Life is ...

An organism is any contiguous living system, such as an animal, plant, or fungus_. An organism consist of one or more cells.

Life decreases entropy. (I don't fully understand how or why.) (Can we rebut this by man who kills others?)

Life is distinct from personhood. Some people mistake these as the same, equating discovering life on another planet with life in the womb, and the second being a person.

Viruses, when not replicating, lack any of the characteristics of life.


1   History

The ancient Greeks associated life with fire.

2   Classification

All life can be classified as a tree. This was first suggested by Aristotle.

3   Study

The study of life is biology.

4   Death

5   Extinction

Extinction refers to an event that causes all instances of a life form to die.

Extinction was only accepted as a fact in late 18th century after Georges Cuvier, the father of paleontology_, disproved the old theory that it was impossible for species to go extinct because God wouldn't wipe out a species he spent time creating for his Divine Plan.

6   Evolution

Evolution is the process by which new species come into being.

Evolution works through variation and natural seclection. Variation exists for many reasons, including gene-shuffling and random mutation. Natural selection is the mechanism by which evolution occurs.

Even when evolution was accepted, during the Victorian era people thought evolution had a direction with humans at the top and all other animals evolving toward humans.


There are some additional questions underneath the surface. What exactly is "nature" in "natural selection"? And what exactly is "the environment" to which animals adapt?

Fitness is, roughly speaking, the probability that a given organism will leave offspring. The "fit" is the matching of organisms attribute to environmental demand.

If nature is conceptualized as eternal and unchanging (the demand as static), then evolution is a never-ending series of linear improvements. The still-powerful Victorian idea of evolutionary progress, with man at the pinnacle, is a partial consequence of this model of nature. If produces the erroneous notion that there is a destination of natural selection, and that it can be conceptualized as a fixed point.

However, natures varies, and things change at different rates. Leaves changes more quickly than trees, tress, more quickly than forests. Weather changes fastest than climate.

The order that is most real is the order that is most unchanging, and that is not necessarily the order that is most easily seen. The leaf can blind a viewer to the tree, and the tree can blind him to the forest. And some things that are most real (such as the ever-present dominance hierarchy) cannot be "seen" at all.

The dominance hierarchy is a near-eternal aspect of the environment. Much of what is blamed on more ephemeral manifestations is a consequence of its unchanging existence.

Empedocles was the first to theorize of natural selection.

Most mutations don't pan out. It seems unlikely that animals may have developed certain features because of `survivorship bias`_.

There are certain evolutionary hurdles. This seems to be because certain branches of evolution lead to local optima that will never lead them to cross certain milestones. For example, intelligence will probably never achieved by most branches of evolution given any finite amount of time. Language has only ever been seen in humans.

It's similar to being able to use tools (which we've seen in many species) versus being able to create tools (which we've seen e.g. in certain corvids). The former is a significant first step but the later is what proves a certain amount of abstract thinking beyond the immediate here and now that goes far beyond mere instinct.

There are documented cases of falcons spreading fire in Northern Australia.

6.1   Genetic variation

All genetic variation between individual organisms, including individuals belonging to the same or different species, can be traced back to a series of random mutations. [3]

In isolation, random mutation without tests of effectiveness would be useless. It is effective because each random mutation is tested for effectiveness and mutations that are not effective for survival and reproduction are not stored-- instead they are eliminated. [3]

6.2   Traits

A trait is ...

When organisms share a trait due to common ancestry, it is called a homologous trait. For example, all vertebrate animals (frogs, birds, fish, people) have skeletons because the ancestor of the vertebrates had a skeleton and passed that trait on to all of its descendants.

Traits that are similar due to reasons other than relatedness are called analogous. Such similarities can result from random chance or because unrelated organisms have adapted to similar environments. For example, many animals have wings, such as bats, birds, and many insects. However, wings between these type of animals vary greatly. Insects have two pairs of wings, while bats and birds each have one pair. Butterfly wing are covered in scales, bird wings in feathers, and bat wing with bare skin. [1]

The reason that left-handed people still exist, is probably likely due to an evolutionary stable strategy..

