Science & Nature Archive

Wednesday, April 13, 2016

New Book - Future Humans

A friend of mine, Scott Solomon, has just finished writing his first book, Future Humans: Inside the Science of Our Continuing Evolution.

Future Humans book cover
Publisher's Page
Buy from Amazon

Here's the description from the publisher's website:

In this intriguing book, evolutionary biologist Scott Solomon draws on the explosion of discoveries in recent years to examine the future evolution of our species. Combining knowledge of our past with current trends, Solomon offers convincing evidence that evolutionary forces still affect us today. But how will modernization--including longer lifespans, changing diets, global travel, and widespread use of medicine and contraceptives--affect our evolutionary future?

Solomon presents an entertaining and accessible review of the latest research on human evolution in modern times, drawing on fields from genomics to medicine and the study of our microbiome. Surprising insights, ranging from the rise of online dating and Cesarean sections to the spread of diseases such as HIV and Ebola, suggest that we are entering a new phase in human evolutionary history--one that makes the future less predictable and more interesting than ever before.

Scott Solomon is an evolutionary biologist and science writer. He teaches ecology, evolutionary biology, and scientific communication at Rice University, where he is a Professor in the Practice in the Department of BioSciences. He lives in Houston, TX.

I read one of the draft manuscripts, and so can say that it really was an interesting, engaging read. And while you might worry that a book about future human evolution might be hokey or too speculative, you can rest assured that this book is well grounded and sticks to reasonable inferences.

You can pre-order the book from Amazon right now. It will be shipped in October.

Friday, April 8, 2016

Answering Quora - Is technology replacing spirituality?

In keeping with the spirit of my recent entry, Does spirituality provide anything that science cannot provide?, this week I'm answering a related question that was recently posted on Quora, Is technology replacing spirituality?. Here is my answer.


Below is perhaps my favorite photograph of all time, the The Chandra Deep Field South*:

Deep Look Into Space

That's only a very low-res version. Go visit the ESO page, A Pool of Distant Galaxies, download the full image, and take some time to look at it and marvel (really, I mean it, you won't be disappointed). Practically every point and smudge of light in that image is an entire galaxy, not just a single star. And that image covers a portion of the sky smaller than the full moon. The image is awe-inspiring, humbling, and marvelous all at the same time. Thousands of years ago when people looked up at the night sky, they thought the stars were shiny objects embedded in a firmament, or mythological beings. There was no conception at all of how unimaginably vast the universe really is. It's only technology that makes images like this one possible, and that reveal to us our place in the universe.

And how did I come to find this image personally? The Internet - a vast collection of networked computers sharing practically all of human knowledge. And this image is but just one example. There's a whole vast array of mind-blowing lessons to be found online, from understanding evolution and our place in the vast tree of life, to the tiniest known portions of nature, subatomic particles, that are only known about because of technologies like the LHC at CERN. And the Internet itself is only possible because of humanity's understanding of semiconductors, electronics, logic, etc. Without that type of technology, I'd be stuck with magazines and other print sources for whatever scraps of information I could find. And even those 'old' information sources rely on printing technology. Before the printing press, my only information sources would have been hand written manuscripts or word of mouth.

Science and technology have revealed so much that would have been impossible to know before. Sure, it's given us distractions, as well. But for those willing to look, it's provided us with a far deeper understanding of nature and the universe and our place in it than any ancient culture could have dreamt of.

*I've used this image before, in the entry, The Universe Is Big. I had a little more explanation putting this image into perspective. And while I was at it, I did take some time to study that image again. It gives me butterflies in my stomach every time.

Friday, March 18, 2016

Answering Quora - Why There Were No 'First' Humans

Human Family TreeIn what has become my modus operandi here recently, I'm going to recycle a Quora answer for this post. This time, the question was, 'would the parents of the first human grandchild have been siblings?'. My response is very similar to parts of a previous answer/post, Which Came First, the Chicken or the Egg? And a Discussion of the Fuzziness of Species, but I think I did a better job this time explaining the example. So, here's my answer, with a few minor edits, and some additional footnotes.


