Saturday, January 24, 2015

Not Understanding vs Not Wanting to Understand - There is a Difference

This is my first time trying to submit to the asexuality blog carnival, and it looks like the topic is nonbinary gender identities. OK. Well, just because I'm a cis asexual shouldn't stop me from writing something about nonbinary people, right?

Problem is: I don't understand nonbinary gender identities.

Admitting that is kind of scary. I bet a lot of people are thinking right now that I'm denying that nonbinary identities exist, or that I'm saying they're wrong, or that nonbinary people should just pick a gender and deal with it. But I'm not saying anything of the sort.

All I'm saying is that I don't understand. I'm willing to try. I can't guarantee that I'll understand if you explain it to me, but I'll try. And even if I don't understand it, I'll take your word for it if you say you're nonbinary.

I remember, up until recently, I didn't understand binary transgender people, either. I have always felt that I'm female because I have female bits, not because of anything in my mind, so it didn't make sense to me that a person with male bits could call themselves female. I thought MtFs and FtMs were just effeminate boys and tomboyish girls who held such rigid gender stereotypes that they assumed having cross-gender interests meant they must be the opposite gender. Like an autistic woman believing so wholeheartedly in the Extreme Male Brain theory of autism, she decides she must be a man. I felt sorry for trans people, and I wouldn't have dreamed of treating them badly, but I didn't understand them one bit, because in my world view, there was physical sex and there were gender norms, but gender identity did not exist.

And then I met an FtM kid at a camp for disabled kids. And the biggest thing that struck me about him was that he wasn't some stereotypically male character. He came across as a boy (in fact, he successfully passed as male to me until a camp counselor outed him), but as a boy with a mix of typically male traits, typically female traits and traits that I didn't associate with gender stereotypes at all. In other words, just like most boys (and girls) I've met. I'd thought of trans people as MtF prom queens and so forth, presenting themselves as stereotypically as possible as their desired gender. Now I realized that real trans people weren't like that. With my theory blown out of the water, and with a kid I wanted to do my best by, I went out researching.

And I came across a theory that made a lot more sense. Phantom limb syndrome, in amputees, is well documented. Weirdly enough, though, even people with congenital limb abnormalities can have phantom limb sensations. It's less common than phantom limb in amputees, but it does happen. Conversely, there are people who have limbs that they feel don't belong to them. And I also noticed that many trans people described feeling sensations that sounded suspiciously similar to phantom limb syndrome or body integrity identity disorder - except the phantom sensations or feeling of not belonging were focused on gender-specific body parts, such as a penis.

Now, as a psych major, I know there's a mental map of our bodies, located along the sensory and motor strips on the border between the frontal lobes and the parietal lobes. And I know that phantom limb sensations come from having part of the sensory strip assigned to a limb that doesn't exist. Now, genitalia are represented on the sensory strip, just like any other body part. (In fact, since we need such acute sensation there, the sensory strip representation is disproportionately large.) So, just as embryos start out physically female and then undergo physical sex differentiation, chances are that the sensory strip of the brain starts out representing a female body, and then differentiates between male and female. And just like physical sex differentiation can go wrong, so can the differentiation of the sensory strip. It would explain why MtFs outnumber FtMs, because female is the default. (Among intersex people, XY girls outnumber XX guys.) It would also explain some nonbinary individuals - if the sensory strip started to differentiate but then didn't go all the way, you could end up in between, like the person I met on a forum who desperately wanted to be castrated but still have a penis. I also found a case report of some people who have alternating phantom genitalia - sometimes they feel physically female, other times they feel physically male - and while I have no clue how the sensory strip can suddenly alter its functioning so dramatically, it's no weirder than many other things the brain does, and I can readily imagine how that would feel.

But I know there's still a piece of the picture I'm missing. There are trans people, and especially nonbinary people, who don't report any issues with their sense of their body. Even the alternating-gender case study I linked to reported a few individuals feeling incongruity between their gender identity and their phantom genitalia at times (eg having a phantom penis while feeling female). So although phantom genitalia are part of the picture, they aren't the same as gender identity. And that leaves me, once again, not knowing what gender identity actually is.

