Darwinbots Forum

General => Biology => Topic started by: Elite on March 04, 2006, 04:03:40 AM

Title: Multicellular organisms
Post by: Elite on March 04, 2006, 04:03:40 AM
In DB, the only thing we have that can hold cells together are ties. This is the only way we can create MBs in DB at the moment.

But what holds the cells of a real-life multicellular organism together?
Title: Multicellular organisms
Post by: Numsgil on March 04, 2006, 02:17:40 PM
The only other way presently I can think to create something similar to a MB would be something similar to what Fish School does (I believe it's in the beastiary).

This link (http://www.btinternet.com/~stephen.durr/volvox.html) describing Volvox demonstrates the only two methods of MBing that I know of at least.  Sticking together with mucilage and cytoplasmic strands (somewhat similar to ties).
Title: Multicellular organisms
Post by: Elite on March 04, 2006, 02:22:24 PM
Maybe we could get the bots to make 'glue' in the same way as slime that will stick them to other bots.

Or maybe some way of getting the cell walls to fuse?
Title: Multicellular organisms
Post by: Numsgil on March 04, 2006, 02:26:14 PM
I've thought about it, but the main hurdle is that I don't know how the physics would work exactly.  Do cells that are stuck together with sticky something have to maintain a certain orientation?  Maybe they can roll against each other but have to stay at a certain distance from each other (always touching).

If you would do some research on the subject, try to find out more about it, that would be a help probably.
Title: Multicellular organisms
Post by: shvarz on March 04, 2006, 07:16:23 PM
This would require flexible bot shapes, because cells interact over an area.  Two circles can interact only over a single point.

But we can have some intermediate solution.  The simplest one would be to that a multibot gets still shown as a circle (with an area representing the sum of areas of fused bots), but certain portions of its border are designated to individual bots.  The exact rules for movement, shots, energy sharing, damage distribution etc can be worked out. This is a very simple solution and can be introduced fairly quickly, because for such a multibot almost everything (including physics) is going to be the same as for current single-bots.

A step towards more advanced things would be for us to agree on certain pre-determined shapes for bots, based on how many edges they have (triangular - 3, square - 4, and so on up to a certain limit).  Then we define a number of ways n which these shapes can hook up to each other and allow bots to choose from these pre-defined scenarios.

I am not too hot about these ideas myself, but they might work...
Title: Multicellular organisms
Post by: Elite on March 06, 2006, 04:38:09 PM
Here's some physics:

Look at the attached image. Two bots stuck together

The first thing the program does is decide where the centre of gravity is between the two bots. This will be somewhere on the line from point A to B.

The bots are stuck pretty fast and won't budge. They will move together as if they were one

One more thing you've got to be aware of - turning force - if bot A decides to go forwards (upward) then:
I) Both bots will be moved forward
ii) The two bots will be spun around their centre of gravity with a force proportional to:

Turning force = force x perpendicular distance from pivot (centre of gravity)

So if bot A decides to move left then there will be no turning force (perpendicular distance remember)


There ya go!  :D
Title: Multicellular organisms
Post by: Numsgil on March 06, 2006, 05:57:01 PM
That would be rigid body mechanics, which is what I'm working on for ties...  So it's a good solution.

The question then is what the difference between ties and this sticky force would be exactly.  If there isn't any practical difference, then there might not be any reason to create a new one.
Title: Multicellular organisms
Post by: MrMound on March 06, 2006, 06:56:29 PM
umm... theres no image up for me! I cant see any thumbnails or anything, do you know why?
Title: Multicellular organisms
Post by: Numsgil on March 06, 2006, 08:19:27 PM
Can you see our Avater pictures?
Title: Multicellular organisms
Post by: Elite on March 07, 2006, 11:24:22 AM
The difference is in application. To fire a tie you have to face and fire. To stick a bot you just need to touch them.

I find ties hard to control sometimes  :wacko:

If I were building a DB replica of quite a complex multicellular organism (10+ cells?) then ties might not be enough. It would be insanely difficult to program such a thing at the moment, but if there was an easier way maybe larger MBs could be made.
The most complex MB that I know of to date is PYs Hexagonis (6 cells), and even that is pushing the limits, and although it is quite a marvelous feat of cellular engineering it's not that good a fighter (or at surviving at all very well).

I'm not that keen on my sticky method either though  :( what might be good is to have a permanent birth tie.

What keeps the cells of higher organisms (like us) together?
Title: Multicellular organisms
Post by: Numsgil on March 07, 2006, 11:50:37 AM
Intelligent sticking :P
Title: Multicellular organisms
Post by: MrMound on March 07, 2006, 02:26:04 PM
ya I can see the avatars.
Title: Multicellular organisms
Post by: MrMound on March 07, 2006, 02:27:24 PM
I am on a differant computer now and I can see them so it must have something to do with the computer.
Title: Multicellular organisms
Post by: shvarz on March 07, 2006, 02:51:44 PM
The major problem of "rigid sticking" is the same as for rigid ties - when you form a multicellular organism you want individual cells to move, bend, stretch and do other un-rigid things.  It is only possible to do when you have multiple semi-flexible links over a certain area.  Then some of these links can "let go", but the structure will be maintained by other links.
Title: Multicellular organisms
Post by: Elite on March 08, 2006, 10:53:28 AM
Shvarz - what do you think the most realistic solution to this would be? What holds human cells together?
Title: Multicellular organisms
Post by: shvarz on March 08, 2006, 12:50:15 PM
Imagine two water-filled sacs covered in velcro tape (both hooks and pads mixed on the same surface).  The surface of contact is very flexible, but quite sturdy, although each individual connection is not very strong (a single hook of velcro).  That would be a very good imitiation of real life.  To make the picture complete you can imagine different kinds of velcro in small patches - some are very strong, others are weak, some stick only to their own kind others are pretty general.
Title: Multicellular organisms
Post by: Numsgil on March 08, 2006, 12:57:54 PM
Which probably only really works in real life if the area of surface contanct is greater than a single point.  Another limitation of abstraction ;)
Title: Multicellular organisms
Post by: shvarz on March 08, 2006, 02:01:20 PM
Yes, of course.  A lot of things in real biology depend on "summing up" a large number of small signals.  The velcro is an example of cooperative binding - attachment of one hook helps attachment of the next and so on.  The final force becomes very large.  

These systems are usually characterized by sigmoidal shape.  If you plot number of "hooks" connected versus the total affinity (also called avidity) then it is very small at low numbers and increases slowly but after some threshold it goes up exponentially and then plateaus.   This approach allows a lot more control over the avidity.  Imagine different velcros with different density of hooks.  The more hooks/area a velcro has, the faster the exponential phase appears.  Very easy for cells to control the strength of binding to another cell - just change the number of adhesion molecules on the surface.

Similar mechanisms are used by immune system to detect patigens and by neurons to detect signals and by rodes and cones in the eyes to detect light.