Spore devs say the evolution game's previews were more ambitious than what they were actually making, and they 'built a fantasy in people's minds that was unachievable'

The evolution sim that was never meant to be.

PC Gamer

I played the simple shape demo of the creature world.

It was vastly superior to the crap they launched. It had an actual ecosystem, but admittedly led to you dying a lot at low tiers because you were the equivalent of a meal worm.

the simple shape demo of the creature world

What game is that? Searching any of those terms give me nothing

It might be one of these

www.spore.com/comm/prototypes

Community

I think they are referring to one of the showcased demos of Spore, of which the most prominent is the 2005 GDC one.

spore.fandom.com/wiki/Removed_features#Creature_S…

Behavior of creatures

The behavior of the creatures also had more depth than the final game. In today’s Spore creatures rarely leave the perimeter of their nest, and possibly has a simpler ecosystem (until Space Stage). This feature was prominent in earlier versions, as in the footage of the 2005 version, small creatures hopped around, grazed, or simply wandered off with no nests for them.

I love Spore, but replaying it today I see how much is missing from making each stage really fleshed-out. Being honest, the Creature Stage is clearly what received the most attention, while subsequent Stages are not as fun.
A lot of it is to be attributed to Maxis and Will Wright: apparently much of what was shown in 2005 and 2006 was never really playable.
But things like this suggest a heavy involvement of the publisher as well:

During the SXSW 2007 demo, Will Wright said that the Aquatic Stage was on the verge of being cut. He also said that, if cut, the Aquatic Stage would be one of the first things to add via an expansion pack, though ultimately no such expansion was released.

There was a plan to add the Aquatic Stage into the full game via an expansion pack titled “The Depths”, although it was never publicly announced. except for one advertisement.

Removed features

Spore has had several major changes since first demonstrated at the GDC 2005 show. Some of the listed features were possibly removed either because they were dysfunctional and/or glitchy, or because they were going to be removed and reused in a future expansion--the prime example of these two reasons is an Aquatic Stage. Some features could have also been removed because Maxis was experimenting with which parts would work, and which might not, and to see what players wanted. Will Wright...

SporeWiki
It was a downloadable demo, yeah. Just had various polygonal shapes on a black background, top down and could move with WASD and could interact with plant sprites and creature sprites. Very simple graphics, but had different level creatures wandering around, so it was hard to stay alive when you had level 5 creatures hunting near the starting beach.