So please, bear with me, people. I'm trying to understand, I really am.

And I think there's a lesson here beyond my specific failure to understand gender identity. Many people really struggle to accept the idea of someone not understanding a person's identity - either as the person who doesn't understand, or the person not being understood. A lot of people act like 'if I don't understand it, it doesn't exist'. And in response, a lot of people take not being understood as an act of hostility, claiming they don't exist.

But there's a difference between not understanding something and not believing it exists. If you're willing to let go of your confidence in knowing everything, you can approach something with an attitude of 'what is that? tell me more'. And that's where learning comes from.

Now, I just wish more people would take that attitude to me, when I tell them I'm asexual.

Monday, January 19, 2015

When an Ideal Upbringing Isn't in the Cards

As a society, we generally agree that children need to have the best possible upbringing. And it's possible to look through the scientific literature to get a pretty good idea of what an ideal upbringing is like. A consistent caregiver present throughout the child's life, who has enough support to effectively manage the stress of child-rearing, is sensitive and responsive to their child's emotional needs and comforts them when they need comforting, and disciplines by rewarding good behaviour, explaining rules clearly and having consistent, logical consequences, which they administer while remaining calm.

But what if that's not an option?

Research has found a critical period for attachment, that seems to start between 9-12 months of age, and ends somewhere around 3-5 years. Experiences during this age range have a critical, lasting effect on the child's attachment, emotional regulation, and the neural architecture of their brain. Both inadequate caregiving (eg abuse or neglect) and separation from caregivers have the potential to cause lasting harm, especially in this age range. On the other hand, children in this age range are better able to respond to a change for the better than an older child would be.

So, imagine an 15 month old child, already well within this critical period. His mother has a serious drug addiction, which is making it very difficult for her to provide sensitive and responsive care to her child. In reaction, her child has developed a disorganized attachment style, which puts him at higher risk for both internalizing and externalizing psychological problems.

But he is attached to his mom. And his attachment is better than it could be - he shows no sign of reactive attachment disorder (RAD), the most severe end of attachment disturbance. He still gets some comfort from his mother's presence, still prefers her to a stranger, and feels safe enough with her watching over him that he's willing to play and explore. His attachment style is not optimal - he often seems to be in a double bind, wanting mom's comfort but also being afraid of her - but there's still room for it to get worse.

And this puts us in a tough situation. If we remove this child, we could put him into a foster home, with a foster parent who will probably provide him with sensitive and responsive care. However, since this child is attached to his mom, losing her will be traumatic for him. He might recover from his trauma and attach to his foster carer, potentially forming a better attachment style in the process, or he might not, and start sliding towards RAD. And if he does attach to his foster carer, how long will that relationship last? Foster homes aren't intended as permanent homes. Although some children stay in one foster home for years, and some are even adopted by foster parents, many foster children end up being moved from home to home. And if this little boy, who's already showing a disorganized attachment, gets moved several times during the critical period for attachment, then we can virtually guarantee that he will develop RAD.

Alternatively, we could try to get his mom to stop using. If she does go clean, her parenting will improve, and her baby is still young enough to respond to that - especially if we give her attachment-focused parent training as well. But what if she relapses? Or even gets worse? Her child may need to be removed anyway, months later, having missed out on several more months of good care in the critical period for attachment. We could end up back at square one, except with a 28 month old instead of a 15 month old. And now that he's two, it's that much harder for him to transfer his attachment from mom to a foster carer, and that much harder for the foster carer's parenting to sink in and change his view of relationships.

There is no one option that will put this child on the best road to life. All we have are different bad options, each of which could be putting the child at further risk, but if not, we might be able to make things a bit better. And the best outcome will still fall short of where this kid could have been, if he'd gotten sensitive and responsive care from birth.