As many others have pointed out, there was no 'first human'. Evolution is a gradual process that occurs in populations. Trying to pinpoint the exact individual that was the first human is like trying to pinpoint the exact second when twilight becomes nighttime.

Some people have a bit of a hard time understanding this, even people who claim to accept evolution. They'll say that if we exist as humans now, while in the past there were no humans, there must be some individual that we can identify as the 'first human', even if it's an arbitrary distinction. But this still doesn't work.

For the sake of argument, let's say you want to arbitrarily define a certain set of genes as 'human', and any organism lacking those genes as not human*. It's just semantics, but let's see what would happen. Let's say that around 100,000 years ago, there was a population of hominids that was very, very close to fitting your definition of 'human', but lacking one last mutation that would give them the full set of genes to make them 'human'. And lo and behold, one day a couple has a child that acquired this last critical mutation, and now, by our semantic definition, it's fully 'human'**. How different will it look from its parents because of that one different gene? Once it grows up, how much of a problem will it have finding a mate among the rest of the population and producing children of its own. The answers are that it will look as much like its parents as any child, and it won't have a problem at all finding a mate and having children (at least, not because of that mutation). So, even though it fits our semantic definition of 'human', it's not a different species from its parents or the rest of the population using the biological species concept.

But let's take it further. Once this first 'human' finds a mate and has children, because its genes are being mixed with its mates, and because it likely only has one copy of this new gene, anyway, only around 1 in 2 of its children are going to contain this critical gene that makes them 'human', while the rest of its children are going to lack this critical mutation and be almost but not quite 'human'***. But those children will all grow up to have children of their own, and on and on. So at first, this particular gene was only present in one individual, so only one individual in the entire population was fully 'human'. Then in the next generation, the gene was present in roughly 50% of its children, so there were a handful more 'humans' in the population. Then, in the next generation, the gene was passed on to yet more children. And since we know in hindsight that this gene is necessary to be 'human', we know that the individuals with the gene will end up having slightly more surviving children than individuals without the gene, so that eventually, after many generations it will have spread throughout the entire population, and the entire population will be fully 'human'.

That's the problem with trying to define a 'first human'. Whatever genetic criteria you pick is going to be arbitrary. An individual with 99.9999% of the correct DNA wouldn't be human by this definition, but it would still be the same species and able to interbreed with an individual with 100% of the correct DNA. And at some point in time, there will be a population of organisms mixed between 99.9999% 'humans' and 100% 'humans', and a 100% 'human' could have a mix of human and non-quite-human children. But the only reason we'd be classifying these organisms any differently is because of hindsight, knowing that in their future, only one version of a specific gene is going to be dominant. In their own time, they'd look just like any other population with a mix of genetic diversity.

And even all that's using an arbitrary definition of exactly what genes are needed to be 'human'. In the example above, we could be tempted to say, alright, that 'almost-human' population of hominids is close enough - let's call them fully human. But now you've just shifted the same problem a few generations back. There will be a moment in time when their ancestral population was a mix of individuals with their same genes and very slightly different genes. Depending on which specific arbitrary traits are required for the definition of 'human', you could shift the first humans by tens or hundreds of thousands of years.

So, to answer the question, there never were only two individual parents that were the only ancestors of all of humanity. Our ancestors have always been members of large interbreeding populations. And because evolution is a gradual process, it's impossible to pinpoint any single individual as the 'first human'.

Image Source: Pinterest

* You'd probably be more focused on alleles than genes. Alleles are different variants of the same gene. But, since it's just a semantic definition, anyway, genes work for the discussion. It's also an over-simplified example. It's not as if the population was a bunch of genetic clones. Even among individuals in the population, there will be genetic diversity.

