Friday, May 17, 2019

Gelernter's Strong Arguments Against Intelligent Design Creationism

Having just written about David Gelernter's weak arguments against Darwinian evolution in his Claremont Review essay, I thought I should also write about his strong arguments against intelligent design creationism.  The people at the Discovery Institute--like David Klinghoffer--have been celebrating Gelernter's "wonderful essay" as a triumph for the cause of intelligent design theory.  But they have to reluctantly admit that while Gelernter has been persuaded by Stephen Meyer's criticism of Darwinian science, he rejects Meyer's claim that the best replacement for Darwin is intelligent design.

I have written (here) about the dishonesty and sophistry of Meyer's intelligent design theory.  Gelernter doesn't recognize Meyer's dishonesty, but he does recognize one of Meyer's two sophistical fallacies.

At the end of his essay, in the section on "Darwin's Limits," Gelernter indicates that Meyer hasn't offered any proof for intelligent design, because he hasn't explained exactly when, where, and how the intelligent designer has intervened.
". . . What was his strategy?  How did he manage to back himself into so many corners, wasting energy on so many doomed organisms?  Granted, they might each have contributed genes to our common stockpile--but could hardly have done so in the most efficient way.  What was his purpose?  And why did he do such an awfully slipshod job?  Why ae we so disease prone, heartbreak prone, and so on?  An intelligent designer makes perfect sense in the abstract.  The real challenge is how to fit this designer into life as we know it.  Intelligent design might well be the ultimate answer.  But as a theory, it would seem to have a long way to go."
By seeing that Meyer's critique of Darwinian science does not prove intelligent design, Gelernter recognizes, at least implicitly, that intelligent design reasoning depends completely on the fallacy of negative argumentation from ignorance, in which intelligent design proponents like Meyer argue that if evolutionary scientists cannot fully explain the step-by-step evolutionary process by which complex forms arise, then this proves that these complex forms of life must be caused by the intelligent designer.  Gelernter sees that this is purely negative reasoning, because the proponents of intelligent design are offering no positive explanation of their own as to exactly when, where, and how the intelligent designer caused these forms of life.  Meyer insists that the proponents of evolutionary science satisfy standards of proof that he cannot satisfy, because his sophistical strategy is to put the burden of proof on his opponents, while refusing to accept that burden of proof for himself.

Meyer has admitted that this argument from ignorance is a fallacy, but he tries to show that proponents of intelligent design theory do not really commit this fallacy, because they offer explanations of intelligent design with positive content.  When he tries to do this, however, he must use the fallacy of equivocation--in the equivocation between human intelligent design and supernatural intelligent design.  We have all had the experience of how human intelligent agents create artificial products by intelligent design.  But it does not follow logically from this that we have all had the experience of how supernatural intelligent agents create artificial products by intelligent design.

Gelernter has not spotted this fallacy of equivocation in Meyer's reasoning.  Nor has he spotted the dishonesty in Meyer's claim that intelligent design theory is a purely secular scientific theory that does not depend on religious belief.  Gelernter says that "intelligent design as Meyer explains it never uses religious arguments, draws religious conclusions, or refers to religion in any way."  Gelernter is such a sucker.

If he knew more about the history of Meyer's work with the Discovery Institute, he would know about the founding document--"The Wedge Document"--of Meyer's Center for the Renewal of Science and Culture.  And he would know that the primary goal of the Center is declared to be "to defeat scientific materialism and its destructive moral, cultural, and political legacies," and "to replace materialistic explanation with the theistic understanding that nature and human beings are created by God."

The Wedge Document was written only for private circulation among potential donors to the Discovery Institute.  They wanted this to be kept private because in public their rhetorical strategy was to deny that their attacks on Darwinian science and defense of intelligent design were designed to promote biblical creationism.  They needed this dishonest rhetoric as a way of getting around the decision of the U.S. Supreme Court in Edwards v. Aguillard in 1987, which said that teaching "creation science" in public school biology classes was an unconstitutional violation of the First Amendment's ban on any governmental "Establishment of Religion."  Their way around this was to replace the term "creation science" with "intelligent design theory," and then to insist that the later had nothing to do with the former, because "intelligent design" was a purely scientific idea that had nothing to do with any religious belief in the Creator.

Clearly, Meyer's dishonest rhetoric has succeeded in fooling people like Gelernter.

I have written (here) about how Intelligent Design Theory should be understood as one of four leading positions on the creation/evolution debate among biblical theists--along with Young Earth Creationism, Old Earth Creationism, and Evolutionary Creation.

Wednesday, May 15, 2019

Gelernter's Weak Arguments Against Darwinian Evolution in "The Claremont Review of Books"


The spring 2019 issue of The Claremont Review of Books has an essay by David Gelernter entitled “Giving Up Darwin” that summarizes some of the arguments against Darwinian evolution as developed by proponents of “intelligent design” theory at the Discovery Institute.  Gelernter is silent about the many objections to these arguments, and thus he conveys to his readers the impression that these arguments are irrefutable.  Actually, the arguments are so weak as to be easily refuted.

THE ORIGIN OF SPECIES
Gelernter makes four claims.  His first claim is that while Darwinian science rightly explains microevolution (changes within a species), it cannot explain macroevolution (the emergence of new species from ancestral species).  He mentions “changes to fur density or wing style or beak shape” as examples of “the fine-tuning of existing species,” which is microevolution as distinguished from the macroevolutionary origin of species.

He offers no evidence or argumentation to support this first claim.  He simply asserts it as if it were obviously true.  His reference to “beak shape” might be pointing to the famous studies of the finches in the Galapagos Islands by Peter and Rosemary Grant, who have seen changes in beak size and shape on the island of Daphne Major as evolution in action.  Gelernter seems, then, to be suggesting that this shows microevolution (changes within one finch species) but not macroevolution (changes leading to the emergence of a new finch species).

He is silent about the fact that the Grants have observed the evolution of a new species of finch.  In 1981, a large male cactus finch (Geospiza conirostis) mated with a medium ground finch (Geospiza fortis).  They produced offspring who have bred within the hybrid lineage for over 30 years.  Genetic analysis has recently confirmed that this is a distinctive species separate from the other 18 species of finches on the Galapagos Islands. (I have written about this herehere, and here.)

Gelernter is also silent about the fact that some intelligent design proponents (like Michael Behe) and some scientific creationists (like Ken Ham) have admitted that evidence like this proves the Darwinian evolution of new species.  Ham and others have conceded that Darwin proved that species are not fixed, and that new species can evolve, although they argue that since God created separate “kinds” of life in Genesis, this must mean that some taxonomic level of classification (perhaps “families”) must be God’s fixed creation.  Similarly, Behe accepts the Darwinian account of the evolution of species by common descent from ancestral species—including the common descent of chimps and humans.  (I have written about this herehere, and here.)

