flax

woman will be happy when I spend all day gathering 1000 tiny seeds to make tahini with instead of clubbing a deer

 While nuts are well-accepted as paleolithic foods, seeds are little more contentious. Technically nuts ARE seeds, but botanics aside, what we think of as nuts are big enough that gathering a decent amount of calories from them in the wild is feasible. The same can't be said for seeds- most are tiny and it can take a long time to harvest enough to make anything out of. I learned this harvesting pigweed seeds. I was hoping to get enough of this amaranth relative to make porridge with, but I ended up with only enough to garnish a piece of fish. 

What about their place in a modern paleo diet? After all, we eat plenty of things that would have been tough to gather. For me, the problem with seeds is that if you eat large amounts of them you will be eating nutrients in ratios and amounts that are not appropriate for us evolutionarily. Furthermore, the polyunsaturated fats in them go rancid easily. While some might find hemp useful, I think it's a bad food, at least in the US because you cannot buy it whole and how long has that hemp powder been sitting on the shelf? Probably long enough to render some of those nice omega-3 fatty acids rotten. Flax is a popular ingredient in "paleo" baked goods, but ground and shoved in the oven, the fats can't be good. 

Furthermore, if you eat lots of seeds with the exception of flax, the ratio of omega-6 fatty acids to omega-3 fatty acids is likely to tip towards the latter, which is probably not a good thing. 

Several sources of information suggest that human beings evolved on a diet with a ratio of omega-6 to omega-3 essential fatty acids (EFA) of approximately 1 whereas in Western diets the ratio is 15/1-16.7/1. Western diets are deficient in omega-3 fatty acids, and have excessive amounts of omega-6 fatty acids compared with the diet on which human beings evolved and their genetic patterns were established. Excessive amounts of omega-6 polyunsaturated fatty acids (PUFA) and a very high omega-6/omega-3 ratio, as is found in today's Western diets, promote the pathogenesis of many diseases, including cardiovascular disease, cancer, and inflammatory and autoimmune disease

Furthermore, the conversion of any omega-3 from plants in your diet is hampered. The omega-3 fatty acids present in plants, alpha linolenic acid, is not immediately usable in the body. In order to be used, it must be converted to Docosahexaenoic acid. The enzymes that do this conversion are called Holman's enzymes. Unfortunately, they are also responsible for converting omega-6 fatty acids (mostly linoleic acid) to arachidonic acid. Lots of omega-6 means that there is not enough of Holman's enzymes to do the job. This is discussed in Susan Allport's book The Queen of Fats

Data for the US indicate that Americans consume between 11 and 16 grams of linoleic acid per day during the years 1989 and 91 and about 1 to 2 grams of alpha linolenic acid. At that ratio, only about 15 percent of the alpha linolenic acid is converted to DHA and eicosapentaenoic acid. At lower ratios, the conservation rate is much higher. The best conversion occurs at a ratio of 2.3:1

For paleo dieters who eat seafood, this shouldn't be a huge problem, but if not, it can be an issue. 

Let's also talk about phytic acid, an anti-nutrient present in many seeds, can reduce mineral absorption. There are a couple of other issues, like some estrogenic compounds in flax.

So that's why, in the Paleo Foods section of the site, I classify seeds as Not Paleo, but give the pros and cons. Some tahini sauce on your kale probably isn't as bad as some whole bran bread, but I would recommend keeping their consumption low. Use them as if you had to gather them yourself.