3D

  Deoxyribonucleic acid (DNA), the hereditary material is a relatively featureless polymer, of the repeating subunit of a nucleotide (base+sugar+phospategroup). Every DNA molecule of a particular type (A-DNA, B-DNA) looks alike in 3-dimensions. DNA of different sequences looks the same in 3-dimensional space or different DNA sequences have the same 3-dimensional structure(shape).

See Link Below:

https://www.nature.com/scitable/topicpage/discovery-of-dna-structure-and-function-watson-397/ 

DNA gets transcribed to the message, ribonucleic acid (RNA), which gets translated to the polypeptide (protein), composed of amino acid subunits.

The polypeptide "folds" in 3-dimensional space over time, to give rise to the final structure of the polypeptide.  Proteins may consist of a single polypeptide or multiple polypeptides interacting with each other. Polypeptides of differing sequences look different in 3-dimensional space, i.e. polypeptides of different sequences have different 3-dimensional structures (shapes and size).

See Link Below:

https://www.researchgate.net/publication/269806015_Toxicological_evaluation_of_proteins_introduced_into_food_crops 

Each protein has a different function, depending on its structure. 

The final folded structure of the protein depends on the amino acid sequence, with each type of amino acid possessing a "sidechain", different from the other. It is these side chains that contribute to the feature of the protein molecule. 

 The structure (size and shape) of an ant is different from that of an elephant, and both differ from humans. Humans recognize other humans, presumably via identifying common physical (face and body) features. To a human, an ant is a relatively small living organism, with no common physical (face and body) features. 

At the outset, all icosahedral viruses look similar in shape, due to the icosahedron coat, but differ in size. Bacteria are grouped as rod-shaped, spherical-shaped, spiral-shaped. There are varying species of ants with differences, but they are all grouped under the category of ants sharing similar body sizes and shapes. On the other hand, elephants share similar body shapes and sizes with each other, which differ from ants. 

These differences in size and shape between different species could be one of the factors responsible for species specificity and relatively rare inter-species mating.

Maybe the transition of looking the same to looking different is a "feature" of evolution, that is working at different scales.