THE CAMBRIAN EXPLOSION
Gelernter’s second claim is that the “Cambrian explosion”—the seemingly sudden explosion of complex animal forms about 540 million years ago—denies the Darwinian theory of gradual evolution from ancestral forms, because the “predecessors of the Cambrian creatures are missing.”  He is silent about all the fossil evidence for evolutionary predecessors.  There is evidence for multicellular life appearing from about 590 million years ago in China.  Testate amoebae are known from about 750 million years ago.  There are transitional fossils within the Cambrian—such as lobopods (worms with legs), which are intermediate between anthropods and worms.  Most of the animal groups that we are most familiar with—mammals, reptiles, birds, insects, and spiders—appeared after the Cambrian.  Gelernter says nothing about any of this evidence for Darwinian evolution before, during, and after the Cambrian.

THE EVOLUTION OF PROTEIN MOLECULES
His third claim—to which he devotes the most space—is that Darwinian science cannot explain the evolution of protein molecules, because the construction of such complex molecules by random mutation is so incredibly improbable as to be impossible. 

A protein molecule is based on a chain of amino acids with 150 or more elements, with each one chosen from 20 amino acids.  He writes:

So how hard is it to build a useful, well-shaped protein?  Can you throw a bunch of amino acids together and assume that you will get something good?  Or must you choose each element of the chain with painstaking care?  It happens to be very hard to choose the right beads.

                                             .   .   .

What are the chances that a random 150-link sequence will create such a protein [that is functional].  Nonsense sequences are essentially random.  Mutations are random.  Make random changes to a random sequence and you get another random sequence.  So, close your eyes, make 150 random choices from your 20 bead boxes and string up your beads in the order in which you choose them.  What are the odds that you will come up with a useful new protein?

                                          .   .   .

The total count of possible 150-link chains, where each link is chosen separately from 20 amino acids, is 20150 [20 with 150 zeros].  In other words, many, 20150 roughly equals 10195, and there are only 1080 atoms in the universe.

Notice the reasoning here: the fundamental assumption that Darwinian scientists believe that protein molecules arose in evolution by a single all-at-once “at random” trial, and then the assertion that this is probabilistically impossible.  The problem, however, is that this is a “straw man” fallacy, because no Darwinian scientist believes that this is the way evolution works.  On the contrary, scientists believe that biomolecules evolved as the result of a long series of intermediate steps over long periods of time, in which each step was useful in a previous biological context; and this was not purely a “random” process, because while mutations might be random, natural selection is not—natural selection is a directional process that selects variations that are functional for survival and reproduction.  (Notice how, in the second of the three passages quoted above, Gelernter uses the word “random” 6 times in 3 sentences.)
Gelernter treats complex, functional organic structures as vanishingly tiny targets in large search spaces.  He then assumes that evolution must search this space of equiprobable outcomes blindly and randomly to find its target by accident.  This allows him to conclude that the probability of evolution randomly hitting its target in this huge search space is ridiculously improbable.  But this is utterly irrelevant to how evolution by natural selection actually works.
Evolutionary searches take as their starting points already functioning structures.  Evolution never does a global search of all possibilities.  Rather, evolution undertakes a sequence of local searches in the neighborhoods of functional organic structures.
Consider, for example, the human alpha-globin molecule, which is a part of hemoglobin that performs an oxygen transfer function in the blood stream.  This is a protein chain based on a sequence of 141 amino acids.  Choosing from the 20 amino acids common in living systems, the number of potential chains of length 141 is 20141, which is roughly 10183.  And, of course, Gelernter would say that this number is so enormous that the probability of a random search hitting this tiny target—the human alpha-globin molecule—is so low as to be impossible.
But this ignores the fact that a large class of alpha-globin molecules can perform the essential oxygen transfer function, and there is a great variety in alpha-globin molecules across animal species.  This variation shows the record of evolutionary descent.  Humans and chimpanzees have the same arrangement of alpha-globin genes, while other primates show differences from humans and chimps, but similarities to other mammals.
This indicates that the evolution of the human alpha-globin molecule did not search randomly for its target in a huge search space, as Gelernter assumes.  Rather we should say, it started with the alpha-globin molecule of the common ancestors of humans and primates.  The alpha-globin molecules of our primate ancestors functioned well for them.  By starting there, evolution could move step-by-step to select the alpha-globin molecules that would function well for us—to enhance our survival and reproductive fitness.  What matters is not the rarity of functional proteins in the whole conceivable search space of possible amino-acid combinations, but rather isolation within that portion of the space that must be searched (in this case, the variety of functional alpha-globin molecules among primates as the starting point for natural selection in the evolution of the human alpha-globin molecule).
Gelernter asks: “Can you throw a bunch of amino acids together and assume you will get something good?”  Well, no.  But this question is irrelevant to how evolution really works.

THE EVOLUTION OF BODY PLANS
Gelernter’s fourth claim is that Darwinian science cannot explain “the big body-plan changes required by macro-evolution,” because the major mutations required for such big changes in body plans would be fatal.  But in making this claim, he is silent about the emergence over the past 30 years of “evolutionary developmental biology” (Evo-Devo), which resolves this problem.  (Sean Carroll has provided some of the best surveys of this research.) 
The question is how to explain the remarkable diversity of animal life forms, and particularly, how to explain the diversity of animal species from ancestral species. We might assume, as Gelernter does, that the diverse forms of animal bodies must arise from radically different genes. So, for example, we might think that the wing of a fly and the arm of a human being require major genetic mutations. In fact, however, the "tool kit genes" for building animal bodies are remarkably similar across all animals. This became apparent when the human genome project showed that human beings have only about 22,000 genes, which is about the same number as other animals.

The differences between animal species come not from differences in their "tool kit genes" but differences in their "genetic switches," which are devices in DNA that tell tool kit genes when, where, and how to act. The gene controlling the formation of a fly's wing is the same as the gene controlling the formation of a human arm. The difference arises during embryonic development as regulatory genes turn the other genes on and off at different times and places in the body.

The beauty of this explanation is that it allows us to explain the origin of new species. Small changes in the timing and pace of these genetic switches can lead to the evolutionary development of new species. So, for example, a fish with fins can evolve into a fish with primitive legs for crawling onto land, when small changes in the genetic switches move from creating fins to creating legs.