Friday, December 26, 2014

Thoughts on Bestiality

OK, first of all, I'd like to make it clear that the thought of bestiality grosses me out, and I have absolutely no desire to do it myself. However, I've learnt from the example of homophobia, that just because something grosses you out is not a sufficient justification for banning it. So, I've been taking a look at bestiality lately, to see if I think it can ever be morally justified.

The most common argument against bestiality, that I see, is the idea that animals, like children, can't consent to sex. It does have a certain amount of appeal, I admit. In some ways, animals are like children. For example, my cat Lilly understands physics about as well as 8-12 month old human baby.

But there's an important difference between a cat and a human baby. If we hadn't spayed Lilly, by now, she'd almost certainly have lost her virginity and raised at least one litter of kittens. And this would have been healthy and normal for her species. Not only that, but if she'd grown up without contact with humans, she'd be living independently by now, as well as raising her kittens all by herself. She may understand physics like a human baby, but a 1 year old cat is an adult, just like a 21-year-old human. Meanwhile, her house mate Katrina is very much an elderly lady, and makes this very clear. I often feel as if she's older than me, even though I remember getting her as a kitten, simply because she's so much more mature.

Not only are adult animals adults, rather than children, but they clearly can consent to sex. Many animals will actively seek out sexual partners, and chose which ones they want, communicating their choice with various species specific signals. (For example, many female animals request sex by waving their genital region in the male's face.) Some animals are even sexual predators, who will force themselves on unwilling partners. They may not see the world the way humans do, but they certainly have their own sexuality.

Of course, under normal circumstances, animals only have sex with members of the same species. But this isn't always the case. Mules, jennies, and other interspecies hybrids are testament to the fact that some animals will happily mate with members of closely related species. More distant interspecies sexual behaviour occurs at times, though it doesn't produce offspring. Unneutered male dogs, for example, are notorious for trying to mate with human legs while the humans are sitting. Peter, a dolphin involved in an experiment to teach him how to speak, was sexually interested in the human researcher working with him, and made frequent advances towards her. I've heard a few different versions of Peter's story, arguing different levels of cooperation from the human involved, but in all of them, it's clear that Peter gave clear indications of his desire.

I would even argue that it's possible for an animal to rape a human. In this Youtube video, an amorous donkey pursues a man, who I gather was trying to poop in the field. The guy is clearly unwilling, but the donkey persistently tries to mount him. I would argue that this is a case of attempted (or maybe successful, hard to tell) interspecies rape with a human victim.

But what if the man had been willing? There is a segment of the human population who are sexually attracted to animals. If one of these people found an animal who was sexually interested in them, and both clearly indicated consent in a way that the other could accurately interpret, then what?

Personally, my litmus test for whether a sexual act is wrong is whether it causes harm. A human forcing themselves on an animal probably harms the animal, and an animal forcing themselves on a human could very well harm the human. But if we've established that both parties are able to consent, and they both do, then it seems unlikely that either is harmed by the experience.

It's also interesting to point out, from a sociological perspective, that our society thinks humans having sex with animals is disgusting, but thinks it's just fine for a human to sexually stimulate a male animal in order to collect semen, and then implant that semen in a female of the same species, which sometimes involves sexually stimulating the female as well. It seems like kind of a strange distinction to me.

Thursday, December 18, 2014

'But It's Not Healthy!' Why Fat-Shaming Cannot Be Excused Based on the Health Effects of Fat

A few years ago, my brother was a regular soccer player, liked to go swimming, and was starting to get interested in karate. He's always been a big boy, tall for his age, with broad shoulders and lots of muscle, but back then, his weight was fine. He liked to eat, but he didn't eat more than he needed. Although he wasn't super-athletic, he was healthy.

Since then, he's had a couple moves and some bullying, with kids calling him 'fat' - a label that was initially inaccurate. He's had a gym teacher shame him for not being able to run as many laps as other kids, and his high school forced him to do a calorie-counting assignment.

