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In this lesson students view scenes from the Tremors series of movies. Students take notes on the animal’s biology: external anatomy, internal anatomy, lifecycle and behavior. We use our notes to speculate on the evolution and anatomy of these creatures, called Graboids.


Based on the scenes, have the students explain the graboid lifecycle.

Graboid lifecycle

Graboids and sounds

How do graboids navigate underground and detect food sources?

Sonar is the use of sound to navigate, communicate with, or detect objects – on or under the surface of the water – such as another vessel.

Active sonar uses a sound transmitter and a receiver. Active sonar creates a pulse of sound, often called a “ping”, and then listens for reflections (echo) of the pulse. Here we see an animation from the US Navy made in the 1940’s, showing how sonar works.

Old Navy Sub sonar GIF

Some animals have natural sonar, such as bats and whales.

The Tremors movies imply that graboids have a similar way of detecting prey.

Graboid sonar

Internal anatomy

As this is a science fiction movie these creatures aren’t real. But the film makers made it clear that these animals would have realistic internal as well as external anatomy.  In this section we ask students to speculate what kind of organs a creature like this would or wouldn’t have, based on the available information.

Students work in groups to come up with answers – and they have to justify their conclusions. For instance, they might claim that the animal has no skeleton: If so, explain why they conclude this. Or they might claim it does have a skeleton: if so, explain why they conclude this.

graboid anatomy Christopher Stoll dbaubpv

from deviantart.com/christopher-stoll


Evolution of graboids

Based on the observed characteristics, what animals are graboids most closely related to?

What animals in the past might they have evolved from?

Could students make a speculative family tree/cladogram, showing the possible evolution of graboids?

clades & phylogenies

clades rotate = equivalent phylogenies

Gradualism vs. Punctuated Equilibrium

Introductory material

This packet is given to students at the beginning of the class. TBA


Teacher reference material


You may choose to make some of this material available to students during or after viewing the scenes. However, withhold the majority of this material until after the students finish the section in which they speculate and justify their conclusions.


1.0 Introduction

2.0 External Anatomy
2.1 – Graboids
2.2 – Shriekers
2.3 – AssBlasters

3.0 Internal Anatomy

4.0 Ecology

5.0 Evolutionary Overview
5.1 – Evolutionary History
5.2 – Issues of Reproduction
5.3 – Development of Shrieker Legs
5.4 – AssBlasters’ Reproductive Role
5.5 – AssBlaster Biochemistry

6.0 Hypothetical Taxonomy

7.0 Historical and Mythological References

8.0 Threat Assessment

Monster Guide




External anatomy


Internal anatomy




Evolutionary history


The following is from www.scifi.com/tremors/monsters/analysis/06_taxonomy.html

Graboid SyFy

The proper taxonomical classification of Graboids, Shriekers and AssBlasters was a curious challenge because the Graboid species does not clearly belong to any previously known Family grouping. To complete its zoological nomenclature, we were forced to look much deeper into the evolutionary tree than we had expected.

Graboids have been described by some witnesses as being “reptilian,” but this is probably no more accurate than describing the AssBlaster as a bird because it flies or the Shrieker as a frog because it undergoes a metamorphosis. The Graboid does not appear to possess any of the features of true reptiles, though the Shrieker and AssBlaster, curiously, each possess some, such as clawed toes. However, they share just as many similarities with birds and mammals, so a reptilian classification was not indicated.

In fact, Graboids, Shriekers and AssBlasters do not appear to belong to any existing class of vertebrates. They clearly are not fish, and it takes only a slightly more professional observer to see that they they are also neither amphibians nor reptiles, neither birds nor mammals.

It is doubtful that they are even vertebrates, although they do seem to possess endoskeletonlike structures. Vertebrates, it should be stressed, derive from a family of creatures called notochords, which gave rise to fish. Also descended from notochords are amphibians, reptiles, birds and mammals. All these different forms share a heritage of organs and anatomy, ranging from bilateral symmetry to a similarity of organ/tissue types and functions.

The three known forms of genus Caederus lack many of the features inherent to members of the vertebrate line. Most obviously, they lack eyes. Their multistage life cycle is similarly dissociated from known vertebrate reproductive models. In fact, research has not yet yielded any proof that the Graboid species is connected to the vertebrate line.

Regardless, the Graboid, the Shrieker and the AssBlaster are all highly sophisticated lifeforms, which implies that they represent the culmination of a long evolutionary history. Only three other non-vertebrate lines of animal life on Earth have reached a similar level of sophistication: arthropods, annelids and mollusks.

Arthropods (including insects, arachnids, crustaceans and other forms) typically have hard, segmented or jointed exoskeletons, and generally remain small in size when compared with vertebrates. Most arthropods evolved with multiple external limbs and some form of eyes. All these traits are inconsistent with the speculated evolution of C. americana.

Available evidence suggests the Graboid also is not a member of the subphylum Annelida. Annelids — earthworms — share some traits with the Graboid, such as an underground habitat, stiff hairs in the skin to assist in locomotion and an ability to extract nutrients directly from the soil. No annelid, however, has ever possessed anything resembling an endoskeleton or semirigid support system, which C. americana is believed to possess. In addition, C. americana and C. mexicana possess other features not found in annelids: segmented jaws; prehensile mouth tentacles; a multiphase life cycle; and thermal sensors. The Graboid is also larger and more sophisticated than any known annelid, making it highly unlikely that genus Caederus belongs in this subphylum.

Genus Caederus might be unique, in a class of its own. It might even be extraterrestrial. More likely, though, it is a form of mollusk.

The subphylum Mollusca is one of the oldest, most diversified and successful on Earth. It includes clams, mussels, snails, slugs, cuttlefish, nautili, squids and octopi. The most advanced form of mollusks are the cephalopods (octopi and squids), which share many important features with the Graboid.

Cephalopods have multiple tentacles, ranging from eight to dozens, all surrounding a mouth or gullet — an arrangement that resembles the Graboid’s tentacled mouth structure. Furthermore, some cephalopods (such as the prehistoric ammonites or the modern nautilus) have external shells or carapaces, as does the Graboid.

At least one cephalopod, the cuttlefish, has a Graboid-like external carapace, or bony structure. In addition, octopi have enough control over the muscles of their skin to change their texture from craggy to smooth, suggesting a skin musculature similar to that of the Graboid, although of different degree.

The “wing structure” of the AssBlaster bears at least a passing resemblance to the rippling “fins” of the cuttlefish. Although no known aquatic cephalopod ejects combustible compounds, it is a compelling similarity that several eject prodigious clouds of ink as a defensive mechanism, and some have a hydrojet-like propulsive organ that resembles the AssBlaster’s dramatically fiery self-launching ability.