This same evolutionary mechanism can explain what makes us uniquely human, with our human capacities for thinking, feeling, and acting. Our human uniqueness depends on the uniqueness of our brains in their size and complexity. The evolution of those brains from smaller and simpler primate brains could arise from evolutionary changes in the genetic regulation of the development of primate brains and nervous systems.

As a consequence of that evolution of the brain, we human beings can debate the truth of Darwinian science and of alternatives like intelligent design theory and scientific creationism.  If we use our brains properly, we can see through the specious arguments against Darwinian evolution, like those offered by Gelernter.
I have written a series of posts on the evidence for evolution (herehere, and here.)

Tuesday, May 14, 2019

Bees Know Nothing: The Evolutionary Psychology of Zero and Plantinga's Evolutionary Argument Against Naturalism




                             Alvin Plantinga's Evolutionary Argument Against Naturalism

I have written some posts answering Plantinga's evolutionary argument against naturalism (here and here).  Plantinga claims that the theistic doctrine of the human mind created by God in His image provides the necessary support for the validity of human thought, including the validity of natural science.  If we embrace Naturalism--the view that nothing exists except Nature, and so there is no God or nothing like God (like Plato's Idea of the Good)--we are caught in self-contradiction: if human thought originated not from a divine Mind but from the irrational causes of Nature, then we cannot trust our minds as reliable sources of true beliefs, and thus we cannot trust our belief in Naturalism as being true.  Naturalism thus destroys itself by destroying the rationality of believing in Naturalism, or anything else.  Insofar as science--including evolutionary science--depends on the validity of human thought, and insofar as theism is the indispensable support for trusting in the validity of human thought, science is not only compatible with theism, science depends upon theism.

As I have argued, the weak link in Plantinga's argument is his assumption that the evolutionary natural selection of the mind for adaptive behavior is completely unrelated to true beliefs.  He argues that natural selection rewards adaptive behavior and punishes maladaptive behavior.  But natural selection does not care about the truth or falsity of an animal's beliefs.  If beliefs produce adaptive behavior, they will be favored by natural selection regardless of whether the beliefs are true or false.  Therefore, he infers, the evolution of adaptive behavior in our prehistoric ancestors did not guarantee or even make it probable that our cognitive faculties would be reliable in generating mostly true beliefs.  For all we know, we could have naturally evolved for being in a state of complete and perpetual delusion.

Against this line of reasoning, I have argued that the evidence of evolutionary history suggests that evolution produces cognitive faculties that are reliable but fallible.  The mental abilities of animals, including human beings, are fallible because evolution produces mental adaptations that are good enough (for survival and reproduction) but not perfect, and this results in the mental fallibility that is familiar to us.  But despite this fallibility, the mental faculties of animals cannot be absolutely unreliable or delusional.

Plantinga concedes this point when he says that in the evolution of animals, "adaptive behavior requires accurate indicators."  So, for example, a frog must have sensory equipment that allows him to accurate detect flies so that he can catch them with his tongue.  A frog with a brain prone to put him into a completely delusional view of the world around him would not survive and reproduce.

Another good example of the adaptive value of "accurate indicators" is the waggle dance of honey bees.  The accuracy of the bee's waggle dance in communicating with other bees shows the capacity for natural evolution--even without any divine guidance--to produce animal cognition and communication that gives the animal an accurate--even if fallible--representation of the world as it pertains to the needs of the animal.

Last year, we saw another example of this from the honey bees when scientists published research showing that bees have some knowledge of arithmetic as even including the concept of zero, which is a difficult concept even for human beings as indicated by the fact that some human civilizations have not had the concept of zero as a number.  The difficulty of this concept should be clear: How can "nothing" be "something"?  How can the absence of quantity be quantifiable or countable?

The scientists testing bees for their number sense devised a simple but clever experimental procedure (Howard et al. 2018; Nieder 2018).







Two groups of 10 bees each were lured to a rotating screen with four panels showing different numbers of black shapes.  Half of the bees were rewarded with a sugar solution for flying to the display showing a greater number of items, while the other half were rewarded for flying to the display showing a lesser number of items.  The bees who were taught the "less than" rule were then tested with some panels having multiple items and others being blank.  Most of the bees flew to the blank panels, suggesting that they somehow understood that the blank panel was "less than" the panels with one or more shapes.  This seemed to show some understanding of the concept of zero.

Until about 50 years ago, scientists generally assumed that the capacity for counting was uniquely human.  But then experiments showed that crows and ravens could carry out simple numerical tasks.  And now there is plenty of evidence that many different species of animals have some number sense, although they do not have the human capacity for comprehending mathematical symbolism.

In humans and other primates, the core areas of the brain for processing numerical quantity are in the left and right parietal lobes and the left frontal lobe (Butterworth et al. 2017; Butterworth 2017).  The abnormal development of the parietal lobes is associated with dyscalculia, a congenital disability in learning about numbers and arithmetic (Butterworth et al. 2011).  Given the small size of the bee brain--about the size of a sesame seed--it is remarkable that bees have any capacity for counting at all.


That such a wide range of species have some number sense suggests that this is a case of convergent evolution of numerical capacity.  Different species that are very distant from one another phylogenetically have converged on the same adaptive solution to computational problems posed by their socioecological environments: being able to count the number of items in a set has been favored by natural selection because this mental capacity has enhanced the chances of survival and reproduction.

This, then, is another illustration of how the evolutionary adaptation of animal minds really does require "accurate indicators" of the world, and so Plantinga is wrong in assuming that a natural process of evolution unguided by the Mind of the Creator could never produce minds capable of generating true beliefs about the world.

But, still, the claim that bees understand the concept of zero is puzzling.  After all, doesn't the fact that the concept of zero has appeared only recently in some human civilizations suggest that conceptualizing numbers is a cultural invention rather than a purely biological activity, and that this depends on a uniquely human capacity for symbolic abstraction?

That will be the question for my next post.


REFERENCES

Butterworth, Brian, et al. 2011. "Dyscalculia: From Brain to Education." Science 332 (27 May): 1049-1053.

Butterworth, Brian, et al. 2017. "Introduction: The Origins of Numerical Abilities." Philosophical Transactions of the Royal Society B 373: 20160507.

Howard, Scarlett R., et al. 2018. "Numerical Ordering of Zero in Honey Bees." Science 360 (8 June): 1124-1126.

Nieder, Andreas. 2017. "Number Faculty Is Rooted in Our Biological Heritage." Trends in Cognitive Sciences 21 (June): 403-404.

Nieder, Andreas. 2018. "Honey Bees Zero in on the Empty Set." Science 360 (8 June): 1069-1071.