** Mutations happen regularly. Pretty much every person alive has at least some mutations differentiating them from their parents. Granted, a whole new gene is a much bigger change than just an allele, but it happens. More Info: Understanding Genetics - How new genes are made

***Remember that we have two copies of all of our genes. So, if this hypothetical individual had a mutation that created a new gene or new allele, it would have probably occurred on only one copy of the original gene, i.e. one strand of the double helix. Since reproduction involves random mixing of our genes for making sperm and eggs, since our individual only has one copy of this new gene, only around half of it's eggs/sperm will contain the new gene, while the other half will retain the old version.

Friday, March 4, 2016

Genetic Evidence for Evolution - Vitamin C Pseudogene

This entry is part of a collection on Understanding Evolution. For other entries in this collection, follow that link.

Histoire et culture des orangers, A. Risso et A. Poiteau. -- Paris Henri Plon, Editeur, 1872As I've been doing a lot recently, I'm going to recycle a Quora answer for this entry. The Quora question this time was What are 3 facts that prove the biologic evolution theory?. After a bit of preamble about science not being able to 'prove' anything (for example, see my essay, Confidence in Scientific Knowledge), I got down to the answer - genetics, and the specific example of the GLO pseudogene*. Here's an edited version of that portion of my Quora answer**.


I'm only going to look at one narrow piece of evidence for evolution in our DNA. But as an aside before getting to the meatier answer, just the general similarity in genes of all organisms is already a decent argument in support of common descent. Why else should organisms have common genes? If it was special creation, why even use DNA in all organisms, and not get a little more creative in how to store genetic material. But the similarity in DNA goes beyond just genes. It's also in the structure of our chromosomes, in regions in the DNA that don't code for genes (much of it quite frankly junk - Is Most of Our DNA Garbage?), and in regions that used to code for genes that have since become non-functional due to mutation (pseudogenes).

One particularly striking example is one of the genes involved in the synthesis of vitamin C, L-gulono-γ-lactone oxidase, or GLO. All but three lineages of mammals can synthesize their own vitamin C and don't need to get it from their diets like us. The three lineages that can't synthesize vitamin C are anthropoid primates (which includes us), guinea pigs, and bats. All three of those lineages contain a form of the GLO gene, but in each lineage, mutations to the gene have damaged it to the point of disabling vitamin C production. But the thing is, the specific mutations are different in each lineage, but common to all members of those lineages. In other words, the damage to the GLO gene is the same in all anthropoid apes, but different from the damage in either guinea pigs or bats. Similarly, all guinea pigs share the same damage, which is different from that in primates or bats. Ditto with bats.

When you think about that, that's hugely indicative of common descent. With similarities in functional genes, a creationist or Intelligent Design advocate can always say that common purpose means common design, and God (or the designer) simply used the same genes in different animals. And creationists can even sort of explain isolated pseudogenes as a result of The Fall, where mutations have damaged what was supposedly at one time a perfect creation. But having the same broken genes in closely related species, and broken in the same way, is a whole lot harder to understand from a creationist perspective. The chances of those same mutations occurring in the same manner in all of the anthropoid primates is simply too unlikely to be taken seriously (and that unlikelihood is only compounded by each of the other lineages with mutations to GLO). So, absent common descent, that would mean all those broken genes would have had to have been present in all anthropoid primates from the very beginning. Why would a god (or intelligent designer) have put broken genes into organisms in the first place, and why break them in the same way in all anthropoid primates, but then in a different way in guinea pigs and yet a different way in bats (and in yet more ways in non-mammals that I didn't discuss). From an evolutionary perspective, it makes perfect sense. The damage occurred once in the common ancestor of anthropoid primates through a particular set of mutations, and that broken gene was then passed on to all it's descendants. At another time in another place, damage of a different sort occurred in some ancestral guinea pig, which was then passed on to all the descendant guinea pigs. And the same thing for bats, and all the non-mammals that have damage to GLO.

