Overview: An informative exploration of the role testosterone plays in sex differences and biology. The book is strongest when it is centred on the science and weakest when Carole Hooven expresses her personal and political views. Fortunately, the former makes up most of this book.

Testosterone is the third and final book of an unintended trilogy I’ve read recently which could be called ‘The Science of Sex Differences’. The other two books in this ‘trilogy’ are the ones I’ve reviewed on this blog: Bad Men by David Buss and The Ape That Understood the Universe by Steve Stewart-Williams.

Like Bad Men, I wasn’t planning on reading and reviewing Testosterone but I was interested after seeing it mentioned in discussions on sex differences on Twitter. Steve Stewart-Williams also praised the book and, since I mostly enjoyed his own work, I thought Testosterone was worth looking into.

Carole Hooven is a lecturer in the Department of Human Evolutionary Biology at Harvard University which is also where she studied her PhD in sex differences and testosterone.

Chapter 1: The Controversy Surrounding Testosterone

In 1999, Carole Hooven spent 8 months studying chimpanzees in the Kibale forest in Uganda after applying for a program run by primatologist Richard Wrangham, whose work fascinated her. In January of that year, she witnessed an incident that would become the subject of an article in Time magazine a few years later. A male chimp, named “Imoso”, who was the “mayor” of a “town” called Kanyawara, attacked a female named “Outamba” with a large stick. Carole Hooven told Richard Wrangham what had happened and was told that she was the first researcher to observe a wild animal using a tool as a weapon against its own species. The stick was later recovered by field assistants and Dr. Hooven saw it again in 2002 as explored in the Time article ‘The Wife Beaters of Kibale.’ I managed to find the actual article which can be seen below and you can read the article here.

Dr. Hooven noted the contrasting behaviour between the male and female chimps: the female chimps were relatively peaceful whereas the male chimps were more aggressive and obsessed with hierarchy. While male chimps are not violent all of the time, they will use violence for several purposes, such as to show dominance, fight over a sexual opportunity or to make a female more sexually compliant in future. This last example may have been the reason that Imoso attacked Outamba.

From this and other experiences, the author “longed the understand men” and began work on her PhD on testosterone.

According to Dr. Hooven:

“Testosterone is present in our blood in minute quantities. Both sexes produce it but men have ten to twenty times as much as women.”

Testosterone in an androgen hormone, with ‘andro’ meaning “man” and ‘gen’ meaning “generating.” Possibly to avoid the writing becoming cumbersome, the book commonly refers to testosterone as “T” which I will do as well. Although both sexes have T, we commonly associate it with men than we do with women. Dr. Hooven notes:

“If the Y chromosome is the essence of maleness, then T is the essence of masculinity, at least in the popular mind.”

The association with T and masculinity is reflected in political debates, such as the contrasting perceptions towards Donald Trump. Commentators on the political Left believed Trump had too much T whereas those on the political Right thought that mainstream conservatives who opposed Trump had the opposite problem:

“According to the left-wing Huffington Post, Trump’s presidency is “testosterone-fueled”, making it “an extremely dangerous one” that could lead to war. According to the right-wing American Spectator, the problem is not too much T, but too little, among some prominent conservatives.”

It’s interesting that Joe Biden’s left-wing and presumably less “testosterone-fueled” presidency has coincided with the disastrous withdrawal of troops from Afghanistan and Russia invading Ukraine, both of which make the world a more dangerous place.

From a biological perspective, the role of T is thought to help increase male’s reproductive output by affecting anatomy, physiology, behaviour and energy which is directed towards competing for mates. T also plays an important role in aggression, which can be seen in the difference in violence and crime rates between men and women. The author writes that men are:

“responsible for around 70 percent of all traffic fatalities and 98 percent of mass shootings in the United States, and worldwide commit over 95 percent of homicides and the overwhelming majority of violent acts of every kind, including sexual assault.”

Like I wrote in my review of The Ape That Understood the Universe, which also describes this difference between the sexes, I believe women’s relationship with crime and violence is more complicated than we like to think, but I’ll go into more detail about this later on in this review.

As the reader is no doubt aware, talking about sex differences and the effects of T can be controversial. Some academics and researchers have expressed scepticism towards some of the findings about T. For example, Rebecca Jordan-Young, a ‘gender studies’ scholar, and Katrina Karkazis, an anthropologist, wrote a book called Testosterone: An Unauthorized Biography, in which they attempt to debunk, in their minds, some of the claims made about T.

