Daniel Brady Mills, Ludwig Maximilian University of Munich; Jason Wright, Penn State, and Jennifer L. Macalady, Penn State

A popular model of evolution concludes that it was incredibly unlikely for humanity to evolve on Earth, and that extraterrestrial intelligence is vanishingly rare.

But as experts on the entangled history of life and our planet, we propose that the coevolution of life and Earth’s surface environment may have unfolded in a way that makes the evolutionary origin of humanlike intelligence a more foreseeable or expected outcome than generally thought.

The hard-steps model

Some of the greatest evolutionary biologists of the 20th century famously dismissed the prospect of humanlike intelligence beyond Earth.

This view, firmly rooted in biology, independently gained support from physics in 1983 with an influential publication by Brandon Carter, a theoretical physicist.

In 1983, Carter attempted to explain what he called a remarkable coincidence: the close approximation between the estimated lifespan of the Sun – 10 billion years – and the time Earth took to produce humans – 5 billion years, rounding up.

He imagined three possibilities. In one, intelligent life like humans generally arises very quickly on planets, geologically speaking – in perhaps millions of years. In another, it typically arises in about the time it took on Earth. And in the last, he imagined that Earth was lucky – ordinarily it would take much longer, say, trillions of years for such life to form.

Carter rejected the first possibility because life on Earth took so much longer than that. He rejected the second as an unlikely coincidence, since there is no reason the processes that govern the Sun’s lifespan – nuclear fusion – should just happen to have the same timescale as biological evolution.

So Carter landed on the third explanation: that humanlike life generally takes much longer to arise than the time provided by the lifetime of a star.

To explain why humanlike life took so long to arise, Carter proposed that it must depend on extremely unlikely evolutionary steps, and that the Earth is extraordinarily lucky to have taken them all.

He called these evolutionary steps hard steps, and they had two main criteria. One, the hard steps must be required for human existence – meaning if they had not happened, then humans would not be here. Two, the hard steps must have very low probabilities of occurring in the available time, meaning they usually require timescales approaching 10 billion years.

Do hard steps exist?

The physicists Frank Tipler and John Barrow predicted that hard steps must have happened only once in the history of life – a logic taken from evolutionary biology.

If an evolutionary innovation required for human existence was truly improbable in the available time, then it likely wouldn’t have happened more than once, although it must have happened at least once, since we exist.

For example, the origin of nucleated – or eukaryotic – cells is one of the most popular hard steps scientists have proposed. Since humans are eukaryotes, humanity would not exist if the origin of eukaryotic cells had never happened.

On the universal tree of life, all eukaryotic life falls on exactly one branch. This suggests that eukaryotic cells originated only once, which is consistent with their origin being unlikely.

The other most popular hard-step candidates – the origin of life, oxygen-producing photosynthesis, multicellular animals and humanlike intelligence – all share the same pattern. They are each constrained to a single branch on the tree of life.

However, as the evolutionary biologist and paleontologist Geerat Vermeij argued, there are other ways to explain why these evolutionary events appear to have happened only once.

This pattern of apparently singular origins could arise from information loss due to extinction and the incompleteness of the fossil record. Perhaps these innovations each evolved more than once, but only one example of each survived to the modern day. Maybe the extinct examples never became fossilized, or paleontologists haven’t recognized them in the fossil record.

Or maybe these innovations did happen only once, but because they could have happened only once. For example, perhaps the first evolutionary lineage to achieve one of these innovations quickly outcompeted other similar organisms from other lineages for resources. Or maybe the first lineage changed the global environment so dramatically that other lineages lost the opportunity to evolve the same innovation. In other words, once the step occurred in one lineage, the chemical or ecological conditions were changed enough that other lineages could not develop in the same way.

If these alternative mechanisms explain the uniqueness of these proposed hard steps, then none of them would actually qualify as hard steps.

But if none of these steps were hard, then why didn’t humanlike intelligence evolve much sooner in the history of life?

Environmental evolution

Geobiologists reconstructing the conditions of the ancient Earth can easily come up with reasons why intelligent life did not evolve sooner in Earth history.