Monday, May 06, 2019

The Chimpanzee Politics of the Mueller Report, Impeachment, and Trump's Mininum Winning Coalition

The debate over whether the Mueller Report justifies Trump's impeachment should remind the readers of this blog of how the power of an American president resembles the dominance of an alpha male chimpanzee in depending on a minimum winning coalition.

No ruler--either among humans or among chimps--can rule alone.  To win and hold power, every ruler requires a minimum coalition of powerful people who are loyal to him.  When a ruler is abandoned by his loyalists, he loses his power.  The only difference between a dictator and a democratic leader is the size of the loyal coalition.  A dictator depends on a small coalition.  A democratic leader depends on a larger coalition.  But in any case, the dominant coalition is less than the whole community.

The dominance of an alpha male chimpanzee depends on the support of a coalition of high-ranking males, perhaps combined with some support from the high-ranking females.  The overthrow of a dominant male chimp can come either through violence or non-violent resistance.  The assassination of the alpha male chimp is extremely rare.  Scientists have observed this only a few times.  Usually, the challenge to the alpha male comes from bluffing displays that only threaten violence.  Although chimps will kill other chimps in war with other outside groups, within the group fighting usually ends without fatal injuries, as one side submissively surrenders to the other.

Similarly, human rulers are overthrown when they lose the support of their winning coalition, and this overthrow can come either through violence (sometimes including assassination) or through non-violent resistance.  So, for example, in Venezuela today, the political drama is over whether Nicolas Maduro can retain the loyalty of a few hundred or a few thousand military people who constitute his minimum winning coalition, and part of the battle depends on the attempts of the non-violent resistance movement of protestors who are trying to persuade the military to desert Maduro.  If he loses, he could be killed, or he could resign and leave the country.

Under the U.S. Constitution, Trump's alpha male dominance depends on a minimum winning coalition that is defined in two ways--enough electoral votes in the Electoral College to win the presidency and enough support in the Senate to avoid impeachment.  In the 2016 election, Clinton won the popular vote by 2.8 million votes, a margin of 2.1%.   Trump won only 46.1% of the popular vote.  And since only 60% of the eligible voters voted in 2016, Trump won only 27.6% of the eligible voters!  Still, Trump won the electoral college by 304 to 228.  Clinton lost the Electoral College because of the low turnout of Democratic voters in swing states like Wisconsin, Michigan, and Pennsylvania.  What this illustrates dramatically is that the minimum winning electoral coalition for electing a president is often a tiny minority of the electorate.

But then once he has won alpha male dominance, a president must avoid losing it by being thrown out, and someone with such a small winning electoral coalition as Trump is particularly vulnerable, as indicated by the fact that impeachment has been a looming threat from the day of his inauguration.  In this way, Trump is like Luit, who became the alpha male chimp in the group observed by Frans de Waal in Chimpanzee Politics.  Yeroen had been the alpha male until he was overthrown by Luit.  But then once Yeroen formed a coalition with Nikkie, which won the support of the females, Luit fell from power, and Nikkie became the alpha male.  Eventually, Luit returned to power, but finally he was assassinated by Nikkie and Yeroen.

Throughout much of European history, kings often lost power by being killed.  In England, the House of Commons could vote for impeaching royal officials, and then a trial could be held in the House of Lords.  But the monarch was above the law and could not be impeached, or even tried for any crime.  When Charles I was tried before the Rump Parliament of the New Model Army in 1649, he denied that they had any legal power to indict him.  He argued: "no earthly power can justly call me (who is your King) in question as a delinquent . . . no learned lawyer will affirm an impeachment can lie against the King."  Nevertheless, the Rump Parliament convicted him of tyranny, and he was beheaded.

After their Declaration of Independence in 1776, the American colonists extended the impeachment power so that their new state governors could be impeached by the legislature for "offending against the State, either by maladministration, corruption, or other means" (Virginia Constitution of 1776).  In the Constitutional Convention of 1787, some of the delegates said that a congressional power to impeach the president was "rendered indispensable by the fallibility of those who choose, as well as by the corruptibility of the man chosen" (George Mason).  Some of the delegates were especially worried about likelihood that the president would be corrupted by foreign governments, and impeachment would be the only way to remove a president who had colluded with foreign powers.  (This material can be found at the website for The Founders Constitution.)

The Constitution gives the sole power of impeachment to the House of Representatives and the sole power to try impeachment to the Senate, in which conviction would require two-thirds of the Senate.  So, today, that means that at least 67 Senators must vote for impeachment for a conviction.  Consequently, as long as at least 34 Senators vote against impeachment, this constitutes the minimum winning coalition for the president to stay in office.  Today, there are 41 Republican Senators; and so conviction of Trump would require that all the Democratic Senators and at least 8 of the Republican Senators vote for his impeachment.  This seems unlikely, given the partisan commitments of the Republicans to Trump.

This requirement for a supermajority in the Senate for impeachment is one reason why impeachment has been so rare.  Only two presidents have been tried (Andrew Johnson and Bill Clinton), and neither of these were convicted in the Senate.

This goes against the expectation of the Constitutional framers that the impeachment of presidents would be a frequent response of the Congress to presidential "maladministration," "corruption" (such as collusion with foreign governments), and "abuse of power" (such as usurping the powers of Congress).  Responding to those critics of the Constitution who thought the president could become an elected monarch, Alexander Hamilton argued in Federalist Number 69 that the president was unlike the British monarch in crucial ways--one being that the president would be liable to impeachment, while the British monarch was not subject to impeachment.  So, to the extent that presidents do not have to worry about impeachment, the presidency becomes monarchic.

Another reason for the rarity of impeachment is that the only impeachable offenses are "Treason, Bribery, or other High Crimes and Misdemeanors," and many people--including many in the Congress--have assumed that this requires proof "beyond a reasonable doubt" that the president has committed some indictable crime.  Any careful study of the Constitution and of the pertinent documents from the founding shows that this is incorrect, because "High Crimes and Misdemeanors" was understood as "maladministration" or serious "abuse of power," which was a political judgment rather than a criminal judgment.  The standard of evidence for such a political judgment is not "beyond a reasonable doubt" but rather "preponderance of the evidence" or more-likely-than-not.

By giving the sole power of impeachment to the House of Representatives, the Constitution gives the House the sole power to investigate the conduct of the president to determine whether he should be impeached.  But the House has created confusion by allowing for the appointment of a "special prosecutor" by the Department of Justice to investigate misbehavior by the president.  The first problem this creates is that the appointment of a "prosecutor" suggests the normal standards of criminal prosecution, the same standards that govern any of the U.S. attorneys in the Department of Justice.  This obscures the point that impeachment requires a political judgment by the Congress of abuse of power rather than a regular judicial judgment of criminality.  The second problem is that when Congress allows the Department of Justice to appoint a special prosecutor to investigate presidential conduct subject to impeachment, this puts what should be a congressional investigation under the supervision of the Executive Branch and thus subject to the president's power to dismiss executive officers under his power.