And now, he's noticeably overweight. He's quit soccer, rarely goes swimming, and never goes to karate. He spends most of his time inside, playing video games, and tells me he often feels like he can't go outside because he doesn't want people seeing him. He eats not only out of actual hunger, but also to comfort himself when he's feeling down - and he's been feeling down a lot.

I would like him to lose weight - not because I think he looks bad, but because his doctor says he has high cholesterol and may be at risk for heart disease. But whenever I make the slightest reference to his weight, his diet, or his level of exercise, he gets depressed. I can look at the cholesterol levels of my own snacks and substitute a high-cholesterol snack for a low-cholesterol one without getting upset. He can't. Merely thinking about cholesterol sends him in a downward spiral.

So, when I hear people say that fat acceptance is bad because fat is unhealthy, I get really upset. If being 'fat' wasn't worthy of insults and humiliation, then, ironically, my brother may never have become fat. And even if he did, I could get him to make changes to help him lose weight, just like I've done with myself.

Depression is not conducive to eating healthy or getting plenty of exercise. Depression saps your energy, makes you want to hide inside. Depression messes up your ability to regulate eating, making you eat more or less than you should. Depression makes you want to go for comfort foods, foods that taste good and make you feel a bit better, instead of the food you know is healthy.

If you hate your body, any reminder of how you look will trigger depression - an emotional state associated with lack of motivation and energy, comfort eating, and poor regulation of eating. This makes it harder, not easier, to make a positive change in your eating and exercise habits. Sure, some people do it anyway, but those people are exceptions, just like the former alcoholics who can sit in a bar with friends and not drink. It's not a tactic that will work for most people.

So if you think making fun of someone for being fat, or rejecting them because of their weight is in any way justified, think again. You're not helping them, you're hurting them. You're making it harder for them to lose weight, and you're making their life miserable.

So stop being an asshole, and try being nice instead. Leave comments about weight to doctors, who (hopefully) actually know what they're talking about, and give them a compliment instead. If you want to help them lose weight, invite them to go swimming with you or something else fun and active. Tell them not to worry about how they look or how well they can do the activity - the point is to just move around and enjoy doing it.

Thursday, November 06, 2014

Can Fiver the Raccoon Count? An SPSS Post.

Awhile back, I came across these two videos:








The videos depict a wild female* raccoon ('Fiver'), being trained to give 'high fives' in exchange for dog kibble. In the first night, in response to Fiver spontaneously tapping the woman's hand while getting kibble, she decides to start telling Fiver to 'give me five' and rewarding pats to the hand with kibble. Fiver's variable number of pats and seeming confusion and hesitation lead the woman to wonder if Fiver may have been expecting more pats to lead to more food. On the second night, therefore, the woman starts giving Fiver the same number of kibble pieces as Fiver's pats, to see if Fiver learns the association.


I decided to tabulate the results of these two videos and run some statistical analyses on Fiver's behavior.


Hypothesis

If Fiver does know how to count, and can tell that more pats leads to more kibble, what should we expect?


Assuming she wants to maximize her kibble reward, Fiver should react to the link between her pats and the kibble she gets by increasing the number of pats over time. Therefore, she should provide more pats per trial on the second night than on the first night. In addition, over the second night, she should increase her number of pats as she learns the contingency.


Method


I coded Fiver's pats based on carefully watching the video, as well as listening to the woman's comments. I also coded the amount of kibble Fiver received. In addition, I recorded whether the woman commented on the number of pats Fiver gave her. Each exchange of pats & treats was considered a single trial.


On two occasions on night 2, Fiver gets interrupted by another raccoon coming near (the first time, the other raccoon actually displaces Fiver and gets some kibble). Since Fiver seemed to take a while to get back into the flow of things after these interruptions, I decided to consider each interruption as the end of a 'session'. Therefore, on the two nights, Fiver had four sessions - one session of 10 trials on night one and three sessions of 25, 58 and 24 trials on night 2 - for a total of 117 trials.


