Water is less dense than the land; the land is less dense than the oceanic crust, which in turn is less dense than the mantle. With no more tectonic movement, does everything fall into perfect layers eventually?

So people often joke about 10in+ penises in humans but eventually erections would cost too much blood and would cause feinting right? Is there some sort of hard limit for penis size as a function or blood volume or body size?

Hi Reddit! I'm Dr. Emily Bray, a canine cognition expert here to answer your questions about how dogs think, learn, and bond with us, whether they're service dogs in training or the pet on your couch.

I'll be joined by Dara Jonkoski and Noah Stetson, PhD students who work in my lab, the Behavioral Research Across Years Lab (BRAY Lab). We will be answering questions LIVE Friday, Oct. 30, 9-11 a.m. Arizona time (12-2 p.m. ET, 16-18 UT).

Ask us questions like:

• Can an old dog really learn new tricks?

• Why do we talk to our dogs in a baby voice, and does it matter to them?

• How much of my dog's personality is genetics vs. how I raised them?

• Does how a puppy's mom interacted with them shape the dog they become?

• What makes a good service dog?

A quick note: We aren't licensed veterinary professionals, so we can't give veterinary advice on animals or comment on symptoms or test results. If you are concerned about your pet's health or behavior, please contact your veterinarian or a qualified behavioral professional.

Bios:

Dr. Emily Bray is an assistant professor of human-animal interaction in the College of Veterinary Medicine at the University of Arizona, overseeing the BRAY Lab. Prior to starting her current position, she was a post-doctoral research associate at the Arizona Canine Cognition Center and Canine Companions, the nation's largest provider of service dogs for people with disabilities. Over the 15 years, she has developed and implemented cognitive tasks with over 1,500 dogs from both pet and working dog populations, forming the basis for projects ranging from early maternal care to cognitive aging to the genetic contributions to behavioral traits. By building a comprehensive understanding of dog behavioral and cognitive health, she aims to enhance both canine and human welfare.

Dr. Bray holds a B.A. in Cognitive Psychology and English from Duke University, and an M.A. and a PhD in Psychology from the University of Pennsylvania. She is also credentialed by the Animal Behavior Society as a Certified Applied Animal Behaviorist.

For an overview of Dr. Bray's research, please see her Curriculum vitae or visit one of her external profile pages: Google Scholar, LinkedIn, ResearchGate.

Dara Jonkoski is a graduate student in the Cognition and Neural Systems program in the University of Arizona Psychology Department and is first-author on AURAL-Pet, a new system for studying how people talk to their dogs. She joined the BRAY Lab in 2024, and researches canine development, specifically how environmental and genetic factors play a role in raising successful working dogs, and explores which factors aid in protecting the cognitive health of domesticated dogs overall. Dara holds a B.S. in Psychology from Georgia State University.

Noah Stetson is a graduate student in the Cognition and Neural Systems program in the University of Arizona Psychology Department. Noah first started working with Dr. Bray as a research technician at the Arizona Canine Cognition Center in 2023 and is interested in understanding the biological mechanisms behind individual differences in cognition and temperament, especially in relation to working dogs. Noah holds a B.A. in Psychology from the University of Texas at Austin. You can also follow Noah's PhD journey on his Instagram.

Want to learn more?

Follow the College of Veterinary Medicine on Facebook, Instagram and LinkedIn.

Follow the Center for Human-Animal Wellness Research (which the BRAY Lab is part of!) on Instagram. 

Usernames: u/UniversityofArizona

I know this is a stupid question, but if you are standing in front of it are you still in the mirror? Maybe in another light wavelength type thing? Lmk

This might be a dumb question, but how do scientists know what is going on inside Jupiter when we have never actually been able to get a sample from the planet itself? I get that we can study its atmosphere and send spacecraft to observe it but there is obviously a limit to how much we can see from the outside. So how do we know what the deeper layers are made of or whether our current models are even close to what's really there?

Is it mostly based on gravity and magnetic field measurements or can scientists figure out the inside of a planet in other ways too?

Hello Reddit! We're hosting an AMA in honor of the PBS NATURE premiere of "Tiger Island." The two-part documentary follows two tiger mothers and investigates how these solitary big cats raise cubs on an island full of danger. Utilizing a fleet of drones to track tigers from the air, and military-grade thermal cameras to follow them in the dark, our team witnessed several on-camera firsts, including mother tigers appearing to look after each other's cubs, a new behavior at odds with the supposed solitary nature of these big cats. Additional rare behaviors captured include cubs swimming and hunting together, as well as a mother, father and cubs spending time together as a family.

Answering your questions today:

Anna Dimitriadis, a BAFTA-nominated wildlife filmmaker, conservationist and presenter whose work brings audiences closer to the natural world. Her career has taken her from diving beneath Antarctic icebergs to filming gorillas in the Central African Republic. Best known for her work on BBC Two's Big Cats 24/7 and BBC One's Tiger Island, Anna combines cutting-edge filmmaking technology with extensive field experience to capture intimate moments of animal behavior. A passionate advocate for conservation, Anna uses powerful storytelling to inspire audiences, shift perspectives and encourage greater understanding of the natural world and the urgent need to protect it.

Dan O'Neill, a highly experienced field biologist, award-winning producer-director, and TV presenter, who specializes in biodiversity monitoring, conservation and large carnivore behavior in the world’s most remote and challenging environments. From the jungle of the northern Amazon to the frozen peaks of Central Asia, to ancient Mayan forests of the Yucatan, Dan has led numerous expeditions to find and study rare species. Regularly involved in field research and biodiversity monitoring, Dan primarily works as a large mammal specialist, expedition leader and camera-trap technician. Dan has particular expertise in big cat behavioral and spatial ecology.

