Free will and determinism
Arguments for determinism
Research into the human genome is producing increasing evidence of genetic influences on behaviour. The more we discover, the more it appears that our behaviours (not just our physical characteristics) are determined by our egens. For example, research on Alzheimers disease, intelligence and on depression has identified specific genes.
However... It is doubtful that 100% genetic determination will ever be found for any behaviour. For example, studies that compare identical twins find about 70 - 80% similarity on a range of characterisitics such as intelligence and depression. In other words, if one twin has a high IQ or has developed depression there is only a 70% chance that the other twin will be the same. Therefore genes do not entirely determine behaviour.
Scientific research is based on the belief that events have a cause and effect. If we don't take a determinist view of behaviour then this rules ot psychological research into explaining causes of behaviour. It also means that, at a personal level, you wouldn't be able to predict what anyone else is about to do - which would make social relationships quite difficult. An 'anti-determinist' view would suggest that the human world is totally unpredictable - and that is contray to most people's experience.
However... It may be that psychology is not a science. Even if it were a science, Dennet (2003) argues that, in the physical sciences, it is now accepted that there is no such thing as total determinism. Chaos theory proposes that very small changes in intial conditions can subsequently result in major changes, someties called the 'butterfly effect'. The conclusion is that causal relationships are probabilistic rather than determinist.