Carole Hooven also describes another controversial idea that is debated in academia, the evolution of sexual behaviours like rape. Randy Thornhill put forward a theory suggesting that males across many species will rape females if they are unable to provide resources and may be one reason why males tend to be larger than females in humans. Dr. Thornhill and his theory will be familiar to anyone who has read Part 3 of my review of David Buss’ book Bad Men. Dr. Hooven admits to being “triggered” when she first heard about Randy Thornhill’s theory as an undergraduate. At the time, she called him an “asshole” but was told by her professor to respond to the data and argument without getting emotional:

“It wasn’t an easy process. My emotions didn’t evaporate. And I’m still not thrilled with what strikes me as tone-deaf writing about a sensitive topic. But I learned that I could evaluate the evidence for an upsetting hypothesis on its merits; that by itself was empowering.”

This quote illustrates that Carole Hooven is an academic who believes in objective truth and knows what they are supposed to do when debating controversial ideas: to try and look at the facts without emotions and personal feelings from interfering too much. She did, in fact, later meet Randy Thornhill and said he seemed like a nice guy.

Dr. Hooven has incorporated into her course other individuals who have had caused controversy from talking about sex differences. In 2006, Lawrence Summers ended up resigning from his position as President of Harvard following a speech he gave where he suggested that women’s underrepresentation in science courses was partly due to “intrinsic aptitude, and particularly of the variability of aptitude” between the sexes. A decade later, James Damore lost his job at Google for suggesting that sex differences in preferences are one explanation for the lack of gender parity at the company and their aim to achieve parity was “misguided.” During both of these controversies, Dr. Hooven realised she was “on the wrong side of the divide” for embracing the scientific information behind both men’s claims.

Here Carole Hooven also explores the “feminist backlash” towards claims of sex differences and expresses some sympathy towards this sentiment:

“the fact is that women have good reason to be suspicious of “biological” explanations of sex differences. Scientists and philosophers – mostly men – have a history of confidently expounding on the alleged biological basis of women’s inferiority.”

While I admire Dr. Hooven’s commitment to objective truth and scientific inquiry, this quote seems, to me, to be an example of ‘feminist thinking’ affecting the author’s viewpoint. Why should we assume that whatever male scientists and philosophers wrote about women in the past was simply chauvinism and ignorance? We can certainly debate about particular claims men may have historically made about women, but it is important to understand the context behind those claims as well.

Similarly, the book presents Charles Darwin’s claim about “man’s attaining to a higher eminence, in whatever he takes up, than can woman – whether requiring deep thought, reason, or imagination, or merely the use of the senses and hands.” This can obviously sound offensive to our modern sensibilities, but the observation is accurate in the sense that men are more likely than women to be over-represented in exceptional achievements and endeavours. Of course, it can also be said that men are over-represented in many unfavourable ways as well.

In response to Darwin’s claim, Dr. Hooven writes:

“From our more enlightened perspective, we can create an obvious alternative hypothesis: women are simply being held back by constraints imposed primarily by society rather than by their naturally inferior mental capacity.”

Carole Hooven could be accused here of doing the same thing as those who opposed Lawrence Summers and James Damore: rejecting a claim about sex differences on the basis that she personally dislikes and disagrees with it. I suppose I could be accused of doing this as well if you’ve read any of my previous posts where I have disagreed with an apparent sex difference. However, I try to acknowledge any bias on my part and explain what I disagree with and why. I don’t always share the author’s opinion on certain sex differences in this book either, which will come up later on in this review. The “more enlightened perspective” line is similar to people who claim to be “on the right side of history” or argue that certain words or ideas are unwelcome because “it’s [the current year].” Why should we assume that what we think is superior to what people thought in the past or assume that people in the future will agree with us?

Feminist opposition towards sex differences and how hormones like T may influence those differences is motivated in part by fears that these facts will be used to “uphold patriarchy.” Books such as Testosterone Rex by Cordelia Fine and The Gendered Brain by Gina Rippon which challenge findings about sex differences are motivated by this fear. Carole Hooven makes a good point here:

“In general, if you find a hypothesis distasteful, a red flag should immediately go up: there is a clear and present danger that you will discount the evidence that supports the hypothesis.”