Despite the pressure to be a right handed person, in a world where 90 % of people are right-handed, there is just enough of an incentive to be left. We can only hypothesise what that incentive is (but we DO know there is one, because there are still left-handed people). But one working hypothesis is the sword hand. In a world where 90%+ people are using their right hand for swordfighting, everyone practices against right hands (including the lefties) most of the time. In combat, lefties defeat righties, because they have more practice. Cool. But if the number start to shift towards the lefties, the incentive starts to go away (in our example, because there are more lefties that everyone gets some practice against them) and the pressure from the speech centre effect pushes humans back towards being more right handed. The see-saw effect wavers around 90% right handed. Tonnes of cool examples in nature like this. My favourite is

about spiders and involves genes: There exists a species of spider where there are about 10% of females that never mate because they eat the males before copulating instead of afterwards like their more successful procreating sisters. HOW can this possibly exist? Wouldn't evolution destroy this behaviour? Not necessarily. Imagine that the behaviour for eating males after you copulate I controlled by two alleles on the same gene. Instead of having a dominant allele, there is a co-dominant effect. That means having 'AA' on that gene leads to NOT eating the male and no advantage to the female. Having 'Aa' leads to the preferred behaviour, eating after copulating. Advantage to the females that do, they get an extra snack to help their new brood. But some females are 'aa' which leads to eating the male before copulation - Advantage 0. (This is why this is sometimes called game theory, because of similarity to the prisoners dilemma). In a POPULATION of spiders, the most favourable allele combination in males and females is 'Aa' and therefore it is the most common. Evolutionary pressure favours this combo. 'AA females are selected away, and 'aa' obviously strongly away. BUT, the offspring of two adults carrying 'Aa' have one quarter 'aa' female children (Aa x Aa = 1AA + 2Aa +1aa) so even though it is slected against, it will be retained in the population..... Hope that was ELI5 enough.

Next step was a stroke of brilliance IMO, he started to look back at the stone tools in museum collections, in order to trace when humans stopped being ambidextrous (like most ape species, so he knew there was a point when this occurred), and there was a clear sign at about 500,000 years ago. This is the same time that human skull differentiation showed clear signs of growth in the speech centres, such that language was becoming more important. The theory at the moment stands that handedness is an accident of this development of the side of the brain that controls speech.

You like this answer but it never really answered your question. You asked why aren't we ambidextrous? And that answer is that all individuals of most complex animal species display a "handed-ness" (aka "bilaterally asymmetric motor behavior"). This is likely simply related to the very basic development program that developing organisms undergo. Because bi-lateral organisms are rarely fully symmetric, there's going to be left/right component to development. Even worms have a handedness. What's unique about humans (and a number of other species) is that rather than a population of individuals being split 50-50 between left and right handedness, one type of assymentric motor behavior dominates.

The existence of a trait is not in itself meaningful. The fact that left-handedness persists does not necessarily mean that there is an incentive to be left handed. Evolution only cares if something is advantageous or disadvantageous. There are plenty of "neutral" traits that simply just "are" and that's it. We call such traits spandrels because they seem like they might be meaningful, but really are just the byproducts of other traits, and do not themselves entail a fitness cost or benefit. So a species that has developed a bias toward left- or right- handedness may simply be because there was no pressure to keep that ratio @ 50-50.

There's a principle called Guiard's law of bimanual skill. This states that we typically we have one hand dedicated to fine movements, like writing with a pen, and another hand that is dedicated to broad supporting movements, like holding a piece of paper in place. Think of it like this, when you use an iPad you use one hand to hold and orientate the iPad, and you use the other hand to make fine motions on the touchscreen. Both are required and work together to complete the task.

Why hasn't evolution caused mammals to have more females than males?

The underlying reason for this conundrum was first outlined by Ronald Fisher and is still known as Fisher's Principle. It doesn't just hold true for mammals, but for most sexually reproducing organisms.

