Practice English Speaking&Listening with: Why do we Care about Family? (Even Plants)

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Thale cress grown close in rows like this. If the rows were made up of plants from the

same family, their leaves would bend away from thr row, looking like they were trying

to get away from one another. In the rows where they were from different families they

didn't seem to do this so much. Bending away like this will decrease the amount

of light they're blocking for a neighbor, but they end up blocking light for themselves.

It looks like they're trying to help their neighbors at their own expense. But only for

relatives. It seems to be a plant... that cares about

family Let's look at some important things that happen

to DNA. Segments of DNA are used as the design for

proteins. And pretty much everything that happens in the cell is done by proteins, so

DNA ends up being the code for everything that a cell will be, do and build.

DNA gets copied. One copy of which is to go into another cell. And eventually DNA and

the cell will fall apart. Replicating is why we are all here. Why cells

don't just die and we all go away forever. It's the cells that can replicate more or

more reliably that we should expect to see more of.

A gene can code for proteins that can do any number of things. But if it does something

that helps the cell reproduce, like makes the cell chase after resources it can use

or run away from dangers, then that gene will be reproducing more. Because that cell is

reproducing more. Even though it may be having negative impacts on the reproduction of that

cell like using up resources to make that protein, if it has a net benefit on reproduction,

then we should expect this gene to reproduce more. And we should expect to see more genes

like that. In reality, how a gene is going to help or

hurt reproduction has to do with the environment it interacts with. Including the other proteins

of that cell. What works and doesn't work for reproduction is always changing and it's

hard to predict and quantify. Here we're just talking hypothetically.

Genes that code for proteins that have a net cost on reproduction, like making the cell

swim in a circle for no reason, or if this protein when excreted is followed by predators

like a bread crumb trail, those genes would be reproducing less and we should expect to

see less genes like that. So then how can we see proteins that are helping

other cells reproductively, at their own expense? That's a waste of resources. Cells with these

genes should reproduce less and that trait should go away. But if this mutation came

earlier and this cell was produced through mitosis and they were genetically identical.

Then this protein is reproductively helping DNA that designs that protein. As long as

the reproductive benefits are greater than the reproductive costs, that code should do

OK. Even though it's not helping the exact DNA molecule that was worked from to assemble

it. Let's say the proteins these genes code for

will guarantee a copy of the cell ... for whatever reason. Whether a protein is guaranteeing

a copy in the cell it came from, or a protein is guaranteeing a copy in another identical

cell, the same number of copies are made. The effect on the replication of a gene would

be the same. Because DNA is ultimately going to fall apart. Whether that DNA will continue

is about whether the protein it codes for helps it leave behind more copies. Both of

these genes would be accomplishing that and we should expect to see proteins that help

other cells just like we see proteins helping the cell they came from.

But if it guarantees a copy in this stranger cell, a cell that doesn't share the gene,

it's not helping itself reproduce. That gene isn't there when it tries to help that cell

and it's a waste of resources. The other cell needs to share that gene and we shouldn't

expect genes that help strangers to do very well.

One example is slime mould. Single celled protist, usually goes about doing its asexual

single cell thing. Eating. A-sexing. When the food runs out, they get together with

thousands of cells and form these fruiting body things. The cells at the top will produce

spores that can survive without food for a while. Being up a little stem means they can

be picked up easier by things like passing insects easier or ingested and excreted and

then deposited somewhere where there's food. In the right conditions the spores will form

single celled slime moulds again. The bottom cells of the fruiting body die

and won't reproduce anymore. But because the top cells are clones whatever genes are involved

in that behaviour are actually reproducing better because of it. So we should continue

to see that behaviour. From the perspective of reproducing code, a few cells dying doesn't

really matter It's kind of like the cells that make up humans.

Most of our cells aren't going to reprod uce for very long. But body cells will continue

to exist because they're helping the reproduction of the sex cells that carry the same DNA.

Reproductively our bodies are kind of like, slime mould bottom cells.

But the relationship is a little bit different when there's sex cells in the mix. Like between

parent's cells and children's cells. Chromosome pairs get split up with meiosis,

and combined with someone else's at sexing. For a chromosome, on average only half of

the offspring are going to share that same DNA. And the same goes for siblings, on average

only half of the siblings are going to share any given chromosome.