Like David Buss in Bad Men, Carole Hooven believes that understanding the science behind behaviour, such as the effects of T, can help us to deal with the “darker parts” of human nature.

Chapter 2: A History of T: Experiments, Cultural Practices and Discovery

The second chapter in this book is my favourite as it covers two subjects I particularly like: history and biology. Specifically, this chapter explains how the effects of T were known for millennia before its discovery and isolation in the 20th Century. This was because humans could separate the primary source of T from the body of a male human or animal without killing them and then observe the changes that followed from this. To put it bluntly, cutting off the testicles rids the body of its main supply of T. Although humans weren’t aware of the hormone, or even the idea of hormones in general, they knew that performing this procedure had dramatic effects.

Aristotle, for example, observed that castrated male birds “cease to crow” and “forego sexual passion” following the procedure and birds castrated when young never develop these behaviours. Boys who were castrated before puberty never grew facial hair or experienced voice changes and male pattern baldness in adulthood. “What would be the point in castrating boys and men, other than as a cruel experiment?”, you may well ask. It was often done to punish enemies, rapists or prevent the mentally unfit from having children.

“Eunuchs” or castrated servants were often used to guard harems of women in civilisations such as Ancient Greece and Rome. In Imperial China, eunuchs not only guarded harems but also performed government operations and so could wield political power. Their position meant that they could be a source of gossip and advice. Eunuchs in this position seem similar to the character Varys in the Game of Thrones TV series and A Song of Ice and Fire books. Some men willingly became eunuchs despite the obvious disadvantages as it meant they could have comfort and possibly power although many were made eunuchs by force.

What follows is a description of how the Ancient Chinese performed the castration procedure which I’ll be generous and not relay to you here. As the reader might imagine, it was not pleasant and could result in agonising death. I never realised until reading this that the penis was also removed (see what I mean?) during the operation.

Whilst people could observe what happened when testicles were removed from males, advances in science led to people attempting to work out why doing this had such transformative effects. They likely knew that something in the testes was transmitted to the rest of the body, and that removing testes cut off this supply, but they did not know what the thing was, or whether it was transmitted through the nerves or the bloodstream. Like with many other scientific discoveries, it would take a series of independent experiments before scientists could determine that T works through blood rather than nerves.

In the 19th Century, Arnold Berthold performed an experiment in which he castrated some cockerels then reattached the testicles in the cockerels’ abdomens. In two of them, Berthold attached a testis from one bird into the other or a “foreign” testicle to observe any differences. He discovered that “masculinization” returned to the castrated cockerels upon reattachment then found after killing them and cutting them open that the testes had vascular connections to the colon. From this he concluded that whatever was in the testes acted via the bloodstream.

A little later, Charles Edouard Brown-Sequard theorised that diseases were caused by insufficient tissue secretions and injecting organisms with tissue extracts could treat various diseases. He pursued his theory by injecting himself with “crushed testicle extracts” of various animals and reported that he developed “mental clarity”, increased focus, strength, handgrip and stamina. Many other men repeated the procedure which became known as the “Brown-Sequard Elixir.” It is now thought that the effects were simply a placebo but it influenced further studies and contributed to the discovery of hormones.

This discovery emerged at the beginning of the 20th Century from the work of Ernest Starling and William Bayliss who operated on a dog to study its digestive system. Sodium bicarbonate is secreted from the pancreas during digestion to neutralise acids in the stomach and small intestine. The secretion is triggered by a hormone and the two men observed the secretion occurring in the blood. This led to the first isolation of a hormone, which they named secretin. Further research led to the discovery of more hormones such as oestrogen (of which there are three kinds) and testosterone a couple of decades later.

Here are some other interesting facts from this chapter:

• In some animals, testicles remain inside the body like ovaries in females. This is the case for elephants, seals, whales, dolphins and frogs. Testicles are on the outside of the body in humans and other animals like dogs to keep sperm at a temperature ideal for sperm production which is lower than body temperature. It is not known why some male animals have internal testicles and some do not.

• Castrated men can be tall and gangly despite lacking T. This is because T increases bone growth but also stops it. The growth spurt that may occur in such men is a product of “extended childhood growth.” Other effects of castration on males includes having smoother skin, increased fat and being physically weaker. Castrated cockerels or capons are created for this effect as they will have larger and more tender meat.