To explain why, first I have to clear up a bit of a misconception. You say: So, I was thinking.. optimally as a specie to survive, wouldn't it make more sense to have X females per male?

But in truth natural selection favors things that help individuals, not species. Something can be great for a species or terrible for a species, but that won't effect whether selection favors it. Instead, it favors things that help individuals, even if those traits are less than optimum for the species as a whole.

So, why have equal numbers of males and females? Well, basically, imagine a situation where 100 females were born for every male. Now imagine some individual has a mutation that causes them to produce more male offspring, instead of just having 1 in 100. All their male offspring will do very well. They'll go on to impregnate dozens of females and produce lots of offspring. The gene for having more males will spread. The gene for having more females will not keep up, because individuals with that gene will only produce females, and those will only produce a few offspring. Eventually, though, there will be lots of males. At that point, it will be the males who have trouble finding mates, while all females are guaranteed a chance to get lucky. And so production to produce more females will be favored. This all evens out to favor a nearly 50-50 sex ratio at birth. Basically, selection favors having offspring that have the most opportunity to reproduce, and this means having offspring of the less common sex. This is known as negative density dependent selection.

6.3   Selection by females

All male birds used to have penises. But now only 3% do (e.g., ducks). The others just have a hole. One theory for this is that females chose males which were less sexually violent.

7   Aging

Lobsters do not die due to aging. They become stronger and more fertile with age due to the presence of enzyme telomerase which tepairs DNA sequence.

8   Lindy effect

The Lindy effect is a concept that the future life expectancy of some non-perishable things like technology or an idea is proportional to their current age. Where it applies, mortality rate decreases with time. In contrast, living creatures and mechanical things follow a "bathub curve" where after "childhood", the mortality rate increases with time.

The flip side of this is Nassim Nicholas Taleb's Thanksgiving Turkey.

A turkey is feed for 1000 days by a butcher, and every day confirms to the turkey and the turkey's economics department... that the butcher loves turkeys. But on day 1001, there will be a surprise for the turkey...

9   Ethics

Citizens lose their right to life upon joining the military. As a solider, they may be ordered into situations where they will die.

Trump once remarked to a widow of a solider that "he knew what he was getting into". This caused many responses by people in the military saying it was inappropriate and antithetical to the values of the military.

The military is generally committed to making sure you survive and not to place soldiers in unnecessary danger. Your commander, and the military at large, will not leave you behind.

10   See also

11   References

[1]Dr. Mary Kathryn Whitson. Animal Adaptations: Homologous vs. Analogous Traits.
[2]Jordan B. Peterson. Jan 16, 2018. 12 Rules for Life: An Antidote to Chaos.
[3](1, 2) John Sweller, Paul Aryres, Slava Kalygua. 2011. Cognitive Load Theory.

Breasts are secondary sexual characteristics. They tend to be 'runaway' traits, which are a weird combination of dramatic and unstable. More on that below.

Also, sexually-selected characteristics tend to get a second life as measures of mutational load and overall fitness. Basically since they're hard to make, they're the first things to show genetic 'errors' if they exist, so if a person's big boobs are messed up that's a visible sign they don't have the best genes. So the human body is a bit 'careful' not to make boobs bigger than it can make look good. As well, there is a 'handicap' nature to the whole affair, where the hormonal traits (like high estrogen) necessary to make things like large breasts are disadvantageous to overall health, therefore only the very most fit individuals can 'waste' the health burden necessary to create and maintain them.

In a similar way, testosterone levels during puberty are correlated with facial attractiveness in men - wide jaw, thick beard, brow ridges, etc...however, testosterone decreases the function of the immune system. So only men with the very best health and vitality can afford the hit to the immune system required to form a 'handsome' face.

Testosterone levels correlate with sleep. Once I started sleeping more in adulthood the bone-growth stage was past, but my muscle mass jumped up.

