In search of other life
The Mars landing is a reminder that we never know what—or whom—we might discover out there.
There is much to celebrate with NASA's spectacular landing of its new unmanned probe InSight onto Martian soil.
The landing, the eighth on Mars, made news across the world and was broadcast live on the Nasdaq Stock Market tower in New York City's Times Square. The mission's goal is to explore the planet's interior using a variety of instruments and techniques, learning about its early geological activity and history.
The mission will determine if there are “marsquakes," and whether Mars' core is liquid or solid. The more we learn about our solar system's other rocky planets, the more we know about our own planet's history and, as consequence, our own. Even though this is not a mission to explore life on Mars, you can't disentangle the history of life on a planet from its life history. This provides us with our entry point for today, the uniqueness (or not) of life on Earth.
Disclaimer: By “life" I mean any self-sustaining chemical reaction network capable of metabolizing energy from the environment and of reproduction following Darwinian natural selection. So, I'm not considering highly advanced “spiritual" machines, bizarre star-dwelling intelligent clouds, or wormhole-inhabiting swarms of nanobots. Flying spaghetti monsters are fine.
With that cleared out of the way, we can start. Perhaps the most striking result of modern science is that the same laws of physics and chemistry apply across the vastness of space and time. Think of it: we are now able to look at stars and baby galaxies billions of light years away and billions of years old, and we find that they have the same chemical elements (albeit with different proportions) and that they evolve according to the same dynamic laws as our own sun and galaxy. The physical and chemical laws are the same everywhere and everywhen.
We also know—and this is another striking result from modern astronomy—that most stars come with a court of planets, and that planets tend to have their lot of moons. Each one of these is its own world, with different physical properties and chemical makeup. There are large and small planets, rocky and gaseous, with many moons or with just a few or with none. Planets may spin with a large or small tilt (the Earth's is 23.5 degrees from the vertical; Uranus's is an amazing 97.7 degrees). Planets have thicker or thinner atmospheres with different gases. And so on.
A trillion worlds
In round numbers, and just in our own Milky Way galaxy, there should be over a trillion worlds, each unique and with its own story to tell.
To these we add hundreds of billions of other galaxies within our cosmic bubble and we come to some trillion trillion worlds in our universe, give or take a factor of one hundred. (A geeky comment: funny that this is so close to Avogadro's number, the number of atoms in one gram of hydrogen or, more generally, the approximate number of protons and neutrons in a gram of matter—a 6 followed by 23 zeros.)
At this point, you may say, well, within this staggering variety, pretty much everything is possible. Well, no! The unity of the laws of physics and chemistry act as a very powerful constraint on what can and cannot exist. Even if in science—as long as the laws of physics are satisfied—we can't really rule out what can't exist, we can use the laws of physics and chemistry to infer what might. Case in point: the flying spaghetti monster is quite plausible—a cousin of the octopus that ventured out of the pond some billions of years ago in planet Mumba and, after some millions of years, grew feathers on its tentacles and took flight. Or, if not feathers, some ballooning mechanism with hot air from its digestive tract. The eerie heptapods from the movie Arrival (pictured at the top of this page) come to mind.
What can we expect?
So, what can we expect to find as we scan the vast collection of worlds and search for living creatures? No one truly knows the answer to this question, although we can make a couple of educated guesses:
First, life will be carbon-based. Why? Because carbon is the easy-going atom, able to concoct all kinds of chemical bonds better than any other. A poor imitation is silicon, but its biochemistry would be severely limited in comparison. And life needs versatility to thrive; that's its main prerogative.
And second, life needs liquid water. Yes, you can find frozen bacteria in the permafrost, but they aren't living. Since life is, in essence, a biochemical reactor, it needs a solvent, a medium where the reactions can unfold. Ammonia is sometimes proposed as a possibility. But it's a gas at room temperature and liquid only below -28˚F at a normal pressure. So, a cold planet with heavy atmosphere could have liquid ammonia, but that's pushing it. Water is this magic substance that is transparent, has no smell, no taste, expands as it freezes (a key property for water-based life in colder climates since there is liquid water below the ice), and is our own main ingredient.
Given these two constraints, the essence of life should be simple: carbon + water + other stuff (at a minimum, nitrogen, oxygen, and hydrogen). The details, though, are not. Since a planet that may contain life will have its own history, life there will have its own history, completely contingent on its host planet. This means that natural selection acts as a history-based pressure for survival, each tale a different one. And life can also transform the planet and its history, as it happened here on Earth early on and, with the Anthropocene, is happening again.
As a consequence, and despite its common carbon-water essence, there won't be identical life forms on different planets—or at least the odds will be extremely low. And the more complex the life form, the lower the odds that it will be replicated elsewhere.
If the flying spaghetti monster exists, it will exist only in one world. Same to us: we exist in only one world. We are the only humans in this universe. And if we consider what we have learned from the history of life on Earth, chances are that intelligent life elsewhere is extremely rare. I present this argument in more detail in my book A Tear at the Edge of Creation. While intelligence is clearly an asset in the struggle for survival among different species (our fellow cavemen clubbed to death all the mastodons, didn't they?), it is not a purpose of evolution. Evolution has no purpose, no final goal, apart from forcing life to be successful at reproducing itself.
