Part 1: The Quickening
The Way the Spirit Comes to the Bones
- Our brains are attuned to difference between living and nonliving things — bias towards biological patterns
- Similar for other animals
- Leads to “our overweening confidence that we know what it means to be alive, even when we don’t.”
- Question of what it means to be alive → significant in context of abortion policy— when does live begin?
- Different kinds of life: a human and a human cell can both be considered alive
- At moment of conception, fertilized egg is actually not viable— contains 69 chromosomes until a vesicle with 23 pinch off from egg (starts with 46)
- Stupid to say that life begins at conception → would have to account for the 10-40% of pregnancies naturally lost before implanting in uterus
- Advances in IVF, organoids, reprogramming cells also complicate the matter— more and more cells with possibility of developing independent life
The question of when life begins is answered according to the purposes for which we ask it. (Joshua Lederberg, 1967)
Death is Resisted
- Ancient intuition: to be alive is to not be dead
- Lineage of apes developed deeper understanding of death from other primates about 30 mya; humans even more so only about 100k years back
Life consists in the sum of the functions, by which death is resisted. (Xavier Bichat, late 1700s)
- Set of species that inhabit a gray zone of existence between life and death → can “resurrect” after long periods of dormancy (nematodes, tardigrades, flies, fungi)
- Controlled by loss of water and dehydration; create compounds like the sugar trehalose that protect DNA and other molecules when dried out
- Controversy of “brain death” — how to ensure the whole brain is not functioning?
Part 2: The Hallmarks
Dinner (Metabolism)
- Snakes, esp pythons, have remarkable spike in metabolism after eating (45-fold!)
- Upreg of growth pathway genes → literally grow their intestines, etc.
- After meal, metabolism drops rapidly until next feeding
Decisive Matter (Decision-making)
- Slime molds → exceptional “intelligence” given that they consist of only one cell
- Can find food in maze, determine optimal path between locations (mimic US interstate system)
- Solve the Knapsack problem: how to optimally combine elements with differing costs/benefits (in this case, food sources at diff distances and diff compositions, but applies to concepts like investing, transporting goods)
Preserving Constant the Conditions of Life (Homeostasis)
- Hibernation of bats → equilibrate to new set point
- Periodically awake when water is running low
- Many species devestated recently by white-nose syndrome, fungus that “wakes” in colder temps and disrupts hibernation, causes bats to use their energy stores too fast
Copy/Paste (Reproduction)
- Trees produce pigments before dropping leaves to give them a chance to move chlorophyll into winter storage, or else would have to expend a lot of energy to re-absorb nitrogen required for the molecule come spring
- In fall, maples also produce bud scales among branches, protected from sun by anthocyanin pigment, which hold potential to grow into flowers
- Samaras = wing-like structures carrying maple seeds
Darwin’s Lung (Evolution)
- Can be used therapeutically— bacteria that infects lungs of people with CF ultimately causing tissue damage is susceptible to infection itself by a certain phage
- In response to phage, population evolves to be more resistant → side effect of also being less inflammatory → trials on spraying this virus into lungs of Cf patients
Part 3: A Series of Dark Questions
The Astonishing Multiplication
[Life is] not the matter of the body—anatomy, chemistry, the ‘mix’ of fluids—but rather their interdependence. (Georg Ernst Stahl, 1708)
The Astonishing Multiplication
- Bizarre nature and regeneration of the hydra
Irritability
The Sect
- Is there something about organic molecules that makes them essentially different than others? No, proved you could make them artificially, too (first with urea)
The Mud Was Actually Alive
- 1800s → belief that the ocean floor was covered in a primordial ooze, a “protoplasm” that had given rise to all life
- Unfortunately, eventually the gel was found to be a side effect of mixing mud with alcohol
A Play of Water
- Life has diff features at diff scales— from biochemical level (enzymes & metabolic rxns) to individuals and populations
- All life shares some hallmarks, but none is necessary & sufficient
The Script
- Question of the nature of life collided with quantum physics— similar themes to matter/energy of considering it a duality; ideas that life’s essence was something at the atomic or subatomic levels
- Shrödinger’s What is Life? → very popular, even though mostly wrong
- Intrigued Crick and Watson
- NASA definition: Life is a self-sustained chemical system capable of undergoing Darwinian evolution.
Part 4: Return to the Borderland
Half Life
- What about viruses? Not really able to replicate without a host
- Still, important sources of biological diversity, and integrated with ecosystems through the virome
- RBCs: no nucleus or mitochondria → should they be considered alive?
- Amazonian mollies = fish species that cannot reproduce with its own species… are they alive?
Data Needed for a Blueprint
- When considering origins of life, must remember that the planet looked very different then than it does now (eg. no oxygen)
- Stanley Miller → invented field of prebiotic chemistry with experiments in mixing inorganic compounds, stimulating with electricity, observing what, if any, organic molecules formed
- RNA as first gene molecule seemed likely— but like only RNA-based life on Earth today, would require some kind of host to survive
- RNA → could act as enzymes and store genetic info (ribozymes) → “RNA world”
- Requirement for some kind of lipid that could self-assemble into lipisomes → containers for chemical reactions = necessary; discovered that source could have been from meteorites
- Playing around with single membrane/protein combinations & how this could uptake nucleus acids (protocells) → method of reading DNA based on size of bases and electrical current as they passed through channel (Deamer) → basis for Oxford Nanopore
- Experiments with mixing waters from volcanic ponds with building blocks of organic molecules, subjecting to cycles of heating and cooling → see whether polymers began to form
No Obvious Bushes
- Similar experiments of mimicking environments, exposing to electrical currents, etc. taking place to explore whether life may have formed on other planets
- Formation of “chimneys” of sediments that can generate current (like hydrothermal vents?) → could provide source of energy for life on exoplanets too far from sun
Four Blue Droplets
- These days, a plethora of definitions of life, and no clear consensus among scientists
- Geneticist Edward Trifonov → analyzed structure and linguistics of the definitions → all agree that life is self-reproduction with variation (but still doesn’t draw a clear line)
- Instead, define life by family resemblances, forming clusters of things we consider alive and not (similar to how we would define “game”, Lisa Feldman Barrett’s emotions)
- Philosopher Carol Cleland → no point in coming up with a definition— rather, we are still working towards a theory that explains life
- Assembly theory: perhaps something about complexity of organic molecules (doesn’t take more than 15 steps to break apart any inorganic molecule) → flow of information