• Ernest Starling coined the name for hormones – from the Greek ‘ormao’ – meaning to excite or arouse.

• Testosterone is a steroid hormone, which are made from cholesterol. The receptors for T are inside the cell. Attaching to receptors allows T to influence physical and behavioural changes mainly relating to reproduction.

Chapter 3: The Effect of T on Developing Boys and Girls

In this chapter, Carole Hooven writes about a student of hers who has a difference of sex development (DSD) condition called “complete androgen insensitivity syndrome” (CAIS). The student, named Jenny (possibly a pseudonym to protect her identity) has XY chromosomes, T and has testicles instead of ovaries but appears, in the author’s words, “ultrafeminine.” How can this be?

Jenny has testicles but they are inside the abdomen where the ovaries would normally be. In addition, Jenny has female genitalia but no connection to the uterus. Throughout her life, she has had female primary and secondary sex characteristics. Jenny could thus be designated as “intersex” which in distinct from “transgender” which is explored in Chapter 9 of the book. Carole Hooven worked with Jenny as part of an independent study of her condition.

The reader may have worked out from the name of Jenny’s condition that her physical traits are a result of her body not being able to respond to the testosterone it was producing. Jenny’s case is useful to understand how boys and girls develop and differentiate when they are growing in the womb.

Carole Hooven explains how this happens using the analogy of baking cookies and hand-drawn diagrams such as below:

I do a little bit of drawing myself (observe the artistic masterpiece that is my Mystery Man logo!) so I thought these drawings were a nice touch and make the book stand out from other ones which may use standard diagrams and charts. Graphs shown in the book are also presented as drawings which I thought was a clever idea. Below is a graph from Chapter 1 showing differences in height between men and women:

If Carole Hooven had done the drawings herself (spoiler: she didn’t) I would have been tempted to give her book an even higher rating.

Like with baking cookies (or any food), humans require a certain set of ‘ingredients’ and ‘instructions’ in order to be healthily produced. Sex hormones stimulate the sex-specific traits we observe in men and women rather than sex chromosomes:

“Both sexes come genetically equipped to express all the traits typical of either sex. It’s just a matter of which genes are active, at which levels, in which bodies.”

Until week six of foetal development, boys and girls both possess “primordial” or “bipotential” gonads which then differentiate to become male or female. A protein called SRY, meaning “sex determining region of the Y chromosome” in males increases the transcription of certain genes on other chromosomes. If the reader is uninitiated in how gene transcription works, basically, DNA is unravelled and certain genes are ‘transcribed’ to make proteins:

SRY protein upregulates the production of another protein called SOX9 which helps turn the primordial gonad into testicular cells. Low levels of SRY and SOX9 will result in the development of ovaries instead of testicles even if the baby has XY chromosomes:

“XX and XY chromosomes are traits that are features of sex (in mammals), not ones that define sex.”

Here Dr. Hooven presents a hypothetical twin brother for Jenny she calls “James” to contrast how boys and girls develop differently during pregnancy and why Jenny possesses both male and female traits. In addition to the development of testes or ovaries from shared primordial gonads, both sexes have primordial duct systems that also diverge at around week eight. There are initially two sets of these ducts but, depending on the sex of the foetus, one set will degenerate and the other set will continue to develop. Boys will develop “Wolffian ducts” whilst girls will develop “Mullerian ducts” This diagram from the book may make this clearer:

The testes release Mullerian inhibiting hormone which causes the Mullerian ducts to degenerate which is what happened to Jenny. It is here that T also plays a role: the Wolffian ducts are stimulated to eventually form male genitalia. In the absence of T, the Wolffian ducts will degenerate:

“The female duct system is the default: it will develop without any specific hormonal stimulation, unlike the male duct system.”

Unlike her “brother” James, T had no effect on developing Jenny’s Wolffian ducts leaving her with neither set of duct. This explains why Jenny has testes instead of ovaries, as she has the SRY gene, but also female genitals, as her body does not respond to T to create male genitals.

Jenny’s lack of response to T is due to having a mutation on an androgen receptor meaning that T cannot bind to it. In normal circumstances, T binds to an androgen receptor and then both move into the cell nucleus to increase transcription of certain genes. Since T cannot bind to a receptor in Jenny’s body, it cannot upregulate other proteins that will create male characteristics. As a result, Jenny developed female traits instead of male ones:

“Making a female, in many ways, is easier than making a male – the external structures develop in the female direction in the absence of any hormonal signal.”