I analyzed correlations between pats, trial number and kibble received for each session individually, and also compared the same variables across nights and sessions.


Results


Over both nights, Fiver gave a single pat 51% of the time, two pats 28% of the time, and 3-7 pats on the remaining trials. The trial with 7 pats (on the first night) appears to be an outlier, with the next highest number of pats in one trial being 5. She received 1 kibble in 59% of trials, two kibbles in 25% of trials, and 3-5 kibbles in the remaining trials.


Apart from the 7-pat trial, when she received 4 kibbles, all other trials on the first night resulted in 1 kibble per trial, despite her giving 1-4 pats (1 pat in 2 trials, 2 pats in 3 trials, 3 pats in 1 trial and 4 pats in 3 trials). As a result, once the outlier was excluded, there was no possible correlation between number of pats and number of kibbles. In addition, the woman never commented on the number of pats Fiver gave her. (Though she commented on the quality of the pats at times.) There was no correlation between trial number and number of pats Fiver gave, suggesting that Fiver did not show a trend towards increasing or decreasing pats over time on this night.


On the second night, Fiver received 1-5 kibbles for 1-5 pats, with a correlation of .965 between pats and kibbles. This correlation did not vary appreciably between sessions (.933-.991). Despite this, Fiver showed a negative correlation between trial number and number of pats (-.256), suggesting that she gave fewer pats as the night went on - the opposite of the predicted result. Within session, the negative correlation was stronger in session 4 (-.442) and nonsignificant in sessions 2 and 3 (.030 and .184). The woman gave frequent verbal feedback on trials, saying a single number in 45% of trials (92% of which were 1-pat trials, and the rest were 2-pat trials) and counting aloud in 38% of trials. In all cases where the woman commented on the number of pats, she gave the same number of kibble pieces as her comment indicated.


A T-Test comparing the two nights revealed that Fiver showed significantly greater variance in number of pats on the first night than on the second night (SD 1.83 vs .94). In addition, contrary to the hypothesis that Fiver would produce more pats on the second night, there was an almost significant difference in the opposite direction (p = .053), with Fiver producing an average of 3 pats per trial on the first night and 1.71 pats on the second night.


An ANOVA revealed a significant difference between sessions (P <.001). Post-hoc tests revealed that Fiver produced significantly more pats in session 1 (on the first night) than in sessions 3 (p = .003) and 4 (p <.001). In addition, Fiver produced significantly more pats per trial in session 2 (at the start of the second night) than in session 4 (p = .022). All other comparisons were non-significant.


Discussion

Overall, the results found were the opposite of what the hypothesis predicted. Rather than increasing her number of pats per trial, Fiver actually decreased the number of pats she produced over the second night.


These results could indicate that Fiver was unable to perceive a link between the number of pats and the number of kibbles she received. Alternately, Fiver may not have wanted to receive multiple kibbles at one time. The presence of rival raccoons may have made her wary of potential theft, leading to a strategy of requesting only as many kibbles as she could eat in one bite. In addition, since Fiver performed 107 trials on the second night, the decline in number of pats over time could be attributed either to fatigue or satiation. Certainly, Fiver seems to be less motivated as the night goes on, although part of this is undoubtedly because she's watching out for her rivals.


With the current data, we can't determine whether Fiver's behavior represented a deliberate strategy or a simple lack of understanding.


Anecdotally, Fiver does seem to respond more promptly and with less coaxing in the second night than in the first. However, this is not necessarily due to the change in contingency, since there are several other factors that might influence her behavior.


Firstly, from what I can gather, the session on the first night started after Fiver had already been given a lot of kibble noncontingently. The sudden shift between noncontingent to contingent reward may have confused and/or frustrated Fiver. In contrast, on the second night, the reward was contingent to begin with, and Fiver had already had several trials of contingent reward the night before.


