  Assuming an intrinsic `Band' shape spectrum and an intrinsic
energy-independent emission profile we have investigated the connection between
the evolution of the rest-frame spectral parameters and the spectral lags
measured in gamma-ray burst (GRB) pulses by using a pulse model. We first focus
our attention on the evolution of the peak energy, $E_{0,p}$, and neglect the
effect of the curvature effect. It is found that the evolution of $E_{0,p}$
alone can produce the observed lags. When $E_{0,p}$ varies from hard to soft
only the positive lags can be observed. The negative lags would occur in the
case of $E_{0,p}$ varying from soft to hard. When the evolution of $E_{0,p}$
and the low-energy spectral index $\alpha_{0}$ varying from soft to hard then
to soft we can find the aforesaid two sorts of lags. We then examine the
combined case of the spectral evolution and the curvature effect of fireball
and find the observed spectral lags would increase. A sample including 15
single pulses whose spectral evolution follows hard to soft has been
investigated. All the lags of these pulses are positive, which is in good
agreement with our theoretical predictions. Our analysis shows that only the
intrinsic spectral evolution can produce the spectral lags and the observed
lags should be contributed by the intrinsic spectral evolution and the
curvature effect. But it is still unclear what cause the spectral evolution.