Until it becomes intelligent, life is happy just replicating; with intelligence, it will be unhappy just replicating.
Putting all this together, we realize that we are indeed connected to the rest of the cosmos chemically and that we share the same basis for life as any other hypothetical living thing out there.
At the same time, we are unique, as are all other living creatures on this planet. Life is this amazing force that, from a carbon-based code and a common genetic ancestor, can create a staggering diversity of wonders in this and possibly other worlds.
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Evolution doesn't clean up after itself very well.
- An evolutionary biologist got people swapping ideas about our lingering vestigia.
- Basically, this is the stuff that served some evolutionary purpose at some point, but now is kind of, well, extra.
- Here are the six traits that inaugurated the fun.
The plica semilunaris<img class="rm-lazyloadable-image rm-shortcode" type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTA5NjgwMS9vcmlnaW4ucG5nIiwiZXhwaXJlc19hdCI6MTY3NDg5NTg1NX0.kdBYMvaEzvCiJjcLEPgnjII_KVtT9RMEwJFuXB68D8Q/img.png?width=980" id="59914" width="429" height="350" data-rm-shortcode-id="b11e4be64c5e1f58bf4417d8548bedc7" data-rm-shortcode-name="rebelmouse-image" />
The human eye in alarming detail. Image source: Henry Gray / Wikimedia commons<p>At the inner corner of our eyes, closest to the nasal ridge, is that little pink thing, which is probably what most of us call it, called the caruncula. Next to it is the plica semilunairs, and it's what's left of a third eyelid that used to — ready for this? — blink horizontally. It's supposed to have offered protection for our eyes, and some birds, reptiles, and fish have such a thing.</p>
Palmaris longus<img class="rm-lazyloadable-image rm-shortcode" type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTA5NjgwNy9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYzMzQ1NjUwMn0.dVor41tO_NeLkGY9Tx46SwqhSVaA8HZQmQAp532xLxA/img.jpg?width=980" id="879be" width="1920" height="2560" data-rm-shortcode-id="4089a32ea9fbb1a0281db14332583ccd" data-rm-shortcode-name="rebelmouse-image" />
Palmaris longus muscle. Image source: Wikimedia commons<p> We don't have much need these days, at least most of us, to navigate from tree branch to tree branch. Still, about 86 percent of us still have the wrist muscle that used to help us do it. To see if you have it, place the back of you hand on a flat surface and touch your thumb to your pinkie. If you have a muscle that becomes visible in your wrist, that's the palmaris longus. If you don't, consider yourself more evolved (just joking).</p>
Darwin's tubercle<img class="rm-lazyloadable-image rm-shortcode" type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTA5NjgxMi9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY0ODUyNjA1MX0.8RuU-OSRf92wQpaPPJtvFreOVvicEwn39_jnbegiUOk/img.jpg?width=980" id="687a0" width="819" height="1072" data-rm-shortcode-id="ff5edf0a698e0681d11efde1d7872958" data-rm-shortcode-name="rebelmouse-image" />
Darwin's tubercle. Image source: Wikimedia commons<p> Yes, maybe the shell of you ear does feel like a dried apricot. Maybe not. But there's a ridge in that swirly structure that's a muscle which allowed us, at one point, to move our ears in the direction of interesting sounds. These days, we just turn our heads, but there it is.</p>
Goosebumps<img class="rm-lazyloadable-image rm-shortcode" type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTA5NzMxNC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYyNzEyNTc2Nn0.aVMa5fsKgiabW5vkr7BOvm2pmNKbLJF_50bwvd4aRo4/img.jpg?width=980" id="d8420" width="1440" height="960" data-rm-shortcode-id="8827e55511c8c3aed8c36d21b6541dbd" data-rm-shortcode-name="rebelmouse-image" />
Goosebumps. Photo credit: Tyler Olson via Shutterstock<p>It's not entirely clear what purpose made goosebumps worth retaining evolutionarily, but there are two circumstances in which they appear: fear and cold. For fear, they may have been a way of making body hair stand up so we'd appear larger to predators, much the way a cat's tail puffs up — numerous creatures exaggerate their size when threatened. In the cold, they may have trapped additional heat for warmth.</p>
Tailbone<img class="rm-lazyloadable-image rm-shortcode" type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTA5NzMxNi9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY3MzQwMjc3N30.nBGAfc_O9sgyK_lOUo_MHzP1vK-9kJpohLlj9ax1P8s/img.jpg?width=980" id="9a2f6" width="1440" height="1440" data-rm-shortcode-id="4fe28368d2ed6a91a4c928d4254cc02a" data-rm-shortcode-name="rebelmouse-image" />
Image source: Decade3d-anatomy online via Shutterstock<p>Way back, we had tails that probably helped us balance upright, and was useful moving through trees. We still have the stump of one when we're embryos, from 4–6 weeks, and then the body mostly dissolves it during Weeks 6–8. What's left is the coccyx.</p>