We have seen both of these problems manifest in Robert Mueller's work as special counsel to investigate the collusion of the Trump campaign in 2016 with the Russians and Trump's obstructions to the investigation.  Mueller conducted what should have been a purely congressional investigation under the supervision of the Department of Justice.  This exposed Mueller to being dismissed at any time during his investigation.  And then once he gave his report to the Attorney General, the Attorney General was free to act as Trump's lawyer in suppressing anything in the report that Trump might want to cover up.

The other problem is that Mueller was given two contradictory assignments in his original appointment by Acting Attorney General Rod Rosenstein on May 17, 2017.  First, he was authorized to investigate "any links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump."  Second, he was also "authorized to prosecute federal crimes arising from the investigation of these matters."

The standards of evidence for these two kinds of investigation are not the same.  First, deciding whether there were any links between the Trump campaign and the efforts of the Russian government to interfere in the U.S. elections in favor of Trump is a matter of deciding whether the weight of the evidence supports a conclusion that such links were very likely.  But, second, deciding whether these links were such as to justify prosecution as federal crimes required evidence "beyond a reasonable doubt," which is the high standard for criminal convictions.

The Mueller Report makes it clear that there was compelling evidence for links between the Trump campaign and the Russian government in the 2016 election, and this would justify the Congress in impeaching Trump.  But the Report also makes it clear that these links did not justify criminal charges.  So, at one point, the Report declares: "while the investigation identified numerous links between individuals with ties to the Russian government and individuals associated with the Trump Campaign, the evidence was not sufficient to support criminal charges" (vol. 1, p. 9).  Similarly, on the question of whether Trump was guilty of obstruction of justice in impeding the special counsel's investigation, the Report concluded: "while this report does not conclude that the President committed a crime, it also does not exonerate him" (vol. 2, p. 8).  Here, again, the compelling evidence that Trump tried to obstruct the investigation could justify impeachment by the Congress, even though there was not evidence "beyond a reasonable doubt" to justify conviction for a federal crime.

Consequently, it was easy for Attorney General Barr, acting as Trump's personal lawyer, in his letter of March 24 to Congress, to quote the Mueller Report as saying that "the investigation did not establish" that the Trump campaign "conspired or coordinated with the Russian government in its election interference activities."  And Trump could shout "No Collusion!" on his Twitter account.  But then Mueller, in his letter to Barr on March 27, could rightly complain that Barr's letter "did not fully capture the context, nature, and substance of this Office's work and conclusions," and thus it sowed "public confusion about critical aspects of the results of our investigation."

The ultimate source of this "public confusion," however, is the Congress's failure to assert its sole authority over impeachment--not to be shared with "special prosecutors" in the Department of Justice--as well as the Congress's failure to insist that impeachment is a political judgment of the Congress and not a legal judgment of prosecutors or the courts.

These failures of the Congress to properly exercise its impeachment power have rendered that power largely ineffective in checking the propensity of the president to become an elected monarch.  But there is also a failure here on the part of the constitutional framers: by requiring a supermajority of the Senate for an impeachment conviction, the framers lowered the minimum winning coalition for the president to 34 Senators obstructing impeachment.  If the framers had required only a simple majority of the Senate for an impeachment conviction, impeachments would have been more frequent.  Certainly, Trump's impeachment would have been much more likely if only 51 Senators were required to vote for impeachment.

As long as Trump has a minimum winning coalition among the Republican Senators to avoid impeachment, the only challenge to his alpha male dominance will be the next presidential election.  As someone who was elected with only 46% of the votes and 27% of the eligible voters, he is vulnerable to challengers.  Just as Luit was overthrown by a coalition of Yeroen and Nikkie, so that Nikkie could become alpha male, a candidate who could mobilize many of the eligible voters who did not vote in the 2016 presidential election could defeat Trump.  The stunning defeat of so many Trump candidates in the 2018 mid-term elections suggests that once the anti-Trump voters are motivated to vote, Trump cannot attain the minimum coalition for winning.  Moreover, that Trump is not impeached might actually be desirable if his running for reelection leads to a catastrophic defeat for the Republican Party that might then bring a realignment of the political parties and a new party system.

Some of my posts on the chimpanzee politics of a minimum winning coalition and Trump's chimpanzee personality can be found herehereherehereherehereherehere, and here.

Saturday, May 04, 2019

The Neural Circuitry of Parental Care in Mice and Humans

At the end of my last post, I said that Paul Zak's studies of oxytocin's influence on human social behavior were too shallow, because they did not reveal the complexity of exactly where, when, and how oxytocin acts in the brain.  This is an important point, because biological explanations of human life are often criticized for being crudely simplistic in their reductionism, and Zak's exaggerated claims for oxytocin as the "moral molecule" seem to confirm that charge.  Actually, good biological explanations for animal behavior must always be complicated in that there are always multiple causes interacting in complex ways at multiple levels of explanation.

As an example, consider how oxytocin contributes to the explanation of parental care as one of the 20 natural desires that I first listed in Darwinian Natural Right, published in 1998. In my chapter on "Parent and Child," I agreed with biological anthropologists like Aristotle, Charles Darwin, and Sarah Hrdy who argue that the social nature of human beings is a natural extension of the maternal care of children.  The maternal love for children is the model for, and natural origin of, all forms of love, friendship, and affiliative behavior.

The Darwinian biology of animal behavior can support this conclusion by explaining parental care at four levels of analysis: (1) functional causes, (2) phylogenetic causes, (3) developmental causes, and (4) immediate causes.  Human parental care has a functional cause in that it has been favored by natural selection as serving the survival and reproductive success of human beings.  It has a phylogenetic cause in that it has emerged from an evolutionary history that human beings share with other primates and other mammals.  It has a developmental cause in that the desire to care for children emerges as an outcome of the normal development of children into adults.  And, finally, it has immediate causes in that it arises as a response to physical and social stimuli in the environment that elicit processing in the neural circuitry in the brain that produces parental caregiving behavior.

A full explanation of parental care--and of all the other natural desires--would have to move through these four levels, with each level requiring a complex explanation.  Although the complexity here is so great that we will probably never achieve full scientific explanations, we can still make progress.

So in my chapter on parental care, I spoke of oxytocin and vasopressin as part of the immediate causes of parental care.  At least in prairie voles, oxytocin promotes the female's care of her offspring and bonding to her mate, while vasopressin promotes the male's paternal care and pair-bonding.

