Opening on the 200th anniversary of Charles Darwin's birth, the 175th conference of the world's largest science society was always likely to have a celebratory feel to it.
There was indeed a palpable buzz yesterday in the subterranean conference rooms of the two downtown Chicago hotels where the American Association for the Advancement of Science (AAAS) is holding its annual meeting. The real excitement, however, has had much less to do with Darwin than with the most famous former resident of America's second city - Barack Obama.
This AAAS meeting has been a coming-out party for American scientists after eight years in which they have felt marginalised and ignored. Few sections of American society found George W. Bush's presidency quite as dispiriting as its scientists. From climate change to stem-cell research, the White House was at odds with researchers over virtually all the issues they most cared about.
President Obama has changed all that. With an extra $65 billion (£45 billion) promised for energy and research in his stimulus package, with new policies on global warming and stem cells, and above all with a list of appointments that includes some of the most glittering names in American science, he has transformed the mood of the nation's laboratories - and the mood of this conference.
Debates and lectures that would until recently have been ignored by the White House now stand a real chance of influencing policy. Al Gore, for example, was due to give the keynote address last night. The climate change campaigner and former Vice-President is an insider again now, and many scientists attending the AAAS conference are starting to consider themselves insiders too.
In his inaugural address, President Obama promised to "restore science to its rightful place". When announcing his science team, he said that "promoting science isn't just about providing resources - it's about protecting free and open inquiry. It's about ensuring that facts and evidence are never twisted or obscured by politics or ideology." US scientists feel that they finally have in Mr Obama a president who not only supports and values what they do, but who also understands them.
"This Administration is looking at science very differently," said James McCarthy, the AAAS president. "He [President Obama] sees the value of science not just as a way of keeping those strange members of our society employed who want to go off and do quirky things. It plays a really important role in decisions this Administration has to make. He is really valuing the product."
Sean Carroll, a geneticist and evolutionary biologist at the University of Wisconsin, who gave last night's plenary lecture at the conference, said that the mood had changed overnight. "We haven't ever seen a president talk about the role of science in our culture quite in this way before," he said. "It's a sea change, and an inspiration.
"The past eight years have been a dark period. Very well-established science, like that of climate change, was denied. There was pressure to alter the work of government scientists. The promotion of areas such as stem-cell research was thwarted. In the realm of science education, intelligent design got a lot of attention,
and even encouragement, from the President. That is ridiculous and also demoralising. These were horrible errors, and sent a terrible message to young, aspiring scientists."
That message is already starting to change. Just three days after President Obama's inauguration, the US Food and Drug Administration approved the first human trial of an embryonic stem-cell therapy, which had been held up for months.
He has allowed states to impose strict fuel economy regulations, which Mr Bush had blocked. The US is now expected to lead, rather than to obstruct, efforts to negotiate a new world climate accord in Copenhagen at the end of the year.
There is also great excitement at the President's choices to fill key scientific roles in his Administration. As the AAAS conference opened on Thursday, the Senate began confirmation hearings for John Holdren, the nominee for chief scientific adviser to the White House, and Jane Lubchenco, the nominee for head of the National Oceanographic and Atmospheric Administration.
Both are eminent environmental scientists with impeccable academic credentials. Professor Holdren is a former president of the AAAS, and Professor Lubchenco is a marine biologist. Her predecessor, appointed by President Bush, is an admiral.
As Energy Secretary, the President chose Steven Chu, a Nobel prizewinning physicist who is among the world's most creative thinkers about renewable energy.
"The appointment of talent is spectacular," Professor Carroll said. "He's not just got good people; he's got some of the best people who walk the planet to join his team."
Professor McCarthy, an oceanographer at Harvard University, said that he was particularly impressed with the speed with which this team had been assembled, and that so many stellar scientists agreed to serve. Both were signs of the seriousness with which Mr Obama takes science. "Obama picked and announced it during his transition period. That is, to my knowledge, unprecedented."