Jenny being, according to Dr. Hooven, very feminine is not just the result of ineffectiveness of T on her body. Oestrogen, in many ways the female equivalent of T, is actually produced from it:

“in everyone, all estrogen comes from testosterone (or other androgens). In other words, testosterone is an estrogen precursor.”

[Carole Hooven, being American, uses the US spelling ‘estrogen’.]

Therefore, Jenny has had the effects of oestrogen produced from T.

The chapter ends by briefly talking about differences in behaviour in boys and girls, referring to the famous nursery rhyme:

“What are little boys made of? Snips, snails and puppy-dog’s tails…What are little girls made of? Sugar and spice and all things nice.”

Carole Hooven writes about her young son Griffin, whom she dedicated the book to, to highlight typical boy behaviour – fantacising about destruction of planets, battles, rough-and-tumble play, etc. As mentioned in the first chapter, some feminists take issue with assumptions about typical boy and girl behaviour and there are a number of feminists who present counter-arguments that distinctive behaviour between the sexes is a result of culture rather than biology.

There is an experiment, for example, in which baby boys and girls were dressed to look like the opposite sex and presented to test subjects this way. The subjects said that the boys who they thought were girls showed behaviour that was typical of girls (and vice versa for girls dressed as boys) reflecting that attitudes can be reinforced by how children are presented to us. I once watched a documentary that also presented this experiment. However, it’s important to note that it’s harder to tell if babies are boys or girls, other than the obvious checks, than it would be if this experiment was performed with toddlers or older children. Baby behaviour is also fairly consistent between the sexes although there are still some differences.

The author contrasts her son’s play with what is typical of most girls:

“What kind of fantasy play do girls tend to act out? Those that involve relationships, romance, and domestic concerns, like getting married, parenting, going shopping, or taking care of household responsibilities. Much of girl’s play, in contrast to that of boys, omits the blowing up of planets but instead focuses on coming together and finding safety after being under threat.”

Although girl’s play may not include conflict of the planet-blowing-up variety, I would point out that relationships, romance and domestic concerns are not free of conflict themselves. Consider the popularity of soap operas and gossip magazines, which involve lying, cheating partners, abuse, and murder often to a degree that would be extreme in real life. These genres have a predominantly female audience than a male one, albeit women instead of girls. There’s a clip from the comedy show Taskmaster whereby the comedians have to create their own soap cliffhanger. The female comedians come up with this scene which wouldn’t look out of place on a soap like Eastenders.

Boys and girls’ toy preferences are also different as boys tend to like toys relating to transportation or weapons whereas girls tend to like toys such as dolls and tea sets. The author points out that boys who have been banned from playing with toy weapons for fears it will influence dangerous behaviour often use other toys as weapons instead:

“Boys, it seems, are resistant to efforts to condition them away from battle and weaponry.”

I would also argue that this assumption that boys playing with toy guns or other weapons may cause them to be violent is a little shallow. Does girl’s play make them entirely caring and non-violent? I often think feminists make more stereotypical assumptions about sex differences than other people do.

Chapter 4: The Effect of T on Male and Female Behaviour

A second DSD condition is described in this chapter using another case study. An Indonesian girl called “Taman” started to develop a penis at puberty as well as other male traits like a drop in voice. Taman, like Jenny in Chapter 3, was biologically male, or at least intersex, but had the physical features of a girl. Unlike Jenny, Taman’s androgen receptors work. The problem was also not with T, but another androgen, dihydrotestosterone or DHT. This is produced from T by the enzyme 5-alpha reductase. DHT provides extra stimulation in the development of the penis and scrotum.

5-alpha reductase didn’t work in Taman’s body, a condition known as 5-alpha reductase deficiency (5-ARD), so T was not converted into DHT. As a result, Taman’s penis did not develop properly until puberty when an increase in T was sufficient to do it.

Interestingly, although Taman was thought to be a girl until puberty, she (or he) was always a “tomboy” or a girl who displays behaviour more typical of boys. Carole Hooven argues that T had had an effect on Taman’s brain but not on Taman’s body, indicating that differences in boys and girls’ brains start in the womb therefore nobody is a ‘blank slate’.