Cephalopods are water-breathers, but other mollusks, including snails and slugs, exist on dry land. Many cephalopods, as well as certain bivalve mollusks, are able to survive for short durations out of the water.

Cephalopods are the most intelligent non-vertebrate animals known to exist. Studies have indicated that they might possess a capacity for memory, learning and problem-solving, and witnesses have reported signs of social behavior among groups of squid and octopi. Cephalopods might well be as intelligent as some species of birds or mammals; certainly, they seem to show a level of “smart” behavior similar to that of genus Caederus.

Finally, cephalopods have managed to achieve significant size and mass in aquatic habitats. The giant squid, for instance, is a deep-ocean-dweller that might rival the Graboid in size. The largest known giant squid have weighed several tons and stretched up to 55 feet from their flukes to the extremity of their longest tentacle.

Although the Graboid and its related forms possess features previously undocumented among cephalopods (such as jointed limbs, endoskeletons and a multiphase life cycle), these differences do not disqualify their categorization as mollusks. For example, bivalve mollusks (clams and mussels) possess hinged shells; it is not unreasonable to assume that the Graboid family of mollusks may have developed hinged internal shells and eventually evolved more complex internal skeletons.

However, no mollusk has evolved anything resembling the thermal sensors of the Shrieker and AssBlaster; likewise, the incendiary metabolism of the AssBlaster is unique to the Graboid species. Furthermore, no cephalopod or other mollusk possesses a life cycle nearly as complex as that of genus Caederus.

Still, the shared traits documented above and elsewhere in this document are significant enough to justify a tentative classification of the Graboid, the Shrieker and the AssBlaster as distant, terrestrial relatives of class Cephalopoda.

Next piece to add






Learning Standards

This unit addresses critical thinking skills in the Next Generation Science Standards, which are based on “A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas”, by the National Research Council of the National Academies. In this document we read

“Through discussion and reflection, students can come to realize that scientific inquiry embodies a set of values. These values include respect for the importance of logical thinking, precision, open-mindedness, objectivity, skepticism, and a requirement for transparent research procedures and honest reporting of findings.”

Next Generation Science Standards: Science & Engineering Practices
● Ask questions that arise from careful observation of phenomena, or unexpected results, to clarify and/or seek additional information.
● Ask questions that arise from examining models or a theory, to clarify and/or seek additional information and relationships.
● Ask questions to determine relationships, including quantitative relationships, between independent and dependent variables.
● Ask questions to clarify and refine a model, an explanation, or an engineering problem.
● Evaluate a question to determine if it is testable and relevant.
● Ask questions that can be investigated within the scope of the school laboratory, research facilities, or field (e.g., outdoor environment) with available resources and, when appropriate, frame a hypothesis based on a model or theory.
● Ask and/or evaluate questions that challenge the premise(s) of an argument, the interpretation of a data set, or the suitability of the design

Science and engineering practices: NSTA National Science Teacher Association

Next Gen Science Standards Appendix F: Science and engineering practices


Osmosis & Diffusion labs

Egg-cellent Ideas for Osmosis and Diffusion

Basic ideas behind diffusion:

Diffusion 2

Basic idea behind osmosis

Osmosis GIF by popolopo

Osmosis GIF by popolopo, at mind42.com/mindmap/4791d8e2-b1df-4ef6-875c-492c7de0502d

Lab from sciencespot.net

Submitted by Sue Remshak, Lake Bluff Middle School, Lake Bluff, IL

Activity I

During this activity students investigate the concepts of osmosis and diffusion using eggs. To prepare for the activity,:

* measure and record the circumference of the raw egg

* measure mass.

* Place the egg in a beaker filled with white vinegar.

* Students to record their observations.

* Store the eggs in a refrigerator for 24 hours.

* View again and record their observations.

* Return the egg to the refrigerator for another 24 hours.

* View again and record their observations

Student worksheet: http://sciencespot.net/Pages/osmdiff.html

Teacher Info:

A chemical reaction occurs between the vinegar and the calcium carbonate in the egg shell. The bubbles of carbon dioxide that form on the egg and rise to the surface are evidence of this reaction. The shell dissolves in the vinegar and leaves a film on the surface of the vinegar.

However, the membrane remains on the egg. The size of the egg increases because of the movement of water in the vinegar through the cell membrane.

Since water moves from an area of high concentration to an area of low concentration, this process is called osmosis. Obviously, none of the materials on the inside of the egg are able to pass through the membrane.

Activity II

Materials: water, blue water (food coloring in water), molasses, and corn syrup.

First, have the students determine the mass of the egg and record it in the table.

They should pour 150 ml of each substance into its own beaker.

Add the eggs and store in a refrigerator for 24 hours.

After 24 hours, remove the eggs from the beakers and record their observations.

Students should record the volume of liquid in the beaker as well as the mass of the egg.

Use a toothpick to pop the egg membrane and record their observations. Be sure to have paper towels handy as some eggs may squirt!)

Teacher Info

The egg in plain water and blue water will become slightly larger because water will pass into egg through the membrane by the process of osmosis. There will be blue food coloring in the egg from the blue water since both water and food coloring can pass through the membrane.

The egg in corn syrup and molasses will decrease in size because water from inside the egg flow through the membrane into the syrup or molasses. It moves from a higher concentration inside the egg to a lower concentration in the corn syrup. Once again, this is called osmosis. The corn syrup and molasses molecules are too large to pass through the membrane. Observant students will not only notice an increase of volume in the beaker, but they will also see a thin layer of water resting on top of the syrup and molasses.


To illustrate the concept of diffusion, add a drop or two of extract (vanilla, bubble gum, lemon, or cinnamon) into a deflated balloon.

Blow up the balloon, tie it off, and place inside a shoe box. To make sure the lid stays on the box, use masking tape to secure it. During class, ask students to life one end of the shoe box lid and smell the contents. Their eyes should remain closed when they do this. Ask each student to reveal what they smelled. Show the class what was inside the box and instruct them to draw a picture and record their observations. Challenge students to write an explanation (using the correct vocabulary) of why the box smells like the scent when it was only put inside the balloon.

Teacher Info

The shoe box smelled of the scent even though it was only placed on the inside of the balloon due to the process of diffusion. Every balloon has microscopic holes in its surface. The vapors were able to pass through the membrane from an area of high concentration to an area of low concentration. However, the liquid scent molecules were too large to pass through the membrane.

Another way to illustrate osmosis and diffusion is using a tea bag and some water. During class, place a tea bag in a beaker of warm water. Allow time for students to record their observations. Challenge them to write an explanation using the correct vocabulary.

