# Naked Science Forum

## General Science => General Science => Topic started by: AlmostAHerb on 19/04/2019 17:40:45

Title: Why Do I Have 5 Digits?
Post by: AlmostAHerb on 19/04/2019 17:40:45
Are the number of digits on a hand/foot related to our deep genetic past?
Does it go all the way back to plants?”

I realise I am probably seeing a correlation and picking examples that match my theory.

This came about from the classic observation about sunflowers/pine cones that seeds form in spirals with consecutive Fibonacci numbers and that bone structures in the arm/leg seem to follow a similar sequence (1 bone in upper arm, 2 in lower arm, 3 (missing) 5 digits). This also seems to follow in other animals (EG star fish = 5, octopus = 8, insects = (6 legs + 2 Antennae)??, spiders = 8). I’d like to look at things like jelly fish to see if the sequence continues there.

I can make a case for plants creating leaves (and as flowers are modified leaves by extension flowers and therefore seeds) in a Fibonacci series as follows:
1 – A plant tries to maximise the area of leaves to get as much energy from the sun
2 – Leaves should not overlap as the shade would reduce the energy in the shaded areas
3 – Assuming a rosette plant, the leaves should divide the circle in the most irrational way (that is if the leaves divide the circle in two, the third leaf would shade the first and there is a large amount of the circle not covered in leaves)
4 – The most irrational number is PHI. That is it is the number that is least well approximated by a fraction. This means that a plant should put it’s leaves out with an ange of 360/PHI degrees (about 222 or 138 degrees). At least looking at my Venus flytrap, it seems to be about right.
5 – Dividing consecutive Fibonacci numbers gives an approximation to PHI

So this gives a reason for plant systems forming Fibonacci sequences, Is this the same reason for Fibonacci sequences appearing in the animal systems?

It would mean that animals split from plants after this sequencing is baked into the genes which would mean it was after plants were developed enough to form leaves, so I think it’s a bit of a stretch so I wonder if there is something else going on?
Title: Re: Why Do I Have 5 Digits?
Post by: RD on 19/04/2019 18:23:43
So this gives a reason for plant systems forming Fibonacci sequences,
Is this the same reason for Fibonacci sequences appearing in the animal systems?

It would mean that animals split from plants after this sequencing is baked into the genes which would mean it was after plants were developed enough to form leaves, so I think it’s a bit of a stretch so I wonder if there is something else going on?

As with the plants, geometry selects (https://en.wikipedia.org/wiki/Natural_selection) for phi ...

https://www.goldennumber.net/human-hand-foot/

So convergent-evolution (https://en.wikipedia.org/wiki/Convergent_evolution), rather than originating in a common ancestor of humans & plants (https://en.wikipedia.org/wiki/File:Collapsed_tree_labels_simplified.png).
Title: Re: Why Do I Have 5 Digits?
Post by: Bored chemist on 19/04/2019 19:01:18
As with the plants, geometry selects for phi ...
No, that's numerology selecting for phi.
Unless you think the ratios are the same in all your fingers.
Title: Re: Why Do I Have 5 Digits?
Post by: RD on 19/04/2019 20:16:58
No, that's numerology selecting for phi.
Unless you think the ratios are the same in all your fingers.

Even the ratio between one finger and the next is close to phi ...
Quote from: livescience.com
Fingers: The length of our fingers,
each section from the tip of the base to the wrist is larger than the preceding one by roughly the ratio of phi.
https://www.livescience.com/37704-phi-golden-ratio.html

It's not magical divine-design: as with the plants, there's natural-selection for optimal-geometry.
Some individuals will have different ratios, but the average is close to phi.
Title: Re: Why Do I Have 5 Digits?
Post by: Bored chemist on 19/04/2019 21:29:54
It's also close to pi/2 and to the ratio of my phone number to my dad's
Title: Re: Why Do I Have 5 Digits?
Post by: Colin2B on 19/04/2019 22:54:50
I realise I am probably seeing a correlation and picking examples that match my theory. ......

......(1 bone in upper arm, 2 in lower arm, 3 (missing) 5 digits).
As @RD says, geometry is important for selecting ratios. Function is also important for selecting numbers.
The single bone in the upper arm can rotate in its socket, but it is limited and you wouldn’t want to use that part of the arm for twisting motions. On the other hand [ :)] the 2 bones in the lower arm allow greater flexibility, torque and movement, when twisting.
3 is not missing, many animals have 3 toes and 4 is also common.

Title: Re: Why Do I Have 5 Digits?
Post by: alancalverd on 19/04/2019 23:39:03
I think practically all mammals have 5 digits but in many species some are fused or vestigial. We also all have 7 cervical vertebrae: the basic structure is very adaptable.

It seems counterinituitive to me that only primates have a fully developed thumb and opposing fingers. It's unlikely that nature endowed the first protomammal with little prototype bits in the hope that it would eventually evolve into something that could use a thumb. Far more likely that it had the full kit and gradually disposed of bits that weren't needed for running or supporting a huge body or whatever, so a sloth or a dog would represent a more recent evolution than homo sapiens which, like the apes,  carries all the parts of the original - hate to say it - "universal design" .