Any overall explanation of breast size variance needs to take into account the origin of large breasts as well, however. Some people think that the reason they developed in the first place is as a defense against pedophilia. Basically, since women's fertility declines so quickly men developed a preference for younger-looking women. Women therefore began to compete sexually based upon how neotenous (having child-like characteristics) they were. This is why women have smaller jaw, higher voices, less body hair, bigger eyes, etc. The unfortunate downside is that men were literally becoming sexually attracted to child traits; breasts developed as a means to unambiguously signal 'I'm sexually mature.'

But they piggybacked on all sorts of other intertwined traits. Immaturity was basically meshing with maturity. And everything was meshing with hormones actually responsible for crucial reproductive processes. This created gigantic boobs instability in the selection process. And the traits still haven't 'stabilized.' We haven't formed robust biological means to create 1) fertility 2) neoteny and 3) mammary maturity signals all in the same person,

simultaneously, reliably.

Runaway sexual selection is like that. Runaway traits create an immense amount of change quickly, and it just takes a while for the traits to 'stabilize' and become reliable.

One of the most fascinating parts of Margaret Boden's history of the cognitive sciences is her accounting of the cognitive and evolutionary origins of ritual and belief in the supernatural. A particular case in point is the demise of a loved one. The inability to "turn off" the intense feelings and bonds we have for others once they cease to live is an enormous problem. Hence the belief in ghosts, immortal souls, and the hope that somehow, somewhere, the people we knew and loved still exist in some higher form.

Sex is arguably more of an essential aspect of human existence than even survival--as individuals we survive to have sex, not visa versa. This is not to suggest that simply because sex is critical to the survival of the species that it's somehow a moral imperative. Rather, I'd postulate, for example, that our hard-wired mechanism for self-assessment and mood regulation looks, perhaps above anything, at the frequency and quality of our sexual encounters.

Ben Shapiro during Q&A

Sentience as qualifer as life.

Is it okay to stab you if you're in a coma from which you may wake up?


So you believe in potential sentience, and therefore should be against abortion.

Also made an interesting point that drawing line on life such as hearbeat on brain, can do the same for adults in comas or brain-dead..

This is the Valonia Ventricosa, the world's largest single-celled organism. At full growth, a single unit can be as large as a tennis ball. Scientists have been baffled by its structure for over a century.

Memento mori (Latin: "remember that you have to die") is the medieval Latin Christian theory and practice of reflection on mortality, especially as a means of considering the vanity of earthly life and the transient nature of all earthly goods and pursuits. It is related to the ars moriendi ("The Art of Dying") and similar literature. Memento mori has been an important part of ascetic disciplines as a means of perfecting the character by cultivating detachment and other virtues, and by turning the attention towards the immortality of the soul and the afterlife.

No OP, but having worked in dangerous jobs: When you regularly see how easy it is for someone to die, especially from something stupid (not heroic, glamorous, important) you just lose a lot of the cultural romanticism we've built around death. There's less reflection about "At least Pete lived to the fullest." And more "Wow, Pete just got his head crushed by a swinging log. That was horrible to watch. His wife and two kids just had their lives destroyed in an instant. They're probably going to end up homeless because he was the breadwinner. Sucks that he died that way. I should really GTFO of this job before it kills me."

Compare an office drone to a soldier. The office drone thinks "maybe I should go home early today to spend time with my family because you never know!" while the soldier, who on a daily basis is already wondering if any second he'll be killed or permanently disabled, is reminded that he may very well die, leaving his family in a bad situation.

Or maybe a coal miner, who is risking his life to support his family, and someone coming up and telling him "yeah, you may very well die today, lol". Doesn't do him much good.

Seneca's pessimistic aphorism: 'What need is there to weep over parts of life? The whole of it calls for tears.'

Hereditary means something you inherit from your parents, genetic means something related to your DNA.

Or course DNA is inherited, so most genetic medical conditions are hereditary. But not all genetic conditions are hereditary. If they are caused by a mutation they won't have been inherited.

But not all hereditary things are genetic. Royalty for example. When a king dies their child inherits the throne. That's hereditary. But it's not genetic because there's no gene that's makes you royalty.