For example, 90% of Earth’s history elapsed before the atmosphere had enough oxygen to support humans. Likewise, up to 50% of Earth’s history elapsed before the atmosphere had enough oxygen to support modern eukaryotic cells.

All of the hard-step candidates have their own environmental requirements. When the Earth formed, these requirements weren’t in place. Instead, they appeared later on, as Earth’s surface environment changed.

We suggest that as the Earth changed physically and chemically over time, its surface conditions allowed for a greater diversity of habitats for life. And these changes operate on geologic timescales – billions of years – explaining why the proposed hard steps evolved when they did, and not much earlier.

In this view, humans originated when they did because the Earth became habitable to humans only relatively recently. Carter had not considered these points in 1983.

Moving forward

But hard steps could still exist. How can scientists test whether they do?

Earth and life scientists could work together to determine when Earth’s surface environment first became supportive of each proposed hard step. Earth scientists could also forecast how much longer Earth will stay habitable for the different kinds of life associated with each proposed hard step – such as humans, animals and eukaryotic cells.

Evolutionary biologists and paleontologists could better constrain how many times each hard-step candidate occurred. If they did occur only once each, they could see whether this came from their innate biological improbability or from environmental factors.

Lastly, astronomers could use data from planets beyond the solar system to figure out how common life-hosting planets are, and how often these planets have hard-step candidates, such as oxygen-producing photosynthesis and intelligent life.

If our view is correct, then the Earth and life have evolved together in a way that is more typical of life-supporting planets – not in the rare and improbable way that the hard-steps model predicts. Humanlike intelligence would then be a more expected outcome of Earth’s evolution, rather than a cosmic fluke.

Researchers from a variety of disciplines, from paleontologists and biologists to astronomers, can work together to learn more about the probability of intelligent life evolving on Earth and elsewhere in the universe.

If the evolution of humanlike life was more probable than the hard-steps model predicts, then researchers are more likely to find evidence for extraterrestrial intelligence in the future.

Daniel Brady Mills, Postdoctoral Fellow in Geomicrobiology, Ludwig Maximilian University of Munich; Jason Wright, Professor of Astronomy and Astrophysics, Penn State, and Jennifer L. Macalady, Professor of Geoscience, Penn State

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Zachary Price, University of California College of the Law, San Francisco

Because of the Trump administration’s efforts to cut staff and spending, Congress’ “power of the purse” has been in the news lately. Many of these actions have been challenged in court.

I’m a law professor who has written about Congress’ power of the purse and some of the legal and constitutional issues that surround it. Here’s a brief explanation of the concept – and of why you should care about it.

How it works

Under the U.S. Constitution, Congress holds what’s commonly called the “power of the purse.” Congress, in other words, holds the authority to control government expenditures.

Concretely, Congress may enact laws that raise revenue through taxes and import duties, and it may also spend money for “the common Defence and general Welfare,” terms in the Constitution that are understood to cover almost any spending that Congress thinks is a good idea.

The Constitution, however, provides that “[n]o Money shall be drawn from the Treasury, but in Consequence of Appropriations made by Law.” Because of this clause, officials may not spend any government money unless a statute “appropriates,” or makes available, specific funds for the relevant purpose.

Although the Constitution forbids any appropriation for the Army that lasts longer than two years, Congress can choose in other contexts whether to provide an appropriation permanently or only for a prescribed length of time. Some benefits programs such as Social Security today have permanent appropriations, but most government agencies receive funds for their operations for just a year at a time.

Leverage over policy and presidents

Why does all of this matter?

Historically, the British Parliament’s control over government funds created a powerful check on the crown, and Parliament developed the practice of annual appropriations to ensure that it would always have leverage over royal policy.

Reflecting this history, James Madison, the fourth president and a leading figure in the Constitutional Convention, wrote in the Federalist Papers that the power of the purse was “the most complete and effectual weapon with which any constitution can arm the immediate representatives of the people, for obtaining a redress of every grievance, and for carrying into effect every just and salutary measure.”