Men with 5-ARD have been found worldwide, and often in remote areas where inbreeding and lack of medical intervention is common. In the 1970s, the endocrinologist Julianne Imperato-McGinley studied a group of 5-ARD-affected children in the Dominican Republic. Like Taman, some of the children thought to be girls seemed to turn into boys at puberty. Such children were given the name “guevedoces”, literally “eggs at twelve”, referring to the development of male genitalia. Following puberty, most “guevedoces” identify as men which is likely because they felt more like boys than girls during childhood. Countries like Indonesia and the Dominican Republic have more traditional expectations of men and women so it can be difficult for such people as Taman or the guevedoces to fit in although they may be recognised as a “third sex.”

These cases, along with Jenny in the previous chapter, show that there is a complexity to male and female identity as intersex people, as well as people with “gender dysphoria”, do exist. Nonetheless, it’s also important to consider that there must be distinctions between males and females otherwise we would not notice when there are these complications. Professor Imperato-McGinley’s research was published in the journal Science in 1974. A “feminist scientist” named Ruth Bleier accused Imperato-McGinley of “lacking scientific objectivity” which seems like the pot calling the kettle black.

DSD conditions enable us to see the importance of hormones in influencing male and female differences as the ineffectiveness of certain hormones like T or DHT is transformative. Since it is unethical to perform potentially dangerous and life-changing experiments removing gonads or altering sex hormones in humans, conditions like 5-ARD are useful in researching how the sexes differ and develop over time.

An alternative is to study other animals like rats. Rats who, depending on their sex, have been castrated or had their ovaries removed display behaviour that is often atypical. For example, castrated male rats will show indifference to fertile female rats but, as seen in Chapter 2, will behave like normal males when injected with T. Female rats with removed ovaries will not show attraction to males or display the reflexive “lordosis pose” common in many female animals. In the lordosis pose, female mammals lower their front legs, curve their backs inward and stick their rear end up to present themselves to males for mating.

Since castrated male rats recover their sexual behaviour following injection of T, it was theorised that female rats given male levels of T would show the typical male response. Experiments in the 1930s tested this hypothesis on pregnant rats but found no difference in behaviour from females. However, the female offspring had genitals that resembled male’s. Later it was suggested that genes were responsible for the programming of sexual behaviour rather than hormones.

In the late 1950s, the scientist William C. Young reported an experiment in which T was given to female rats in utero and then again in adulthood. Unlike the previous experiment, these female rats displayed male-typical sexual behaviour such as mounting. This suggested that the T given later activated areas of the brain that had been developed by T in the womb. Young performed a similar experiment with guinea pigs which had identical results. Also, female guinea pigs given T in the womb and whose ovaries were removed would not show female sexual behaviour when injected with oestrogen or progesterone. In contrast, females who had developed normally but who later had their ovaries removed would show sex-typical behaviour when given these hormones.

Why is it necessary for T to act on the brain in utero to prepare for a second increase in T during puberty? One reason may be to initiate distinctive play behaviour in male and female young. Play behaviour in children and baby animals is thought to be in part preparation for behaviours in adulthood. Males in many animals will play fight more than females which is indicative of male competition when males mature. Males who are prevented from play fighting have been shown to be less likely to reproductively successful.

Congenital adrenal hyperplasia (CAH) is a rare genetic disorder that has similar effects as the experiments giving T to female rats and guinea pigs. During pregnancy, CAH boys and girls are exposed to high levels of T due to, in most cases, an inability to produce cortisol from progesterone. Instead, the body produces excessive intermediate androgens like T. Since girls are more sensitive to androgen exposure, the effects of CAH are often more dramatic than in boys.

Experiments have been carried out on CAH-affected boys and girls to see if their behaviour is any different from healthy boys and girls. In a 2005 study, children with and without CAH were given a variety of toys to play with, ranging from boy’s toys, girls’ toys and neutral ones. CAH girls were found to prefer playing with boy’s toys than ordinary girls and parents had little effect on this preference. CAH boys showed little difference in their play preferences with ordinary boys. Girls with higher T than average have also been observed to play with boy’s toys more.

Sport is a common domain for play in both sexes throughout their lives and T’s effect on performance in sport is explained in the next chapter. This will be covered in Part 2.