blade runner - Why do replicants have a short lifespan?

In Blade Runner the replicants have a limited lifespan, which is of course a key part of the film. When Deckard and Bryant are talking, Bryant states the short lifespan was deliberately built in to kill the replicants before they develop their own emotional responses. But the conversation between Roy and Tyrell suggests the life span is a consequence of the technology used rather than a deliberate design feature.

I know there's no real answer to this, especially as there's no mention of a limited lifespan in the book, but I'd be interested to know what the panel think about this.

For some reason I always thought it was an accident of the replicant design rather than deliberate, but a recent argument with a Blade Runner loving friend has made me wonder. I found the script online, and Bryant is unambiguous about his position, but then Bryant is a policeman not a scientist. Tyrell, who designed the replicants says:

You were made as well as we could make you.

Anyhow, I'd love to know if there is a generally accepted answer to this. Where did the short lifespan of replicants originate?

Answer

Yes there is a conflict between Bryant and Tyrell's statements, but lets consider the two situations:

• 
  

  Bryant is talking to Deckard: a man who used to report to him and who he is in a position to force to do things; indeed he also voices the rather unsavory opinion that there are "cops" and "little people". He has no particular need to lie and his character doesn't seem given to subterfuge without reason.

  
  


• 
  

  Tyrell is in the presence of a being who he knows to be

  
  
  
  
  1. A physcial threat even unarmed
  
  
  2. Mental very competent (possibly smarter than Tyrell, as he is beating him in chess)
  
  
  
  3. Illegally present on the planet and not afraid to kill to get what he wants.
  
  
  4. Has arranged to have J.F. provide him entry. Tyrell probably thinks of J.F. as a bit simple, but he must wonder what lever was used.
  
  
  
  

  Tyrell has a very good reason to lie to Roy Batty--if he thinks he can get away with it--and he seems comfortable with subterfuge, trickery and lies by omission if they suit his purposes.

  
  

---

Aside: a out-of-universe reason to think the same thing is that Bryan's conversation with Deckard has the feel of the dreaded "exposition of the rules" scene. It's a better than average example of the class, and serves a second purpose in the story, but still...

Accordingly I take it to be definitive.