Secondly, Fiver is a wild raccoon, and the woman who posted the videos describes her as 'new' in the first video. This suggests that Fiver was unfamiliar with the woman, and may have been a bit afraid of her. (Fiver often backed away between trials, supporting the fear interpretation.) Once again, on the second night, Fiver knows better what to expect - this woman will feed her kibble and not try to hurt her. Wild animals are often neophobic, especially towards humans. Though city-dwelling animals often have a lower flight distance than rural animals, coming close enough to eat from her hand may have still been a bit outside of Fiver's comfort zone.


Thirdly, miscommunication may have played a part. On three occasions on the first night, immediately after accepting the reward, Fiver did a very fast, very light pat, which the woman refused to reward her for. After each of those quick pats, Fiver paused and acted as if she was waiting to be rewarded, and seemed to get confused when the reward didn't come. On the second night, I saw only one such unrewarded pat, which occurred early on in session 2. It's unclear whether Fiver learnt to give better pats or the woman became more consistent in rewarding all of her pats, but the proportion of unrewarded pats was certainly far lower on the second night.




* The woman mistakenly refers to Fiver as male in the video, but Fiver has since had pups, making it clear that she's actually female.

Sunday, October 12, 2014

Too Young to Remember

There's a common belief that if a child was exposed to trauma when xe was very young, too young for xim to consciously remember the trauma, it won't really affect xim. Since xe doesn't remember the trauma happening, and (unless told about it) probably won't know it happened at all, xe shouldn't have any lasting effects, right?

Wrong.

Laboratory rats demonstrate this effect pretty clearly. Like human toddlers, 18-day-old rats soon forget many of the memories they've laid down (such as the association between a sound and an electric shock). The rate of forgetting is quicker in rats than in humans, but the mechanism is thought to be the same.

If a rat can't remember being 18 days old, they certainly can't remember being 14 days old or younger. But when rat pups are removed from the nest for 3 hours each day (a stressful experience for a rat pup) from 2-14 days old, they show long-lasting changes in physiology and behavior. Even though they presumably have no memory of being removed from the nest, it still makes them anxious, hypersensitive to stress, and prone to alcoholism. (Little know fact: rats like alcoholic drinks about as much as humans do, with the same range of individual variation in voluntary drinking.)

The same is true of humans. Studies of children adopted from institutions* between around six months and three years old (when most children will have little or no memory of their life pre-adoption) has shown that these children nevertheless tend to function poorer than children adopted at younger ages or non-adopted children, with different ages being crucial for different specific symptoms. In this study of children from Russian orphanages, for example, the latest age at adoption was 27 months old (a little over 2 years), but even so, later-adopted children had poorer self-control than earlier-adopted children. And this study found that children adopted from well-run but emotionally deprived institutions between 13-24 months old had significantly more behavior problems than children adopted from similar institutions before 13 months. (Interestingly, though, few studies have shown any lasting effect of trauma occurring before 6 months, even though some studies show short-term effects. It seems that experiences in later infancy and toddlerhood can completely reverse the effects of experiences before 6 months of age.)

In both humans and rats, conscious memories of trauma are only one part of the impact that trauma can have on an individual. Far more significant is the impact that extreme stress can have on brain structure and function - and since young children's brains are growing and changing much more dramatically than older children or adults, the effects of trauma on the brain can be even greater** in these children.

So don't discount the effect of a trauma the child was too young to remember. It could have reshaped the child's brain, changing the way xe thinks and feels in ways xe can't tie to any conscious memories.

* Adopted children are the best to study the effects of early childhood trauma, because the change in home environment usually means the child suffers no trauma in later childhood that could confound the results.
** The study linked to, though old, is the only one I know of that directly compares adopted children who experienced good infant care and trauma in later childhood to children experiencing early trauma. Unfortunately, it's only available through institutional access. If you'd like to read it, let me know your e-mail address in the comments and I'll mail it to you.

Sunday, July 27, 2014

Daughters of Neanderthal Men - Haldane's Law, Culture, or Both?