What this means for genes is that any given gene that's helping the offspring's cells

reproduce, is only helping a copy of itself on average half as often. Compared to a gene

that's helping the bunch of cells it came from. When it's not helping a copy it's basically

helping a stranger. It's a waste of resources. So a gene that tries to help a offspring or

a sibling, will have on average half the reproductive benefit. Because of all the times it's not

helping a copy of itself. Or maybe you can think about it like, if a

gene guarantees an offspring for this mass of cells, on average there is a 50% chance

that the offspring will have that gene. So for the gene, it's really only guaranteeing

on average half a copy. If it guarantees an offspring for one of its

offspring, without knowing which offspring shares that gene, it's really only guaranteeing

on average a quarter of a copy. Because on average only a quarter of those grandchildren

are going to share any given chromosome. A gene guaranteeing an offspring doesn't really

make any sense. But that doesn't matter. The idea is just that proportionally, a gene that's

helping an offspring, parent or sibling, is getting relatively less reproductive benefit

than it would helping itself. SO we wouldn't expect genes that help family

members to do as well. And they would be less common. Genes that help grandchildren, cousins,

grandparents and other more distant relatives would be even less prevalent. But still, more

prevalent than genes that help strangers. With mitosis, a gene can give equally good

reproductive benefit to its copies. But reproductive benefits are reduced between meiosis relatives

because chromosomes are getting split up. Would an offspring ever help their parents

reproduce? Offspring's cells are the ones that have to continue to code. So if cells

age and die, shouldn't the helping genes only go towards the offspring? And otherwise it

would be counter-productive to long term reproduction? But children's cells are the copies that need

to continue the genes. If cells age, surely the helping relationship should only go one way towards the children? Wouldn't siblings helping the parents reproduction be sort of

counterproductive to long term reproduction? It does make a certain sense. Especially for

us. We put a lot of work into taking care of our kids. We're mammals. We have appendages

that shoot out liquid child caring. Yes if a gene makes them help the parents

reproduce, and then never reproduce themselves, they would go extinct. But if some of the

offspring do reproduce at some point, then a helping gene can pass on in the same way

we've been talking about. And you're starting to get something that looks like the social

structure of bees, ants, termites and other animals.

With the European honey bee, the queen's worker children gather food for her and the hive.

A queen may live on average three to four years. And she'll create hundreds of thousands

of workers throughout her life. Workers will only live weeks to months and

most of them won't reproduce. New queen are produced young workers or from a queen's drones

that go off and mate with other queens. So reproduction in these bees is sort of carried

out queen to queen. The workers assist that relationship by helping

the queen and her drones. They also feed and raise the new worker. Those workers can then

go on to help the queen, the drones and new workers. So that those workers can go on to

help the queen, the drones and the new workers and so on.

OK, while you can trace the line of reproducers from mother queens to daughter queen, the

majority of the bees only live to help their parents and siblings and there doesn't seem

to be much "helping offspring" behaviours. They seem to be helping their parents live

and reproduce more reliably. Whether a protein results in the reproduction

of its gene in the cell that assembled it, or another cell. Whether those cells are attached

or separated they are causing the DNA that designed that protein, to reproduce.

This seems to be a big part of why we see family.

Why belding's ground squirrels will risk making alarm calls about ground predators much more

frequently when with family. Why White-Fronted Bee-Eater offspring will

often stay and help their parents with their new kids rather than leave and make a nest

of their own. Why a dominant male turkey's brother will

help scare away other male turkeys, and give a backup display for his brother, but never

mate with any of those females himself. It's genes in one cell that have had an effect

that reproduced those same genes in another cell.

But then, if my cells have the family caring genes, and your cells have the family caring

genes, why don't we just treat each other as family? Surely if a woman were to nurse

any other human not just their family, that's mammary glands helping the genes for mammary

glands reproduce? Why don't we see that? You know why are we talking about the probability

a gene will be shared? Why don't they just identify which offspring has that gene?

And otherwise how do proteins and cells recognize what other cells are family? How does that

dumb plant do it? And how did those bees become non breeding

workers? They're not clones of their future reproducing siblings the way slime mould cells

are? I'm going to leave you with these. There is

some additional information on this and some other stuff in the notes below.

This episode is brought to you by, Hamilton's Grass-fed Human Milk.

Huma Mumma Yumma Liqua Human Milk.

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