Welcome back to Nature League!

While producing videos for this channel, we've received a lot of interesting and fun questions from viewers on social media and in the comments section. We love your curiosity about life on Earth and Nature League, so why not dig into some of these topics.

Yep -- it's time for a Q and A video! [CHEERY INTRO MUSIC]. Well, we've obviously got to start with sharks. It's well known that baby sharks doo doo are younger than mommy sharks doo doo, but how do you actually age a shark?

There are several ways to estimate the ages of individual organisms, and sharks are no exception. The most common aging technique used on sharks and their relatives is counting growth zones on calcified structures. Bony fish are typically aged by using calcified structures like fins and ear bones.

However, sharks skeletons don't have true bones, and they lack these structures that are used to age other species. Luckily, sharks and their relatives have other different structures that will calcify. These include structures like vertebrae, spines, and caudal thorns.

These calcified pieces can be processed in a way that allows counting of growth zones, which are patterns of bands that differ in appearance -- sort of similar to counting growth rings in trees. Age validation has proven to be really tricky for shark researchers, and some recent reviews have reported that most ages have actually been underestimated in the past. Nevertheless, identifying and counting growth bands in calcified structures is the most common approach.

But if that doesn't work, you can always just ask them how old they are...unless they're a lady shark, in which case that's considered rude in finer company. Why do smaller dog breeds live longer than large breeds? The longest lived mammals on Earth tend to be big... really big.

Like, whales, for example. However, on average, small domestic dog breeds live longer than large breeds, which seems to be contrary to other patterns on Earth. This is sort of an open question in veterinary science, but I'm happy to share some leading theories and patterns.

First, the leading cause of death in large dog breeds is cancer- so, there might be something going on with cell growth and proliferation in these breeds. Additionally, larger breeds actually grow faster, meaning they're aging at an accelerated pace. This could have some kind of impact on processes that initiate abnormal cell growth and cancer.

As stated in a 2013 journal article on the topic, large dogs die young mainly because they age quickly. However, more research is still needed. Reusable “green” products are trending with a lot with some companies, but what about with the scientific community?

Specifically, do biodiversity experts follow certain trends when it comes to consumption of resources? This one is complicated, and that's because new evidence is coming out all the time, and everyone within a single field never really agrees. For example, even though organic farming doesn't use pesticides, which is good for many species, a new study came out suggesting that organic farming is worse for climate change, which is bad for many species.

Things have always and will always keep changing with new evidence. That said, most international biodiversity conservation organizations publish guidelines by experts in the field, and these are publicly available. For example, the World Wildlife Fund's 2018 Living Planet Report states that over-exploitation and agriculture are the biggest drivers of current biodiversity loss, and these are both due to increasing human consumption.

But let's be clear -- the best way to go about reducing our impact through sustainable resource consumption depends on local communities and their needs. While some global solutions might be suggested, values and needs of humans differ across the world, and this makes a silver bullet for this issue close to impossible. The next question has to do with… my hands.

Comments on SciShow Psych and Nature League videos include the occasional mention of my… hand gestures. Which are, you know, pretty noticeable I've be told. Let me be honest, me doing a podcast is losing almost half of my communication ability….

I have never studied sign language formally, or in school. However, my best friend's mom was deaf and I learned some American Sign Language through her family when I was growing up. I'm by no means fluent, and a lot of my vocabulary includes family-specific slang, but I do love sign language and can hold my own in simple conversations if need be.

Sign language aside, my hands overall just can't be stopped when I'm talking…. What are mushrooms exactly? Where are they on the tree of life?

Are they okay for vegan and vegetarian diets? Ah mushrooms- the odd man out in the plants and animals game. That's because mushrooms are a type of fungus, and belong to the kingdom Fungi.

Despite their look and behavior, fungi are actually more closely related to the animal kingdom than the plant kingdom. The major difference between these kingdoms is the way that they eat: animals take in food, plants photosynthesize, and fungi release enzymes that break nutrients down outside of themselves before absorbing them. And speaking of diets, the plant, animal, and fungus kingdoms are considered distinct- that means mushrooms aren't animals and that they're okay to eat in both vegan and vegetarian diets, at least according to how we currently define these diets.

And speaking of mushrooms, what proportion of wild mushrooms are lethal to humans? How can someone tell edible mushrooms apart from toxic ones? A 2017 paper estimated that there are likely between 2.2 and 3.8 million species of fungi on Earth, and less than 8% of those have been named.

This is for fungi overall, but the number of mushrooms species specifically is surprisingly high. In terms of harm to humans, mushrooms overall aren't particularly more dangerous than other groups of organisms. A small proportion of mushrooms have poisonous properties, but an even smaller proportion of those are actually lethal to a person if eaten.

More than 90% of fatal mushroom poisonings in humans are mushroom species in the genus Amanita. This genus has close to 1,000 species, but the majority of these don't actually produce toxins associated with death in humans. More specifically, about 100 described species in genus Amanita are considered poisonous, and only some of those are truly lethal if eaten.

And of course, how likely it is to come across a species that's dangerous to eat depends on where you live. If in doubt, either consult a professional or just don't eat it. As they say, better safe than lethal Amanita...

What would be the global impact of losing mosquitoes? This is one I've heard many a miserable person back home in Florida ask whilst ruing summer nights spent outside. Frickin' mosquitoes.

To consider impact, we've got to think about what mosquitoes actually do. First of all, they serve as food for a ton of different species. So, if they went away, species that eat them would have to find a different food source.

This might not be a big deal for some species, but for others it could be problematic, depending on how many alternatives exist in the ecosystem. Mosquitoes also serve as pollinators for several plants...but again, there are other insects capable of taking their place if they disappeared. So the real question is: what are mosquitoes uniquely capable of doing, and what happens when that goes away?

The answer here is an incredible ability to take blood from one organism and put it into another, efficiently spreading pathogens worldwide thanks in part to having a highly adapted, uniquely effective needle face. So, if mosquitoes go away, we can say with high confidence that the incidence of certain diseases in humans goes down...which, you know, is generally good for humans. But for the sake of contrarian argument, I'll point out that more humans could negatively affect other species on Earth, particularly if our population numbers went up quickly.

Without diseases like malaria, this could potentially be the case. On Nature League, we've discussed species that are in danger of extinction, but which species are the least likely to go extinct? Which animals will most likely still be here in a few hundred years?

To think about this question, I like to consider what the environment of Earth will look like in the future, and which species will be best adapted to those conditions. In general, species with low extinction risk tend to have smaller body sizes, general instead of specific habitat and food needs, produce lots of offspring, and reproduce early in life. If we consider current trends, the environments and habitat available on Earth in the next couple centuries will most likely have a massive human impact.

Even if the human growth rate slows down, there will most likely still be increased development throughout the world. This means that the species most likely to still be around in a few hundred years are ones that thrive alongside humans. Some of these species might be urban exploiters, and do well with human cities as the backdrop to their day to day routines.

I can't be sure, but the general picture I get in my head is pizza rat and trash pandas. And ants. Ants are outrageous.

Thanks for watching this Q and A episode of Nature League! If you have any questions, you can always ask me in the comments below or on Twitter @Nature_League. And to keep going on life on Earth adventures with us, make sure you go to youtube.com/natureleague, subscribe, and share.