But now, 20 years after the publication of Darwinian Natural Right, we know much more about the biological causality of parental care, in which oxytocin and vasopressin act only through complex interactions with many other factors.  Last year, a team led by Catherine Dulac at Harvard University published the first description of the neural circuitry in the brains of mice supporting parental care (Kohl et al. 2018; Kohl 2018).  A summary of their study can be found here.

Dulac's team offered this proposed model for how galanin-expressing neurons in the medial preoptic area (MPOA) orchestrate components of parental behavior.  Abbreviations: PAG, periaqueductal gray; VTA, ventral tegmental area;  MeA, medial amygdala; PVN, paraventricular nucleus of the hypothalamus; AVP, vasopressin; OXT, oxytocin; CRH, corticotropin-releasing hormone.  In this model, oxytocin produced in the PVN of the hypothalamus plays only a small part in a complex circuitry.

Medial Preoptic Area (MPOA) of the Hypothalamus in the Mouse Brain

Medial Preoptic Area of the Hypothalamus in the Human Brain


Despite the uniqueness of the human brain, it shows similarities with the mouse brain as a result of mammalian evolution, which is why studies of the neural circuitry for parental care in mice can guide studies of the human circuitry for parental care.

In 2014, Dulac and her team found that MPOA neurons expressing the neuropeptide galanin are crucial for parental behavior in both female and male mice.  The question then was how such a small population of neurons--10,000 out of a total of 100 million in the mouse brain--can control such a complex behavior as parental care, which includes a wide repertoire of behavior--retrieving pups to the nest, grooming them, female nursing of them, attentiveness to infant stimuli, diverting attention from nonparental behaviors such as mating.  Moreover, there are differences between males and females.  Virgin male mice typically attack pups, and they engage in parental care only a few weeks after mating with the mother.  By contrast, female mice exhibit maternal caregiving regardless of whether they have pups of their own.

Dulac and her team found that the galanin-producing neurons in the MPOA are at the hub of an integrated circuitry, receiving inputs from about 20 brain areas and sending out projections to a similar number of areas.  They found that different pools of neurons serve distinct elements of parental care.  Some pools control actions such as grooming of pups, so that when the researchers activated these neurons, even virgin males, who normally attack rather than nurture pups, would groom them.  Other pools send signals to the brain's reward center to motivate parental care.  Other pools project to the amygdala, which processes emotion.  Other pools modulate the production of oxytocin, vasopressin, and other hormones in the hypothalamus.  Thus, this circuitry integrates distinct sets of cells to stimulate the behavioral, motivational, emotional, and hormonal changes involved in the parental care of young.

This is all very complex, but it's even more complex when one sees that this is only the level of immediate or proximate causes, and that a full biological explanation of the natural desire for parental care requires understanding not only these immediate causes in the brain, but also the developmental, phylogenetic, and functional causes of parental care.

The complexity increases when one realizes that parental care varies according to differences in the individual personalities of animals and in the cultural history of animal groups.


REFERENCES

Kohl, Johannes. 2018. "Circuits for Care: A Small Population of Hypothalamic Neurons Orchestrates Parenting Behaviors." Science 362 (12 October): 168-69.

Kohl, Johannes et al. 2018. "Functional Circuit Architecture Underlying Parental Behaviour." Nature 556 (19 April): 326-31.

Thursday, May 02, 2019

Paul Zak on Oxytocin as the Moral Molecule for Smithian Liberalism: Where's the Evidence?

I have long been attracted to Paul Zak's argument that the neuropeptide oxytocin provides the evolved biological foundation for both the morality of Adam Smith's Theory of Moral Sentiments and the economics of his Wealth of Nations.  In his book The Moral Molecule, Zak explains this as his eureka moment: "What if oxytocin was, in fact, the chemical signature for that elusive bonding force Smith had called mutual sympathy?  Then, thinking back to my research on the prosperity-enhancing power of trust, I had to laugh.  What if this 'Moral Molecule'--if that's what oxytocin was--is also an essential element in what Smith called the wealth of nations?" (24)

I have written about this in some previous posts (herehere, and here), in which I agreed with much of what Zak argues, but I also pointed out the weaknesses in the empirical evidence that he claims to support his position.  I had to think more about this at the Liberty Fund conference on Sapolsky's Behave, because Zak was one of the discussants, and he criticized Sapolsky for saying that oxytocin has a "dark side"--"Oxytocin, the luv hormone, makes us more prosocial to Us and worse to everyone else.  That's not generic prosociality.  That's ethnocentrism and xenophobia" (Behave, 117).  No, Zak insisted, there is no such "dark side" to oxytocin.

In the context of Zak's general argument, this debate over the neurophysiological influence of oxytocin on behavior raises a question about Smith's moral and economic philosophy: Does the Smithian liberalism of morals and markets require that human beings cooperate with one another indiscriminately and unconditionally as based on a universal humanitarian sympathy, or does in-group bonding and cooperation tend to promote aggressive protection of the in-group from perceived out-group threat?

Oxytocin (OT) is a nine-amino acid neuropeptide and peptide hormone that evolved among mammals to support the birth of offspring, maternal bonding and care of offspring, and sometimes monogamous mating of parents who jointly care for their offspring.  In humans and some other animals, OT seems to be associated generally with emotional bonding, empathy, and trust.  But the interaction of the OT system with other neurophysiological systems and with environmental circumstances is so complicated that it is hard to study, and there is no agreement among scientists as to exactly how and where it works in the brain.  The Wikipedia article on OT is a good summary of the research and the controversies.

Zak was a coauthor of an influential paper published in 2005 in Nature entitled "Oxytocin Increases Trust in Humans."  Their experiment was to have people play the "Trust Game."  Two people are each given some amount of money, say $12.   One person, designated the "investor," can either keep his money or transfer some of it to the person designated the "trustee."  The money transferred is tripled.  So if the trustee has received $8 from the investor, the trustee would then have $36.  The trustee can then either keep all of his money or transfer some of it to the investor.  The trustee who transfers some of his money shows trust in the trustee--trusting that the trustee will not selfishly refuse to share some of his gain.  The trustee who does share some of his money shows his trustworthiness.  Of course, this is designed to mimic the economic gains from trade in market exchanges.  Zak and his colleagues showed that if some players of this game have OT sprayed into their noses before playing the game, and others have a placebo sprayed into their noses, those investors who have received OT will show more trusting behavior in transferring money, although trustees who have received OT do not show a statistically significant higher rate of back transfer than those in the placebo group.