The palmar grasp reflex<img class="rm-lazyloadable-image rm-shortcode" type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTA5NzMyMC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYzNjY0MDY5NX0.OSwReKLmNZkbAS12-AvRaxgCM7zyukjQUaG4vmhxTtM/img.jpg?width=980" id="8804c" width="1440" height="960" data-rm-shortcode-id="67542ee1c5a85807b0a7e63399e44575" data-rm-shortcode-name="rebelmouse-image" />
Palmar reflex activated! Photo credit: Raul Luna on Flickr<p> You've probably seen how non-human primate babies grab onto their parents' hands to be carried around. We used to do this, too. So still, if you touch your finger to a baby's palm, or if you touch the sole of their foot, the palmar grasp reflex will cause the hand or foot to try and close around your finger.</p>
Other people's suggestions<p>Amir's followers dove right in, offering both cool and questionable additions to her list. </p>
Fangs?<blockquote class="twitter-tweet" data-conversation="none" data-lang="en"><p lang="en" dir="ltr">Lower mouth plate behind your teeth. Some have protruding bone under the skin which is a throw back to large fangs. Almost like an upsidedown Sabre Tooth.</p>— neil crud (@neilcrud66) <a href="https://twitter.com/neilcrud66/status/1085606005000601600?ref_src=twsrc%5Etfw">January 16, 2019</a></blockquote> <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>
Hiccups<blockquote class="twitter-tweet" data-conversation="none" data-lang="en"><p lang="en" dir="ltr">Sure: <a href="https://t.co/DjMZB1XidG">https://t.co/DjMZB1XidG</a></p>— Stephen Roughley (@SteBobRoughley) <a href="https://twitter.com/SteBobRoughley/status/1085529239556968448?ref_src=twsrc%5Etfw">January 16, 2019</a></blockquote> <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>
Hypnic jerk as you fall asleep<blockquote class="twitter-tweet" data-conversation="none" data-lang="en"><p lang="en" dir="ltr">What about when you “jump” just as you’re drifting off to sleep, I heard that was a reflex to prevent falling from heights.</p>— Bann face (@thebanns) <a href="https://twitter.com/thebanns/status/1085554171879788545?ref_src=twsrc%5Etfw">January 16, 2019</a></blockquote> <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script> <p> This thing, often called the "alpha jerk" as you drop into alpha sleep, is properly called the hypnic jerk,. It may actually be a carryover from our arboreal days. The <a href="https://www.livescience.com/39225-why-people-twitch-falling-asleep.html" target="_blank" data-vivaldi-spatnav-clickable="1">hypothesis</a> is that you suddenly jerk awake to avoid falling out of your tree.</p>
Nails screeching on a blackboard response?<blockquote class="twitter-tweet" data-conversation="none" data-lang="en"><p lang="en" dir="ltr">Everyone hate the sound of fingernails on a blackboard. It's _speculated_ that this is a vestigial wiring in our head, because the sound is similar to the shrill warning call of a chimp. <a href="https://t.co/ReyZBy6XNN">https://t.co/ReyZBy6XNN</a></p>— Pet Rock (@eclogiter) <a href="https://twitter.com/eclogiter/status/1085587006258888706?ref_src=twsrc%5Etfw">January 16, 2019</a></blockquote> <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>
Ear hair<blockquote class="twitter-tweet" data-conversation="none" data-lang="en"><p lang="en" dir="ltr">Ok what is Hair in the ears for? I think cuz as we get older it filters out the BS.</p>— Sarah21 (@mimix3) <a href="https://twitter.com/mimix3/status/1085684393593561088?ref_src=twsrc%5Etfw">January 16, 2019</a></blockquote> <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>
Nervous laughter<blockquote class="twitter-tweet" data-lang="en"><p lang="en" dir="ltr">You may be onto something. Tooth-bearing with the jaw clenched is generally recognized as a signal of submission or non-threatening in primates. Involuntary smiling or laughing in tense situations might have signaled that you weren’t a threat.</p>— Jager Tusk (@JagerTusk) <a href="https://twitter.com/JagerTusk/status/1085316201104912384?ref_src=twsrc%5Etfw">January 15, 2019</a></blockquote> <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>
Um, yipes.<blockquote class="twitter-tweet" data-conversation="none" data-lang="en"><p lang="en" dir="ltr">Sometimes it feels like my big toe should be on the side of my foot, was that ever a thing?</p>— B033? K@($ (@whimbrel17) <a href="https://twitter.com/whimbrel17/status/1085559016011563009?ref_src=twsrc%5Etfw">January 16, 2019</a></blockquote> <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>
Ultimately, this is a fight between a giant reptile and a giant primate.
The 2021 film “Godzilla vs. Kong" pits the two most iconic movie monsters of all time against each other. And fans are now picking sides.
The more you see them, the better you get at spotting the signs.