Teacher Info

Water flows by osmosis into the tea bag. The students can see this if you remove the tea bag from the beaker and squeeze it to see the water come out. The tea leaves diffuse through the tea bag and into the water; this changes both the color and flavor of the water in the beaker.

Source: http://sciencespot.net/Pages/classbio.html

When Children Say They’re Trans

By Jesse Singal, The Atlantic, July/August 2018

Gender identity and sexual orientation

image from Between the (Gender) Lines: the Science of Transgender Identity, Science In The News, Harvard U.

Claire is a 14-year-old girl with short auburn hair and a broad smile. She lives outside Philadelphia with her mother and father, both professional scientists. Claire can come across as an introvert, but she quickly opens up, and what seemed like shyness reveals itself to be quiet self-assuredness. Like many kids her age, she is a bit overscheduled. During the course of the evening I spent with Claire and her mother, Heather—these aren’t their real names—theater, guitar, and track tryouts all came up. We also discussed the fact that, until recently, she wasn’t certain she was a girl.

Sixth grade had been difficult for her. She’d struggled to make friends and experienced both anxiety and depression. “I didn’t have any self-confidence at all,” she told me. “I thought there was something wrong with me.” Claire, who was 12 at the time, also felt uncomfortable in her body in a way she couldn’t quite describe. She acknowledged that part of it had to do with puberty, but she felt it was more than the usual preteen woes. “At first, I started eating less,” she said, “but that didn’t really help.”

Around this time, Claire started watching YouTube videos made by transgender young people. She was particularly fascinated by MilesChronicles, the channel of Miles McKenna, a charismatic 22-year-old. His 1 million subscribers have followed along as he came out as a trans boy, went on testosterone, got a double mastectomy, and transformed into a happy, healthy young man. Claire had discovered the videos by accident, or rather by algorithm: They’d showed up in her “recommended” stream. They gave a name to Claire’s discomfort. She began to wonder whether she was transgender, meaning her internal gender identity didn’t match the sex she had been assigned at birth. “Maybe the reason I’m uncomfortable with my body is I’m supposed to be a guy,” she thought at the time.

Claire found in MilesChronicles and similar YouTube videos a clear solution to her unhappiness. “I just wanted to stop feeling bad, so I was like, I should just transition,” she said. In Claire’s case, the first step would be gaining access to drugs that would halt puberty; next, she would start taking testosterone to develop male secondary sex characteristics. “I thought that that was what made you feel better,” she told me.

In Claire’s mind, the plan was concrete, though neither Heather nor her husband, Mike, knew about any of it. Claire initially kept her feelings from her parents, researching steps she could take toward transitioning that wouldn’t require medical interventions, or her parents’ approval. She looked into ways to make her voice sound deeper and into binders to hide her breasts. But one day in August 2016, Mike asked her why she’d seemed so sad lately. She explained to him that she thought she was a boy.

This began what Heather recalls as a complicated time in her and her husband’s relationship with their daughter. They told Claire that they loved and supported her; they thanked her for telling them what she was feeling. But they stopped short of encouraging her to transition. “We let her completely explore this on her own,” Heather told me.

To Claire’s parents, her anguish seemed to come out of nowhere. Her childhood had been free of gender dysphoria—the clinical term for experiencing a powerful sense of disconnection from your assigned sex. They were concerned that what their daughter had self-diagnosed as dysphoria was simply the travails of puberty.

As Claire passed into her teen years, she continued to struggle with mental-health problems. Her parents found her a therapist, and while that therapist worked on Claire’s depression and anxiety—she was waking up several times a night to make sure her alarm clock was set correctly—she didn’t feel qualified to help her patient with gender dysphoria. The therapist referred the family to some nearby gender-identity clinics that offered transition services for young people.

Claire’s parents were wary of starting that process. Heather, who has a doctorate in pharmacology, had begun researching youth gender dysphoria for herself. She hoped to better understand why Claire was feeling this way and what she and Mike could do to help. Heather concluded that Claire met the clinical criteria for gender dysphoria in the DSM-5, the American Psychiatric Association’s diagnostic manual. Among other indications, her daughter clearly didn’t feel like a girl, clearly wanted a boy’s body, and was deeply distressed by these feelings. But Heather questioned whether these criteria, or much of the information she found online, told the whole story. “Psychologists know that adolescence is fraught with uncertainty and identity searching, and this isn’t even acknowledged,” she told me.

Heather said most of the resources she found for parents of a gender-dysphoric child told her that if her daughter said she was trans, she was trans. If her daughter said she needed hormones, Heather’s responsibility was to help her get on hormones. The most important thing she could do was affirm her daughter, which Heather and Mike interpreted as meaning they should agree with her declarations that she was transgender. Even if they weren’t so certain.

As heather was searching for answers, Claire’s belief that she should transition was growing stronger. For months, she had been insistent that she wanted both testosterone and “top surgery”—a double mastectomy. She repeatedly asked her parents to find her doctors who could get her started on a path to physical transition. Heather and Mike bought time by telling her they were looking but hadn’t been able to find anyone yet. “We also took her kayaking, played more board games with her and watched more TV with her, and took other short family trips,” Heather recalled. “We also took away her ability to search online but gave her Instagram as a consolation.” They told her they realized that she was in pain, but they also felt, based on what they’d learned in their research, that it was possible her feelings about her gender would change over time. They asked her to start keeping a journal, hoping it would help her explore those feelings.

Claire humored her parents, even as her frustration with them mounted. Eventually, though, something shifted. In a journal entry Claire wrote last November, she traced her realization that she wasn’t a boy to one key moment. Looking in the mirror at a time when she was trying to present in a very male way—at “my baggy, uncomfortable clothes; my damaged, short hair; and my depressed-looking face”—she found that “it didn’t make me feel any better. I was still miserable, and I still hated myself.” From there, her distress gradually began to lift. “It was kind of sudden when I thought: You know, maybe this isn’t the right answer—maybe it’s something else,” Claire told me. “But it took a while to actually set in that yes, I was definitely a girl.”
Claire believes that her feeling that she was a boy stemmed from rigid views of gender roles that she had internalized. “I think I really had it set in stone what a guy was supposed to be like and what a girl was supposed to be like. I thought that if you didn’t follow the stereotypes of a girl, you were a guy, and if you didn’t follow the stereotypes of a guy, you were a girl.” She hadn’t seen herself in the other girls in her middle-school class, who were breaking into cliques and growing more gossipy. As she got a bit older, she found girls who shared her interests, and started to feel at home in her body.