And that's just one example of one pseudogene. There are other pseudogenes, genes, regulatory stretches of DNA, and regions of junk DNA that all make the genetic evidence for evolution one of the strongest lines of evidence there is. But it's hardly the only line. To echo something I wrote in yet another Quora answer, if you're willing to put in a little reading, there are some great books on the subject. My two favorite introductory books are Jerry Coyne's Why Evolution Is True, and Donald Prothero's Evolution: What the Fossils Say and Why It Matters, which cover topics like fossil evidence for evolution, vestigial organs, embryological evidence, evidence from poor 'design', and biogeographical evidence. Given the enormity of the evidence in support of evolution, a single book can't come close to being comprehensive, but both of those books present enough evidence to be very convincing. Why Evolution Is True is my favorite of the two, and is a little more broad in the types of evidence it covers, as well as covering a bit more of the theory and mechanisms, not just evidence. If you want to get even more on the mechanisms and theory of evolution, but still in a book aimed at non-biology majors, Carl Zimmer's The Tangled Bank: An Introduction to Evolution is very good (though a bit on the expensive side - you might look for it at a library).

The Genetics of Vitamin C Loss in Vertebrates

Image Source: Wikimedia Commons

* GLO had previously been mentioned briefly on this site before in Ein Sophistry's Genetic Evidence of Evolution.

** This Quora answer itself was adapted from a comment I left to another Quora answer, Niall Harman's answer to What is the evidence for biological evolution and what is the evidence supporting creationism?

Want to learn more about evolution? Find more at Understanding Evolution.

Friday, February 19, 2016

What Would Technologically Advanced Aliens Be Like

Alien Clip ArtRecently, I came across various versions of the question that's the title of this post, such as this Popular Mechanics article, What Would Aliens Actually Look Like? We Asked 7 Experts, and multiple Quora questions (Would aliens look humanoid and if so, why?, What are the odds that if aliens exist, they would look like how they are portrayed in science fiction?, What might alien life look like?, Is it possible that aliens look like humans?, and What do aliens look like?). People's responses range from thoughtful to idiotic (even in the Popular Mechanics article among so called experts). But, it's an intriguing question, so I thought I'd give it a go at an answer.

First of all, I'm focusing specifically on intelligent, technological alien life. Just a look at all the varied life forms that exist and have existed on this planet shows all the crazy paths life can take, from giant sequoias to mantis shrimp to sponges to pterodactyls to clams to flying fish to dolphins to snakes to bombardier beetles to mushrooms to ants to Venus fly traps to amoebas to orchids to cuttlefish... There are seemingly endless ways to go about the business of survival and reproduction. But the type of intelligence and body that can produce technology is something a bit more specific, and perhaps something where I can conjecture a bit more constructively.

Venus Fly Trap Cuttlefish Amoeba Mantis Shrimp
Click any image to embiggen. All above images from Wikimedia Commons.

To be clear, I'm not saying it's likely that we'll ever discover technologically advanced aliens. In fact, I think it's distinctly unlikely. Life existed on this planet as solely single-celled life for billions of years. And even after multicellular life appeared, it was nearly another billion years before us humans evolved with our technologically advanced civilization. And our civilization has only been around for mere thousands of years - note even a drop in the bucket compared to the total history of life on this planet. This entry is looking at the prerequisites to developing technologically advanced life.

One thing to keep in mind is that, just like on Earth, aliens, or at least their original natural form if they've entered into a realm of genetic engineering or artificial intelligence, are going to be the products of evolution, just like us. And we know from the way evolution works here, that it doesn't produce anything miraculous. Sure, there are very, very interesting forms that have evolved. But evolution is limited by contingency, and every feature of an organism is a tradeoff between advantages and disadvantages, not least of which is the nutrition needed to grow and maintain that feature. And everything everywhere is still governed by the same natural laws - physics, chemistry, etc. So we shouldn't expect aliens to have any 'superpowers' relative to what's seen on this planet - no magic levitation abilities, no telekinesis, no telepathy, no absurdly strong muscles, etc. And we shouldn't expect features that are nearly impossible to imagine evolving in a stepwise manner, like wheeled axles. Aliens will be organisms that evolved naturally to fit a niche.