This sort of leverage over policy still matters. American presidents today exercise vast powers. Over time, Congress has conferred extensive regulatory authorities on administrative agencies that operate under the president’s supervision.

Congress has also established a large Army, Navy, and Air Force over which the president is commander in chief. Presidents, moreover, have claimed the power to employ these armed forces in significant ways even without a declaration of war or other specific authorization from Congress.

Congress’ power of the purse gives it a say in how these powers are exercised. If Congress doesn’t like what an administrative agency is doing, it can cut its budget or deny funds for enforcing certain regulations – something it does regularly.

Likewise, Congress can deny funds for certain military operations or impose constraints on military activities – something it also does with some regularity. In the 1970s, Congress helped end the Vietnam War in part by withholding appropriations for military activities in Indochina.

Who’s in charge here?

Annual appropriations also give rise to the frustrating phenomenon of government “shutdowns”: If annual funding runs out before Congress enacts new appropriations, government agencies generally must halt operations.

On the whole, however, annual appropriations continue to serve much the same purpose in the United States that they did in Britain: They provide a potent check on the executive branch.

Given how strong this check is, it may not be surprising that presidents have sought ways to get around it.

Based on debatable legal claims, President Barack Obama continued certain health insurance subsidies under the Affordable Care Act even after Congress denied appropriations for them. President Joe Biden attempted massive student debt relief without clear authority from Congress. Courts blocked both those actions, but now the new Trump administration has adopted several controversial policies that implicate Congress’ power of the purse.

On the one hand, the administration has apparently offered many federal employees nine months of paid leave if they agree to resign from federal service. But the legal basis for these offers is unclear, and it may be that no current appropriation by Congress provides funds for them.

On the other hand, the administration has attempted to “pause” certain government spending, even though existing appropriations made by Congress may require at least some of this spending.

These actions could violate not only Congress’ constitutional power of the purse but also specific statutes that Congress has enacted to reinforce its constitutional power.

The buyout offers could violate a law called the Anti-Deficiency Act that makes it unlawful, and sometimes criminal, for government officials to commit to spending money without an appropriation providing the necessary funds.

For their part, the pauses could violate a 1974 law called the Impoundment Control Act that generally forbids the government from delaying or withholding spending that Congress has mandated. Courts are now considering challenges to these actions based on these laws and other issues.

Trump may be hoping that Congress will cure any legal problems by ratifying these actions after the fact in its next round of appropriations legislation. But if Trump is indeed defying Congress’ spending laws and yet faces no consequences, his actions could chip away at Congress’ authority to check presidential policies in the future through its spending choices.

James Madison would not have been pleased.

Zachary Price, Associate Professor of Law, University of California College of the Law, San Francisco

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Leo Gugerty, Clemson University

President Donald Trump’s signature promise during his campaign was to carry out the “largest deportation” operation in U.S. history, targeting all migrants “who violated the law coming into this country.”

Since anyone living in the U.S. without legal permission has broken civil immigration law, Trump would have to deport all of the 11 million to 12 million immigrants living without legal authorization in the U.S., not just people who have committed serious crimes. Most immigrants living in the country illegally have been here longer than 10 years, so many longer-term residents would be deported.

Trump has claimed that his election victory gives him a “powerful mandate” for such actions. But what do the American people really think about mass deportation?

News outlets like CBS and Scripps News have been reporting since mid-2024 that a majority of Americans support Trump’s plans to deport most or all undocumented immigrants.

These stories rely on some polls during 2024 that showed majority support for mass deportation. Meanwhile, other polls in 2024 found public support for deportation below 40%.

I am a psychologist with expertise in survey research and the influence of political ideology on people’s beliefs about news events. And I believe the key to making sense of these conflicting polls lies in understanding the psychological principles that underlie opinion polling.

Conflicting polls

Extensive psychological research research demonstrates that people make better decisions about complex, high-stakes problems when they think about and compare multiple courses of action, instead of narrowing in on one option.

When it comes to deportation, the main policy alternative offered by presidents as far back as George W. Bush has been allowing immigrants to become legal permanent residents if certain conditions are met, like passing a background check.