Genetic research has now proven that Neanderthals and homo sapiens interbred, and that Neanderthal-human hybrids contributed to the human genetic pool. (I myself am 3% Neanderthal, according to the genetic test I had.)

Oddly enough, however, neither Neanderthal mitochondrial DNA (passed down from mothers to their children) nor Neanderthal Y chromosomes (passed down from fathers to sons) have survived in the human population. This implies that our Neanderthal ancestry doesn't come equally from all of the possible types of hybrid children. Instead, we appear to be specifically descended from women with Neanderthal fathers, who inherited human mitochondrial DNA and no Y chromosome. Why?

Two research articles I've seen have put forward two possible explanations. This article suggests Haldane's Law as an explanation. Haldane's Law is a pattern often seen in interspecies hybridization, where the heterogametic offspring (males in mammals) have poorer fertility than the homogametic offspring (females in mammals). This would predict that among Neanderthal-human hybrids, the daughters would be fertile, but the sons would be sterile. However, this doesn't explain why daughters of Neanderthal women (with Neanderthal mitochondrial DNA) didn't contribute to our genetic pool.

Other accounts have suggested cultural explanations, rather than biological ones. Perhaps, for whatever reason, daughters of Neanderthal men were the only hybrids who actually mated with humans. The others, rather than being sterile, either remained celibate or mated only with Neanderthals. But what would cause this pattern of behavior?

Both chimpanzees and bonobos, despite their behavioral differences, show female-biased dispersal - males stay with their home troup, while their sisters leave and find new troups to join. This study suggests that Neanderthals showed a similar pattern of sex-biased dispersal, with the men in a Neanderthal tribe being more related to each other than the women were. Modern human cultures vary quite a bit in this practice, but given our relatives, patrilocality was probably the ancestral pattern for us as well. So, for the sake of argument, let's assume both humans and Neanderthals were patrilocal.

It's also important to note that humans show two different mating strategies. As far as I know, every culture has a normative expectation that men will live with and support the mother (or mothers) of their children. (If someone knows of a culture where this is not the norm, let me know.) However, in most cultures, a subset of men buck this pattern, impregnating women (through rape, voluntary flings, or feigned commitment) and then playing no part in the support of the resulting children. Let's assume, for the sake of argument, that Paleolithic human men showed the same two patterns of behavior, fathering children both in and out of committed relationships. Maybe Neanderthal men did so as well.

The big question is - which strategies resulted in hybrids?

If men of both species - or just human men - took wives of the other species occasionally, then we'd expect their wives to come live in their tribe, and the hybrid children would grow up with their father's people. Patrilocality would predict that the sons would stay in the tribe, while the daughters went off to marry men of one or both species. Sons of Neanderthal women would have a human Y chromosome, and their Neanderthal mitochondrial DNA would not be passed on to their children. However, their sisters would pass on Neanderthal mitochondrial DNA. So unless human men were willing to marry Neanderthal women but not hybrid women (which seems unlikely), intermarriage should have led to Neanderthal mitochondrial DNA surviving in human populations.

Conversely, if men had sex with the other species but didn't marry them, then the hybrids would be raised by their mother, either as a single mother or with a stepfather of the same species as her (who may or may not have realized the kids weren't his - though hybrids would undoubtedly look pretty unusual). Children with Neanderthal mothers would have grown up among Neanderthals, and both genders would most likely have taken Neanderthal partners, with their descendants dying out along with the other Neanderthals. However, children with human mothers would have lived with humans and intermixed with humans.

This account neatly explains why no Neanderthal mitochondrial DNA survived in human populations. But why didn't Y chromosome sequences survive? After all, hybrid men with Neanderthal fathers are expected to have married human women. But if we combine this account with Haldane's Law, then these men would have been sterile, and left no descendants. Only their sisters succeeded in passing on their genes, mingling down the generations until everyone in their group had a little bit of Neanderthal ancestry.