With the caveats out of the way, let's start at the most basic level, first. Aliens will most likely use carbon based chemistry. Carbon simply offers the richest chemistry of any element in the periodic table. To quote Wikipedia, "The most important characteristics of carbon as a basis for the chemistry of life are, that it has four valence bonds, that the energy required to make or break a bond is at an appropriate level for building molecules, which are stable and reactive. Because carbon atoms bond readily to other carbon atoms allows for the building of arbitrarily long complex molecules and polymers." In fact, many of the building blocks of life, such amino acids, have been found naturally occurring in non-biological conditions, such as in comets. The fact that these basic building blocks will spontaneously form given the right conditions certainly suggests that they could be present in some primordial body of water and, given further appropriate conditions, give rise to life. About the only other element with a chance of being the basis for life is silicon, but its chemistry isn't as rich as carbon's, and nobody has yet found the type of naturally occurring large molecules and polymers with silicon as what occurs with carbon.

Alien life will more than likely have some type of long chain molecule (a polymer) similar to DNA. There can be lots of interesting chemistry without this type of molecule, but probably not to the same complexity, and not with the same basis for duplication with slight mutations that's the foundation of evolution. But that DNA like molecule need not necessarily be DNA. In an interview for the Guardian article, DNA alternative created by scientists, Phillip Holliger, who's studied alternatives to DNA, stated, "There is nothing Goldilocks about DNA and RNA. There is no overwhelming functional imperative for genetic systems or biology to be based on these two nucleic acids." Holliger has created and studied alternative polymers, collectively known as XNAs. Perhaps one of these would be the basis for alien life.

Moving past the basic level, I'm going to jump quite a bit ahead in the aliens' evolution. They'll almost surely be terrestrial. As I said before, keep in mind that we're focusing on technologically advanced, not just intelligent. You can certainly have intelligent animals evolve in any environment (e.g. dolphins). But it's hard to imagine how advanced technology could develop in an aquatic habitat. For one thing, so much of our technological development has hinged on fire, from cooking, to smelting metals, to combustion engines, etc. Without fire as an energy source, it's hard to see how many of those technologies could have been developed. Then there's materials science and chemistry. In a terrestrial environment, it's easy to isolate solids and liquids in different containers, allowing chemistry to get started. How do you isolate liquids when you're underwater.

The overall size of the aliens would probably be in the ballpark of us, but would depend an awful lot on the specifics of the planet they're from. As a first cut, we can probably say that they wouldn't be much smaller than us. Being smart takes a certain amount of raw brain power, and brain power that can be devoted to general intelligence, not just the normal 'housekeeping' chores of processing nerve impulses or controlling organs. There's no telling just how exactly an alien brain would work, but assuming that it's about as efficient as the brains that have evolved on this planet, it will be proportionately sized to the organism. For example, a spider will never be as smart as a person, because it's just too small to have a brain big enough to do the job. To have a brain big enough to have a high level of intelligence, the aliens will have to be reasonably sized. As far as an upper limit on size, that's probably going to be very specific to the planet and the organisms' physiology. On this planet, gravity and the square cube law place upper limits on how big terrestrial organisms can get. If aliens came from a planet with lower gravity, they could probably grow larger. But even on this planet, humans are nowhere near the upper limit for how big terrestrial animals can get. The largest land mammals ever probably weighed around 20 tons, while the largest dinosaurs were probably around 70 tons. Moreover, ancient elephants are contenders for largest land mammal, and they also happen to be among the smartest mammals. So, I think about the best range I can estimate is from a low end of several dozen pounds to a high end of several tons, or even larger if the planet has lower gravity.

Big Animals Compared to a Person
Click image to embiggen. I got that from a forum - not sure of actual original source.

