On the grounds that evolution is the mutation and subsequent selection of genes, and that therefore the organisms that have the highest rate of reproduction are the "most evolved".
Bacteria have a very high rate of reproduction, meaning there are more chances for mutation.
Humans in comparison have a very low rate of reproduction in comparison, meaning there are less chances for mutations to occur.
At some point back in the evolutionary history of life, some bacteria developed into multi-cellular organisms, and some didn't, remaining single-celled to this day (yet still evolving at a fast rate). The multi-cellular line's reproduction rate slowed as the organism got larger, since it is harder to replicate at such levels. Eventually the advent of sexual reproduction meant that reproduction rates were made abysmally slow in comparison.
As for "complexity", it's a term that is still confusing to define. How do you measure complexity from a subjective level? Not very well. One could argue that mentally we are more complex, but then again most other organisms have the ability to produce Vitamin C within themselves, and we cannot. Various other abilities we lack (or are inferior to other organisms) could also be used to measure complexity.
C-values (amount of DNA in he nucleus) have been suggested as a measure for certain aspects of complexity. Whilst science shows that C-values are not correlated with how complex organisms are, they are useful for showing a correlation between many other factors (such as organ complexity, cell division rate, and extinction risk). It has also been suggested that given the ambiguity of the word "complexity" and how you define it, that C-values would be a good starting point at coming up with a new picture of how "complex" organisms are.
Bacteria have a very high rate of reproduction, meaning there are more chances for mutation.
Humans in comparison have a very low rate of reproduction in comparison, meaning there are less chances for mutations to occur.
At some point back in the evolutionary history of life, some bacteria developed into multi-cellular organisms, and some didn't, remaining single-celled to this day (yet still evolving at a fast rate). The multi-cellular line's reproduction rate slowed as the organism got larger, since it is harder to replicate at such levels. Eventually the advent of sexual reproduction meant that reproduction rates were made abysmally slow in comparison.
As for "complexity", it's a term that is still confusing to define. How do you measure complexity from a subjective level? Not very well. One could argue that mentally we are more complex, but then again most other organisms have the ability to produce Vitamin C within themselves, and we cannot. Various other abilities we lack (or are inferior to other organisms) could also be used to measure complexity.
C-values (amount of DNA in he nucleus) have been suggested as a measure for certain aspects of complexity. Whilst science shows that C-values are not correlated with how complex organisms are, they are useful for showing a correlation between many other factors (such as organ complexity, cell division rate, and extinction risk). It has also been suggested that given the ambiguity of the word "complexity" and how you define it, that C-values would be a good starting point at coming up with a new picture of how "complex" organisms are.