Heather thinks that if she and Mike had heeded the information they found online, Claire would have started a physical transition and regretted it later. These days, Claire is a generally happy teenager whose mental-health issues have improved markedly. She still admires people, like Miles McKenna, who benefited from transitioning. But she’s come to realize that’s just not who she happens to be.

The number of self-identifying trans people in the United States is on the rise. In June 2016, the Williams Institute at the UCLA School of Law estimated that 1.4 million adults in the U.S. identify as transgender, a near-doubling of an estimate from about a decade earlier. As of 2017, according to the institute, about 150,000 teenagers ages 13 to 17 identified as trans. The number of young people seeking clinical services appears to be growing as well. A major clinic in the United Kingdom saw a more than 300 percent increase in new referrals over the past three years. In the U.S., where youth gender clinics are somewhat newer—40 or so are scattered across the country—solid numbers are harder to come by. Anecdotally, though, clinicians are reporting large upticks in new referrals, and waiting lists can stretch to five months or longer.

The current era of gender-identity awareness has undoubtedly made life easier for many young people who feel constricted by the sometimes-oppressive nature of gender expectations. A rich new language has taken root, granting kids who might have felt alone or excluded the words they need to describe their experiences. And the advent of the internet has allowed teenagers, even ones in parts of the country where acceptance of gender nonconformity continues to come far too slowly, to find others like them.

But when it comes to the question of physical interventions, this era has also brought fraught new challenges to many parents. Where is the line between not “feeling like” a girl because society makes it difficult to be a girl and needing hormones to alleviate dysphoria that otherwise won’t go away? How can parents tell? How can they help their children gain access to the support and medical help they might need, while also keeping in mind that adolescence is, by definition, a time of fevered identity exploration?

There is no shortage of information available for parents trying to navigate this difficult terrain. If you read the bible of medical and psychiatric care for transgender people — the Standards of Care issued by the World Professional Association for Transgender Health (Wpath) — you’ll find an 11-page section called “Assessment and Treatment of Children and Adolescents With Gender Dysphoria.” It states that while some teenagers should go on hormones, that decision should be made with deliberation: “Before any physical interventions are considered for adolescents, extensive exploration of psychological, family, and social issues should be undertaken.” The American Psychological Association’s guidelines sound a similar note, explaining the benefits of hormones but also noting that “adolescents can become intensely focused on their immediate desires.” It goes on: “This intense focus on immediate needs may create challenges in assuring that adolescents are cognitively and emotionally able to make life-altering decisions.”

The leading professional organizations offer this guidance. But some clinicians are moving toward a faster process. And other resources, including those produced by major LGBTQ organizations, place the emphasis on acceptance rather than inquiry. The Human Rights Campaign’s “Transgender Children & Youth: Understanding the Basics” web page, for example, encourages parents to seek the guidance of a gender specialist. It also asserts that “being transgender is not a phase, and trying to dismiss it as such can be harmful during a time when your child most needs support and validation.” Similarly, parents who consult the pages tagged “transgender youth” on glaad’s site will find many articles about supporting young people who come out as trans but little about the complicated diagnostic and developmental questions faced by the parents of a gender-exploring child.

HRC, glaad, and like-minded advocacy groups emphasize the acceptance of trans kids for understandable reasons: For far too long, parents, as well as clinicians, denied the possibility that trans kids and teens even existed, let alone that they should be allowed to transition. Many such organizations are primarily concerned with raising awareness and correcting still-common misconceptions.

A similar motive seems to animate much of the media coverage of transgender young people. Two genres of coverage have emerged. Dating back at least to the 1993 murder of the Nebraska 21-year-old Brandon Teena, which inspired a documentary as well as the film Boys Don’t Cry, a steady stream of horror stories has centered on bullying, physical assault, and suicide—real risks that transgender and gender-nonconforming (TGNC) young people still face.

More recently, a wave of success stories has appeared. In many of these accounts, kids are lost, confused, and frustrated right up until the moment they are allowed to grow their hair out and adopt a new name, at which point they finally become their true self. Take, for example, a Parents.com article in which a mother, writing pseudonymously, explains that she struggled with her child’s gender-identity issues for years, until finally turning to a therapist, who, after a 20-minute evaluation, pronounced the child trans. Suddenly, everything clicked into place. The mother writes: “I looked at the child sitting between my husband and me, the child who was smiling, who appeared so happy, who looked as if someone finally saw him or her the way she or he saw him or herself.” In a National Geographic special issue on gender, the writer Robin Marantz Henig recounts the story of a mother who let her 4-year-old, assigned male at birth, choose a girl’s name, start using female pronouns, and attend preschool as a girl. “Almost instantly the gloom lifted,” Henig writes.

Accounts of successful transitions can help families envision a happy outcome for a suffering child. And some young people clearly experience something like what these caterpillar-to-butterfly narratives depict. They have persistent, intense gender dysphoria from a very young age, and transitioning alleviates it. “Some kids don’t waver” in their gender identity, Nate Sharon, a psychiatrist who oversaw a gender clinic in New Mexico for two and a half years, and who is himself trans, told me when we spoke in 2016. “I’m seeing an 11-year-old who at age 2 went up to his mom and said, ‘When am I going to start growing my penis? Where’s my penis?’ At 2.”

But these stories tend to elide the complexities of being a TGNC young person, or the parent of one. Some families will find a series of forking paths, and won’t always know which direction is best. Like Claire’s parents, they may be convinced that their child is in pain, but also concerned that physical transition is not the solution, at least not for a young person still in the throes of adolescence.

We are still in the earliest stages of understanding how physical transitioning affects dysphoric young people. While the specifics depend on your child’s age, and can vary from case to case, the transition process for a persistently dysphoric child typically looks something like the following. First, allow your child to transition socially: to adopt the pronouns and style of dress of their authentic gender, and to change their name if they wish. As your child approaches adolescence, get them puberty-blocking drugs, because developing the secondary sex characteristics of their assigned sex could exacerbate their gender dysphoria. When they reach their teen years, help them gain access to the cross-sex hormones that will allow them to develop secondary sex characteristics in line with their gender identity. (Until recently, hormones were typically not prescribed until age 16; it’s now more common for 15- and 14-year-olds, and sometimes even younger kids, to begin hormone therapy.)

In the United States, avoiding puberty became an option only a little more than a decade ago, so researchers have just begun tracking the kids engaged in this process, and we don’t yet have comprehensive data about their long-term outcomes. Most of the data we do have involve kids who socially transitioned at an early age, but who hadn’t yet physically transitioned. The information comes from a University of Washington researcher named Kristina Olson. Olson is the founder of the TransYouth Project, which is following a cohort of about 300 children for 20 years—the longest such longitudinal study based in the U.S. The kids she is tracking appear to be doing well—they don’t seem all that different, in terms of their mental health and general happiness, from a control group of cisgender kids (that is, kids who identify with the sex they were assigned at birth).

