly understand that we are unable to do something, we sometimes use the longer form cannot. For example, when you talk on the phone and you have to explain a problem, you want to be sure that the other person understands you. So you might choose to use the form cannot. For example, if you are locked out of a room or locked out of a building, you might say, I've tried the key over and over and I cannot open the door. Yeah, cannot gives emphasis to the meaning. As we explained in a previous lesson of the day, emphasis is spelled E-M-P-H-A-S-I-S. It means extra importance and is similar to the word stress. Another reason we might choose to say cannot when speaking on the phone is because there is only a small difference in pronunciation between the positive form can and the negative form can't. Sometimes you can hear the letter T when we say can't, but other times it is harder to hear and it just sounds like this, can't. In American English, we call that a held T. Instead of pronouncing the T, your tongue just comes to a stop against the hard part of the roof of your mouth just behind the upper front teeth. Maybe we'd better say that location one more time. Good idea. I'll repeat that. The tongue comes to a stop against the hard part of the roof of your mouth just behind the upper front teeth. In the pronunciation video of lesson 20, you can hear Pete first pronounce can't with the letter T. And then the next time you hear him pronounce it with the held T, can't. Let's listen. No, I can't code. I can't teach. I can't cook. Anna, I can't do anything. I noticed that when people send text messages, they often send a message saying I can when I'm sure they mean I can't. I think that's because they're using their voice to write or dictating, you know. The text and the phone software cannot tell the difference between the two words. How can we help our listeners hear and say the forms correctly? Listen to these examples. I can, I can't. I can, I can't. When we say the positive form, we pronounce the letter N longer. The N sound, N, N, N, N, lasts longer than in the negative form. In fact, in the negative form, because the tongue and voice stop, there is almost no sound of the letter N. Can't. So again, listen to the difference. I can, I can't. I can, I can't. There is a difference, but it is small. If you cannot hear the difference, don't worry. Usually, you will know that it's the negative form, just from the situation. From all the other information you'll get from the conversation. And if you are speaking and want to be very clear, simply pronounce the letter T like can't. I'm Jill Robbins and you're listening to the Lesson of the Day on the Learning English Podcast. Andrew, earlier in the lesson, you said you were going to give the listeners more examples. That's right. We're going to give examples of how we pronounce the verb can when we speak quickly. Jill. You can just ask me a question and I'll answer it. That sounds pretty easy. Are you ready? Ready. Can you do it? Yeah, I can do it. Can you see it? Yeah, I can see it. Can you come over? Yeah, I can come over. Can you send it to me? Yeah, I can send it to you. Can you hear a difference? Yeah, I can hear a difference. Can you smell it? I can smell it. Can you put it in the oven? I can put it in the oven. Can you open the door? I can open the door. Can you give me a hand? I can give you a hand. Can you give me a minute? I can give you a minute. Can you give me all your money? I don't think so. I cannot give you all of my money. Let's check to see if you were really listening. What can you give me? Hmm, good question. I can give you, let's see, I can give you free advice. Advice? You mean you can give me suggestions for how to fix a problem. Sure. Well, I don't have any problems. You don't have any problems? Not today. Well, lucky you. I think maybe you should give me advice. So how about this? I can thank you for helping me and our listeners with the Learning English podcast. It's the high point of my day. But I can't believe we spent the whole lesson talking about this one little word. I can. Getting all the details of American pronunciation takes time and people need lots of examples. And there's much more our listeners can learn from lesson 20 of Let's Learn English. In our next lesson of the day, we'll talk about an important topic from lesson 20, having skills and knowing how to use them. That is a great topic. I look forward to speaking with you about it. Until then, thanks for listening to the lesson of the day on the Learning English podcast. I'm Andrew Smith. And I'm Jill Robbins. And that's our program for today. Join us again tomorrow to keep learning English through stories from around the world. I'm Ashley Thompson. And I'm Dan Novak.