It's hard to predict what type of skeleton aliens would have (not even getting into the chemistry of it, just the basic structure), but we can narrow it down somewhat. There are four types of structural support that animals on this planet use - endoskeletons (like us), exoskeletons (like insects), hydrostatic skeletons (like earthworms or starfish), and muscular hydrostats (like octopus and squid). Considering that we've already narrowed down our technological aliens to terrestrial organisms, I think we can rule out those latter two types of support. While they're sometimes used in certain structures of large terrestrial animals on this planet (like our tongues or an elephant's trunk), the only terrestrial animals we know of that use them for their entire structure are rather small. It seems that to support large bodies, some type of hard skeleton is required (assuming that gravity isn't drastically lower on their planet). But whether aliens would use endo- or exo- skeletons is tougher to answer. The largest known terrestrial animal from this planet to use an exoskeleton was Arthropleura, an 8 ft long millipede that weighed several hundred pounds (one site I saw said 1000 lbs). So, it doesn't appear that an exoskeleton is necessarily a limit to growing large. In fact, most of the articles I've seen describing why insects don't grow larger explain that it's mainly due to how they breathe. They rely on small tubes and diffusion, rather than lungs (e.g. Why can't insects grow much bigger?). If an organism had an exoskeleton AND lungs, it might just be able to grow to much larger sizes than current insects. So, I'm going to say that we can't narrow this down any further.

I've already discussed that the aliens would require a certain sized brain, but there's another aspect about brains worth considering - they take a lot of energy. Now, perhaps alien evolution would strike on a nervous system that was more efficient than ours, but I think chances are that naturally evolved biological computers will always take a lot of energy, especially if the organisms are using those brains full-time to think about things. And that type of energy means the organisms will probably be warm-blooded - chemical reactions and metabolism can be much more efficient when they're operating at a consistent warm temperature. And the vast, vast majority of warm blooded terrestrial animals on this planet have some type of insulation for a body covering - hair or fur in practically all mammals, feathers in birds and other dinosaurs, and pycnofibers in pterosaurs. Humans are one of the rare exceptions to this pattern. So, more likely than not, intelligent aliens will have something similar to fur or feathers covering their bodies for insulation.

Speaking of energy requirements, one of the reasons we can have such energetic metabolisms is oxygen. Oxygen is very reactive. That's very clear from watching a fire burn. The metabolism that takes place within our cells is a more controlled version of those types of reactions. So, in order to have the metabolisms to support those energy intensive brains, technological aliens will probably be living on a planet with lots of free oxygen in the atmosphere, which also goes back to what I mentioned before about the importance of fire for driving technological development. (And as an interesting aside, this also tells us something about the other life on that planet - go read about the Great Oxygenation Event to see how Earth got its oxygenated atmosphere.) And to get that oxygen distributed throughout their bodies, aliens are going to need some type of circulatory system (and some type of respiratory system, as well). And a circulatory system needs blood. But what type of blood? Here's an article discussing different types of blood in creatures on this planet, Crabs have blue blood; why don't we?. In short, iron and copper appear to be the best suited elements for transporting oxygen, and so intelligent aliens would probably have blood based on one of those elements. Though the article also mentions vanadium based blood, so I suppose there's a small chance their blood could use some other element.

Aliens will have various sensory organs. From physics, many will probably be similar in function to ours - touch, taste, and smell as very obvious senses, interacting directly with the matter in their environment. Hearing to detect sound is also pretty likely, seeing as how that has evolved in many lineages of animals on Earth (insects use a tympanal organ). Sight also seems very likely, considering how many animals on this planet have eyes. But what type of eyes would aliens have? Eyes have evolved numerous times on Earth, but almost all fall into two camps simply because of the constraints of physics - compound eyes and camera-type eyes. In fact, as complex as camera-type eyes may seem, even they have evolved multiple times, in both us and molluscs. And while camera-type eyes may offer potentially higher resolutions, both camera and compound eyes are effective means of forming an image. There is a third possibility that we know of from telescopes, and that I just learned is actually used in scallops - a reflector eye. But, out of all the eyes in the animal kingdom, reflector eyes seem to be pretty rare, so I think we can narrow down our aliens to either compound or camera-type eyes, but no further than that.

