Epicurus was great. It's a shame he's not more widely taught. People come up learning Aristotle and thinking the Greeks had their heads up their asses, but don't end up learning about the guy discussing light as quantized particles moving very quickly two millennia before Einstein wins a Nobel for experimentally proving that behavior, or writes about natural selection nearly two millennia before Darwin.

And yes, Darwin was actually familiar with the same book through his peers (though he claimed to have never read it). But you see rather remarkable level of detail for a lot of the core concepts:

In the beginning, there were many freaks. Earth undertook Experiments - bizarrely put together, weird of look Hermaphrodites, partaking of both sexes, but neither; some Bereft of feet, or orphaned of their hands, and others dumb, Being devoid of mouth; and others yet, with no eyes, blind. Some had their limbs stuck to the body, tightly in a bind, And couldn't do anything, or move, and so could not evade Harm, or forage for bare necessities. And the Earth made Other kinds of monsters too, but in vain, since with each, Nature frowned upon their growth; they were not able to reach The flowering of adulthood, nor find food on which to feed, Nor be joined in the act of Venus.

For all creatures need Many different things, we realize, to multiply And to forge out the links of generations: a supply Of food, first, and a means for the engendering seed to flow Throughout the body and out of the lax limbs; and also so The female and the male can mate, a means they can employ In order to impart and to receive their mutual joy.

Then, many kinds of creatures must have vanished with no trace Because they could not reproduce or hammer out their race. For any beast you look upon that drinks life-giving air, Has either wits, or bravery, or fleetness of foot to spare, Ensuring its survival from its genesis to now."

• De Rerum Natura book 5 lines 837-859

Sometimes children take after their grandparents instead, Or great-grandparents, bringing back the features of the dead. This is since parents carry elemental seeds inside – Many and various, mingled many ways – their bodies hide Seeds that are handed, parent to child, all down the family tree. Venus draws features from these out of her shifting lottery – Bringing back an ancestor’s look or voice or hair. Indeed These characteristics are just as much the result of certain seed As are our faces, limbs and bodies. Females can arise From the paternal seed, just as the male offspring, likewise, Can be created from the mother’s flesh. For to comprise A child requires a doubled seed – from father and from mother. And if the child resembles one more closely than the other, That parent gave the greater share – which you can plainly see Whichever gender – male or female – that the child may be.

• book 4 lines 1217-1232

You can sometimes see a criticism of the first passage claiming that Leucretius saw those intermediate mutations as all existing all at once at the start, but that interpretation really seems to be putting too much weight on "in the beginning" and ignoring things like:

They take us by the hand and show that animals arise From things with no sensation at all.

• book 2 lines 870-871

Especially since this world is the product of Nature, the happenstance Of the seeds of things colliding into each other by pure chance In every possible way, no aim in view, at random, blind, Till sooner or later certain atoms suddenly combined So that they lay the warp to weave the cloth of mighty things: Of earth, of sea, of sky, of all the species of living beings.

• book 2 lines 1058-1063

And it's been pretty wild seeing a Christian sect quoting from a book that contains such an on point description of naturalism as we see it today.

For example, another parallel is the Epicurean attitudes about avoiding false negatives. They were adamant not to prematurely discard explanations for why something occurred, but rather to keep them around concurrently (it's a large part of why they got so much right). Which is a bit similar to the discussion of leaving seeds alone when you don't know which is wheat and which is weeds as eventually it will become clear and you can harvest the one and discard the other. An even more interesting saying in the context of a sect's claiming the mustard seed was about an indivisible point as if from nothing or that the sower parable was about seeds scattered upon the world "through which the whole cosmical system is completed."