At the prestigious Center of Expertise on Gender Dysphoria, at Vrije Universiteit University Medical Center, in Amsterdam—often referred to simply as “the Dutch clinic”—an older cohort of kids who went through the puberty-blockers-and-cross-sex-hormones protocol was also found to be doing well: “Gender dysphoria had resolved,” according to a study of the group published in 2014 in Pediatrics. “Psychological functioning had steadily improved, and well-being was comparable to same-age peers.”

These early results, while promising, can tell us only so much. Olson’s findings come from a group of trans kids whose parents are relatively wealthy and are active in trans-support communities; they volunteered their children for the study. There are limits to how much we can extrapolate from the Dutch study as well: That group went through a comprehensive diagnostic process prior to transitioning, which included continuous access to mental-health care at a top-tier gender clinic—a process unfortunately not available to every young person who transitions.

Among the issues yet to be addressed by long-term studies are the effects of medications on young people. As Thomas Steensma, a psychologist and researcher at the Dutch clinic and a co-author of that study, explained to me, data about the potential risks of putting young people on puberty blockers are scarce. He would like to see further research into the possible effects of blockers on bone and brain development. (The potential long-term risks of cross-sex hormones aren’t well known, but are likely modest, according to Joshua Safer, one of the authors of the Endocrine Society’s “Clinical Practice Guideline” for treatment of gender dysphoria.)

Meanwhile, fundamental questions about gender dysphoria remain unanswered. Researchers still don’t know what causes it—gender identity is generally viewed as a complicated weave of biological, psychological, and sociocultural factors. In some cases, gender dysphoria may interact with mental-health conditions such as depression and anxiety, but there’s little agreement about how or why. Trauma, particularly sexual trauma, can contribute to or exacerbate dysphoria in some patients, but again, no one yet knows exactly why.

To reiterate: For many of the young people in the early studies, transitioning—socially for children, physically for adolescents and young adults—appears to have greatly alleviated their dysphoria. But it’s not the answer for everyone. Some kids are dysphoric from a very young age, but in time become comfortable with their body. Some develop dysphoria around the same time they enter puberty, but their suffering is temporary. Others end up identifying as nonbinary—that is, neither male nor female.

Ignoring the diversity of these experiences and focusing only on those who were effectively “born in the wrong body” could cause harm. That is the argument of a small but vocal group of men and women who have transitioned, only to return to their assigned sex. Many of these so-called detransitioners argue that their dysphoria was caused not by a deep-seated mismatch between their gender identity and their body but rather by mental-health problems, trauma, societal misogyny, or some combination of these and other factors. They say they were nudged toward the physical interventions of hormones or surgery by peer pressure or by clinicians who overlooked other potential explanations for their distress.

Some of these interventions are irreversible. People respond differently to cross-sex hormones, but changes in vocal pitch, body hair, and other physical characteristics, such as the development of breast tissue, can become permanent. Kids who go on puberty blockers and then on cross-sex hormones may not be able to have biological children. Surgical interventions can sometimes be reversed with further surgeries, but often with disappointing results.

The concerns of the detransitioners are echoed by a number of clinicians who work in this field, most of whom are psychologists and psychiatrists. They very much support so-called affirming care, which entails accepting and exploring a child’s statements about their gender identity in a compassionate manner. But they worry that, in an otherwise laudable effort to get TGNC young people the care they need, some members of their field are ignoring the complexity, and fluidity, of gender-identity development in young people. These colleagues are approving teenagers for hormone therapy, or even top surgery, without fully examining their mental health or the social and family influences that could be shaping their nascent sense of their gender identity.

That’s too narrow a definition of affirming care, in the view of many leading clinicians. “Affirming care does not privilege any one outcome when it comes to gender identity, but instead aims to allow exploration of gender without judgment and with a clear understanding of the risks, benefits, and alternatives to any choice along the way,” Aron Janssen, the clinical director of the Gender and Sexuality Service at Hassenfeld Children’s Hospital, in New York, told me. “Many people misinterpret affirming care as proceeding to social and medical transition in all cases without delay, but the reality is much more complex.”

…. Wpath and other organizations that provide guidance for transitioning young people call for thorough assessments of patients before they start taking blockers or hormones. This caution comes from the concerns inherent in working with young people. Adolescents change significantly and rapidly; they may view themselves and their place in the world differently at 15 than they did at 12.

“You’ve got the onset of puberty right around the age where they develop the concept of abstract thinking,” said Nate Sharon, the New Mexico psychiatrist. “So they may start to conceptualize gender concepts in a much richer, broader manner than previously—and then maybe puberty blockers or cross-sex hormones aren’t for them.” That was true for Claire: A shift in her understanding of the nature of gender led her to realize that transitioning was not the answer for her.

For younger children, gender identity is an even trickier concept. In one experiment, for example, many 3-to-5-year-olds thought that if a boy put on a dress, he became a girl. Gender clinicians sometimes encounter young children who believe they are, or want to be, another gender because of their dress or play preferences—I like rough-and-tumble play, so I must be a boy—but who don’t meet the criteria for gender dysphoria.

In the past, therapists and doctors interpreted the fluidity of gender identity among children as license to put gender-bending kids into the “right” box by encouraging—or forcing—them to play with the “right” toys and dress in the “right” clothes. Until about five years ago, according to one clinician’s estimate, social transition was often frowned upon. For decades, trans-ness was sometimes tolerated in adults as a last-ditch outcome, but in young people it was more often seen as something to be drummed out rather than explored or accepted. So-called reparative therapy has harmed and humiliated trans and gender-nonconforming children. In her book Gender Born, Gender Made, Diane Ehrensaft, the director of mental health at UC San Francisco’s Child and Adolescent Gender Center, writes that victims of these practices “become listless or agitated, long for their taken-away favorite toys and clothes, and even literally go into hiding in closets to continue playing with the verboten toys or wearing the forbidden clothes.” Such therapy is now viewed as unethical.


When max robinson was 17, getting a double mastectomy made perfect sense to her. In fact, it felt like her only option—like a miraculous, lifesaving procedure. Though she had a woman’s body, she was really a man. Surgery would finally offer her a chance to be herself.

I met Max, now 22, in an airy café in the quiet southern-Oregon town where she lives. She was wearing a T‑shirt with a flannel button-down over it. On her head, a gray winter cap; at her feet, a shaggy white service dog. By the time we met, we’d spoken on the phone and exchanged a number of emails, and she had told me her story—one that suggests the complexity of gender-identity development.