Here's the abstract for their article:
"Trust pervades human societies.  Trust is indispensable in friendship, love, families, and organizations, and plays a key role in economic exchange and politics.  In the absence of trust among trading partners, market transactions break down.  In the absence of trust in a country's institutions and leaders, political legitimacy breaks down.  Much recent evidence indicates that trust contributes to economic, political, and social success.  Little is known, however, about the biological basis of trust among humans.  Here we show that intranasal administration of oxytocin, a neuropeptide that plays a key role in social attachment and affiliation in non-human animals, causes a substantial increase in trust among humans, thereby greatly increasing the benefits from social interactions.  We also show that the effect of oxytocin on trust is not due to a general increase in the readiness to bear risks.  On the contrary, oxytocin specifically affects an individual's willingness to accept social risks arising through interpersonal interactions.  These results concur with animal research suggesting an essential role for oxytocin as a biological basis of prosocial approach behavior" (Kosfeld et al. 2005).
Notice the extraordinary claim here--that the pervasive basis of all social bonding is the trust that can be elicited by oxytocin.  The international publicity about this and later articles about the power of oxytocin for fostering trust, empathy, and affection stirred world-wide excitement about oxytocin as the "love hormone."  People started buying spray bottles of oxytocin to intensify their love lives--oxytocin was linked to orgasms--to help close a business deal, or perhaps to spray up the noses of world leaders to secure world peace.  It was said that when people hug, this creates a surge of oxytocin.  So Zak gave popular lectures and interviews advising people to hug one another at least eight times a day to enjoy the benefits of oxytocin.  He was soon called "Dr. Love."  Zak's charming style is on display in a widely-viewed TED talk.

But then, this orgasmic excitement over oxytocin was deflated in two ways.  First, beginning in 2010, Carsten de Dreu of the University of Amsterdam and his colleagues published a series of papers on oxytocin as promoting xenophobic--in/group versus out/group--behavior (de Dreu et al. 2010, 2011, 2012).  Popular journalists reported this as the "dark side" of oxytocin that Zak and his colleagues had ignored.

The second deflating development in the study of OT, beginning around 2015, was a series of articles by scientists who pointed out that the scientific study of OT was so empirically and theoretically dubious that there was no scientific consensus on exactly when, where, and how OT acted in the brain; nor was their any agreement on the behavioral effects of OT (Nave, Camerer, and McCullough 2015; Shen 2015).  There is very little evidence that intranasal OT crosses the blood-brain barrier and reaches its target tissues in the brain.  Alternatively, researchers have shown correlations between OT-related brain processes and peripheral measures of OT in body fluids (blood plasma, saliva, or urine).  Zak has relied on drawing blood and measuring levels of OT in the blood.  But it is not clear that peripheral OT measures are reliable indicators of what OT is doing in the brain.  Furthermore, the attempts to replicate the finding that OT is connected to trust have largely failed.

I asked Zak about whether there was any research to support his denial of de Dreu's showing of OT being associated with xenophobic Us/Them bias, or what has been called "parochial altruism"--being cooperative with members of one's own group but defensively competitive with those outside one's group.  (I have written about the coevolution of parochial altruism and war here and here.)  Zak responded by citing a recent article that he coauthored with his colleagues (Terris et al. 2018) with the title "Endogenous Oxytocin Release Eliminates In-Group Bias in Monetary Transfers with Perspective Taking."

Here's the abstract for the article:
"Oxytocin (OT) has been shown to facilitate trust, empathy, and other prosocial behaviors.  At the same time, there is evidence that exogenous OT infusion may not result in prosocial behaviors in all contexts, increasing in-group biases in a number of studies.  The current investigation seeks to resolve this inconsistency by examining if endogenous OT release is associated with in-group bias.  We studied a large group of participants (N = 399) in existing groups and randomly formed groups.  Participants provided two blood samples to measure the change in OT after a group salience task and then made computer-mediated monetary transfer decisions to in-group and out-group members.  Our results show that participants with an increase in endogenous OT showed no bias in monetary offers in the ultimatum game (UG) to out-group members compared to in-groups.  There was also no bias in accepting UG offers, though in-group bias persisted for a unilateral monetary transfer [in the dictator game (DG)].  Our analysis shows that the strength of identification with one's group diminished the effects that an increase in OT had on reducing bias, but bias only recurred when group identification reached 87% of its maximum value.  Our results indicate that the endogenous OT system appears to reduce in-group bias in some contexts, particularly those that require perspective-taking [that is, in the UG but not in the DG]" (Terris et al. 2018, 1).
Notice that while the title says that endogenous OT release "eliminates" in-group bias, this is not quite true, because the authors concede that strong group identification supports in-group bias even with an increase in OT.  Notice also that they concede de Dreu's finding by saying that exogenous OT infusion can increase in-group biases in some contexts.  In the article, they say that "studies using exogenous OT often pit an in-group against an out-group by asking people to make decisions that explicitly benefit their group," which shows "that exogenous OT increases the effect of primed group competition by intensifying a situational feature in the experiment" (Terris et al. 2018, 2).

One theory of how OT acts is that it increases the "social salience" of phenomena in the circumstances of action; and if an experiment creates "primed group competition," then increased OT can shine a spotlight on that context of group competition so as to stimulate an in-group bias.  "Social salience is the likely cause of the so-called 'dark side' of OT, namely bias of one's preferences toward in-group members" (Terris et al. 2018, 2).  So, they suggest, there really is a "dark side" to OT, at least in those circumstances where group-against-group competition is prominent.

But then, the authors admit that even in their experiment, where there was no "primed group competition," a high degree of group identification produced a bias towards one's in-group after a surge of OT (Terris et al. 2018, 6-7).

Recognizing this natural human propensity to in-group bias is compatible with Adam Smith's account of how the natural human desire for a mutual sympathy of sentiments supports morals and markets.  Smith knows that we do not feel sympathy (or empathy or trust) indiscriminately and unconditionally for all of humanity.  Rather, our sympathy is stronger for those close to us (our family, our friends, our fellow citizens) than for those far away, those outside our group.  And so, whenever there is any competition between groups, we naturally favor our in-group over any out-group.  Love of one's own is natural.  In The Theory of Moral Sentiments, Smith writes:
"Every independent state is divided into many different orders and societies, each of which has its own particular powers, privileges, and immunities.  Every individual is naturally more attached to his own particular order or society, than to any other.  His own interest, his own vanity, the interest and vanity of many of his friends and companions, are commonly a good deal connected with it.  He is ambitious to extend its privileges and immunities.  He is zealous to defend them against the encroachments of ever other order or society" (VI.ii.7).
This natural in-group bias is manifest in Smith's Wealth of Nations in his insistence that the first duty of government is military force to defend society against the violence and invasion of other societies (V.i).