Cuttlefish Eye Dragonfly Eye Cat Eye Trilobite Eye
Click any image to embiggen. All above images from Wikimedia Commons.

Aliens will need mouths of some sort. They're going to need to eat, and a mouth, by definition, is the orifice that gets food into the digestive tract. But from there, who knows what those mouths might look like. Chances are decent it will have some type of hinge to facilitate biting, but even that's not a given. Really, just take a look at a small sampling of the mouths from organisms on Earth.

Horseshoe Crab Mouth Starfish Mouth Butterfly Mouth Ant Mouth
All of those images are available in their full glory on the websites I stole them from just by clicking on the thumbnails. And while they're all good, you really, really have to click on that fourth one.

These aliens are going to have some types of limbs or appendages, if only for the reason that they'll need something to manipulate their environment very finely to be able to develop and build their technology (again, because we're looking at prerequisites to technologically advanced aliens, not that there's any inherent reason why this type of feature would necessarily evolve on an alien planet). We have hands. Elephants have trunks, and it's very easy to imagine that if they had two trunks, they'd be building things. Squids have tentacles that they're very adept at using. And while it's conceivable these aliens could be slug-like with muscular tentacles, since we've previously determined that they're probably going to be warm-blooded, energy hungry organisms, they'll probably be more active and need to get around faster than what slugs can do. So, at least some of their limbs are probably going to be for locomotion. So, how many limbs will they have? For an interesting discussion of limb evolution on Earth, check out this article, A Tale of Three Arms. It discusses the independent evolution of limbs in vertebrates like us, arthropods (including insects), and molluscs. A lot of the reason life looks they way it does now is because of those evolutionary histories and contingencies. We have four limbs because our lobe-finned fish ancestors had four fins. If they'd had six fins, we'd likely have six limbs. And if they'd had segmented bodies like millipedes, we might have a hundred limbs. To set a minimum, I'd say terrestrial animals will almost always have at least four limbs. It's the minimum required to make walking easy for the first organisms to venture onto land. Above that, there's no telling. If their manipulatory limbs were modified from locomotion limbs like us, they could still have as few as four limbs. If they evolved from six- or eight- or ten-limbed ancestors, they'd probably retain that number. And if they had so many limbs, there's no reason to think they'd only be limited to two manipulatory limbs. Or, like I already hinted at above, their manipulatory limbs might have evolved from something other than locomotion limbs, similar to an elephant's trunk.

As far as behavior, they'll almost certainly be social. Developing technology depends on building on the knowledge from others that came before you. And you can't share that knowledge effectively without being social and interacting with others. And that sharing will require some type of language - not necessarily spoken with sound waves, but some way to transfer concrete and abstract ideas from one individual to another.

So to summarize, my best guess is that if any intelligent technologically advanced aliens have evolved, they will probably be carbon based, with some type of polymer genetic chemical, though not necessarily DNA, terrestrial, either similar in size to us or much larger, have some type of hard skeleton, either internal or external, warm-blooded with some type of fur or feather like insulation covering their bodies, oxygen-breathing with iron or copper based blood, with various sensory organs similar to ours and either compound or camera-type eyes with a slim possibility of reflector eyes, mouths that we can only narrow down to being some type of orifice to take in food though a hinge of some sort is possible, have at least four limbs if not more, and will be social with language. Now, take all that and try to imagine what it would look like coming together, and there's a near limitless number of possibilities.

Title Image Source: Wikimedia Commons

Updated 2017-11-07: Add paragraph about technologically advanced alien life being unlikely, along with related caveat in final paragraph.


Selling Out