Max recalled that as early as age 5, she didn’t enjoy being treated like a girl. “I questioned my teachers about why I had to make an angel instead of a Santa for a Christmas craft, or why the girls’ bathroom pass had ribbons instead of soccer balls, when I played soccer and knew lots of other girls in our class who loved soccer,” she said.

She grew up a happy tomboy—until puberty. “People expect you to grow out of it” at that age, she explained, “and people start getting uncomfortable when you don’t.” Worse, “the way people treated me started getting increasingly sexualized.” She remembered one boy who, when she was 12, kept asking her to pick up his pencil so he could look down her shirt.

“I started dissociating from my body a lot more when I started going through puberty,” Max said. Her discomfort grew more internalized—less a frustration with how the world treated women and more a sense that the problem lay in her own body. She came to believe that being a woman was “something I had to control and fix.” She had tried various ways of making her discomfort abate—in seventh grade, she vacillated between “dressing like a 12-year-old boy” and wearing revealing, low-cut outfits, attempts to defy and accede to the demands the world was making of her body. But nothing could banish her feeling that womanhood wasn’t for her. She had more bad experiences with men, too: When she was 13, she had sex with an older man she was seeing; at the time, it felt consensual, but she has since realized that a 13-year-old can’t consent to sex with an 18-year-old. At 14, she witnessed a friend get molested by an adult man at a church slumber party. Around this time, Max was diagnosed with depression and generalized anxiety disorder.

In ninth grade, Max first encountered the concept of being transgender when she watched an episode of The Tyra Banks Show in which Buck Angel, a trans porn star, talked about his transition. It opened up a new world of online gender-identity exploration. She gradually decided that she needed to transition.

Max’s parents were skeptical at first but eventually came around, signing her up for sessions with a therapist who specialized in gender-identity issues. She recalled that the specialist was very open to putting her on a track toward transition, though he suggested that her discomfort could have other sources as well. Max, however, was certain that transitioning was the answer. She told me that she “refused to talk about anything other than transition.”

When Max was 16, her therapist wrote her a referral to see an endocrinologist who could help her begin the process of physical transition by prescribing male hormones. The endocrinologist was skeptical, Max said. “I think what she was seeing was a lesbian teenager,” not a trans one. At the time, though, Max interpreted the doctor’s reluctance as her “being ignorant, as her trying to hurt me.” Armed with the referral from her therapist, Max got the endocrinologist to prescribe the treatment she sought.

Max started taking testosterone. She experienced some side effects—hot flashes, memory issues—but the hormones also provided real relief. Her plan all along had been to get top surgery, too, and the initially promising effects of the hormones helped persuade her to continue on this path. When she was 17, Max, who was still dealing with major mental-health issues, was scheduled for surgery.

Because Max had parental approval, the surgeon she saw agreed to operate on her despite the fact that she was still a minor. (It’s become more common for surgeons to perform top surgeries on teenagers as young as 16 if they have parental approval. The medical norms are more conservative when it comes to bottom surgeries; Wpath says they should be performed only on adults who have been living in their gender role for at least one year.) Max went into the surgery optimistic. “I was convinced it would solve a lot of my problems,” she said, “and I hadn’t accurately named a lot of those problems yet.”

Max was initially happy with the results of her physical transformation. Before surgery, she wasn’t able to fully pass as male. After surgery, between her newly masculinized chest and the facial hair she was able to grow thanks to the hormones, she felt like she had left behind the sex she had been assigned at birth. “It felt like an accomplishment to be seen the way I wanted to be seen,” she told me.

But that feeling didn’t last. After her surgery, Max moved from her native California to Portland and threw herself into the trans scene there. It wasn’t a happy home. The clarity of identity she was seeking—and that she’d felt, temporarily, after starting hormones and undergoing surgery—never fully set in. Her discomfort didn’t go away.

Today, Max identifies as a woman. She believes that she misinterpreted her sexual orientation, as well as the effects of the misogyny and trauma she had experienced as a young person, as being about gender identity. Because of the hormone therapy, she still has facial hair and is frequently mistaken for male as a result, but she has learned to live with this: “My sense of self isn’t entirely dependent on how other people see me.”

Max is one of what appears to be a growing number of people who believe they were failed by the therapists and physicians they went to for help with their gender dysphoria. While their individual stories differ, they tend to touch on similar themes. Most began transitioning during adolescence or early adulthood. Many were on hormones for extended periods of time, causing permanent changes to their voice, appearance, or both. Some, like Max, also had surgery.

Many detransitioners feel that during the process leading up to their transition, well-meaning clinicians left unexplored their overlapping mental-health troubles or past traumas. Though Max’s therapist had tried to work on other issues with her, Max now believes she was encouraged to rush into physical transition by clinicians operating within a framework that saw it as the only way someone like her could experience relief. Despite the fact that she was a minor for much of the process, she says, her doctors more or less did as she told them.

Over the past couple of years, the detransitioner movement has become more visible. Last fall, Max told her story to The Economist’s magazine of culture and ideas, 1843. Detransitioners who previously blogged pseudonymously, largely on Tumblr, have begun writing under their real names, as well as speaking on camera in YouTube videos.

Cari Stella is the author of a blog called Guide on Raging Stars. Stella, now 24, socially transitioned at 15, started hormones at 17, got a double mastectomy at 20, and detransitioned at 22. “I’m a real-live 22-year-old woman with a scarred chest and a broken voice and a 5 o’clock shadow because I couldn’t face the idea of growing up to be a woman,” she said in a video posted in August 2016. “I was not a very emotionally stable teenager,” she told me when we spoke. Transitioning offered a “level of control over how I was being perceived.”

Carey Callahan is a 36-year-old woman living in Ohio who detransitioned after identifying as trans for four years and spending nine months on male hormones. She previously blogged under the pseudonym Maria Catt, but “came out” in a YouTube video in July 2016. She now serves as something of an older sister to a network of female, mostly younger detransitioners, about 70 of whom she has met in person; she told me she has corresponded online with an additional 300. (The detransitioners who have spoken out thus far are mostly people who were assigned female at birth. Traditionally, most new arrivals at youth gender clinics were assigned male; today, many clinics are reporting that new patients are mostly assigned female. There is no consensus explanation for the change.)

I met Carey in Columbus in March. She told me that her decision to detransition grew out of her experience working at a trans clinic in San Francisco in 2014 and 2015. “People had said often to me that when you transition, your gender dysphoria gets worse before it gets better,” she told me. “But I saw and knew so many people who were cutting themselves, starving themselves, never leaving their apartments. That made me doubt the narrative that if you make it all the way to medical transition, then it’s probably going to work out well for you.”