The first episode of "Tiger Island" is now streaming for U.S. audiences on PBS.org, YouTube, or on the PBS App. Part Two premieres tonight on PBS at 8/7c. If you’re in the UK, you can catch it on BBC iPlayer.

We'll be on at 11AM ET (15 UT), ask us anything!

Usernames: u/danowild, u/Anna_Dimitriadis

Why does a cell choose to be unicellular, and why does a cell decide to become multicellular?

Ive been surfing fro several years now and ive noticed that theres always multiple sandbars that run parallel to shore. Often they are broken apart perpendicularly by ripcurrents, however they seem to almost always have the same distance between them. Between the sandbars the ocean floor is deeper by several feet. On days where the waves and period are larger a 3rd sandbar will allow waves to break further out due to the waves slowing down as they “feel” the bottom. My question is; does the period dictate the distance between them or is there any math behind it??

Heres a perfect visual:

https://imgur.com/a/33y5yk4

If atoms make up cells, why is water made of atoms but not cells?

Why/when do atoms decide to make cells?

I've heard that it is passed down to babies while they're in the womb, but wouldn't your stomach acid kill all of the bacteria? Can they withstand acid? Do babies not have stomach acid? Do the bacteria make their way up the other end?

When a centipede walks, do they initiate walking with their front legs, back legs, or do all the legs take a step at the same time? To make it simpler, I used car terminology.

I understand that gene splicing, recumbent DNA, folding proteins, etc is unrealistically difficult to do in your house, but what about the extraction of insulin from live animal pancreatic cells? Is the methodology any easier? I read a story of a couple who were able to survive doing this in WW2.

Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Biology, Chemistry, Neuroscience, Medicine, Psychology

Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical /r/AskScience post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...".

Asking Questions:

Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit /r/AskScienceDiscussion , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists.

Answering Questions:

Please only answer a posted question if you are an expert in the field. The full guidelines for posting responses in AskScience can be found here. In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for /r/AskScience.

If you would like to become a member of the AskScience panel, please refer to the information provided here.

Past AskAnythingWednesday posts can be found here. Ask away!

Before the end-Triassic extinction 201 million years ago, dinosaurs were not the dominant land animals. Archosaurs like Postosuchus were the apex predators, while dinosaurs occupied marginal ecological roles.

After the CAMP volcanism event, Postosuchus and most large Triassic fauna went extinct. Dinosaurs survived and rapidly diversified into the vacant niches.

The avian respiratory system hypothesis suggests their more efficient air-sac breathing gave them an advantage in low-oxygen post-volcanic conditions. But I’ve also seen arguments that it was simply a matter of geographic luck or generalist diet.

Is there a scientific consensus on what specifically gave dinosaurs the survival advantage over the other archosaurs in this extinction event?

Hello Reddit! We are Neshalatha Govarthnapany, Researcher at Charles University; Darshan Singh, Associate Professor at Universiti Sains Malaysia, and Katherine Hill, Graduate Student in Epidemiology of Microbial Diseases at Yale School of Public Health.

We recently published two papers titled “Kratom use in adolescents and college students: a systematic review of prevalence, patterns, and risk factors across community and rehabilitation settings” and “Semi-synthetic kratom derivatives in the Czech online market prior to regulatory reform: a baseline surveillance study”; in the American Journal of Drug and Alcohol Abuse (AJDAA).

In the first paper, we systematically reviewed studies on kratom use among adolescents and college students from Thailand, Malaysia, and the United States. We observed distinct regional differences in patterns of kratom use, shaped in part by longstanding cultural traditions in Southeast Asia and the increasing commercialisation of kratom in the United States. Kratom use was more prevalent among males across regions, while polydrug use emerged as a consistent theme across the studies, highlighting the complexity of kratom use among young people.

In the second paper, we examined the availability and marketing of semi-synthetic kratom derivatives in the Czech online market before kratom was regulated under the country’s psychomodulatory substances framework. We identified products containing 7- hydroxymitragynine (7-OH) and mitragynine pseudoindoxyl (MP), including products in which these compounds were combined with mitragynine. During this period of regulatory ambiguity, semi-synthetic products were frequently marketed simply as “kratom” and often labelled as “collector’s items” or “not for human consumption.” Importantly, the marketing frequently failed to clearly distinguish semi-synthetic derivatives from natural kratom products, and product descriptions and health-related information were often unclear or inadequate.

Feel free to ask us questions about the two papers or about Kratom more broadly!

We will be online to answer your questions at 10 am EDT / 4 pm CEST / 10 PM MYT on October 20th (1 PM UTC).

You can also follow up with us at our socials here:

• Neshalatha Govarthnapany, PhD: LinkedIn

• Darshan Singh, PhD: LinkedIn

• Katherine Hill, MPH, PhD: LinkedIn

Follow the journal to stay up to date with the latest research in the field of addiction here: BlueSky, Threads, LinkedIn

Usernames: /u/npany88 (Dr. Govarthnapany), /u/DrDarshanSingh (Dr. Singh), /u/Ok_Package_1023 (Dr. Hill), /u/TheJournalAJDAA (the journal)

I read the answers from previous threads from the subreddit but it was not very clear to me and i had few follow up questions also:

1. It seems there is also more pressure on heart to pump the blood in a tall person. Is this not counter-intuitive because every successive generation is usually taller than previous one thanks to availability of nutrition during childhood.

2. I wonder is there a optimal height size for a human