Does Buddhism uphold/advocate the theory of Evolution [Nichirenism]?

I think you should put your mind at ease and enjoy the uncertainty :) Also, it is probably best to stick with your Christian faith and don’t worry too much about Buddhism or what Buddhists think.

Whether the theory of evolution is true or not is completely independent of whether we believe it, right? So either you are descended from an ape or you are not; there is no other third option. Crucially, it makes not one lick of difference whether you believe it!

Consider how the fact or our own birth is similar. Either we were born on such and such a date at such and such a place or we were not. Perhaps we were not “born” at all and have always existed and the universe is one big cosmic masquerade? Maybe you are the only actual person alive and all the rest of us are just dreams? Either this is true or it is not and similarly it does not make one lick of difference in its factual status whether you believe it :)

Yes and no, I guess.

Darwin's theory was about the origin of species, a topic which is of very little concern to Buddhism. I think that On the Origin of Species talks about what Buddhists would call form (e.g. the body), and about adaptive behaviour (e.g. the English proverb, "birds of a feather flock together"), conversely a lot of Buddhism is more about mind and mental phenomena (feeling, intention, concentration, etc.).

I think that Buddhism does teach that almost everything changes (and that there's no eternal God, nor a soul, such as a Christian might have been taught), including individual "people" -- I think it's fair to say that most forms of Buddhism teach that it's possible for people to change, and that you may become better or worse, e.g. depending on what your intentions and views and actions are.

Buddhism might even teach that people who live like animals, who lust and fight like animals, ignorant like animals, might become "reborn" as animals.

It certainly doesn't tell people that they are animals, though -- being born human is viewed as a special, rare, precious opportunity -- to become more enlightened (like the Buddha) and less like an animal.

It also tells people to be compassionate towards animals -- they're considered "sentient beings" too, even if unlike people they're much less capable of ethical behaviour and higher knowledge etc.

I must say there are different forms (schools) of Buddhism too (as there are of Christianity):

• When you talk about Nichiren Buddhism outside Japan, I wonder if you're referring to SGI.
• Another modern form of Buddhism, specifically in India, is the Navayana of Dr. Ambedkar

I think that different schools tend to emphasise or de-emphasise different aspects of Buddhist doctrine (I think that Navayana for example maybe discounts the doctrines about rebirth).

I think that the regular practice of SGI centres on chanting a mantra, which (I don't know) might be a practice that's in some ways analogous to some forms of Christian prayer.

I think that a standard Buddhist view is that the "origin" is unknowable or not evident -- one of the famously unanswered questions, which the Buddha wouldn't answer, because the answer wouldn't be helpful.

I think that Buddhism is more concerned about this life.

According to one Buddhist sutta, life came to earth from ahassara brahma, a world of another galaxy -- you can read the details of this from the Aggañña Sutta.

According to Agganna sutta, life coming from ahassara brahma world didn't have a physical body, they just had a spiritual body; with time they used to eat the soil of earth, on that time earth soil was like honey, after they began to eat earth soil their bodies became hard and their body light disappeared. The time mentioning here is million years ago from now, so we have to know these first life beings were ones much before apes, dinosaurs, etc.

So like that Buddhism suggests life came to earth from an another world, and then there is a space also for the Evolution. Life came like that then granted on the earth and with time it faced to evolution and came to present situation

An interesting thing about Aggañña Sutta is that it's told to contradict Brahmins, who say that, "The Brahmin caste is the highest caste", that, "other castes are base", and so on.

It mentions that Buddhist monks (who have "gone forth") disregard their birth caste:

Vasettha, all of you, though of different birth, name, clan and family, who have gone forth from the household life into homelessness, if you are asked who you are, should reply: “We are ascetics, followers of the Sakyan.” He whose faith in the Tathagata is settled, rooted, established, solid, unshakeable by any ascetic or Brahmin, any deva or mara or Brahma or anyone in the world, can truly say: “I am a true son of Blessed Lord, born of his mouth, born of Dhamma, created by Dhamma, an heir of Dhamma.”

Instead of identifying themselves by their "caste", they should identify themselves as "followers of the Buddha" and "heirs to the Dhamma".

Instead of "caste" (or "outcaste") being determined by birth, another Buddhist sutta teaches that anyone doesn't become "brahmin" nor "villain" from birth. Instead, it's acts they do which decide that.

Na jaccā vasalo hoti,
Na jaccā hoti brāhmaṇo;
Kammunā vasalo hoti,
Kammunā hoti brāhmaṇo.

One’s not an outcaste caused by “birth”,
not by “birth” a brahmin is;
caused by karma one’s outcaste,
a brahmin is by karma caused.

-- Who is the outcaste? (Snp 1.7)