Carey said she met people who appeared to be grappling with severe trauma and mental illness, but were fixated on their next transition milestone, convinced thatwas the moment when they would get better. “I knew a lot of people committed to that narrative who didn’t seem to be doing well,” she recalled. Carey’s time at the clinic made her realize that testosterone hadn’t made her feel better in a sustained way either. She detransitioned, moved to Ohio, and is now calling for a more careful approach to treating gender dysphoria than what many detransitioners say they experienced themselves.

In part, that would mean clinicians adhering to guidelines like Wpath’s Standards of Care, which are nonbinding. “When I look at what the SOC describes, and then I look at my own experience and my friends’ experiences of pursuing hormones and surgery, there’s hardly any overlap between the directives of the SOC and the reality of care patients get,” Carey told me. “We didn’t discuss all the implications of medical intervention—psychological, social, physical, sexual, occupational, financial, and legal—which the SOC directs the mental-health professional to discuss. What the SOC describes and the care people get before getting cleared for hormones and surgery are miles apart.”


…. Within a subset of trans advocacy, however, desistance isn’t viewed as a phenomenon we’ve yet to fully understand and quantify but rather as a myth to be dispelled. Those who raise the subject of desistance are often believed to have nefarious motives—the liberal outlet ThinkProgress, for example, referred to desistance research as “the pernicious junk science stalking trans kids,” and a subgenre of articles and blog posts attempts to debunk “the desistance myth.” But the evidence that desistance occurs is overwhelming. The American Psychological Association, the Substance Abuse and Mental Health Services Administration, the Endocrine Society, and Wpath all recognize that desistance occurs. I didn’t speak with a single clinician who believes otherwise. “I’ve seen it clinically happen,” Nate Sharon said. “It’s not a myth.”

… Even some of the clinicians who have emphasized the need to be deferential to young people acknowledge the complexities at play here. A psychologist with decades of experience working with TGNC young people, Diane Ehrensaft is perhaps the most frequently quoted youth-gender clinician in the country. She is tireless in her advocacy for trans kids. “It’s the children who are now leading us,” she told The Washington Post recently. She sees this as a positive development: “If you listen to the children, you will discover their gender,” she wrote in one article. “It is not for us to tell, but for them to say.”

But when I spoke with Ehrensaft at her home in Oakland, she described many situations involving physical interventions in which her work was far more complicated than simply affirming a client’s self-diagnosis. “This is what I tell kids all the time, particularly teenagers,” she said. “Often they’re pushing for fast. I say, ‘Look, I’m old, you’re young. I go slow, you go fast. We’re going to have to work that out.’ ” Sometimes, she said, she suspects that a kid who wants hormones right now is simply reciting something he found on the internet. “It just feels wooden, is the only thing I can say,” she told me.

…Suicide is the dark undercurrent of many discussions among parents of TGNC young people. Suicide and suicidal ideation are tragically common in the transgender community. An analysis conducted by the American Foundation for Suicide Prevention and the Williams Institute, published in 2014, found that 41 percent of trans respondents had attempted suicide; 4.6 percent of the overall U.S. population report having attempted suicide at least once. While the authors note that for methodological reasons 41 percent is likely an overestimate, it still points to a scarily high figure, and other research has consistently shown that trans people have elevated rates of suicidal ideation and suicide relative to cisgender people.

But the existence of a high suicide rate among trans people—a population facing high instances of homelessness, sexual assault, and discrimination—does not imply that it is common for young people to become suicidal if they aren’t granted immediate access to puberty blockers or hormones. Parents and clinicians do need to make fraught decisions fairly quickly in certain situations. When severely dysphoric kids are approaching puberty, for instance, blockers can be a crucial tool to buy time, and sometimes there’s a genuine rush to gain access to them, particularly in light of the waiting lists at many gender clinics. But the clinicians I interviewed said they rarely encounter situations in which immediate access to hormones is the difference between suicide and survival. Leibowitz noted that a relationship with a caring therapist may itself be an important prophylactic against suicidal ideation for TGNC youth: “Often for the first time having a medical or mental-health professional tell them that they are going to take them seriously and really listen to them and hear their story often helps them feel better than they’ve ever felt.”

When parents discuss the reasons they question their children’s desire to transition, whether in online forums or in response to a journalist’s questions, many mention “social contagion.” These parents are worried that their kids are influenced by the gender-identity exploration they’re seeing online and perhaps at school or in other social settings, rather than experiencing gender dysphoria.

Many trans advocates find the idea of social contagion silly or even offensive given the bullying, violence, and other abuse this population faces. They also point out that some parents simply might not want a trans kid—again, parental skepticism or rejection is a painfully common experience for trans young people. Michelle Forcier, a pediatrician who specializes in youth-gender issues in Rhode Island, said the trans adolescents she works with frequently tell her things like No one’s taking me seriously—my parents think this is a phase or a fad.

But some anecdotal evidence suggests that social forces can play a role in a young person’s gender questioning. “I’ve been seeing this more frequently,” Laura Edwards-Leeper wrote in an email. Her young clients talk openly about peer influence, saying things like Oh, Steve is really trans, but Rachel is just doing it for attention. Scott Padberg did exactly this when we met for lunch: He said there are kids in his school who claim to be trans but who he believes are not. “They all flaunt it around, like: ‘I’m trans, I’m trans, I’m trans,’ ” he said. “They post it on social media.”

I heard a similar story from a quirky 16-year-old theater kid who was going by the nickname Delta when we spoke. She lives outside Portland, Oregon, with her mother and father. A wave of gender-identity experimentation hit her social circle in 2013. Suddenly, it seemed, no one was cisgender anymore. Delta, who was 13 and homeschooled, soon announced to her parents that she was genderqueer, then nonbinary, and finally trans. Then she told them she wanted to go on testosterone. Her parents were skeptical, both because of the social influence they saw at work and because Delta had anxiety and depression, which they felt could be contributing to her distress. But when her mother, Jenny, sought out information, she found herself in online parenting groups where she was told that if she dragged her feet about Delta’s transition, she was potentially endangering her daughter. “Any questioning brought down the hammer on you,” she told me.

Delta’s parents took her to see Edwards-Leeper. The psychologist didn’t question her about being trans or close the door on her eventually starting hormones. Rather, she asked Delta a host of detailed questions about her life and mental health and family. Edwards-Leeper advised her to wait until she was a bit older to take steps toward a physical transition—as Delta recalled, she said something like “I acknowledge that you feel a certain way, but I think we should work on other stuff first, and then if you still feel this way later on in life, then I will help you with that.”