Darwinian scientists can now explain this natural propensity to xenophobia and war as arising from the evolution of morality through group selection in war.  Darwin himself saw this in The Descent of Man: "an advancement in the standard of morality will certainly give an immense advantage to one tribe over another.  A tribe including many members who, from possessing in a high degree the spirit of patriotism, fidelity, obedience, courage, and sympathy, were always ready to aid one another, and to sacrifice themselves for the common good, would be victorious over most other tribes; and this would be natural selection" (2004, 157-58).  Despite the continuing controversy over evolutionary group selection, many evolutionary scientists see evidence that Darwin was right about the evolutionary importance of group selection through war (Choi and Bowles 2007; Bowles and Gintis 2011).  That's why I have included the natural desire for war as one of the 20 natural desires of our evolved human nature (Arnhart 1998).

If group selection has favored an evolved propensity for cooperating within one's group to compete with out-groups, then, de Dreu has argued, one might explain OT as part of a neurophysiological system to motivate a "tend and defend" response--trust and cooperation within the group and defensive aggression against competing out-groups.  One might predict this from the fact that the ancient evolutionary roots of oxytocin are connected to not only the birth of offspring but also to the group-wide care and defense of offspring.  Thus, de Dreu observes:
"findings here reveal that oxytocin-motivated non-cooperation is driven by the desire to protect vulnerable in-group members, even when immediate self-interest is not at stake.  The male participates in our study behaved as the proverbial Mamma Bear who, while not being immediately in danger herself, lashes out against predators threatening her cubs.  As predicted, such protective behavior emerged especially when participants received oxytocin rather than placebo" (De Dreu et al. 2012, 5).
Remarkably, as already indicated, Zak and his colleagues don't dispute this claim, although they stress that this in-group biased behavior associated with OT arises only in the context of "primed group competition" or when group identification is strong.

It is also remarkable that Zak and his colleagues don't dispute the claim of Nave et al. (2015) and others that the research on the connection between OT and trust in humans has not been replicated.  Ernst Fehr, who led the original Nature study published in 2005, has admitted: "What we're left with is a lack of evidence.  I agree that we have no robust replications of our original study, and until then, we have to be cautious about the claim that oxytocin causes trust" (quoted in Yong 2015

The fundamental problem here is that the "neuroeconomics" research of Zak and others is too shallow to reveal exactly when, where, and how oxytocin modulates neural circuits in the brain to promote social cognition and social behavior.  Spraying oxytocin into people's noses or measuring oxytocin in blood samples does not tell us what oxytocin is doing in the brain.  For deeper research into the neural circuitry of oxytocin, we need to look to the research on oxytocin in the brains of non-human animals, such as Robert Froemke's studies of how oxytocin in the brains of female mice help them to care for and protect their pups (Marlin et al. 2015; Mitre et al. 2016; Valtcheva and Froemke 2019).  But then combining this with research on humans to infer how oxytocin acts in human brains will be difficult.  One way to do this is through neuroimaging studies of how OT works in live human brains (Ma et al. 2016).


PAUL ZAK'S RESPONSE

Paul Zak has sent me an email message about this post.  He has allowed me to post this passage from his message:

"Here's the point I wanted to make: I've spent almost 20 years studying oxytocin and developed several protocols to do this that the scientific community uses.  If a single paper of mine does not replicate, I am not concerned, because science works on consensus.  The vast majority of my work has been replicated and extended by others.  For example, as is typical in science (vs. economics), when I give seminars, I present 10 years or more of research showing a confluence of findings. Camerer et al. wrote one paper on oxytocin.  This does not concern me."


REFERENCES

Arnhart, Larry. 1998. Darwinian Natural Right: The Biological Ethics of Human Nature. Albany: State University of New York Press.

Bowles, Samuel, and Herbert Gintis. 2011. The Cooperative Species: Human Reciprocity and Its Evolution. Princeton: Princeton University Press.

Choi, Jung-Kyoo, and Samuel Bowles. 2007. "The Coevolution of Parochial Altruism and War." Science 308 (October 26): 636-40.

Darwin, Charles. 2004. The Descent of Man. 2nd ed. New York: Penguin.

De Dreu, Carsten, et al. 2010. "The Neuropeptide Oxytocin Regulates Parochial Altruism in Intergroup Conflict Among Humans." Science 328 (11 June): 1408-1411.

De Dreu, Carsten, et al. 2011. "Oxytocin Promotes Human Ethnocentrism." Proceedings of the National Academy of Sciences 108 (January 25): 1262-1266.

De Dreu, Carsten, et al. 2012. "Oxytocin Motivates Non-Cooperation in Intergroup Conflict to Protect Vulnerable In-Group Members." PLOS ONE 7, issue 11 (November): e46751.

Kosfeld, Michael, et al. 2005. "Oxytocin Increases Trust in Humans." Nature 435 (2 June): 673-76.

Ma, Yina, Simone Shamay-Tsoory, Shihui Han, and Caroline F. Zink. 2016. "Oxytocin and Social Adaptation: Insights from Neuroimaging Studies of Healthy and Clinical Populations." Trends in Cognitive Sciences 20 (2): 133-45.

Marlin, Blanca, et al. 2015. "Oxytocin Enables Maternal Behaviour by Balancing Cortical Inhibition." Nature 520 (23 April): 499-504.

Mitre, Mariela, et al. 2016. "A Distributed Network for Social Cognition Enriched for Oxytocin Receptors." The Journal of Neuroscience 36 (8): 2517-2535.

Nave, Gideon, Colin Camerer, and Michael McCullough. 2015. "Does Oxytocin Increase Trust in Humans? A Critical Review of Research." Perspectives on Psychological Research 10 (6): 772-89.

Shen, Helen. 2015. "The Hard Science of Oxytocin." Nature 522 (25 June): 410-12.

Terris, Elizabeth, et al. 2018. "Endogenous Oxytocin Release Eliminates In-Group Bias in Monetary Transfers With Perspective Taking." Frontiers in Behavioral Neuroscience 12 (March): article 35.

Valtcheva, Silvana, and Robert C. Froemke. 2019. "Neuromodulation of Maternal Circuits by Oxytocin." Cell and Tissue Research 375: 57-68.

Yong, Ed. 2015. "The Weak Science Behind the Wrongly Named Moral Molecule." The Atlantic, November 13.

Zak, Paul. 2012. The Moral Molecule: The Source of Love and Prosperity. New York: Dutton.