Because of this, Pew Research, a prominent pollster, suggests that the best way to determine how people feel about issues like mass deportation is to give them a question that forces them to choose between deportation and something else – in this case, legalization.

For example, one July 2024 poll using a “forced-choice” question asked people whether they’d rather see “a way for undocumented immigrants who meet certain requirements … to stay here legally” or “a national effort to deport and remove all illegal immigrants” from the U.S.

Another type of question used by pollsters focuses people’s attention on only one choice by asking them how much they support a policy like deportation, but without mentioning alternatives. Polls that follow this approach ask people’s opinion of deportation in one question, and their opinion of legalization in another.

This is not ideal because research shows it can lead people to exaggerate their support for the named policy.

What the polls say

In total, I found 14 polls conducted during the past eight years that measured Americans’ opinions on both mass deportation and legalizing status. I dropped two from my analysis because they had questions worded in biased language.

The findings from the remaining 12 polls are representative of the diverse demographics of the U.S.

Graph 1 present the results from the eight polls that used a single forced-choice question. I believe these polls give the best picture of how Americans as a group feel about the two immigration policies.

These polls suggest that over the past eight years, Americans’ overall support for mass deportation has increased from around 22% to around 44%. Meanwhile, support for legalizing immigrants’ status has decreased from about 77% to 55%.

However, all four polls conducted in 2024 find support for legalizing status to be above 54% and support for deportation below 45%.

Graph 2 shows the results of the four polls that used separate questions to assess opinions about deportation and legalization.

This chart clearly demonstrates the problem with asking people to rate their support for deportation and legalization in separate questions. Two polls, both taken in the past year – one by Gallup, the other by Times/Siena – found that a majority of respondents supported deportation and that the same group of respondents supported legalization in equal or even greater numbers.

Consider the October 2024 poll where 57% of respondents supported deportation and 57% supported legalization. These percentages add up to more than 100% because many people in the group said they supported both policies. Since mass deportation and general legalization are polar opposites, people who support both policies should not be considered to strongly support either policy.

For this reason, the separate questions technique does not yield good absolute information about the percentage of people who support either deportation or legalization. However, it does give useful relative information like which policy a group supports more and how opinions change over time.

Keeping this in mind, the results of the 12 polls I analyzed indicate that people favored legalizing immigrants’ status over deportation. Eleven polls, including five taken since 2024, showed this pattern. Overall public support for deportation has actually increased since 2016, while support for legalization has decreased.

However, these changes in opinion over time do not hold true for all Americans.

Americans are polarized about immigration

The poll results I’ve discussed so far are averages calculated based on the responses of everyone who responded to the poll. But group averages don’t tell the whole story on any issue – especially when opinions differ widely within a group, as they do with immigration. So let’s look at the results for Republicans and Democrats separately.

Graph 3 breaks down the results by party for the eight polls that used the best practice: forced choice question.

During Trump’s first term, from 2017 to 2020, just over half of Republicans supported legalization; just under half supported deportation. Only within the past year has Republican opinion shifted, with about 70% now supporting deportation.

In contrast, Democrats’ opinions have remained steady for eight years, with about 90% supporting legalization and 10% favoring deportation.

In other words, the apparent shift toward greater support for deportation shown in Graphs 1 and 2 occurred only among Republicans – not for Americans as a whole.

A mandate to legalize

Despite the recent uptick in Republican support for mass deportation, a clear majority of people in the U.S. would rather give undocumented immigrants a path to legal status than have them deported. This has remained true for eight years.

Polls that seem to contradict this conclusion by showing majority support for mass deportation have used the less reliable separate-questions technique. These results are questionable because these poll respondents voiced equal or stronger support for legalizing immigrants’ status.

If Trump has a “powerful mandate” on immigration, my research shows, it’s for getting legal authorization for immigrants who’ve lived in the U.S. a long time without it – not deporting them.

Leo Gugerty, Professor Emeritus in Psychology, Clemson University

This article is republished from The Conversation under a Creative Commons license. Read the original article.