“Other stuff” mostly meant her problems with anxiety and depression. Edwards-Leeper told Jenny and Delta that while Delta met the clinical threshold for gender dysphoria, a deliberate approach made the most sense in light of her mental-health issues.

“At the time I was not happy that she told me that I should go and deal with mental stuff first,” Delta said, “but I’m glad that she said that, because too many people are so gung ho and just like, ‘You’re trans, just go ahead,’ even if they aren’t—and then they end up making mistakes that they can’t redo.” Delta’s gender dysphoria subsequently dissipated, though it’s unclear why. She started taking antidepressants in December, which seem to be working. I asked Delta whether she thought her mental-health problems and identity questioning were linked. “They definitely were,” she said. “Because once I actually started working on things, I got better and I didn’t want anything to do with gender labels—I was fine with just being me and not being a specific thing.”

How best to support tgnc kids is a whiplash-inducing subject. To understand even just the small set of stories I encountered in my reporting—stories involving relatively privileged white kids with caring, involved families, none of which is necessarily the case for all TGNC young people in the United States—requires keeping several seemingly conflicting claims in mind. Some teenagers, in the years ahead, are going to rush into physically transitioning and may regret it. Other teens will be prevented from accessing hormones and will suffer great anguish as a result. Along the way, a heartbreaking number of trans and gender-nonconforming teens will be bullied and ostracized and will even end their own lives.

Some LGBTQ advocates have called for gender dysphoria to be removed from the DSM-5, arguing that its inclusion pathologizes being trans. But gender dysphoria, as science currently understands it, is a painful condition that requires treatment to be alleviated. Given the diversity of outcomes among kids who experience dysphoria at one time or another, it’s hard to imagine a system without a standardized, comprehensive diagnostic protocol, one designed to maximize good outcomes.


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§107. Limitations on Exclusive Rights: Fair Use. Notwithstanding the provisions of section 106, the fair use of a copyrighted work, including such use by reproduction in copies or phone records or by any other means specified by that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research, is not an infringement of copyright. In determining whether the use made of a work in any particular case is a fair use, the factors to be considered shall include: the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes; the nature of the copyrighted work; the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and the effect of the use upon the potential market for or value of the copyrighted work. (added pub. l 94-553, Title I, 101, Oct 19, 1976, 90 Stat 2546)



What is the definition of a dinosaur?


Evolution clades dinosaurs by Zureks

CC BY-SA 3.0, Wikipedia, Evolution of dinosaurs, Zureks


Types of dinosaurs

saurischians (‘lizard hipped dinosaurs’) and ornithischians (‘bird hipped dinosaurs’)

Possible new way of classifying dinosaurs



Ornithoscelida Rises: A New Family Tree for Dinosaurs, Scientific American

Discussion from Carnivoraforum

How did dinosaurs evolve?


What forms of life have evolved from dinosaurs?

Short version: Almost all branches of the dinosaur family tree died out, except for the branch with small feathered dinosaurs. That branch proliferated and developed into the birds that we know today.

Long version: TBA

Bone Growth Evolution Birds by SHAWN GOULD (illustrations) JEN CHRISTIANSEN (cladogram)

Image by Shawn Gould and Jen Christiansen, from How Dinosaurs Grew So Large—And So Small John R. Horner, Kevin Padian and Armand de RicqlèS Scientific American 293, 56 – 63 (2005)


Zina Deretsky NSF air sac birds dinosaur

Zina Deretsky, National Science Foundation. Air sac system of birds and of Majungasaurus.


The origin of birds evolution.berkeley.edu

How did most dinosaurs become extinct?

Short version: Meteor impact – and perhaps associated Deccan traps volcanic event?



How do we learn about dinosaurs? Fossils



and also


The science of Jurassic Park



Mythology and dinosaurs



Which came first, the chicken or the egg?



Reptiles are not a true clade



Learning Standards

Next Generation Science Standards

HS-LS4-1. Communicate scientific information that common ancestry and biological evolution are supported by multiple lines of empirical evidence.

HS-LS4-1. Communicate scientific information that common ancestry and biological evolution are supported by multiple lines of empirical evidence.

HS-LS4-2. Construct an explanation based on evidence that the process of evolution primarily results from four factors: (1) the potential for a species to increase in number, (2) the heritable genetic variation of individuals in a species due to mutation and sexual reproduction, (3) competition for limited resources, and (4) the proliferation of those organisms that are better able to survive and reproduce in the environment.

HS-LS4-3. Apply concepts of statistics and probability to support explanations that organisms with an advantageous heritable trait tend to increase in proportion to organisms lacking this trait.

HS-LS4-4. Construct an explanation based on evidence for how natural selection leads to adaptation of populations.

HS-LS4-5. Evaluate the evidence supporting claims that changes in environmental conditions may result in (1) increases in the number of individuals of some species, (2) the emergence of new species over time, and (3) the extinction of other species.


MCAS Open response

Sarah and her biological sister Danielle have some physical characteristics that are the same and some that are different, as shown in the table below.

MCAS traits

a. Identify the molecule that stores the hereditary information for these characteristics in the chromosomes of every body cell.

b. Identify the total number of chromosomes that should be in one of Sarah’s body cells and the number of chromosomes that should have been contributed by each biological parent.

c. Explain the roles of meiosis and fertilization in achieving the chromosome numbers you identified in part (b).

d. Explain why Sarah and Danielle have some physical characteristics that are different from each other, even though they have the same biological parents.

Sample question: Recognize that the sexual reproductive system allows organisms to produce offspring…


MCAS 2013 open response

MCAS 2014 open response

MCAS 2015 open response

MCAS 2016 open response

MCAS 2017 open response


Cortical homunculus

The cortical homunculus is the part of the brain responsible for processing and integration of motor information (muscles, motion) and tactile information (touch, senses)

The reason for the distorted appearance is that the amount of cortex is proportional to how richly innervated that region is, not to its size.

The resulting image appears as a disfigured human with disproportionately huge hands, lips, and face in comparison to the rest of the body.


Sensory Homunculus Brain



from Wikipedia

Herd immunity

The top box shows an outbreak in a community in which a few people are infected (shown in red) and the rest are healthy but unimmunized (shown in blue); the illness spreads freely through the population.

The middle box shows a population where a small number have been immunized (shown in yellow); those not immunized become infected while those immunized do not.

In the bottom box, a large proportion of the population have been immunized; this prevents the illness from spreading significantly, including to unimmunized people.

In the first example, most healthy unimmunized people become infected, whereas in the bottom example only one fourth of the healthy unimmunized people become infected.

Herd immunity

 The National Institute of Allergy and Infectious Disease (NIAID)


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